#90374: Clinical Management of Ventricular Arrhythmias

Monomorphic VT is commonly seen in persons with ischemic heart disease. It gets its name from the uniform appearance of the QRS complexes in a single ECG lead. Monomorphic VT may be sustained (duration >30 seconds) or nonsustained (duration <30 seconds) [24].

The defining ECG characteristics of monomorphic VT include:

Figure 4 is a sample strip of monomorphic VT. Note the absence of P waves, the bizarre QRS complexes, and the rapid ventricular rate [1,3,25].

SAMPLE STRIP OF MONOMORPHIC VT

Figure 4

Source: Author

Ventricular tachycardia is one type of sustained ventricular arrhythmia. Two other sustained ventricular arrhythmias that may develop in the clinical setting are slow idioventricular escape rhythm and accelerated idioventricular escape rhythm. Both are characterized by the absence of P waves and by widened, bizarre QRS complexes. They differ from VT in terms of rate.

Slow idioventricular escape rhythm is a protective rhythm generated by the ventricles in an attempt to produce adequate cardiac output when the normal sinus and AV nodal (junctional) pacemakers have failed. It occurs at a very slow rate of 30 to 40 bpm and is characterized by wide QRS complexes. It may result in a significant drop in cardiac output and generally requires immediate treatment. Unlike the treatment for VT, the treatment for a ventricular escape rhythm does not focus on suppressing the arrhythmia but on increasing the heart rate through pharmacologic means or temporary external pacing.

Accelerated idioventricular rhythm occurs when cells in the bundle branches or the Purkinje fibers in the ventricles act as a pacemaker for the heart. It is characterized by widened QRS complexes that occur at a rate of 40 to 120 bpm; normal sinus P waves are absent. Referred to as slow VT or accelerated ventricular rhythm (AVR), accelerated idioventricular rhythm may be an escape rhythm that occurs when the sinus node fails to generate an effective heart rhythm. As with rapid VT, it may be a usurping rhythm that takes over the pacemaker function from the sinus node [11,19,26].

On occasion, differentiating a VT from a supraventricular atrial tachycardia can be extremely difficult. By definition, a supraventricular tachycardia is an abnormal rapid rhythm that is initiated at or above the level of the AV node (but outside the SA node). Conduction through the ventricles is typically normal. This differs from a sinus tachycardia with rapid firing of the SA node. The defining characteristics of a supraventricular tachycardia include a heart rate in excess of 120 bpm, an absence of normal sinus P waves, and narrow QRS complexes. Note the absence of the P waves and the normal configuration of the QRS complexes in Figure 5.

SAMPLE STRIP OF SUPRAVENTRICULAR ATRIAL TACHYCARDIA

Figure 5

Source: Author

In theory, one of the major differences between the ECG pattern of supraventricular tachycardia and that of VT is the width and appearance of the QRS complexes. However, due to conduction abnormalities present in the bundle branch system, in some cases the QRS complexes in supraventricular tachycardia may be wider than normal and bizarre in appearance. Differentiating a VT from a supraventricular tachycardia may be impossible from a surface 12-lead ECG. Treatment of a wide complex tachycardia that has not been clearly identified as either VT or supraventricular tachycardia is discussed in a later section on emergency management of ventricular arrhythmias [11].

A re-entry mechanism is responsible for most clinical monomorphic VTs. In re-entry, the normal transmission of the electrical impulse is altered in part of the heart. Instead of the wave of depolarization spreading evenly through the heart, it is slowed or blocked in one area while proceeding normally in an adjoining area. The mix of abnormal and normal conduction in adjoining areas of the heart causes electrophysiologic conditions that create an abnormal conduction loop that allows the depolarization to repeatedly and continuously re-excite the heart at rapid rates. The risk that a re-entry tachycardia will develop increases with factors that increase the risk of a PVC, such as electrolyte imbalances, increased sympathetic nervous system activity, recurrent myocardial ischemia, or uncontrolled heart failure [27,28].

Some persons with monomorphic VT will be completely asymptomatic. Others will experience mild-to-moderate symptoms of decreased cardiac output including a drop in blood pressure, a reduction in activity tolerance, dyspnea, and dizziness or light-headedness. Still others will experience severe symptoms of syncope or near syncope, and some will develop cardiac and respiratory arrest. VT may degenerate into ventricular fibrillation. In persons with already compromised left ventricular function, persistent VT may result in signs of increased heart failure, angina, and acute MI. The impact of the VT on the patient is mediated by a number of factors, including [1]:

Ischemic Heart Disease

Sustained monomorphic VT commonly occurs in individuals with ischemic heart disease. According to data from clinical trials, the combination of a healed MI, nonsustained VT, and a reduced left ventricular ejection fraction (LVEF) greatly increases a person's risk for developing prolonged runs of VT [1]. In an MI, the damage to the heart muscle creates the necessary conditions for a re-entry VT to develop. Areas of the myocardium die and are replaced with scar tissue. The resulting mix of normal tissue and abnormal scar tissue create adjoining areas of normal and abnormal conduction that allow a re-entry rhythm to occur [29]. Damage from an MI can also impair the ability of one or both ventricles to pump effectively. When the left ventricle is damaged, its ability to pump blood into the systemic circulation is reduced. LVEF describes how well the left ventricle is functioning. LVEF is defined as the percentage of the total volume of blood contained in the left ventricle that is pumped from the ventricle with each heartbeat. A normal LVEF at rest falls between 50% and 75%. EF may be measured noninvasively through the use of an echocardiogram or nuclear medicine study or invasively during a cardiac catheterization procedure [30]. Although polymorphic VT is more common during the acute stage of an MI, sustained monomorphic VT may develop. Aside from coronary artery disease, causes of myocardial ischemia that have been found to trigger monomorphic VT include coronary vasospasm, cocaine-induced vasospasm, severe hypertension, and aortic stenosis [1,3,18].

Nonischemic Heart Disease

The occurrence of monomorphic VT also occurs in nonischemic heart disease. It is estimated that dilated cardiomyopathy is the second most frequent type of cardiac disease linked to monomorphic VT, the third most common cause of heart failure, and the most frequent reason for heart transplantation [1,3,31]. Dilated cardiomyopathy is a syndrome in which one or both ventricles dilate abnormally, resulting in enlarged, sluggish chamber(s) that contract poorly [32,33]. Cardiac output is compromised. Dilated cardiomyopathy is a progressive disease characterized by a fairly rapid deterioration in ventricular function. As left ventricular function decreases, the risk of serious ventricular arrhythmias increases. Multifocal PVCs, couplets, and runs of nonsustained VT commonly occur. Sustained monomorphic VT may develop from a re-entry circuit involving the bundle of His and the bundle branches. Causes of dilated cardiomyopathy include underlying genetic disorders and abnormalities, viral infection, excessive alcohol consumption over time, pregnancy, and environmental factors [31,32,33]. Another form of nonischemic heart disease, hypertrophic cardiomyopathy, has also been linked with sudden cardiac death episodes and the development of sustained VT. A disorder of the myocardium, it is characterized by hypertrophy or enlargement of the left ventricular muscle [34]. The enlargement occurs without dilatation of the left ventricular chamber and is not associated with any cardiac or systemic cause. The hypertrophy of the left ventricle impairs normal functioning of the heart during diastole, and the development of arrhythmias and ischemia is common. In some persons with hypertrophic cardiomyopathy, the septum between the right and left ventricle also enlarges, causing significant obstruction of blood flow from the left ventricle during systole [34]. Runs of nonsustained VT occur commonly and are thought to be a marker of poor prognosis and increased risk of sudden death in people older than 25 years of age. Another form of cardiomyopathy, arrhythmogenic right ventricular dysplasia (ARVD), has also been linked to ventricular arrhythmias including PVCs, sustained monomorphic VT, and in some cases, ventricular fibrillation. ARVD is a progressive form of cardiomyopathy in which fatty infiltrates invade and damage the right ventricle. Scarring occurs, and the combination of scarred and normal areas creates the conditions for a re-entry circuit and monomorphic VT to develop. ARVD can also damage the left ventricle [1,3,33].

Idiopathic VT

Although monomorphic VT occurs more often in people with heart disease, it may also occur in the absence of heart disease. Two types of idiopathic VT that may be seen in persons with normal hearts are right ventricular outflow tract VT and idiopathic left VT. In right ventricular outflow tract VT, exercise or some other hyperadrenergic state may induce repetitive bursts of nonsustained VT or episodes of sustained monomorphic VT. Unlike the VT seen commonly in ischemic heart disease, the VT in right ventricular outflow tract is thought to be caused by abnormal impulse formation in the ventricle. The ventricular arrhythmias seen in right ventricular outflow tract have not been strongly linked to sudden cardiac death episodes but may create debilitating symptoms of palpitations, dizziness, or syncope [35]. Right ventricular outflow tract in the absence of a family history for cardiomyopathies and without evidence for structural heart disease are suggestive for idiopathic VT [6].

