Myths and legends of right ventricular septal pacing

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Excerpt

Permanent pacemaker implantation is the only effective treatment for symptomatic bradyarrhythmias.1 Conventionally, ventricular pacing leads are positioned at right ventricular (RV) apex to allow stable anatomical position and stimulation threshold. Nevertheless, as shown by our group and other researchers, chronic nonphysiologic ventricular depolarization is associated with dyssynchronous myocardial contraction, regional perfusion defects, localized histological abnormalities and impaired left ventricular ejection fraction (LVEF).3 These findings concur with the results of subsequent pacing trials, which has confirmed that RV apical pacing increases atrial fibrillation, heart failure hospitalization, thromboembolic events and mortality,6 with the cumulative percent ventricular pacing being predictive of adverse events.8
Nevertheless, RV apical pacing is not avoidable in many patients who require device therapy. Alternatively, positioning the ventricular pacing lead on the septum allows direct or secondary recruitment of the His‐Purkinje system, which results in more physiological ventricular depolarization and hence avoids the deleterious effect of RVA pacing. In this issue, Witt et al. retrospectively reviewed 3,450 patients who had dual chamber pacemaker implanted from 2004 to 2014 to assess the impact of lead positions on long‐term outcomes.9 Using a standardized algorithm, the authors determined the position of the ventricular pacing lead by placing a location grid on the posteroanterior and lateral radiographs.9 The position of the ventricular pacing lead tip was then described as RV apical, septal, or nonseptal nonapical (NSNA) accordingly.9 At 5 years, the authors showed that RV septal pacing was associated with lower all‐cause mortality than RV apical pacing (24% vs. 31%, P = 0.02).9 On the other hand, RV NSNA pacing was not associated with any clinical benefit but an increased need for lead revision.9
The issue of whether RV septal pacing is associated with better clinical outcomes than RV apical pacing remains controversial. Although previous clinical studies performed by our group and other investigators have shown that RV septal pacing is associated with better subsequent LVEF compared with RV apical pacing,10 the Protect‐Pace study, which randomized 240 patients with high‐grade atrioventricular block to RV apical versus high RV septal pacing in a 1:1 ratio, failed to show any significant difference in LVEF and other clinical outcomes at 2 years.13 The negative results of the Protect‐Pace study are not surprising. The overall success rate for RV septal lead placement in this study was only 66%.13 In addition, the drop‐out rate was so high that only 85 patients in the RV apical pacing group and 83 in the high RV septal pacing group retained in the analysis.13 Moreover, the relatively short follow‐up duration could also account for the negative findings of the Protect‐Pace study.13
Although retrospective in nature, Witt et al. included a much larger population with a much longer follow‐up duration, which favors evaluation of hard clinical endpoints.9 Besides, the authors also used stringent criteria to define the position of RV pacing leads, in particular, separating RV septal from NSNA pacing.9 The separation between the two is important, as ventricular activation sequence associated with RV NSNA pacing, such as RV anterior free wall, can even be more nonphysiological than RV apical pacing. As a result, similar benefit to true RV septal pacing should not be expected with RV NSNA pacing. The results of this study are particularly encouraging, as Witt et al. has not only demonstrated that RV septal pacing is associated with lower all‐cause mortality than RV apical pacing, but also shown that RV NSNA is not associated with any clinical benefit.9
However, there are also some unexpected findings in the study by Witt et al.
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