Biventricular pacing reduced mortality and morbidity in patients with atrioventricular block and systolic dysfunction, according to results from the BLOCK-HF (Biventricular Versus Right Ventricular Pacing in Heart Failure Patients With Atrioventricular Block) study, published in the Journal of the American College of Cardiology.
Researchers hypothesized that biventricular pacing would be superior to right ventricular (RV) pacing with regard to a combined end point of death, HF-related urgent care, or left ventricular (LV) remodeling as demonstrated by ≥15% increase in LV end systolic volume index.
Enrolled patients had standard class I or IIa indication for permanent pacing due to atrioventricular block, New York Heart Association (NYHA) functional class I to III systolic HF, and LV ejection fraction (LVEF) ≤50%. Patients who met class I indications for implantable cardiac defibrillators as well as patients with permanent atrial arrhythmias who had intrinsic atrioventricular block or atrioventricular block due to atrioventricular node ablation were also enrolled.
For 30 to 60 days, patients received either cardiac resynchronization therapy pacemaker (CRT-P) or defibrillator (CRT-D) and RV pacing while HF medical therapy was optimized. They were randomly assigned to receive biventricular pacing (both RV and LV pacing outputs ON) or RV pacing (RV pacing output ON, LV pacing output OFF) in a 1:1 ratio. Finally, echocardiographic examination occurred at randomization, and again at 6, 12, 18, and 24 months thereafter.
A patient’s clinical composite score was composed of clinical end points at each follow-up visit as well as absolute change in NYHA functional classification from randomization and absolute change in quality of life (QOL) from randomization.
Of the 918 patients enrolled, 691 were selected; 349 to receive biventricular pacing and 342 to receive RV pacing. Data were pooled across device groups for the main analysis since researchers did not find significant differences between the CRT-D and CRT-P groups in the biventricular-RV comparison. Compliance rates for follow-up were all above 92% for each visit.
“Biventricular pacing was superior to RV pacing at all time points (posterior probability [PP] ≥ 0.99),” researchers wrote. “At 6 months, 53% of biventricular subjects improved, 24% were unchanged, and 24% worsened, whereas with RV subjects, 39% improved, 33% were unchanged, and 28% worsened.”
HF hospitalizations and crossovers due to worsening HF drove the greater percentage of worsening seen in the RV arm.
The biventricular arm showed greater improvement in NYHA functional class (PP=0.99) at 12 months. More than 19% improved, 61% unchanged, and >17% worsened compared with the RV arm, which had >12% improved, 62% unchanged, and >23% worsened.
In addition, the biventricular arm had better QOL scores (PP ≥0.95) compared with the RV pacing group through 12 months of follow-up (26.8 vs 24.9, respectively).
“Because subjects who crossed over from RV to biventricular pacing due to worsening HF may benefit from biventricular pacing, a sensitivity analysis was done substituting NYHA functional classification values at the time of crossover or the most recent value before crossover for post-cross over scores,” researchers noted.
In Bayesian analysis that used the most recent pre-crossover value for patients who crossed over during their first 24 months, there was a superior improvement in NYHA function class at 18 and 24 months among the biventricular-paced patients (PP ≥0.95), which suggests that results may have been affected by the imbalance in crossovers between the 2 arms.
Nonetheless, biventricular pacing demonstrated improvement in important clinical outcomes. Researchers concluded, “The findings with biventricular pacing may reflect prevention of future dyssynchrony and HF as well as treatment of currently existing dyssynchrony.”
Curtis AB, Worley SJ, Chung ES, Li P, Christman SA, Sutton MSJ. Improvement in clinical outcomes with biventricular vs right ventricular pacing. The BLOCK HF study. J Am Coll Cardiol. 2016;67(18):2148-2157. doi: 10.1016/j.jacc.2016.02.051.