After the myocardial cell has depolarized, there is a period of time that the cell cannot generate an action potential in response to another electrical impulse; this is referred to as the "absolute refractory period." As the cell continues to repolarize, an "effective refractory period" occurs in which the cell can transiently depolarize in response to an electrical impulse but generally will not develop enough of an action potential to propagate the impulse to surrounding cells. As repolarization nears completion, the cell is said to be in a "relative refractory period;" in this period, a strong electrical stimulus can trigger the cell to depolarize and create another action potential [13,14].

The electrical events that occur in the heart are reflected in the ECG waveform. Components of a normal beat are illustrated in Figure 1[15].

A PVC is an abnormal beat that is initiated at some point in the ventricles of the heart. With PVC, the electrical impulse is not conducted through the ventricles normally. As a result, ventricular depolarization is abnormal and ventricular contraction is impaired. On a surface ECG, the abnormal ventricular depolarization is represented by a QRS complex that is wider and more bizarre in shape than the normal QRS complex. Frequently, PVC occurs earlier in the cardiac cycle than the next normal beat would occur and interrupts the person's underlying heart rhythm. Other names for PVCs include ventricular ectopic beats, ventricular premature depolarizations (VPDs), or ventricular extra systoles. ECG characteristics of PVC include [1,11,12,18]:

PVCs may occur infrequently and in isolation, or they may occur in an identifiable pattern. Terms commonly used to describe PVC patterns of occurrence include [19]:

The defining ECG characteristics of monomorphic VT include:

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]:

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].

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].

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]:

The most lethal and disorganized ventricular arrhythmia is ventricular fibrillation. In ventricular fibrillation, electrical activity is completely chaotic. No effective depolarization occurs, and there is absolutely no effective contraction of the heart. Complete circulatory collapse occurs, and emergency intervention is required [39]. Defining ECG characteristics include:

Coronary artery disease (CAD) is the single most common etiologic factor predisposing patients to ventricular fibrillation [40]. Other common causes include the deterioration of VT and severe bradycardia caused by MI [40]. Ventricular fibrillation may also develop in persons with severe heart failure. Other conditions that are linked to ventricular fibrillation include [1,18,36]:

The first link in the Chain of Survival concept is recognition and activation. In simple terms, this means that a cardiac arrest victim receives help as soon as possible. Two actions are critical: recognition of the emergency and activation of the emergency medical system. Efforts have been made to strengthen the link of early access through increasing public education that targets individuals who are most likely to witness a cardiac arrest in a community or home setting. Research has shown that a person who witnesses a cardiac arrest is more likely to call other people (e.g., friends, neighbors, physicians) before activating the emergency communication system. Consequently, additional public education has been directed toward a "phone first" campaign that instructs people to notify EMS first before making other calls or initiating cardiopulmonary resuscitation (CPR). Other efforts have been directed toward the establishment of an easily dialed emergency dispatch system and toward public education to ensure that people living in any given community are familiar with the local emergency number to call. Healthcare professionals can help to strengthen the link of early access for patients through patient and family education. Pertinent patient/family education may include helping high-risk patients and family members to make plans for emergencies. When to call for emergency help, how to access the emergency medical system in their local area, and identifying an appropriate, easily visible place to post emergency numbers are key points to include. When appropriate, health professionals can encourage family members to enroll in local CPR courses [41,42,43].

The prompt initiation of CPR as soon as a cardiac arrest is recognized is critical [6]. The structured pattern of chest compressions and ventilations can produce adequate blood flow to the brain and the heart until EMS can arrive and initiate more advanced measures. To strengthen this link, the American Heart Association and American Red Cross have implemented training programs for citizens in an attempt to ensure that bystanders who witness a cardiac arrest will know how to perform CPR. Some data collected suggest that mass training of the civilian population to perform CPR may not be the most effective, because many people who choose to attend training will never see a cardiac arrest. Alternative suggestions for increasing the availability of trained lay rescuers include [6,41,42,43]:

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].

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.

Class IIa Recommendations

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].

Key points to cover in a patient history include:

In persons with structurally normal hearts, isolated PVCs can occur normally and without symptoms. These PVCs carry minimal risk of producing sudden cardiac death and do not require treatment. If the patient experiences symptoms such as palpitations, light-headedness, near syncope, or reduced activity tolerance, treatment to control the PVCs to decrease symptoms may be implemented. Initial treatment may focus on explanation of what the arrhythmia is and why it is causing symptoms coupled with reassurance that the arrhythmia is not dangerous and will not lead to serious problems. Given the serious side effects associated with antiarrhythmic drug therapy, antiarrhythmics are often not the first treatment of choice for these patients. The patient may be assessed for the use of substances such as caffeine, nicotine, cocaine, and some over-the-counter medications that have been known to trigger PVCs. Often, reduction or elimination of the offending substance(s) is sufficient to eliminate the PVCs and related symptoms. For persons whose symptoms persist, the use of antiarrhythmic medications or radiofrequency ablation may be considered. Particularly in hospitalized patients (or persons who are ill), the abrupt occurrence of PVCs or nonsustained VT in persons without heart disease may be triggered by electrolyte imbalances such as hypokalemia or hypomagnesemia. Often, correction of the electrolyte imbalance eliminates the arrhythmias [1,3,25].

