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Right ventricular free wall activation indicative of normal right bundle branch-mediated depolarization
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Normal right ventricular wall activation in intrinsic rhythm was associated with normal right bundle branch-mediated depolarization in patients with HF without right ventricular dysfunction treated with cardiac resynchronization therapy, study findings suggested.
Researchers evaluated epicardial right ventricular activation noninvasively by electrocardiographic imaging in healthy control subjects (n=7) with normal electrocardiograms and compared them with patients who had HF (left ventricular ejection fraction 23 ± 10%; n=14).
During intrinsic conduction in HF (n=12), the durations of QRS and precordial lead rS complexes were 158 ± 24 ms and 77 ± 17 ms, respectively, which, according to researchers, indicated a delayed total ventricular depolarization but also a rapid initial myocardial activation. Echocardiography showed no significant right ventricular disease. Right ventricular epicardial voltage, activation patterns and right ventricular activation duration in HF did not differ from normal. Right ventricular pacing in HF generated variable areas of slow conduction and prolonged right ventricular activation duration (78 ± 33 ms; P<.001), according to the results.
“Although cardiac resynchronization therapy (CRT) LV pacing was not inferior to CRT biventricular pacing in one trial, the significant variations reported here suggest that demonstration of CRT-LV benefit requires attention to individual electrical substrate,” the researchers wrote. “Device programming may be guided noninvasively by dynamic 3-dimensional mapping, such as electrocardiographic imaging, and merits prospective evaluation.”
Martin Bernier, MD, and Mark E. Josephson, MD, both from Beth Israel Deaconess Medical Center, Boston, commented in an accompanying editorial that this study is reminiscent of previous ex vivo models and in vivo studies that were performed using direct intraoperative measurements of ventricular depolarization. The interest of the Varma and colleagues study, they concluded, “is that it attempts to link mechanistic work and its clinical implications, and substantiates the potential mechanism for the deleterious effect of right ventricular pacing in patients who do have native right bundle conduction, via a noninvasive, novel approach.”
Varma N. J Am Coll Cardiol Img. 2010;doi:10.1016/j.jcmg.2009.12.017.