Biventricular pacing bests conventional tx in BLOCK HF trial

DENVER – Biventricular pacing rather than the right ventricular pacing recommended in current guidelines results in significantly better quality of life and symptom status, an analysis of secondary outcomes from the BLOCK HF trial have shown.

In a previous report of the trial’s primary outcome (N. Engl. J. Med. 2013;368:1585-93), the biventricular (BiV) pacing group showed a highly significant 26% reduction in risk of a composite of all-cause mortality, an urgent care visit for heart failure requiring intravenous therapy, or a 15% or greater increase in the left ventricular end-systolic volume index during an average of 37 months of follow-up, compared with patients who had right ventricular (RV) pacing.

Dr. Anne Curtis

The new report on prespecified secondary endpoints including quality of life and symptom status was undertaken because of researchers’ and regulatory agencies’ growing appreciation of the importance of such outcomes in patients with a chronic progressive disease such as heart failure, principal investigator Dr. Anne B. Curtis reported at the annual meeting of the Heart Rhythm Society.

BLOCK HF (Biventricular versus Right Ventricular Pacing in Patients with Left Ventricular Dysfunction and Atrioventricular Block) was a randomized, double-blind, prospective, 60-center clinical trial involving 691 patients in the United States and Canada. All had AV block warranting pacemaker therapy as well as New York Heart Association(NYHA) class I-III heart failure with a left ventricular ejection fraction of 50% or less. All participants got a cardiac resynchronization therapy device featuring BiV pacing. Patients were assigned in double-blind fashion for their device to run in BiV or conventional RV pacing mode, explained Dr. Curtis, professor and chair of the department of medicine at the University of Buffalo (N.Y.).

The new secondary analysis tabulated changes in the Packer clinical composite score, NYHA functional class, and quality of life, as measured by the Minnesota Living With Heart Failure Questionnaire, at 6, 12, 18, and 24 months.

The Packer clinical composite score classifies patients as improved, worsened, or unchanged based on patient global assessment, heart failure hospitalization, change in symptoms, and other factors. At all four time points through 24 months, significantly more patients in the BiV group were rated as improved and significantly fewer as worsened than in the RV group. For example, at 6 months 53% of the BiV group were categorized as improved and 23% as worsened, compared with 39% and 28% in the RV group, Dr. Curtis reported.

From a mean baseline quality of life score of 25, the BiV group improved by an average of 5 points at the 6-month assessment compared with a 0.3-point gain in the RV group. At 12 months, the BiV group still showed a 3.9-point improvement, significantly better than the average 0.9-point gain in the RV patients. At 18 and 24 months, however, there was no longer a significant difference between the two groups in terms of quality of life scores. Dr. Curtis attributed this drop-off to the fact that 86 patients in the RV arm crossed over to BiV pacing because of deteriorating heart failure, compared with 15 crossovers in the BiV group. In the intention-to-treat analysis employed in BLOCK HF, those crossovers to BiV pacing are still counted as being part of the RV group.

"If you could mandate that patients stayed in the same arm, I think you’d continue to see differences over time, but you can’t do that," she said.

An analysis of changes in NYHA functional class showed the BiV group had better outcomes at 12 months, but at not the other time points.

The BLOCK HF trial was undertaken in response to evidence suggesting that sustained RV apical pacing can degrade ventricular function, especially in patients with preexisting systolic dysfunction.

At present, cardiac resynchronization therapy devices aren’t approved by the Food and Drug Administration for patients with AV block with left ventricular dysfunction. Medtronic officials have indicated they plan to seek an expanded indication based on the BLOCK HF data.

One audience member, noting that the study outcomes were better with BiV pacing in patients across the full spectrum of depressed ejection fractions, asked Dr. Curtis if she expects an expansion of cardiac resynchronization therapy indications to include patients with heart block and a normal ejection fraction.

"I would anticipate that the guidelines will change for the type of patients studied here. But we didn’t study patients with a normal ejection fraction because the more normal the patient, the larger the sample size and longer the follow-up you’d need to show a difference. So I doubt that this study will change guidelines for patients with normal ejection fractions," she said.