In persons with known risk factors for heart disease, the abrupt occurrence of PVCs or nonsustained VT may be an indicator of myocardial ischemia or infarction. In these cases, further assessment is necessary. If ischemia is present, measures to reduce the ischemia are indicated. If the arrhythmias are severe, medications such as IV lidocaine may be used to suppress them. In persons with known heart disease who are not experiencing acute ischemia, the occurrence of PVCs and nonsustained VT does not usually lead directly to the development of a sudden cardiac arrest; however, their occurrence may be an indication that the patient's underlying disease has progressed to the point that the patient's overall risk of developing sudden cardiac death has increased. In these patients, the long-term goal of therapy is not the suppression of the PVCs or the nonsustained VT but rather the prevention of sudden cardiac death [1,3,25].

Guidelines from the AHA, ACCF, and HRS regarding device-based therapy for cardiac rhythm abnormalities make extensive recommendations for the appropriate use of ICD therapy. In brief, the strongest (i.e., category I) indications for ICD implantation includes [61]:

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.

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.

A routine feature in any modern ICD is back-up ventricular demand pacing. Sometimes referred to as VVI pacing, back-up ventricular demand pacing was primarily designed to pace the heart if a slow heart rate occurred following the heart's recovery from a defibrillation shock. In persons whose ventricular arrhythmias were thought to result when the patient's heart rate dropped, the VVI function in the ICD could also provide intermittent pacing. However, back-up bradycardic pacing was never designed to function as a full-time pacemaker for the heart. One of the primary limiting factors was battery life; continuous pacing would significantly decrease the battery life of the ICD. For a period of time, if a patient required ICD therapy and pacemaker therapy, two separate devices were implanted. This worked adequately, but device interactions created some programming problems. Now ICDs are designed to provide both full pacemaker and ICD therapies. Options include [8,60]:

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]:

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]:

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:

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:

In the past, a large number of people with ICDs received inappropriate electrical shocks for rhythms other than VT or ventricular fibrillation [77,78]. Non-life-threatening rhythms that the ICD commonly mistook for VT included sinus tachycardia and supraventricular tachycardia [59,79]. Given the enhancements incorporated into current generation ICDs, the risk of shocks for sinus tachycardia or supraventricular tachycardias is much less. In addition, the use of dual-chamber ICDs that can sense electrical activity in the atria has improved the device's ability to discriminate between VT and rapid atrial fibrillation or atrial flutter. When the patient suspects an inappropriate shock in the absence of persisting severe symptoms (e.g., chest pain, shortness of breath, rapid palpitations), he/she should contact the physician and schedule an appointment for interrogation of the device for stored data and testing of lead function [79]. Device problems that may result in delivery of inappropriate shocks include EMI, T-wave oversensing, a dislodged lead, a fractured lead, or a break in the insulation covering the lead [59]. Replacement of the lead may be required.

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].

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.

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]:

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].

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].

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].

Surgery to resect or reconstruct a left ventricle that has been severely damaged from a MI has been used to improve the heart's pumping ability and to reduce ventricular arrhythmias. When the left ventricle is damaged by an MI, an area of scar tissue forms; the size of the scar depends on the extent or severity of the MI. The presence of scar tissue in the heart interferes with the heart's ability to contract normally, producing signs of reduced cardiac output. The scar tissue also interferes with normal conduction of electrical impulses and creates conditions for ventricular arrhythmias to develop. Theoretically, reconstruction of the ventricle to remove the scar tissue permanently from the areas of functioning myocardium should improve the heart's pumping ability and reduce the incidence of arrhythmias. Various techniques have been developed to identify and separate the area of scar. If the area of scar is large, the dead tissue may be surgically removed and a patch applied. In some cases, at least two rows of circulation stitches may be placed around the border of the scar tissue; the stitches are pulled together so the scarred area is permanently separated from the functioning tissue. Reconstructive surgery is a high-risk procedure involving heart-lung bypass and is not indicated for all patients who have reduced left ventricular function following MI. Other names for reconstructive surgery (or similar procedures) include endoventricular circular patch plasty repair, Dor procedure, surgical ventricular restoration, and left ventricular aneurysmectomy reconstruction [104,105].

Long-term follow-up studies have shown that medical care costs are higher in patients with ICDs than in those without [4]. Some clinical trials have included measurements of both cost and clinical effectiveness. Based on available data, the Writing Group for Device-Based Therapy notes that [4]:

Rationale and comments: Patient CC has risk factors for sudden cardiac death, including reduced left ventricular function, ischemic heart disease, the continued presence of PVCs, and episodes of nonsustained VT after CABG surgery. Electrophysiology is indicated to determine if he is at high risk. If he is, implantation of an ICD is indicated. Some patients with heart failure who require an ICD may benefit from cardiac resynchronization therapy as well. In cardiac resynchronization therapy, a biventricular pacemaker is implanted, leads are placed in the right and left ventricles, and the device is programmed to coordinate the contraction of the right and left ventricles to restore a more normal pattern of ventricular contraction. Re-synchronizing ventricular contraction has been shown to improve functional status.