Author + information
- Received December 15, 2006
- Revision received May 15, 2007
- Accepted July 1, 2007
- Published online October 9, 2007.
- Melissa J. Byrne, PhD⁎,2,
- Robert H. Helm, MD⁎,2,
- Samantapudi Daya, MD⁎,
- Nael F. Osman, PhD§∥,
- Henry R. Halperin, MD, MA, FAHA⁎,†,§,
- Ronald D. Berger, MD, PhD⁎,
- David A. Kass, MD, FAHA⁎,†,1 and
- Albert C. Lardo, PhD, FACC, FAHA⁎,†,‡,§,1,⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. Albert C. Lardo, Johns Hopkins School of Medicine, Image Guided Cardiotherapy Laboratory, Division of Cardiology, 720 Rutland Avenue, 1042 Ross Building, Baltimore, Maryland 21205.
Objectives We compared mechanical dyssynchrony and the impact of cardiac resynchronization therapy (CRT) in failing hearts with a pure right (RBBB) versus left bundle branch block (LBBB).
Background Cardiac resynchronization therapy is effective for treating failing hearts with conduction delay and discoordinate contraction. Most data pertain to LBBB delays. With RBBB, the lateral wall contracts early so that biventricular (BiV) pre-excitation may not be needed. Furthermore, the magnitude of dyssynchrony and impact of CRT in pure RBBB versus LBBB remains largely unknown.
Methods Dogs with tachypacing-induced heart failure combined with right or left bundle branch radiofrequency ablation were studied. Basal dyssynchrony and effects of single and BiV CRT on left ventricular (LV) function were assessed by pressure-volume catheter and tagged magnetic resonance imaging, respectively.
Results Left bundle branch block and RBBB induced similar QRS widening, and LV function (ejection fraction, maximum time derivative of LV pressure [dP/dtmax]) was similarly depressed in failing hearts with both conduction delays. Despite this, mechanical dyssynchrony was less in RBBB (circumferential uniformity ratio estimate [CURE] index: 0.80 ± 0.03 vs. 0.58 ± 0.09 for LBBB, p < 0.04; CURE 0→1 is dyssynchronous→synchronous). Cardiac resynchronization therapy had correspondingly less effect on hearts with RBBB than those with LBBB (i.e., 5.5 ± 1.1% vs. 29.5 ± 5.0% increase in dP/dtmax, p < 0.005), despite similar baselines. Furthermore, right ventricular-only pacing enhanced function and synchrony in RBBB as well or better than did BiV, whereas LV-only pacing worsened function.
Conclusions Less mechanical dyssynchrony is induced by RBBB than LBBB in failing hearts, and the corresponding impact of CRT on the former is reduced. Right ventricular-only pacing may be equally efficacious as BiV CRT in hearts with pure right bundle branch conduction delay.
↵1 Drs. Lardo and Kass are consultants for Guidant/Boston Scientific and receive research funding, although none of this funding was used to support the current study.
↵2 Drs. Byrne and Helm contributed equally to this work.
This work was supported by NIH grants PO1 HL077180 (to Drs. Kass and Lardo) and T32 HL07227 (to Dr. Helm). See accompanying online Cardiosource Slide Set.
This work was presented, in part, at the 2006 Scientific Sessions of the American College of Cardiology, March 11–14, 2006, Atlanta, Georgia.
- Received December 15, 2006.
- Revision received May 15, 2007.
- Accepted July 1, 2007.
- American College of Cardiology Foundation