2013, Biventricular versus Right Ventricular Pacing in Heart Failure Patients with Atrioventricular Block, NEJM
BLOCK HF Trial Summary
The Biventricular versus Right Ventricular Pacing in Heart Failure Patients with Atrioventricular Block (BLOCK HF) trial is a prospective, multicentric, double-blinded, industry (Medtronic) sponsored, randomized controlled trial conducted to evaluate role of biventricular (BiV) pacing in patients with high-degree atrioventricular (AV) block (as a surrogate for obligatory RV pacing) and LV systolic dysfunction in comparison to standard right ventricular (RV) pacing.
691 patients were randomized 1:1 to BiV pacing (n=349) or RV pacing (n=342) in 58 centers in the United States and 2 centers in Canada between 2003 and 2011. Initially, patients enrolled in the study received pacemakers only. However, with evidence supporting the use of implantable cardioverter–defibrillator (ICD) therapy in patients with heart failure and left ventricular dysfunction for the primary prevention of sudden cardiac death, the protocol was revised in December 2005 to allow ICD implantation in such patients.
The study included patients with Class I or IIa indication for pacemaker implantation owing to high-degree AV block who also had NYHA class I-III heart failure with LVEF <= 50%. High-degree AV block was defined as documented complete AV block (including patients who had AV node ablation) or demonstration of second-degree AV block or PR interval >= 300 ms when paced at 100 beats/min. It excluded previous recipient of a cardiac implantable electrical device, patients with unstable angina or acute myocardial infarction, percutaneous or surgical coronary intervention within 30 days before enrollment, valvular disease with an indication for valvular repair or replacement and patients with an indication for a CRT device.
Baseline characteristics were similar in both groups. Mean LVEF was 40 +/- 8.3%. Most were NYHA II or III patients. Baseline mean heart rate was 68.8 bpm, QRS duration was 123 ms. 48.8% had third-degree AV block, 31.6% had second-degree and 19.3% had first-degree AV block. 29.8% had left bundle branch block and 21.6% had right bundle branch block. The mean ventricular pacing in both groups was more than 97%.
After mean follow-up of 37 months, there was a statistically significant difference in favor of BiV pacing (45.8%) over RV pacing (55.6%) in the primary outcome of time to death from any cause, an urgent care visit for heart failure (HF) that required IV therapy, or >= 15% increase in left ventricular end-systolic volume index (surrogate marker for LV remodeling) (HR 0.74; 95% credible interval, 0.60 to 0.90). When patients were stratified according to the type of device implanted- pacemaker or ICD, the results were similar (for BiV pacing: HR in pacemaker only cohort was 0.73; 95% credible interval, 0.58 to 0.9; and HR in ICD cohort was 0.75; 95% credible interval, 0.57 to 1.02).
Secondary outcome of – death or urgent care visit for HF, death or hospitalization for HF, and HF hospitalization alone were all in favor for BiV pacing. But death alone was similar for the two groups.
The study concluded that BiV pacing provided significant clinical benefit over RV pacing in patients with LV dysfunction and AV block who required ventricular pacing.
In patients with high-degree AV block and HF with LV systolic dysfunction, the BiV pacing is associated with a approximately 10% absolute risk reduction in death, urgent HF care and adverse LV remodeling compared with RV pacing, and this is primarily driven by reduced HF hospitalizations and reduced LV remodeling.
Trial summarized by Mansour Almunajem, MD
Reviewed by Saurabh Joshi, MD
Affiliation: Department of Cardiovascular disease, University of Connecticut Health Center