Idiopathic left VT also develops in the absence of obvious heart disease. Its underlying mechanism is thought to be a re-entry circuit involving the left side of the His bundle and bundle branch system. Unlike right ventricular outflow tract VT, idiopathic left VT is not precipitated by exercise. It occurs more commonly in younger men and is associated with symptoms of palpitations and (less commonly) syncope. This form of VT rarely leads to sudden cardiac death. However, if the VT occurs incessantly, it may eventually cause a tachycardia-induced cardiomyopathy [3,35].

Torsades de pointes gets its name from the characteristic pattern of its QRS complexes. As the complexes change from upward to a downward deflection, they give the appearance of "twisting" around the baseline [36]. The amplitude of each successive complex gradually increases then decreases, creating an identifiable spindle-shaped pattern. Other ECG characteristics associated with torsades de pointes include [33,36]:

Torsades de pointes is an unstable form of VT. Episodes are often nonsustained; however, torsades de pointes may quickly degenerate into ventricular fibrillation [36]. Most persons who develop torsades de pointes experience noticeable symptoms of decreased cardiac output, including hypotension or a decrease in blood pressure, decreased activity tolerance, syncope or near-syncope, and dyspnea [1,9,11,18,19,33,36].

Pathophysiology of Torsades de Pointes

The occurrence of torsades de pointes is linked to a prolonged period of repolarization. On surface ECG, prolonged repolarization is reflected by a prolonged QT interval. With a prolonged period of repolarization, the effective refractory period is also prolonged and there is an increased risk that an abnormal electrical impulse arising during this period will trigger a rapid ventricular arrhythmia. Factors that increase the risk that torsades de pointes will develop include hypomagnesemia, hypokalemia, or a pre-existing bradycardia. Prolonged QT intervals may be congenital or acquired [36].

Acquired prolonged QT syndrome is usually caused by administration of one or more medications that prolong action potential duration and refractory period of ventricles. Certain antiarrhythmic medications are well known to prolong the QT interval. Less well known is the fact that a number of noncardiac medications have also been found to prolong QT interval and increase the risk of developing torsades de pointes. Table 1 lists examples of medications known to prolong the QT interval. Administration of multiple medications that prolong the action potential duration and refractory period can produce a cumulative effect on the QT interval and can increase a person's risk for developing torsades de pointes [1,18,36].

Less common than acquired long QT syndrome, congenital long QT syndrome is linked to several genetic abnormalities [6]. The initial clinical presentation may be syncope or cardiac arrest that is precipitated by exertion, such as vigorous activity or intense emotions [36]. Symptoms may begin as early as preteen or teenage years (average age is 14 years), or they may not develop until the person is 40 or 50 years of age. Persons with congenital long QT syndrome usually have a first-degree family history of syncopal episodes, sudden cardiac arrest, or unexpected death at a young age. Genetic-specific triggers include emotional stress, exercise, and sleep [6]. In younger persons, syncopal symptoms may initially be misdiagnosed as a seizure disorder. Diagnostic evaluation of prolonged QT syndrome may include screening for prolonged QT intervals in other family members and assessment for any episodes of sudden cardiac death or syncopal spells among other family members [36,38].

To provide more rapid defibrillation in an out-of-hospital setting, public access defibrillation programs have been established. In a public access defibrillation program, a trained lay rescuer uses an AED to analyze the patient's rhythm and to deliver a defibrillatory shock if indicated. An AED is reasonably simple to operate and does not require the operator to master complex skills of rhythm interpretation. Initially, there was some opposition to the use of AEDs by trained lay rescuers; some believed that defibrillation was an intervention that should only be performed by physicians or physician extenders. However, as the need for early defibrillation became obvious and the efficacy of the AED by trained lay rescuers was documented, opposition to the use of AEDs in the United States decreased [41,44,45]. Despite these gains, fewer than 12% of adults have an AED applied before EMS arrival [43]. Because an AED is considered a "restricted medical device" and its use falls under state regulations governing health practice and use of medical devices, public access defibrillation programs must meet certain regulatory requirements. Although details may vary from state to state, in general, these requirements specify that the public access defibrillation program should be overseen by a medical authority that is responsible for supervising the purchase of the AEDs, establishing the treatment protocols, and the training of individuals who will use the equipment. Another problem in the establishment of a public access defibrillation program was the potential liability to the lay rescuer, the physician overseeing the program, and the business or organization providing the program. To reduce liability and promote use of public access defibrillation programs, all 50 states have passed or amended legislation to address the issue of the use of AEDs [46]. In general under the amended Good Samaritan Acts, lay rescuers may be immune from lawsuits resulting from the use of AEDs if [41,44]:

Obviously, emergency medical technicians and paramedics responding as part of an EMS system should be trained to use an AED in the community setting. In addition, groups identified or labeled as public access defibrillation responders should be trained. These include [44]:

Data support the need for increased availability of public access defibrillators and community training in basic life support that is initiated in childhood and repetitive [6].

Before moving on, a more in-depth discussion of AEDs and how they function may be helpful.

AEDs come in various shapes and sizes. Those designed for use in public places by trained lay rescuers are relatively small portable units, approximately the size of a laptop computer. The AED consists of several major parts: a main unit, defibrillator cables, and detachable electrode pads. On the outside of the main unit are the power switch, controls for operating the AED, and a screen for visual display. The microcircuitry that analyzes the victim's heart rhythm and initiates a shock for defibrillation, if it is indicated according to the AEDs programmed algorithms, is housed inside the main unit along with the batteries that provide the necessary power. The electrode pads attach to the defibrillation cables and are placed on the victim's body. The pads detect and transmit information about the victim's heart rhythm back to the circuitry in the main unit. They are subsequently available to deliver a shock for defibrillation if indicated. Specific characteristics of individual AEDs will vary by manufacturer, and individuals using AEDs must be familiar with the specific device that they are likely to use. AEDs may also be combined with conventional defibrillators for use by medical personnel in the hospital setting. These defibrillators generally provide a variety of available therapies including automated external defibrillation, standard defibrillation, cardioversion, and in some devices, the availability of external transcutaneous pacing [47,48].

How an AED Works

As noted, an AED is designed to analyze a victim's heart rhythm to determine if a defibrillatory shock is indicated and then to deliver that shock. The electrode pads placed on the patient's chest pick up information about the patient's heart rhythm and transmit it back to the circuitry in the main unit. The AED analyzes the transmitted information, matching the characteristics of the patient's current heart rhythm to its programmed parameters and determines if a defibrillation shock is indicated. After it completes its analysis, the AED then prompts the rescuer to the appropriate action using audible or visual cues. If the AED determines that a shock is indicated, it initiates a "shock advised" message. If the AED determines that a shock is not indicated, it initiates a "no shock, check pulse" message instead[48]. The use of an AED involves a few basic steps. These steps are discussed here to provide a review or an overview for the reader. However, for rescuers to learn how to actually use an AED requires a structured training program that includes hands-on practice as well as classroom lecture and discussion material. Appropriate courses are offered through AHA locations or local chapters of the American Red Cross. For specific information about available training programs, consult the local chapter or access information available on the websites of the AHA or the American Red Cross (Resources).

Basic Steps in AED Operation

If an AED is available, it should be obtained immediately after the rescuer has determined that the victim is unresponsive and the emergency medical system has been activated. Some state legislation governing the use of AEDs requires that the rescuer notify EMS that an AED is available at the site. To use the AED, the rescuer first turns the device on, then attaches the electrodes to the victim in the designated locations. Diagrams showing proper electrode placement are printed on many of the electrode packages to guide the rescuer in determining proper placement. Electrode pads should not be placed directly over implanted pacemaker or ICD sites or over transdermal medication patches. If needed, transdermal patches may be removed and the skin wiped clean before the electrode pads are applied. After the electrodes are attached, the rescuer must make sure that no one is touching the patient. Once the rescuer is sure that the patient is "cleared," the rescuer depresses the "analyze" button on the AED. If prompted that a shock is indicated, the rescuer again verifies that no one is touching the patient and depresses the "shock" button [41,44]. According to CPR guidelines, delivery of the shock should be followed immediately by chest compressions [10,43].

