Patient A is man, 65 years of age, with dilated cardiomyopathy of seven years duration and a left ventricular ejection fraction of 12%. He presented to the heart failure clinic for a routine evaluation. The patient denied symptoms of heart failure over the preceding months. He was on a regimen of quinapril 20 mg twice a day, furosemide 80 mg daily, and digoxin 0.25 mg daily. The patient had been intolerant of beta-blockers in years past due to profound bradycardia. Physical examination was notable for a blood pressure of 120/90 mm Hg, increased jugular venous pressure, and an audible murmur. TEB revealed a cardiac index of 1.7, systemic vascular resistance (SVR) of 2,249, and a thoracic fluid content of 0.0035. On a previous periodic evaluation four months prior, the cardiac index (a measure of cardiac output) was 2.5 L/min/m2, with an SVR of 1,400 and a thoracic fluid content of 0.0034. In spite of the patient's asymptomatic state, this change in his hemodynamics led to a recommendation to increase his quinapril to 40 mg twice daily.

Upon repeat evaluation four weeks later, Patient A's blood pressure was 108/72 mm Hg, and he had an otherwise negative cardiac examination. Repeat TEB showed a cardiac index of 2.4, with an SVR of 1,398 and a thoracic fluid content of 0.028. In view of the achievement of these target values, no changes were made in his medications on this visit.

On another periodic visit three months later, Patient A again stated that he felt well and denied dyspnea, orthopnea, or edema. His blood pressure was 102/80 mm Hg, and he had increased jugular venous pressure with a mild hepatojugular reflux. However, there were no other pulmonary and cardiac findings. Repeat hemodynamic indices revealed a cardiac index of 2.7, with an SVR of 1,123 and a thoracic fluid content of 0.041. This elevated thoracic fluid content prompted an increase in his diuretic therapy. Two years later, Patient A has remained asymptomatic on this stable medical regimen.

Patient B, a woman 71 years of age with idiopathic dilated cardiomyopathy, an eight-year history of symptomatic heart failure, and an ejection fraction of 25% presented with complaints of fatigue, lethargy, and thirst on a regimen of lisinopril 20 mg daily, digoxin 0.125 mg daily, and bumetanide 2 mg daily. Examination showed a blood pressure of 84/60 mm Hg, pulse rate between 80 and 88 beats per minute (bpm) with atrial fibrillation, clear lungs, no gallop, and no pedal edema. Noninvasive hemodynamics showed a cardiac index of 2.5, with an SVR of 1,497 and a thoracic fluid content of 0.029. It was thought that Patient B's symptoms were likely related to volume depletion, and diuretics were temporarily discontinued. She was scheduled for a follow-up visit, with instructions to measure her weight daily.

Two weeks later, Patient B presented with complaints of abdominal fullness and a one-pound weight gain, without dyspnea or peripheral edema. Blood pressure was 100/80 mm Hg, pulse was 85 bpm, and prominent jugular venous distention was noted. There was an audible mitral regurgitant murmur and moderate hepatomegaly with no peripheral edema. Hemodynamics showed a cardiac index of 1.6, with an SVR of 2,883 and a thoracic fluid content of 0.052. Despite the minimal weight gain, it was apparent that the patient was significantly volume overloaded, and bumetanide was resumed at its previous dose. She was also instructed to take metoprolol 25 mg daily after resumption of bumetanide.

After two weeks, a repeat evaluation revealed complaints of minimal dyspnea, a blood pressure of 90/60 mm Hg, a heart rate of 90 bpm, and a weight decrease of one pound from the previous visit. Neck veins were no longer distended. Per noninvasive readings, the cardiac index was 2.2, the SVR 2,710, and the thoracic fluid content was 0.026. Metoprolol was increased to 50 mg daily and subsequently to 100 mg daily.

Evaluation four weeks later showed a blood pressure of 96/60 mm Hg, a pulse rate of 80 bpm, and a weight decrease of one more pound. The cardiac index at this time was 2.7, with an SVR of 1,626 and a thoracic fluid content of 0.032. Patient B's symptoms, physical findings, and hemodynamic indices remained stable over the ensuing two years on this medical regimen.

