Cardiac resynchronization therapy in patients with right bundle branch block: Analysis of pooled data from the MIRACLE and Contak CD trials

Abstract

Clinical trials of cardiac resynchronization therapy (CRT) have not included many patients with right bundle branch block (RBBB). We pooled data from two randomized controlled trials of CRT (Multicenter InSync Randomized Clinical Evaluation [MIRACLE] and Contak CD) in order to assess outcomes of patients with RBBB. A total of 61 patients with RBBB were identified, 34 of whom were randomized to the CRT group and 27 to the control group. The data from these patients were entered into a new database and analyzed. Baseline demographics were not different between the two groups (mean age 65.5 +/- 11.3 years vs 69.5 +/- 9.6 years; male gender 91% vs 85%; patients with coronary disease 76.5% vs 88%; QRS duration 167 ms vs 164 ms; all P = NS). Outcome variables (New York Heart Association [NYHA] class, 6-minute hall walk distance, peak oxygen consumption (VO2), Minnesota Living with Heart Failure quality-of-life scores, left ventricular ejection fraction, and norepinephrine levels) were analyzed at randomization, 3 months, and 6 months. (1) With the exception of NYHA class, patients with RBBB as the qualifying wide QRS did not derive significant benefit from CRT in any of the other parameters studied at 3 or 6 months. (2) RBBB patients who received active CRT showed significant improvements in NYHA class by 6 months and trends toward improvement in 6-minute walk distance, quality-of-life scores, and norepinephrine levels. However, control patients also showed significant improvement in NYHA class by 6 months but showed no improvement in objective measurements (VO2, 6-minute walk distance, left ventricular ejection fraction, and norepinephrine levels), consistent with a placebo effect. Analysis of a larger cohort of patients with RBBB undergoing CRT may demonstrate significant benefit, but the current analysis does not support the use of CRT in patients with RBBB.