Safety Measures

Despite its simplicity, an AED is a powerful tool. Used correctly, it can promote survival and facilitate resuscitation efforts. Used incorrectly, it can result in harm to the victim or to the rescuers attempting use of the equipment. Specific safety measures should be employed, including [10,41,43,44]:

In 2010, the AHA published updated guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. These guidelines were updated in 2015 and again in 2020 [10,43]. In 2022, the ESC published updated guidelines for the management of patients with ventricular arrhythmias and prevention of sudden cardiac death [6]. Major points are summarized below; for a comprehensive discussion of the recommendations, changes, and accompanying rationale, the published guidelines are available through the AHA and ESC websites (Resources).

The definitive treatment of choice to suppress ventricular fibrillation or pulseless VT is direct current defibrillation [6,10,43]. Chest compressions should be initiated while waiting for the defibrillator to be set up and charged. Then, administer a single defibrillation shock. Most defibrillators currently in use deliver a biphasic waveform. The recommended energy dose for biphasic waveform is 120–200 joules (i.e., the specific dose within the range that has been found effective in terminating ventricular fibrillation/pulseless VT with the specific device in use). If the effective dose for a specific biphasic device is unknown, 200 joules should be used. Alternatively, if the defibrillator is monophasic, use 360 joules. Compressions should not be delayed to check the pulse or rhythm immediately after a shock is delivered.

Immediately resume chest compressions at a rate of 100 to 120 compressions per minute, and continue CPR for approximately two minutes, or five cycles. Resuscitation efforts should be organized to minimize interruptions to chest compressions [43].

If ventricular fibrillation/pulseless VT persists after delivery of CPR and one shock, the use of epinephrine every three to five minutes should be considered. General guidelines for administering medications during CPR include [10,43]:

The recommended sequence of emergency interventions for persistent ventricular fibrillation/pulseless VT is [43]:

Epinephrine has been a treatment of choice in ventricular fibrillation for many years. Epinephrine acts by stimulating adrenergic receptors. This results in an increase in blood pressure and heart rate, which re-routes blood flow to the heart and brain and produces peripheral vasoconstriction. Ironically, its negative effects include an increase in myocardial ischemia, increased myocardial irritability, and increased risk for development of new ventricular fibrillation. The usual initial dose of epinephrine is 1 mg given as a rapid IV push. Administration of epinephrine should be followed by another defibrillator shock. One mg doses of epinephrine may be repeated every three to five minutes during the cardiac arrest. Although higher doses may be considered if 1 mg doses are unsuccessful, higher cumulative doses have been associated with a worse neurologic outcome for the patient [10,37].

If ventricular fibrillation/pulseless VT persists after several shocks, CPR, and administration of epinephrine, the administration of an antiarrhythmic should be considered. The initial drug of choice is amiodarone; the second choice is lidocaine [10,43].

Amiodarone is a Class III antiarrhythmic that exerts multiple effects on the circulatory system. For pulseless VT or ventricular fibrillation, the recommended dose is 300 mg given as a rapid IV bolus [10,37]. If needed, a supplemental dose of 150 mg can be given, followed by 1 mg/min for 6 hours and then 0.5 mg/min for 18 hours [10]. If defibrillation shocks temporarily restore a perfusing rhythm that degenerates again into ventricular fibrillation or pulseless VT, the administration of an additional amiodarone bolus may be considered [10].

Lidocaine may be initiated by a loading dose of 1–1.5 mg/kg IV push, followed by a continuous infusion [10]. Additional doses of 0.5–0.75 mg/kg bolus may be administered every 5 to 10 minutes, with a maximum cumulative dose of 3 mg/kg [10,37].

If a patient has gone into VT but maintains a palpable pulse and blood pressure, the selection of interventions depends on an assessment of the patient's status [6]. As illustrated by the clinical scenarios in the beginning of this section, persons with VT may display symptoms that range from asymptomatic to severe. These symptoms result from a drop in cardiac output. Remember that in VT the normal diastolic filling time is reduced, and ventricular contraction is impaired by the rapid rate coupled with the altered conduction. The severity with which VT impacts an individual person's physiologic functioning may be influenced by many factors, such as the patient's age, presence of co-existing cardiac and noncardiac diseases, the rate of the tachycardia, and the length of time that the VT has persisted. VT may be considered unstable if the patient is experiencing significant symptoms of decreased cardiac output and/or there is a high risk that the rhythm will deteriorate into a pulseless or nonperfusing rhythm. VT may be considered stable if the patient experiences only mild symptoms of decreased cardiac output. (It is important to note that stable VT that persists over time can fatigue the heart and produce symptoms.) Determining whether VT is stable or unstable in an individual patient is not always an easy task. The patient's symptoms may fall somewhere between mild and severe, and the clinician will have to make a decision about whether the patient's status leans more toward unstable or stable. When assessing the impact of the arrhythmia on the patient, look for the following signs and symptoms of a decreased cardiac output:

Also, it is important to consider the patient's overall status and presence of cardiovascular disease to evaluate the risk that the symptoms will exacerbate other underlying problems [6]. For example, does the patient have congestive heart failure? If so, the combination of rapid rhythm seen in VT coupled with a pre-existing ventricular dysfunction can rapidly lead to severe symptoms [1,6,10].

For stable sustained monomorphic VT, recommended interventions include [5,6,10,37]:

Class I Recommendation

Class IIa Recommendations

Class IIb Recommendation

If assessment shows that the patient's status is unstable (or more unstable than stable), synchronized cardioversion or defibrillation is the treatment of choice [5,6]. Defibrillators in use today in the acute care setting are cardioverter defibrillators, with the capability of delivering either a synchronized or an unsynchronized shock.

In synchronized cardioversion, the machine delivers the shock in synchrony with the patient's own rhythm; this avoids the risk that the shock will fall during the vulnerable period of repolarization (represented by the T wave on the ECG) and send the heart into ventricular fibrillation. Cardioversion has been found to be effective for arrhythmias caused by re-entry mechanisms (e.g., those underlying most episodes of monomorphic VT). Setting up for cardioversion usually takes a few minutes longer than preparing for defibrillation. The machine uses a sophisticated sensor to identify the highest point of the R wave in the patient's cardiac cycle to time the delivery of the synchronized shock. For the machine to properly identify the R wave, the electrodes (not the "quick-look" paddles) must be used. Additionally, delivery of a DC shock through the chest wall is extremely painful; if possible, the patient should be sedated before the shock is administered. If the patient's status is rapidly deteriorating or is so unstable that the delay of a few minutes to set up and prepare the patient for synchronized cardioversion jeopardizes his/her status, defibrillation should be used instead [49].

In defibrillation, an electrical shock is delivered at a random point in the cardiac cycle; if the patient has no organized, underlying rhythm (e.g., in ventricular fibrillation), delivery of a random electrical shock poses no additional risk to the patient. The electrical shock depolarizes the entire defibrillating myocardium. For persons with a perfusing rhythm, such as VT with a pulse, the heart has some degree of organized electrical activity. Theoretically, the random delivery of an electric shock may allow the shock to fall on the T wave (i.e., during the vulnerable period of repolarization) and cause the heart to go into ventricular fibrillation. If that occurs, the patient should be immediately shocked again to abolish the ventricular fibrillation and restore a normal rhythm [10]. If the VT does not respond to direct current shock or if it recurs, administration of IV amiodarone may be used [5].

Consider this clinical situation:

Patient M is admitted to the emergency room complaining of palpitations, shortness of breath, and light-headedness. She is 23 years of age and reports that she has been in good health. She has no cardiac history or history of arrhythmias; she denies any cocaine use. The monitor shows that she is in a wide complex tachycardia at a rate of 160–170 bpm. The rhythm is slightly irregular, and the width of the QRS complexes is slightly greater than 0.14 seconds (normal is less than 0.10 seconds). Her blood pressure is 85/50 mm Hg, and her oxygen saturation on room air is 91%.

From the information presented above, it is difficult to determine if Patient M is in a sustained monomorphic VT or a supraventricular tachycardia with aberrant (abnormal) conduction through the ventricles. In some cases, precise identification of a wide QRS complex tachycardia cannot be readily determined from a 12-lead ECG. Expert consultation and/or electrophysiologic testing may be required to diagnose the exact mechanism [6,10].