Patient C, a man 80 years of age with ischemic dilated cardiomyopathy, was referred for optimal medical management because of continuing problems with fatigue despite therapy with furosemide 40 mg twice daily, losartan 50 mg twice daily, doxazosin 2 mg daily, and amiodarone. Physical examination revealed a blood pressure of 122/70 mm Hg, pulse of 60 bpm, flat neck veins, and mitral regurgitant murmur. There was no peripheral edema. Noninvasive hemodynamics showed a cardiac index of 4.0, with an SVR of 770 and a thoracic fluid content of 0.047. It was recommended that Patient C begin beta blockade, and in view of the low SVR, metoprolol (rather than carvedilol) was selected as the drug of choice, at an initial dose of 25 mg daily.

Two months later, Patient C returned complaining of lethargy on this new regimen. His blood pressure was 70/48 mm Hg, the pulse was 58 bpm with mitral regurgitant murmur. His cardiac index was 5.2, the SVR was 428, and the thoracic fluid content was 0.043. Furosemide was discontinued and losartan reduced to 50 mg daily.

On subsequent visits, Patient C's blood pressure rose to 110/78 mm Hg, his pulse was 52 bpm, and his remaining cardiac exam unchanged. The cardiac index was now 4.8, the SVR 751, and the thoracic fluid content was 0.047. On this regimen the patient felt remarkably better. Over the ensuing two years he remained clinically stable, on 100 mg of metoprolol daily, with unchanged hemodynamics [107].

Patient D, a man 79 years of age, presented to the outpatient clinic on continuous home dobutamine. After a 30-year history of progressive dilated cardiomyopathy, with ejection fraction of <15%, he was hospitalized for progressive heart failure despite aggressive outpatient medical management. Pulmonary artery catheterization revealed a cardiac index of 1.3, which increased to 2.0 while on dobutamine. Multiple attempts at discontinuation of the drug proved futile, and he was eventually discharged on an infusion of 5 mcg/kg/min of continuous dobutamine. After six weeks, he presented for an outpatient visit. In addition to dobutamine, he was on spironolactone 25 mg daily, lisinopril 10 mg daily, digoxin 0.25 mg daily, and furosemide 80 mg daily. He felt well, was able to walk one mile without dyspnea, and now denied any symptoms of heart failure. The blood pressure was 110/67 mm Hg, his pulse was about 85 bpm in chronic atrial fibrillation, and central venous pressure was normal. The remaining exam was notable only for a grade II/VI mitral regurgitant murmur. Noninvasive hemodynamics showed a cardiac index of 2.8, an SVR of 1,081, and thoracic fluid content of 0.023. In view of these excellent hemodynamics and the patient's asymptomatic status, dobutamine was discontinued in the office while undergoing continuous hemodynamic monitoring using TEB. Surprisingly, over the ensuing hours his hemodynamics remained unaltered despite discontinuation of the dobutamine infusion. Patient D was sent home off intravenous dobutamine and on escalating doses of metoprolol. Over the ensuing weeks, he remained clinically stable, and repeat thoracic bioimpedance hemodynamics showed a cardiac index of 2.9, an SVR of 932, and a thoracic fluid content of 0.027, despite the reinstitution of metoprolol and the discontinuation of dobutamine. Three months later, a periodic follow-up was done with Patient D on metoprolol 100 mg daily, lisinopril 20 mg daily, spironolactone 25 mg daily, digoxin 0.25 mg daily, and furosemide 80 mg daily. He complained of fatigue but was still able to walk one mile without dyspnea and denied having orthopnea or pedal edema. Physical examination revealed no evidence of volume overload but repeat hemodynamic showed a cardiac index of 1.8, an SVR of 1,752, and a thoracic fluid content of 0.018. In view of the increased SVR and reduced cardiac index, lisinopril was increased to 20 mg twice daily, and in hopes of achieving further sympathetic withdrawal, metoprolol was increased to 150 mg daily. The patient was stable on this clinical regimen and remained asymptomatic [107].

Results of the IMPEDANCE-HF trial support the concept that impedance-guided treatment reduces hospitalizations for acute heart failure as well as the incidence of heart failure and cardiovascular and all-cause mortality [108]. Results of another study found that impedance cardiography did not reliably track stroke volume or cardiac output changes during a rehabilitation program compared with echocardiography. The AHA/ACC/HFSA guideline states that further study of impedance cardiography is needed before it can be recommended for routine clinical care [10].