Septal or Apical RV Pacing in Cardiac Resynchronization Therapy

Study Questions:

How does right ventricular septal (RVS) pacing compare with right ventricular apical (RVA) pacing in terms of its impact on left ventricular (LV) reverse remodeling in patients receiving a cardiac resynchronization therapy defibrillator (CRT-D)?


The SEPTAL CRT Study was a randomized, controlled, single-blind, multicenter trial, in which 263 patients, mean age 63 years, were assigned to RVS (n = 131) versus RVA (n = 132) pacing. The primary endpoint was LV end-systolic volume (LVESV) reduction between baseline and 6 months.


LVESV reduction between baseline and 6 months was not different between the two groups (p = 0.79). RVS pacing was not noninferior to RVA pacing with regard to LVESV reduction (average difference 24.1 ml; p = 0.006). There was no difference in the clinical outcome with an identical benefit in terms of 6-minute walk time and Milton Packer composite score. The percentage of “echo-responders” defined by LVESV reduction >15% between baseline and 6 months was similar in both groups (50%) with no difference in the time to first heart failure hospitalization or death (p = 0.532). Procedural or device-related serious adverse events occurred in 68 patients with no difference between the two groups (p = 0.401).


The authors concluded that RVS pacing in CRT is noninferior to RVA pacing for LV reverse remodeling at 6 months with no difference in the clinical outcome.


Up to one out of three patients undergoing CRT implantation do not derive a clinical benefit. The possible explanations are poor candidate selection, suboptimal device programming, and placement of the leads. RV apical pacing may adversely affect cardiac function in patients with and without cardiomyopathy, and there has been a great deal of interest in finding the ‘optimal’ site for RV lead placement, with some studies suggesting that RV outflow tract (high septal) pacing is better. Retrospective analysis of prior studies suggested that the apical position of the left ventricular lead was associated with poor response to CRT. In the present study, atrioventricular delay optimization was performed before discharge using the iterative mitral flow method under echocardiography, which is generally not performed in clinical practice. I was also surprised by the exceedingly high complication rate of 26%. It would be interesting if the authors had reported the activation delays between the electrodes, a variable which has been associated with differential response to CRT. In the end, it remains unclear as to what is the optimal position of the RV electrode.

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