Recommended interventions for wide complex tachycardia of unknown etiology are based on assessment of the patient's status as stable or unstable [5,6,10]. If the patient's status is unstable, the treatment of choice is immediate cardioversion or defibrillation (as described for unstable monomorphic VT). Adenosine should not be given if the patient's status is unstable as it can lead to ventricular fibrillation. If the patient is stable, assess the rhythm to determine if it is regular or irregular. Regular wide complex tachycardias are most commonly caused by VT, supraventricular tachycardia, and pre-excitation tachycardias that involve an extra conducting pathway. Appropriate interventions include adenosine IV, amiodarone IV, and synchronized cardioversion. Amiodarone can be effective in terminating either VT or supraventricular tachycardia. Adenosine can be effective in terminating a form of re-entry tachycardia or may be used to slow the rhythm down sufficiently so that a clear diagnosis of the underlying arrhythmia may be made. Use of beta blockers and calcium channel blockers should be avoided until the rhythm is definitively identified as supraventricular. Use of these drugs in VT can result in cardiovascular collapse [5,6,10].

Irregular wide complex tachycardias are frequently caused by atrial fibrillation with an uncontrolled ventricular response or multifocal atrial tachycardia [50].

Consider this clinical situation:

Patient N is admitted to the emergency room complaining of severe substernal chest pain. He is diaphoretic, and complains of nausea. His blood pressure is 100/50 mm Hg. The ECG monitor shows that he is having frequent episodes of nonsustained VT. On analysis, the QRS complexes are not uniform in configuration; however, they do not appear to be "twisting" around the baseline in the characteristic pattern of torsades de pointes. His ECG also shows signs consistent with myocardial injury and possible infarct. He is diagnosed with polymorphic VT.

Class I recommendations for the management of polymorphic VT include [5]:

Other points to consider in the management of polymorphic VT include [1,3,5,10]:

If torsades de pointes is caused by a prolonged QT interval caused by a single medication or the interaction of several QT prolonging medications, the offending medication(s) should be immediately stopped [5,10]. Recommended emergent therapies include direct current cardioversion or defibrillation. This may be achieved by [1,5,10,37]:

The AHA/ACC/HRS 2017 guideline recommends IV magnesium as a first-line therapy in patients with torsades de pointes [5].

Consider this clinical situation:

Patient O presents to the emergency room with symptoms of exacerbation of her congestive heart failure. She has a history of end-stage renal disease, peritoneal dialysis, insulin-dependent diabetes, coronary artery disease, and past coronary artery bypass graft surgery. As Patient O is walking into the emergency room, she suddenly collapses. ECG monitoring shows that she is in what appears to be a slow ventricular rhythm. Her QRS complexes are wide with abnormally tall and peaked T waves. Her rhythm rapidly deteriorates, and a sine wave pattern appears on the monitor. Lab analysis shows that her serum potassium level is over 10 mEq/liter (normal is 3.5–5.0 mEq/liter).

Unlike the management of some other ventricular arrhythmias, the management of rhythm changes caused by hyperkalemia must focus on the immediate correction of the potassium level. If the potassium level is not corrected, interventions such as defibrillation and the use of IV medications to restore blood pressure and heart rhythm will be ineffective. Possible urgent/emergency interventions for severe hyperkalemia include the administration of calcium chloride 500–1,000 mg IV or the administration of one ampule of D50W (50% dextrose in water) plus 5–10 units of regular insulin IV to restore a normal serum potassium level [10,19].

Note: Table 2 summarizes drugs used in the emergency management of life-threatening ventricular arrhythmias.

The ICD lead is a small, flexible insulated wire that connects the ICD generator to the patient's myocardium. An ICD lead is used to relay information about electrical activity in the heart and to deliver electrical therapy when indicated. Most commonly, ICD leads are inserted transvenously and positioned into the endocardium. Leads may have a small amount of a steroid in a reservoir at the tip of the lead. When the lead is positioned and attached, the steroid is released. The steroid, through its anti-inflammatory action, reduces the amount of inflammation and scar tissue that could develop around the tip of the lead. Minimizing scar tissue allows the electrode at the end of the lead to deliver electrical pacing impulses more effectively. Lead systems in an ICD can be very complex. For basic ICD function, a single lead, consisting of sense/pace electrodes and defibrillation electrode(s), is implanted into the right ventricle. For dual-chamber systems, both atrial and ventricular leads are implanted. ICD systems that provide dual-chamber biventricular pacing may use three leads, one positioned in each ventricle and one in the right atrium. The specific configuration of ICD leads may vary from manufacturer to manufacturer.

The generator houses the power source, microprocessor, and circuitry for the ICD. The microprocessor interprets signals transmitted from the patient's heart through a lead and determines what, if any, electrical therapy is indicated. Arrhythmia detection and selection of therapy are based on sophisticated programming that makes use of logic circuitry and complex algorithms. The generator is also responsible for generating and delivering electrical therapy through the lead system. Both a cardioverting shock and a defibrillating shock require more energy than the energy required by a pacemaker to send a pacing stimulus to the heart. To permit the higher energy shocks, an ICD generator contains capacitors that accumulate and store the necessary energy. The generator also houses a component that stores data about arrhythmias detected and electrical therapy delivered. This stored data may be retrieved noninvasively for analysis through the use of telemetered communication. Generators are small enough to be implanted in the pectoral muscle.

To function as a defibrillator, an ICD must have the capability of building up a high-energy charge rapidly. ICDs use lithium vanadium pentoxide or lithium silver vanadium pentoxide batteries. The batteries are sealed in titanium to prevent leakage. The average battery life is 8 years or longer and is influenced by the type and frequency of electrical therapy delivered [60]. As with a permanent pacemaker, when the battery is depleted the entire ICD generator must be replaced.

As with a permanent pacemaker, an external programmer may be used to communicate with the ICD to retrieve stored data or to program changes in the ICD's functioning. The programmer consists of a relatively portable specialized computer that is capable of communicating with a transceiver housed in the ICD generator through the use of remote telemetric communication technology. This is sometimes referred to as interrogation of the ICD. To interrogate the implanted ICD, the attending physician or other person trained in the use of programmers holds a wand directly over the generator site. When directed to do so, the wand permits data to be exchanged between the ICD and the programmer. Information that may be retrieved includes the current settings and information about arrhythmias detected and electrical therapy delivered. Analysis of stored data allows the physician to evaluate ICD programming to determine if the ICD is delivering electrical therapy appropriately. Data about the status of the battery and remaining battery life may also be obtained. The retrieved data may be printed for later analysis and/or documentation in the patient's medical record. Changes in ICD settings may also be transmitted from the programmer through the wand to the generator; this permits the physician to noninvasively adjust settings based on analysis of the ICD's past functioning and on assessment of the patient's current status, clinical signs, and symptoms [1,8,59].

The magnet feature is a programmable means to temporarily disable the device and may be programmed on or off. When programmed "on," the ICD will respond to the application of the magnet. In general, when the magnet mode is programmed "on," the direct application of a magnet over an ICD generator can inhibit the generator's ability to detect arrhythmias and to deliver electrical therapy until the magnet is removed. Depending on the manufacturer, programming of other magnet functions may be possible [8,60,62].

When the patient is scheduled for implantation of an ICD, any underlying medical conditions, such as congestive heart failure or recurrent myocardial ischemia, should be treated and under control. Electrolyte imbalances, particularly potassium and magnesium, should be corrected. The length of stay for ICD implantation is usually very short and often involves only an overnight stay in an acute care facility. In most cases, ICD implantation may be safely performed in the cardiac catheterization/electrophysiology laboratory. Occasionally, an ICD will be implanted in the operating room during surgery for coronary artery bypass grafting. The patient should be NPO for six to eight hours prior to the procedure. Basic preimplantation lab work is obtained, including a complete blood count (CBC), serum electrolytes, blood urea nitrogen, creatinine, prothrombin time, partial thromboplastin time, and a urinalysis. A baseline 12-lead ECG, arterial pressure, and lateral chest x-ray are also obtained. Baseline vital signs and physical assessment are performed and documented. The planned site for the ICD generator (usually the right or left subclavicular area) is scrubbed and shaved according to institutional protocol. The signed informed consent form is reviewed. The patient may receive a mild sedative prior to leaving the room, although additional sedation and/or analgesics will be administered during the procedure. Some institutions administer prophylactic antibiotics just prior to the procedure [8,62].

