By Alon Barsheshet
It is well established that chronic apical right ventricular pacing contributes to the development and exacerbation of heart failure. Several clinical studies showed that high proportion of right ventricular pacing is associated with a reduction in left ventricular function, increased risk of heart failure hospitalisation or heart failure-related death. It was suggested that the mechanisms behind these deleterious effects are related to the fact that right ventricular pacing causes an iatrogenic left bundle branch block (LBBB) conduction disturbance and ventricular dyssynchrony. High cumulative right ventricular pacing is also associated with increased heart failure incidence and severity in patients implanted with an implantable cardioverter defibrillator (ICD). The DAVID (Dual chamber and VVI implantable defibrillator) trial evaluated patients with standard indication for ICD therapy who received a combined ICD/dual chamber pacemaker and were randomly assigned to VVI or DDD pacing modes. Because the lower rate programming in the DDD group had a much higher per cent right ventricular pacing than did patients in the VVI group, the combined endpoint of death or hospitalisation for heart failure during a median follow-up of 8.4 months was higher in the DDD group (JAMA, 2002).
There is paucity of data with regard to the effect of right ventricular pacing on long-term mortality among patients who receive an ICD for primary prevention. Most recently, we have evaluated the effect of high right ventricular pacing on long-term mortality among ICD recipients in the MADIT-II population; we also explored the effects of per cent right ventricular pacing on ICD benefit according to QRS morphology at enrolment (Heart Rhythm, 2011). Mortality data were obtained for all patients enrolled in the MADIT II during an extended follow-up period of eight years. The cumulative per cent right ventricular pacing during the trial was categorised as low (≤50%) and high (>50%). The study included a total of 1,057 patients, 490 patients received conventional, non-ICD therapy, 369 patients had ICD and were categorised in the low right ventricular pacing, and 198 had ICD with high right ventricular pacing. During the early phase of follow-up (0–3 years), ICD benefit was evident in both the low and high right ventricular pacing subgroups. However, during the late phase of follow-up (4–8 years), ICD therapy was associated with a significant survival benefit only among patients in the low right ventricular pacing subgroup (40% reduction in mortality risk, p
We also observed that the effects of right ventricular pacing on ICD benefit depend on QRS morphology before ICD implantation. High right ventricular pacing was associated with increased long-term mortality only in patients who did not have LBBB at baseline, whereas patients who had LBBB before device implantation gained a similar benefit from ICD irrespective to per cent right ventricular pacing. Among patients with left ventricular dysfunction high right ventricular pacing may have more deleterious effects in the absence of native LBBB, possibly due to the fact that iatrogenic LBBB induces additional ventricular dyssynchrony in this population.
These findings emphasise the need to programme ICDs to provide minimal right ventricular pacing particularly among patients without LBBB at baseline ECG. In addition, they suggest an important role for the use of a priori combined cardiac resynchronisation-defibrillator therapy in this population.
Alon Barsheshet, Cardiology division, University of Rochester Medical Center, Rochester, USA
Alon Barsheshet carried out this work while receiving the Mirowski-Moss Career Development Award from the University of Rochester Medical Center.