Cardiac resynchronization therapy (CRT)
Also calledBiventricular pacing · BiV pacing · CRT-P · CRT-D · Resynchronization therapy
Definition
Cardiac resynchronization therapy is a pacing therapy that aims to restore or preserve ventricular synchrony by pacing the left ventricle in timed relation to the right ventricle, in heart failure linked to ventricular dyssynchrony such as that caused by left bundle branch block. It most commonly means biventricular pacing, with one lead in the right ventricle and another pacing the left ventricle from a coronary vein reached through the coronary sinus, ideally at the latest-activated region, most often the lateral or posterolateral wall. On the surface ECG, biventricular pacing with the right ventricular lead at the apex usually gives a paced QRS that is dominant (positive) in V1, with a frontal axis usually in the right superior quadrant; the paced QRS is not reliably narrower than the native complex. A CRT-P device is a resynchronization pacemaker, and a CRT-D device is a resynchronization defibrillator.
Clinical noteThe surface ECG can mislead about left ventricular capture: fusion with the patient's own conducted beats can narrow the paced QRS and imitate effective biventricular pacing.
Sources
- Chung MK, Patton KK, Lau CP, et al. 2023 HRS/APHRS/LAHRS guideline on cardiac physiologic pacing for the avoidance and mitigation of heart failure. Heart Rhythm. 2023;20(9):e17-e91. doi.org/10.1016/j.hrthm.2023.03.1538
- Barold SS, Herweg B. Usefulness of the 12-lead electrocardiogram in the follow-up of patients with cardiac resynchronization devices. Part I. Cardiol J. 2011;18(5):476-486. doi.org/10.5603/cj.2011.0002
- Barold SS, Herweg B. Usefulness of the 12-lead electrocardiogram in the follow-up of patients with cardiac resynchronization devices. Part II. Cardiol J. 2011;18(6):610-624. doi.org/10.5603/cj.2011.0024
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.