cardiac resynchronization therapy

Picture two rowers in a boat who have fallen out of time, pulling their oars a beat apart so the boat lurches instead of gliding. Cardiac resynchronization therapy (CRT) is a special pacemaker that gets the heart’s two pumping chambers stroking together again, so each heartbeat is more efficient.

In some people with heart failure, the heart’s electrical signal reaches one ventricle later than the other (often shown as a wide QRS or left bundle branch block on the ECG). The walls then contract out of step, wasting effort. CRT places an extra pacing lead so that both the right and left ventricles are stimulated in a coordinated way — biventricular pacing — restoring a more synchronized squeeze.

CRT is offered to selected patients with reduced ejection fraction, persistent symptoms despite medication, and electrical delay shown by a wide QRS. In suitable patients it can ease symptoms, improve pumping, and lower hospitalizations. It is often combined with a defibrillator (a CRT-D device), but it is not helpful for everyone — those without electrical dyssynchrony generally do not benefit.