Education for the patient and the patient's family begins in the preoperative period and continues throughout the patient's life. Patient education in the preoperative period focuses on addressing the patient's immediate questions and concerns and on providing the patient and family with information about what to expect during implantation and in the period immediately following implantation. Many patients and their families are very anxious about ICD implantation. They may express fears of the ICD firing or the ICD failing to fire when needed. When interacting with them, there are some general points to keep in mind. Many patients who receive ICDs have had a sudden cardiac arrest; this usually represents a major crisis to the patient and to the patient's family. Similarly, because implantation of an ICD is often a graphic reminder that the patient has a life-threatening condition, ICD implantation is also often a time of crisis for the patient and family. During crisis, people do not learn new information or new skills well. They require time to adapt to the changes in the patient's health status and in his or her lifestyle. The short length of stay permitted for ICD implantation limits the amount of information that can be presented or learned. Written instructions should be provided as well as information on outside resources and community support groups (Resources). Patients and their families often have specific concerns about how an ICD may interfere with their normal activities or with their ability to use certain types of equipment. Eliciting any concerns or questions the patient has and responding specifically to those during the preoperative period is very important. Providing specific information about what the patient can expect before, during, and immediately after ICD implantation may also help to reduce the patient's anxiety. The following topics are often helpful to cover in the preoperative period [62,63,64]:

As always, it is important to allow time for the patient and family to ask questions and clarify concerns.

Once the procedure is completed, the patient is generally moved to a recovery area until he/she has recovered from the moderate sedation. Once the patient is awake and stable, he/she may be transferred back to the general unit. The goals of care in the immediate 24 to 48 hours postoperative period are to:

Complications that may develop following permanent ICD implantation include bleeding into the generator pocket, hemothorax, pneumothorax, and dislodgment of the leads. Upon return to his or her room, the patient's vital signs are monitored periodically. Continuous ECG monitoring is initiated. Spot checks of the patient's oxygen saturation level may be performed as needed. The generator site is assessed frequently for signs of excessive bleeding or swelling; if these are present, the attending physician should be notified immediately. Posterior-anterior and lateral chest x-rays are taken to evaluate the position of the leads as well as to rule out the presence of hemothorax or pneumothorax [8,59,60,62,63].

Many patients will not experience an arrhythmic episode during their short stay following ICD implantation. However, in the event that the patient does have an arrhythmia, it is important to know how the ICD has been programmed to respond. That information can be obtained by the staff from the patient's chart or by reviewing the summary sheet from the interrogation of the ICD that occurred at the end of the implantation procedure. The physician may choose to include information about the basic parameters as part of the patient's post-procedure orders. Information important to note includes:

Although complete assessment of ICD function requires specialized training in ICD therapy and arrhythmia management, some indications of abnormal (or inadequate) function may be noted by telemetry monitoring and observation of the patient. The most obvious indications are failure to deliver a shock when the patient goes into VT or ventricular fibrillation and a shock delivered inappropriately when the patient is not having a life-threatening arrhythmia.

Failure to deliver a shock may occur because the device failed to recognize the arrhythmia when it occurred. This may reflect a problem with the lead, which may have become dislodged or loose. It may also reflect a problem with the programmed parameters. Please review the following clinical example:

Patient U has returned to his bed following the implantation of an ICD with back-up bradycardia pacing capability. According to the progress notes, Patient U has ATP programmed for VT followed by a high-energy shock if the ATP is unsuccessful or if the patient goes into ventricular fibrillation. Patient U goes into VT at a rate of 180–190 bpm.

If the ICD is functioning properly, the telemetry monitor would show a group of pacing stimuli delivered rapidly; the spikes would be visible and would be intermixed with the VT beats. If the ATP is effective, the monitor would show the resumption of the patient's normal rhythm. If ATP is not effective and VT continues, the telemetry monitor should show a sharp spike on the screen, indicating the delivery of a high-energy shock. If the ICD failed to deliver therapy, the arrhythmia would continue until spontaneously terminated or terminated by external intervention; no evidence of pacing spikes of or defibrillation shock would be present on telemetry monitoring. Delivery of inappropriate therapy may occur as a result of sensing problems or problems in the ICD's programming.

Patient U's ICD is programmed to deliver ATP first, followed by a defibrillation shock if needed. Telemetry monitoring notes that Patient U's rhythm is his "usual" atrial fibrillation at a rate of 80–90 bpm. Patient U calls the desk abruptly to report that his ICD "just fired." A check of the telemetry record shows that the ICD has fired. The physician is notified; interrogation of the ICD and analysis of the data show that a high-energy shock was delivered inappropriately for atrial fibrillation.

Problems with programming are corrected through noninvasive interrogation and reprogramming of the generator. If a lead has become dislodged, an additional surgical procedure may be required to replace the lead in the correct position.

Assessment of function of an ICD with dual-chamber pacing capabilities can be complex. Consider these situations:

Yes. Patient V's device is also a dual-chamber pacemaker. A spike before the P wave indicates that the pacemaker has fired to depolarize the atria; often, P waves following a pacer spike look slightly different in shape from a normal P wave. A spike before the QRS complex indicates that the pacemaker has fired to depolarize the ventricles; paced QRS complexes are normally wider and more bizarre in shape than normal QRS complexes. Because a dual-chamber pacer can pace both atria and ventricles, it is normal to see pacer spikes in front of P waves, QRS complexes, or both on the same patient over a short space of time. Patient V's rate is within the programmed limits for his pacemaker.

The initial ECG strip obtained on admission shows normal ventricular demand pacing function. The rate is within the rate parameters programmed for the pacing function, and there is a pacing spike in front of each QRS complex. Paced QRS complexes are frequently wider and more bizarre than normal complexes. The second strip, obtained later, does not show normal characteristics for Patient W's device. The rate exceeds the programmed limit, the QRS complexes are wide and bizarre, and there are no pacemaker spikes in front of each QRS. The abnormal shape of the QRS complexes coupled with the rate and change in deflection suggest that this rhythm is probably ventricular. The absence of any response from the ICD may indicate abnormal function; however, more probably, the rate of this rhythm is too slow for the ICD to recognize it as VT.

Patients often experience postoperative pain in the generator site. Depending on multiple factors, patients may describe pain as mild to very severe. The patient's pain level should be routinely assessed using a 10-point pain scale (1 for least, 10 for most). The physician's orders should include analgesic medications; prescribed medications may range from acetaminophen to stronger narcotic analgesics. The effectiveness of pain medication should be assessed and documented. Any complaint of increasing pain despite adequate analgesic medication should be carefully investigated. Increased pain in the generator site may be an indication that bleeding is occurring into the pocket.

Infection related to cardiac device implantation has become a serious and costly issue. The incidence of pocket infection and/or bloodstream infection or device-related endocarditis has risen markedly. Hospitalizations for device-related infections increased out of proportion to the number of new devices implanted. Additionally, the presence of infection increases the risk of in-hospital death by more than twofold [65].

In 2010, the AHA published updated guidelines for the management of cardiovascular implantable electronic device (CIED) infections [65]. In this scientific statement, the writing group presented evidence-based recommendations for prevention and management of non-valvular device infections. Key elements of these guidelines include [65]:

Although infection with Staphylococcus spp. accounts for the majority of cases of CIED infections, other opportunistic pathogens (e.g., Burkholderia cepacia, S. aureus, S. marcescens, Pseudomonas aeruginosa) have also been implicated in CIED infection [66,67].

Early complications associated with ICD implantation include infection of the incision site or the pocket and accidental dislodgment of the leads. To lessen the risk of infection, instruct the patient to avoid getting the incision site wet. Also, the site should be inspected routinely for signs of redness, warmth, or drainage. During the patient's hospital stay, a dressing should be maintained over the incision site. If the dressing becomes dislodged or saturated with blood during this initial period, it may be changed using sterile technique. To lessen the risk of lead dislodgment, instruct the patient to limit the use and movement of the affected arm. Caution the patient to avoid extending the arm above the level of the shoulder. Use of a sling on the affected arm can serve to promote comfort and to remind the patient to limit use of that arm [8].

To decrease the patient's risk of developing a wound infection, include these instructions [8,63]:

To decrease the risk that an ICD lead will accidentally become dislodged during the initial four to six weeks after implantation, instruct the patient to [8,63,68]:

Patients frequently have questions about resumption of activities. Following ICD implantation, a patient may gradually resume his or her usual level of activity. Moderate physical activity is permitted as long as it does not cause dyspnea, chest pain, or other medical problems. To reduce the risk that the ICD may be triggered to fire by an increase in pulse rate caused by exertion, some patients undergo a treadmill stress test to assess their heart rate response to activity. If the patient's maximum heart rate is too close to the rate used in programming the ICD to deliver electrical therapy, the ICD may be reprogrammed or beta blockers may be prescribed for rate control [8,62,63,64].

