Patients with atrioventricular block and mild to moderate heart failure who were randomized in the BLOCK HF trial to biventricular pacing as a whole had better outcomes than counterparts who received conventional right ventricular pacing. The results were published April 25 in the New England Journal of Medicine.
BLOCK HF (Biventricular versus Right Ventricular Pacing in Heart Failure Patients with Atrioventricular Block) is a prospective, multicenter, randomized, double-blind trial that compared two pacing treatments for patients with atrioventricular block, left ventricular ejection fraction (LVEF) of 50 percent or less and New York Heart Association class I, II or III symptoms for heart failure. The trial enrolled 918 patients between 2003 and 2011 and randomized 349 patients to a biventricular pacing group and 342 to a right-ventricular pacing group. All patients had been implanted with a pacemaker or implantable cardioverter-defibrillator (ICD) that was capable of biventricular pacing.
The primary outcome was death from any cause, an urgent care visit for heart failure that required intravenous therapy or an increase in the left ventricular end-systolic volume index of 15 percent or more compared with baseline at randomization. Patients were followed every three months, with clinical assessments every six months and echocardiography at six, 12, 18 and 24 months to measure left ventricular end-systolic volume index and LVEF.
Eighty-three patients in the biventricular-pacing group and 71 patients in the conventional pacing group had missing echocardiograms and consequently were not included in the primary outcome analysis. That analysis showed 45.8 percent of the biventricular-pacing group and 55.6 percent of the right-ventricular pacing group experienced a primary outcome event. Incidence of the primary outcome was lower in the biventricular-pacing group. Patients stratified by pacemaker or ICD had similar hazard ratios.
“Whereas right ventricular pacing achieves the primary goal of restoring an adequate heart rate in patients with atrioventricular block, studies suggest that right ventricular apical pacing may lead to progressive left ventricular dysfunction and heart failure in patients with preexisting left ventricular dysfunction, presumably owing to the electrical and mechanical dyssynchrony that occurs with right ventricular pacing,” wrote Anne B. Curtis, MD, of the University of Buffalo, and colleagues.
BLOCK HF results showed that biventricular pacing was superior to right ventricular pacing and added to evidence in its favor, they proposed. “Given that the hazard ratios and 95 percent credible intervals for the pacemaker and ICD groups were nearly identical, we conclude that the benefit of biventricular pacing in patients with atrioventricular block is similar with the two types of devices.”
They acknowledged that the study was limited by the “fairly high” number of missing echocardiogram data and that the number of crossovers (84) from the right-ventricular pacing group to the biventricular pacing group. But they added the crossovers occurred after a primary outcome event.
The study was funded by Medtronic.