Congestive heart failure affects over 5 million people in the United States, with an annual incidence of over 650,000 new cases a year. Despite lifestyle modifications (diet plus sodium restriction) and optimal medical therapy (angiotensin-converting enzyme inhibitors, beta blockers, diuretics, digitalis, aldosterone inhibitors), a significant percentage of these patients find their way back into the hospital for more intensive therapy. For this population, when optimal medical therapy has reached its limits, cardiac resynchronization therapy (CRT) has proven beneficial.
CRT, or biventricular pacing, is a form of device-based therapy for congestive heart failure caused by dilated cardiomyopathy (ischemic or nonischemic). Using a specialized pacemaker, CRT recoordinates the action of the right and left ventricles in these patients in an attempt to improve heart function.
In approximately 15 percent to 30 percent of all patients with heart failure, an abnormality in the heart’s electrical conduction system known as bundle-branch block causes the two ventricles to beat in an asynchronous manner. Rather than the two ventricles beating nearly simultaneously, they beat slightly out of phase due to regional delays in the electrical activation of the chamber. This asynchrony greatly reduces the efficiency of the ventricles in patients with heart failure by reducing systolic function and increasing systolic volume. Cardiac resynchronization therapy recoordinates the beating of the two ventricles concurrently, whereas typical pacemakers pace only the right ventricle.