Sexual activity may also be resumed with no restrictions as long as strain on the generator site is avoided during the immediate post-op period. As with any activity, the patient should discuss with his/her physician any dyspnea, chest discomfort, or dizziness that occurs with sexual activity. Many patients and their partners have concerns about the resumption of sexual activity. These include the concern that sexual activity will trigger the ICD to fire, concern that sexual activity will trigger the arrhythmia and the ICD will fail to fire, and concern about what the partner might experience if he/she is in contact with the patient when the ICD fires. Patients and their partners should be advised that someone touching them is not harmed if the ICD discharges [60]. Reassurance and a common sense approach can be very helpful [68,69].

Basic safety measures to cover with the patient and family include the ICD identification card, notification of other physicians and healthcare providers, restricted activities, what to do in the event that the patient receives a shock from the ICD, and when and how emergency help should be summoned [62,63,70].

At the time that an ICD is implanted, a temporary identification card is issued. This card lists specific information about the patient's device, including the type, manufacturer, date of insertion, and healthcare provider information. Make sure that the patient receives the temporary card before discharge. Explain that a permanent card will be mailed by the device manufacturer to the patient within a few weeks following discharge. Instruct the patient to always carry the identification card, and encourage a family member to keep and carry an additional copy. Explain that the card contains vital information that a physician would need to know to assess both the patient and the ICD function accurately in the event of a problem.

Instruct the patient and family to let all other healthcare providers, including dentists, know that the patient has an ICD. Some medical and dental procedures may temporarily affect the functioning of the device and will need to be modified. Other procedures, such as magnetic resonance imaging (MRI), are contraindicated for a person with an implanted device. Also instruct the patient to obtain a medic-alert bracelet or other appropriate ID jewelry. If possible and available, assist the patient to complete the form for the identification bracelet prior to the patient's discharge.

Unlike a permanent pacemaker, implantation of an ICD is usually accompanied by restrictions on patient activities. Because the patient may lose consciousness during an episode of VT or ventricular fibrillation, he or she should refrain from activities in which loss of consciousness could result in injury to themselves or to someone else. Driving is a major issue for persons with an ICD. At this time, state laws regarding driving for ICD recipients are not consistent. Commercial driving is generally prohibited. Some authorities recommend that people should not drive for a six-month period following the implantation of an ICD or for six months following the discharge of the ICD [60]. Loss of driving privileges can impose a significant hardship on the patient, and it is thought that many do not adhere to the six-month driving restriction. Some research has been done to attempt to quantify the risks of allowing persons with known life-threatening ventricular arrhythmias to drive. In one study, data showed that patients often had symptoms of arrhythmias while driving but that the occurrence of accidents was lower than the annual national accident rate [71]. In addition to driving restrictions, persons with ICDs are encouraged to avoid performing any activities in isolation (e.g., swimming, boating) where a loss of consciousness could result in injury. Generally, the use of heavy equipment or piloting an aircraft is also prohibited [68,72].

Many patients with an ICD will experience a discharge or shock from the ICD at some time. The experience can be very frightening. It is important to discuss in advance what the patient might expect and what the patient should do in the event of a shock. Make sure to provide written instructions and to review the information verbally. When discussing this with the patient and family, keep these points in mind:

Following a shock, emergency help should be summoned if the patient:

Plans should be made in advance for accessing emergency help. Emergency numbers for EMS or local ambulance companies should be visibly posted near a telephone along with contact numbers for the local hospital emergency room, the patient's physician, and a designated friend or family member.

If the patient's heart rate is frequently paced by the implanted device, the patient or a family member should be taught how to check the pulse. When teaching a patient to check his/her pulse, consider covering these points [73]:

Portable cordless telephones and many cell phones do not interfere with ICDs. However, as cellular phone technology is constantly changing, it is prudent to instruct patients to use some precautions when using or carrying a cell phone. Consider covering the following points [74]:

Generally, a person with an ICD can safely use normal household electrical devices as long as those devices are in good repair and properly grounded. Devices that may be safely operated include [74]:

The following cautions and precautions should be noted:

For more specific information about the use of a particular device, the patient may review the material provided about his/her defibrillator by the manufacturer or, in some cases, obtain additional information from the manufacturer's website.

With the heightened emphasis on security checks at airports, patients and families may have concerns about how to get through airport security safely and with as little hassle as possible. Studies have shown that while airport security devices do not damage an ICD, the security devices will detect the implanted metal and trigger the alarm. To facilitate getting through airport security, instruct the patient to [68,74]:

Commercial antitheft devices are commonly used in many department stores in the United States. These devices have the potential to disrupt the functioning of the pacemaker temporarily. Instruct the patient to walk through the security screening device at a reasonable pace; also instruct the patient to avoid lingering in the area around the antitheft devices.

Most medical and dental diagnostic procedures will not interfere with the proper functioning of a person's ICD. For example, dental x-rays, dental drills, dental ultrasonic probes used in dental cleaning, chest x-rays, CT scans, nuclear medicine studies, mammograms, and fluoroscopy do not cause interference and are considered "safe." Some procedures, however, will disrupt normal ICD functioning. For example, MRI (which uses a very large, extremely powerful magnet) is contraindicated for anyone with an ICD. Other procedures have the potential to disrupt ICD functioning and may cause extra shocks. Instruct the patient to let all healthcare providers know that he/she has an ICD before a procedure is performed. If the procedure has a risk of disrupting the ICD's functioning, the patient should discuss the risks and benefits of having that procedure done with the physicians. In some instances, specific precautions may be taken to reduce the risk that a given procedure will disrupt the ICD's function. ICD manufacturers also recommend that the pacemaker be interrogated to verify proper programming following performance of a procedure that could potentially generate enough EMI to disrupt programming or functioning.

Research has shown that patients with ICDs report strong feelings of fear, terror, and anxiety [60]. If the patient experiences a shock from the ICD, his or her anxiety and fear may increase. If the ICD fires without warning, patients may become additionally anxious and fearful. Common fears include fear of a shock, fear that the device will fail, and fear of death. Persons with an ICD also have been found to experience a strong sense of loss of control. They struggle with the realization that the device may fire without warning and that they have no control over when the device fires. Some people who experience a shock may respond by restricting their activities in an attempt to avoid "triggering" the device another time. They may repeatedly analyze the circumstances of the initial shock, attempting to establish a "cause and effect" that will help them avoid a future shock. Occasionally, people with an ICD develop the phenomenon of a "phantom shock." Briefly defined, a phantom shock occurs when the patient feels that the ICD has fired although the device actually has not discharged an electrical shock. People may experience anger and depression over their loss of independence and their decline in health status [60]. Other issues include employability, maintenance of their current job, obtaining a different job, eligibility and maintenance of insurance coverage, and the costs involved in ICD follow-up and medical care. Patients also report that they experience a variety of physical complaints during the months following ICD implantation. These include insomnia and sleep disturbances, lack of energy, dizziness, weakness, decreased exercise tolerance, and weight loss or gain. Short-term memory loss, difficulties in coping, and problems with family functioning may be experienced. The patient's partner and close family and friends also report anxiety and fear related to the implantation of the ICD. Some express the fear that they "will not know what to do if the ICD fires." Some partners report changes in sexual activity brought about by the fear that such activity will trigger the ICD. Some people are concerned that they might experience a shock if they are touching the patient when the patient's ICD fires. Persons with ICDs report that their partners and other family members often become overprotective [60,62,64,69,70]. Interventions that are helpful to the patient and family include:

People often experience major lifestyle alterations following ICD implantation. Depending on the type of job and the patient's overall status, the patient may or may not return to work. Some studies have shown that many people who return to work choose to retire within the following 6 to 12 months. Reasons individuals give for not continuing to work include a decrease in exercise tolerance, impaired concentration and short-term memory, and poor overall status. The patient's normal patterns of interaction with family and close friends may change; many patients report that they are forced to become dependent on other people for assistance if they cannot drive themselves to the store, medical appointments, and other routine activities. Especially for younger people, participation in previous hobbies and sports may be limited or no longer possible [70].

