April 24th, 2013

BLOCK HF: CRT Superior to Conventional Pacing in Heart Failure Patients with AV Block

Patients with atrioventricular (AV) block generally receive right ventricular (RV) pacing; cardiac resynchronization therapy (CRT) has been restricted to patients with a low ejection fraction and a wide QRS duration. However, RV pacing may worsen LV dysfunction in AV block patients with low ejection fractions. Previous studies have raised the possibility that these patients may benefit from biventricular pacing with a CRT device.

Now, results from the BLOCK HF (Biventricular versus Right Ventricular Pacing in Heart Failure Patients with Atrioventricular Block) trial, published in the New England Journal of Medicine, lend more support for the expansion of CRT devices into this population. Anne Curtis and colleagues randomized 691 patients to standard RV pacing or biventricular pacing. After 37 months of follow-up, a primary outcome event — death, urgent care visit for heart failure that required intravenous therapy, or a 15% or more increase in the LV end-systolic volume index — occurred in 55.6% of the RV pacing group versus 45.8% of the biventricular pacing group (HR 0.74, CI 0.60-0.90).

The results were similar, and remained significant, when only the first two components of the endpoint were considered. The investigators also reported “a remarkably similar clinical effect, despite a marked difference” in ejection fraction, in the pacemaker and ICD groups.

In a comment published in Journal Watch Cardiology, Mark Link writes that the trial “extends the patient population that benefits from cardiac resynchronization therapy to those with left ventricular ejection fractions greater than 35% who are likely to require pacing a high percentage of the time…. The body of evidence is thus approaching critical mass to render future trials comparing right ventricular pacing and CRT unethical, perhaps even in patients with preserved LVEF.”

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