People with advanced heart failure sometimes incur damage to their electrical conduction cells, causing a delay in the spread of electrical activity through the heart. These abnormalities show up as distinctive patterns on ECG tracings and can be corrected with a standard one-lead pacemaker or a dual-lead device that stimulates both the right atrium and the right ventricle. However, evidence suggests that these techniques arenít effective in people with systolic heart failure who have a poorly pumping left ventricle. In the normal two-phase heartbeat, the left side contracts a fraction of a second later than the right. Stimulating only the right side of the heart disrupts the natural coordination of the two pumping systems, a condition called ventricular dyssynchrony. This problem can be overcome by adding a third lead to the device that stimulates the left ventricle. The pacing is timed so that the left ventricle gets the signal to contract slightly later than the right. This technique is called cardiac resynchronization therapy (CRT) or biventricular pacing.
One trial randomly assigned 813 people with moderate to severe heart failure to receive either drug therapy alone or drug therapy plus CRT. Those who received CRT had a lower risk of hospitalization or death from any cause compared with the medication-only group.
Another interesting observation from the evaluation of these devices is that CRT can actually reverse some of the ventricular damage in people with heart failure. Changes in the dimensions of the pumping chambers, less backflow of blood through the mitral valve, and the reduction of left ventricle wall thickness all provide evidence of a stronger heart muscle. Approximately 20% to 40% of people with stage C heart failure could be candidates for this therapy. CRT can be delivered as a standalone therapy, but is more commonly combined with a defibrillator in a single system (CRT-D).