Patients with ICDs should be observed in a dedicated ICD clinic. These patients generally are seen one week after implant for a wound check, one month after implant for device interrogation, and three months post-implant for repeat device interrogation. The follow-up interval then can generally be increased to once every six months if the patient is clinically stable [60]. The generator site should be carefully assessed for indications of impaired healing or signs of complications. Complications that may occur include infection in the pocket, development of a hematoma in the pocket site, and erosion of the generator or the lead through the tissue and skin. Persons with diabetes are more at risk to develop an infection. Persons taking anticoagulants are at risk to form a hematoma in the generator pocket [75]. Signs of impaired healing may include:

Infection, hematoma, and erosion are serious complications. Infection in the ICD site or along the leads necessitates the removal of the device. Because of the risk of sudden cardiac death, the patient may have to remain in the hospital, where emergency equipment is readily available, until the infection resolves and the device can be re-implanted. In addition to wound assessment, the functioning and programming of the ICD should be assessed. Noninvasive interrogation of the generator is done to retrieve stored information and information about any arrhythmia events detected or any delivered therapy. The follow-up visit also provides an opportunity to obtain and document patient information as required by law. U.S. regulations require that medical device manufacturers maintain a correct and current database of all persons in the United States who have an implantable medical device [8,64]. Recorded information includes the patient's address, telephone number, and physician. Patients should be instructed to notify their specific device manufacturer when they change addresses, when they get a new telephone number (or when their area is code is changed), or if they change their physician [8,64].

Long-term follow-up of patients should be done by a physician who is experienced in ICD and arrhythmia management. It should occur in a setting that also provides the services of an experienced cardiovascular nurse and experienced technical support staff. Available equipment should include a programmer, ECG recorder, and an emergency cart with a defibrillator capable of external defibrillation. Facilities for ambulatory monitoring, exercise stress testing, and echocardiography should be readily available if needed for extended evaluation of the ICD function or management of the patient's arrhythmias. There is no universal agreement about a set pattern or frequency of follow-up visits. In general, follow-up should occur at one-to four-month intervals or when indicated by suspected problems in device functioning or changes in the patient's status [4,8,59,63]. Elements of long-term follow-up include:

Because assessment of the patient's defibrillation threshold involves programmed stimulation to induce ventricular fibrillation, the defibrillation threshold is not routinely checked at follow-up visits. It may be checked at the time of implantation or approximately one month following implantation. Changes in the patient's antiarrhythmic therapy or significant medication changes may require a recheck of the defibrillation threshold at some point.

In an "electrical storm," a patient receives multiple appropriate shocks from his or her ICD for VT or ventricular fibrillation within a relatively short period of time. Most sources define an ICD storm more precisely as at least three or more appropriate shocks within 24 hours [81,82,83,84]. Factors that may trigger electrical storm include modification of or noncompliance to drug therapy, worsening of heart failure, early postoperative period, emotional stress and anger, alcohol excess, electrolyte abnormalities, and myocardial ischemia. Most cases, however, occur without any apparent cause [79]. More than 80% of cases of electrical storm are caused by episodes of monomorphic VT; however, it can also occur due to polymorphic VT/ventricular fibrillation. Knowledge of the type of underlying arrhythmia is important when selecting a management strategy. Electrical storm has been reported in 10% to 40% of patients in secondary prevention; the incidence is lower in primary prevention [79].

ICD storm can be extremely frightening and painful for the patient. Patients may be concerned that the device is malfunctioning while at the same time they may be realistically frightened that the increase in ICD shocks indicates deterioration in their cardiac status [79]. Patients who experience ICD storm should be instructed to contact their physician immediately and should expect to come to the clinic or the hospital for evaluation [63,64,79].

During medical evaluation for ICD storm, the patient's ICD is interrogated and stored data about any events detected and therapy or therapies delivered is retrieved and analyzed. From the data and the analysis, one can determine if the ICD accurately detected the arrhythmia and provided the appropriate electrical therapy as programmed. Sharing the information that the ICD functioned as programmed with the patient may reduce some of the patient's anxiety about the reliability of the device's functioning, but it may also increase concerns about changes in his or her health status that may be causing the increase in episodes of life-threatening arrhythmias [63,64]. It is important, therefore, to assess the patient's psychologic reaction by asking about his/her perception of the shocks and addressing any misconceptions; determining whether the patient is feeling anxious or helpless or seems panicked; and ensuring that the patient has a source of support (e.g., family, friends, clinical). If the patient is extremely distressed, stabilizing interventions such as anxiety-reducing medications may be offered, particularly if distress is considered to be a contributing cause of repeated arrhythmias [79].

After ICD interrogation confirms that the shocks were appropriate and that no device malfunction occurred, clinical management focuses on strategies to prevent high-energy shocks through other means of arrhythmia control. The treatment option of choice is the addition of antiarrhythmic medications. Although some antiarrhythmic medications have been linked to increased mortality in patients with heart disease who do not have an ICD, many antiarrhythmic medications may be safely used in persons with an ICD to prevent repeated defibrillation shocks [5]. Antiarrhythmic drugs may be used in persons with an ICD to suppress episodes of nonsustained VT, suppress episodes of sustained VT, slow the rate of VT and increase the efficacy of ATP in terminating the arrhythmia, and prevent the syncope that may be associated with faster rates of VT.

When antiarrhythmic drugs are used, the potential interaction between the actions of the antiarrhythmic drugs and the defibrillator's ability to depolarize the heart effectively should also be considered. Proarrhythmic effects of antiarrhythmic medications can result in the increased frequency of VT, and they can also convert nonsustained VT to sustained VT. Due to changes in conduction caused by antiarrhythmic medications, use of these drugs may make it more difficult for the ICD to sense the heart's rhythm accurately and may result in an increase in the defibrillation threshold (i.e., the energy required to depolarize the fibrillating heart effectively) [79]. Defibrillation threshold testing may be indicated to identify the appropriate setting after the addition of antiarrhythmic drugs. Because of negative inotropic effects on myocardial contraction, the use of some antiarrhythmic drugs can also exacerbate congestive heart failure, creating more arrhythmias or making it more difficult for the ICD to terminate the arrhythmias. To facilitate the efficacy of antiarrhythmic drugs and limit negative side effects, only a single antiarrhythmic drug should be used, if possible. Research has found that the use of multiple antiarrhythmic medications is not helpful, as it can increase the risk of new ventricular arrhythmias and may exacerbate underlying congestive heart failure [1,8,59,63,64].

Factors that increase the likelihood that ventricular arrhythmias will reoccur include the presence of decompensated heart failure, poorly controlled coronary artery disease or recurrent ischemia, and electrolyte imbalances [22]. "Fine-tuning" the patient's medical regimen for optimal management of underlying cardiovascular disease and correction of electrolyte imbalances can help to limit recurrent episodes of VT and ventricular fibrillation. In addition, for a select group of patients, the use of radiofrequency ablation may be used to eliminate re-entry circuits and reduce the frequency of ventricular arrhythmias [79].

Patient Z, a man 75 years of age with ischemic cardiomyopathy, presents to the emergency room with the complaint that his ICD had fired three times over the last 24 hours. When asked, he reports one shock in the early morning and two shocks about three hours apart in the late afternoon. He is placed on continuous telemetry monitoring; the monitor shows frequent runs of nonsustained VT. When his ICD is interrogated, the data confirm that his ICD discharged at the approximate times Patient Z reported and that the discharges were appropriate. On physical exam, Patient Z appears ill and slightly dehydrated. He has a low-grade fever, but his other vital signs are relatively unchanged from his norm. When questioned, Patient Z reports that he has had "the flu" for a couple of days; he reports severe episodes of vomiting and diarrhea. He admits to continuing to take his furosemide but says he has been unable to "keep down" food or his potassium supplements. Lab tests show that his potassium level is 2.8 mEq/L and his magnesium level is 1.2 mg/dl. Immediate IV supplements of potassium and magnesium are administered. The patient is admitted to an inpatient unit for monitoring and stabilization. Patient Z's electrolyte levels return to normal, and he recovers from his illness. No further ectopy is noted. A review of his record finds that Patient Z tends to go into VT when his potassium levels drop. Due to the patient's sensitivity to hypokalemia, the treating physician decides to add an oral antiarrhythmic to Patient Z's regimen. Patient Z is subsequently discharged home.

Amiodarone prolongs action potential duration and the refractory period and slows sinus rate. On ECG, amiodarone can increase PR and QT intervals. Amiodarone has a slow and variable onset of action. A therapeutic effect may be achieved in several days, but it usually takes one to three weeks, even with the use of loading doses. It is eliminated slowly and remains for days following the discontinuation of oral therapy [37].

Chronic amiodarone therapy is associated with severe side effects, including pulmonary fibrosis, liver function abnormalities, photosensitivity, hyper- or hypothyroidism, acute respiratory distress syndrome, corneal microdeposits, and photophobia [1,93,94]. Other side effects include dizziness, fatigue, malaise, anorexia, and constipation [37].

