Usefulness of Baseline Electrocardiographic QRS Complex Pattern to Predict Response to Cardiac Resynchronization

Date Posted: 2/4/2009
Author(s): Adelstein EC, Saba S.
Citation: Am J Cardiol 2009;103:238-242.
Clinical Trial: No

Study Question: Do patients with right bundle branch block (RBBB) or pacing-induced left bundle branch block (LBBB) benefit from cardiac resynchronization therapy (CRT) as often as patients with LBBB?

Methods: This was a retrospective study of 636 patients (mean age 67 years) with heart failure, QRS duration >120 ms, and an ejection fraction (EF) ≤35% who underwent CRT. Patients were classified as having an intrinsic LBBB (n = 407), pacing-induced LBBB (n = 160), or RBBB (n = 59). The outcomes were symptomatic response to CRT, echocardiographic response, and a composite endpoint of death, heart transplantation, or ventricular assist device implantation.

Results: The mean pre-CRT QRS duration was significantly longer in the paced group (199 ms) than in the LBBB (166 ms) and RBBB (168 ms) groups. During a mean follow-up of approximately 3 years, the composite endpoint was more frequent in the RBBB group (77%) than in the LBBB group (60%) and paced group (55%). After controlling for baseline differences, survival in the RBBB group was 41% lower than in the other groups. Symptomatic improvement after CRT was more frequent in patients with LBBB (59%) and in the paced patients (46%) than in the patients with RBBB (14%). The relative improvement in EF was greater in the LBBB group (23%) than in the RBBB group (3%).

Conclusions: RBBB predicts a poor response to CRT.

Perspective: A post-hoc analysis of randomized clinical trials of CRT also indicated that patients with RBBB generally do not respond to CRT. Despite the fact that RBBB may mask a left-sided ventricular conduction delay that results in dyssynchrony, at present there is inadequate evidence to support the use of CRT in patients with RBBB.  Fred Morady, M.D., F.A.C.C.