Biventricular vs RV Pacing for AV Block in Heart Failure
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco does research for Medtronic, is a consultant for Medtronic, Novartis, and St. Jude, and is a speaker for Boston Scientific.
Source: Curtis AB, et al. Biventricular pacing for atrioventricular block and systolic dysfunction. N Engl J Med 2013;368:1585-1593.
The Biventricular vs Right Ventricular Pacing in Heart Failure Patients with Atrioventricular Block (BLOCK HF) trial tested the hypothesis that biventricular pacing (cardiac resynchronization therapy [CRT]) would be superior to right ventricular pacing in patients with mild-to-moderate heart failure, left ventricular systolic dysfunction, and an indication for full-time ventricular pacing. The investigators enrolled patients with a New York Heart Association (NYHA) class I or II A indication for ventricular pacing due to high degree or complete atrioventricular (AV) block and also had some symptoms of heart failure and a left ventricular ejection fraction of 50% or less. Although the initial patient group only included patients who would receive pacemakers, later in the trial patients who received implantable defibrillators (ICDs) and had an indication for ventricular pacing were included. After initial screening, all patients underwent implantation of a pacemaker or ICD with biventricular pacing capability. Patients with persistent atrial arrhythmias with complete or high-grade block could be included. After implantation, the devices were programmed to right ventricular pacing for 30-60 days during which an optimal pharmacologic regimen was established. Patients then returned and were randomized in a 1:1 ratio to receive either biventricular or right ventricular pacing. This post-implant randomization visit was considered to be the baseline visit. Patients were then followed every 3 months with full clinical assessments. Echocardiography was performed to calculate the left ventricular end systolic volume index (LVESVI) and left ventricular ejection fraction (LVEF) at randomization and at 6, 12, 18, and 24 months. The primary outcome measure was a composite endpoint including death from any cause, any urgent outpatient or inpatient visit for heart failure that required intravenous therapy, or an increase from baseline in the LVESVI of 15% or more. Secondary outcomes, including death from any cause and hospitalization for heart failure, were also analyzed. A hierarchical Bayesian proportional hazards model was used for analysis of the primary and secondary outcomes.
The study screened 918 patients and eventually randomized 691. Device implantation was attempted in 809 patients but was unsuccessful in 51 (6.3%). Sixty-seven patients who received a successful device implant did not undergo randomization for various reasons. The mean LVEF was 43% in the pacemaker group and 33% in the ICD group; 484 patients received pacemakers and 207 patients received ICDs. Overall, more than 80% of the patients in the combined group had NYHA class II or III heart failure symptoms.
A primary outcome endpoint was reached by 53.3% of the biventricular pacing group compared with 64.3% of the right ventricular pacing group. The most common primary outcome event was a decrease in LVESVI. This was observed in 56 of 243 biventricular pacing group patients compared to 79 of 241 right ventricular pacing group patients. In the ICD groups, LVESVI-related events also accounted for more than 50% of the events. The raw numbers of deaths and number of urgent care visits for heart failure showed only minor changes. However, when the Bayesian hierarchical model was used to adjust for baseline differences, the hazard ratios for death, urgent visit for heart failure, or hospitalization for heart failure were also significantly lowered.
Adverse events were noted in 113 of the 809 patients in whom implantation was attempted. Of these, 83 events (10.3%) were related to the procedure or the cardiac resynchronization therapy (CRT) system. Left ventricular lead-related complications were noted in 6.4% of patients. The authors conclude that biventricular pacing is superior to right ventricular pacing in patients with left ventricular dysfunction who require ventricular pacing.
It is now generally accepted that right ventricular apical pacing may have adverse hemodynamic consequences in selected patients. Prior studies on CRT have excluded patients who had ventricular pacing indications so that the effects of CRT in patients with bundle branch blocks could be analyzed. BLOCK HF extends the observation that CRT is better than right ventricular pacing to patients who require pacing, but also points out that there are still limitations to CRT. In BLOCK HF, 6.3% of the implant attempts were unsuccessful and an added 6.4% of those who received an LV lead had later complications. Although not addressed in the time frame of this study, battery longevity is also shorter with CRT devices in general. Therefore, before we start CRT routinely in all patients with AV block, we should carefully consider the risk-benefit ratio in each patient. Thankfully, recent innovations in lead design and battery technology may mitigate some of these limitations and I expect that CRT will become standard for patients with any systolic dysfunction and a need for pacing in the near future.