Cardiac resynchronization therapy - CRT

This new heart failure treatment also reduces mortality

Cardiac resynchronization therapy (CRT, which is sometimes called biventricular pacing) is a new form of therapy for congestive heart failure caused by dilated cardiomyopathy. (Click here for a review of cardiomyopathy and heart failure.) Several studies now document the remarkable benefits conferred by CRT on appropriately selected patients with heart failure.

CRT uses uses a specialized pacemaker to re-coordinate the action of the right and left ventricles in patients with heart failure.

In approximately 30% of patients with heart failure, an abnormality in the heart's electrical conducting system (called an "intraventricular conduction delay" or bundle branch block) causes the two ventricles to beat in an asynchronous fashion. That is, instead of beating simultaneously, the two ventricles beat slightly out of phase. This asynchrony greatly reduces the efficiency of the ventricles in patients with heart failure, whose hearts are already damaged.

CRT re-coordinates the beating of the two ventricles by pacing both ventricles simultaneously. This differs from typical pacemakers, which pace only the right ventricle.

Early studies with CRT demonstrated its ability to improve the symptoms, the exercise capacity, and the feeling of well-being of many patients with moderate to severe heart failure. Additional studies showed that CRT can improve both the anatomy and function of the heart - tending to reduce the size of the dilated left ventricle, and improving the energy usage of the heart.

In the fall of 2003, the COMPANION trial showed that CRT can reduce the need for hospitalization, and may improve survival in patients with heart failure.

In the COMPANION trial, over 1600 patients with significant heart failure (including recent prior hospitalizations for heart failure, and intraventricular conduction delays, were randomized to to receive optimal drug therapy, or optimal drug therapy plus CRT. (Half the patients receiving CRT got a CRT device that also acts as an implantable defibrillator; the other half got CRT pacing alone.)

Reults from COMPANION confirm that patients receiving either kind of CRT device had more than a 20% reduction in the composite endpoint of the study (i.e., total hospitalizations and death from any cause.) Furthermore, patients who received the CRT-plus-defibrillator showed a 36% reduction in mortality alone. Those who received CRT without the defibrillator showed a trend toward a 24% reduction in mortality alone, though the trend did not quite reach statistical significance.

What do these results mean for patients with heart failure?

The degree of survival benefit seen in this study, as well as the reduction in hospitalizations, are impressive in their magnitude - and these improvements were seen in patients with heart failure who already had been placed on "optimal" treatment. Even so, COMPANION does not introduce new therapy that has not been previously available; it merely validates that therapy and makes it much more compelling. CRT devices are now FDA-approved, and are being implanted by doctors across the country.

Patients who have heart failure that limits their ability to function, and either an intraventricular conduction delay or bundle branch block on their ECG, should discuss CRT with their doctors. And don't forget - if a heart attack is the cause of your heart failure, you are likely already a candidate for an implantable defibrillator, and you should be asking about a combination CRT device/implantable defibrillator.