It is recommended that amiodarone therapy be initiated in the hospital setting with continuous ECG monitoring. A loading dose may be administered initially by IV or by mouth, followed by decreasing oral doses at a set interval. Usual dosing includes [1,93,94]:

The lower loading and maintenance dosage should be considered for women, elderly patients, and all patients with low body weight [37]. Electrolyte imbalances, especially hypokalemia and hypomagnesemia, should be corrected before amiodarone therapy is initiated. Electrolyte levels should be periodically monitored in patients who are at risk to develop recurrent electrolyte imbalances, such as those with renal failure or those on chronic diuretic therapy [37].

Amiodarone can increase the defibrillation threshold in persons with an ICD. Some sources recommend using it cautiously in persons who already have a high defibrillation threshold [90,93,94,95].

Class II effects slow the heart rate and the rate of conduction through the AV node. Class III effects increase the refractory period of the AV node, prolong ventricular action potential, and increase the effective refractory period in both atrial and ventricular muscle. On surface ECG, it can prolong the QT interval. At low doses, only beta blocking effects are seen. Doses of 160 mg per day or more are required before Class III actions are seen [37].

Proarrhythmic effects associated with sotalol include torsades de pointes, the development of new ventricular arrhythmias, and bradycardia. Sotalol may exacerbate congestive heart failure. The patient should be monitored for an excessively prolonged QT interval or signs of increasing renal compromise [37,93,95].

Only the oral form of sotalol is approved for use in the United States. The initial oral dose is 80–120 mg twice a day. The dose may be gradually increased to a maintenance dose of 160–320 mg in divided doses. The maximum recommended oral dose is 320 mg per day [37,93,95].

Sotalol should not be used in the presence of uncompensated congestive heart failure or bradycardia. It should be used cautiously in persons with renal impairment, pulmonary disease, or diabetes. Lower dosage should be considered with the elderly [37]. If the benefit outweighs the risk, the patient should be admitted to an inpatient setting with telemetry monitoring for the initiation of therapy.

Procainamide increases the refractory period of the atria, the bundle of His-Purkinje system, and the ventricles. It slows conduction through most myocardial tissue, with variable effects in the AV node. Procainamide also decreases myocardial excitability. When metabolized, it converts to N-acetylprocainamide (NAPA), a metabolite with active antiarrhythmic properties [37].

Some persons who take procainamide can develop a positive antinuclear antibody titer with or without the symptoms of a lupus-like syndrome. Significant proarrhythmic effects may be seen with procainamide, including heart block and new or worsening ventricular arrhythmias [1,93,94]. Other side effects include diarrhea, anorexia, agranulocytosis, and seizures [37].

As stated, the oral forms of procainamide are no longer available in the United States. The initial IV loading dose is up to 17 mg/kg administered at 20–50 mg/minute or 100 mg at a rate of 20–50 mg/minute every 5 minutes [1,37,93,94].

The serum level of procainamide should be monitored; the therapeutic level is 4–10 mcg/mL. Toxicity develops with levels over 10–12 mcg/mL. NAPA levels should be monitored as well [37]. Clinical signs of toxicity can include confusion, dizziness, drowsiness, nausea, vomiting, and arrhythmias [93,94].

Mexiletine alters sodium ion transport across the myocardial cell membrane; it decreases the rate of rise of the action potential and the effective refractory period in Purkinje fibers [37]. In patients with normal conducting systems, it does not prolong the QRS or QT.

Mexiletine has significant proarrhythmic effects. Other side effects include dizziness, dyspnea, heartburn, nausea, and vomiting [37,93,94].

An initial loading dose of 150–200 mg is given orally every 8 or 12 hours (may load with 400 mg if necessary). The dose may be increased by 50–100 mg every two to three days to a maximum of 1,200 mg per day. The usual maintenance dose is 200–300 mg every eight hours [37,93,94].

Use of mexiletine is contraindicated in second-or third-degree heart block unless the patient has a pacemaker [37].

Quinidine decreases myocardial excitability and slows conduction velocity [37].

As mentioned, quinidine can have significant proarrhythmic effects, including the development of torsades de pointes. Side effects may be extremely troublesome and cause the patient to discontinue the medication independently. Side effects include nausea, anorexia, abdominal cramping, and diarrhea [37].

Quinidine sulfate in a dose of 200 mg is equal to 267 mg of quinidine gluconate [37]. A test dose of 200 mg taken orally may be administered to adults several hours prior to the full dose to test for adverse effects. Quinidine gluconate is rarely used parenterally. Common doses of quinidine sulfate are 200 mg every six hours or every eight hours for long-acting forms. The dose may be calculated as 15–60 mg/kg/day in four to five divided doses or 6 mg/kg every four to six hours [37,93,94].

Quinidine is no longer recommended for the treatment of asymptomatic PVCs.

Propafenone slows conduction in cardiac tissue by altering normal ion transport [95,96].

In addition to proarrhythmias, propafenone may cause dizziness, constipation, nausea, and vomiting [37].

Propafenone may be initiated at a dose of 150–300 mg every eight hours; the dose may be increased at three-to four-day intervals as needed to up to maximum dose of 300 mg every eight hours. Propafenone should be initiated in an inpatient setting with telemetry monitoring [37,93,94].

Use of propafenone is contraindicated in conduction disorder (unless the patient has a pacemaker), electrolyte imbalances, and uncontrolled congestive heart failure. Lower doses may be used in elderly patients [37].

Disopyramide suppresses ventricular arrhythmias by reducing myocardial excitability and decreasing the speed of conduction. It has negative inotropic effects and therefore can reduce the force of contraction of the heart [37].

Common side effects include constipation, dry mouth, urinary hesitancy, and urinary retention [37].

The initial dose is 300 mg (immediate-release form) followed by 150–300 mg every 6 hours (immediate-release) or 300 mg every 12 hours (controlled-release) [37]. The total dose per day should not exceed 600 mg. For persons with compromised left ventricular function, the dose should be reduced to 200 mg (immediate-release) as an initial dose followed by 100 mg every 6 to 8 hours (immediate-release) or 200 mg every 12 hours (controlled-release) [37,93,94].

Use of disopyramide is contraindicated in the presence of severe conduction abnormalities, such as sick sinus syndrome and second-or third-degree heart block, unless the patient has a permanent pacemaker [37].

Flecainide suppresses ventricular arrhythmias by prolonging the refractory period, and slowing conduction in the atria, AV node, His-Purkinje system, and ventricles [37].

Common side effects include the increased risk of proarrhythmias, headache, and dizziness [37].

The initial oral dose is 50–100 mg twice a day. If indicated, the dose may be increased to 150 mg twice a day. The maximum dose is 400 mg/day [37,93,94].

Flecainide should be used very cautiously in persons with congestive heart failure. It may reduce left ventricular function and exacerbate episodes of congestive heart failure [37].

The preparation for radiofrequency ablation is similar to that for cardiac catheterization. The physician should explain the procedure and obtain informed consent. Risks associated with radiofrequency ablation include bleeding at the insertion site(s), hematoma formation, pneumothorax, and risk of death from arrhythmias that are invoked during the test and not terminated. Prior to the procedure, the electrophysiologist will review any antiarrhythmic medications that the patient is taking and make a recommendation about tapering or stopping those medications before the study. The patient should be NPO for six to eight hours prior to the procedure. Routine lab work, including a CBC, electrolyte panel, prothrombin time/international normalized ratio, and urinalysis should be done. A chest x-ray and ECG are also performed [7,9,27,97]. The ECG is usually performed to assess the location of scarring, if any, and to assess the overall pumping function of the heart [97,98].

A VT ablation is carried out in a specially equipped cardiac catheterization lab. As with cardiac catheterization, the patient is monitored continuously for blood pressure, ECG, and oxygen saturation. Because electrophysiology procedures are frequently very long, a Foley catheter is inserted for comfort and to prevent complications from urinary retention. Intravenous heparin is usually administered to help prevent the formation of blood clots before, during, and after ablation [98]. The patient undergoes moderate sedation, usually with agents such as midazolam and fentanyl [97]. After the patient is sedated, vascular access, most commonly using the femoral vein, is obtained and catheters containing multiple electrodes are passed transvenously to desired positions inside the heart [97].

VT is induced and then a complex process of mapping the arrhythmia occurs. Mapping may include the identification of the arrhythmia's site of origin, spread of activation, and critical site(s) [97]. Only patients who can hemodynamically tolerate sustained VT for a prolonged period can undergo electrophysiology for mapping and possible ablation [7,9,27]. The procedure generally lasts from three to six hours [98].

Postprocedure care is similar to postcardiac catheterization care. The patient's vital signs, oxygen saturation, and ECG rhythm are monitored. The sites used for insertion of the diagnostic catheters are monitored for signs of bleeding or hematoma formation [7,9,27].