LOS ANGELES – Cardiac resynchronization therapy may be on the verge of a strong new indication for the prevention of progression of heart failure in patients with atrioventricular block who are not candidates for the device therapy on the basis of current criteria.
Results of the BLOCK-HF trial comparing biventricular pacing using a CRT device to standard right ventricular pacing demonstrated that in patients with AV block and systolic heart failure, biventricular pacing led to a significant 26% reduction in the combined end point of death, heart failure–related urgent care, or deterioration in heart function as defined echocardiographically by more than a 15% increase in the left ventricular end systolic volume index, Dr. Anne B. Curtis reported at the annual scientific sessions of the American Heart Association.
Dr. Anne B. Curtis
BLOCK-HF (Biventricular Versus Right Ventricular Pacing in Heart Failure Patients With Atrioventricular Block) was a randomized, double-blind, prospective, multicenter study of 691 patients with class I-III heart failure, a left ventricular ejection fraction (LVEF) of 50% or less, and AV block necessitating pacing. None had a class I indication for CRT by current guidelines. All participants received a CRT device programmed for right ventricular pacing only while optimal medical therapy was established, which took 30-60 days. Once that occurred, subjects were randomized double-blind to biventricular or right ventricular pacing. Analysis was by intent-to-treat.
Of those participants, 207 patients received a combined CRT/defibrillator device because they met criteria for a primary prevention implantable cardioverter-defibrillator; the rest got a CRT pacemaker-only device, said Dr. Curtis, BLOCK-HF principal investigator and professor and chair of the department of medicine at the University at Buffalo (N.Y.).
At an average of 36 months’ follow-up, the combined primary end point had occurred in roughly 60% of the biventricular pacing group, representing a 26% relative risk reduction compared with conventional right ventricular pacing. The rate of the two clinical components of the primary end point – mortality and heart failure–related urgent care – was 27% lower in the biventricular pacing group.
Results were the same in patients with a CRT pacing-only device as for those with a CRT/defibrillator, even though those with the CRT/defibrillator had an average LVEF of 33%, compared with an LVEF of 44% in those who got the pacing-only device. Dr. Curtis said that although a formal subgroup analysis based on heart failure functional class is planned, it’s her anecdotal impression that the benefits of biventricular pacing were similar across the board.
A pronounced imbalance in crossovers between the two study arms occurred: 25% of subjects randomized to right ventricular pacing crossed over to biventricular pacing, while 5% assigned to biventricular pacing crossed to right ventricular pacing.
"If anything, this would tend to minimize the differences we found," Dr. Curtis noted.
Roughly 1 million people in the United States have AV block, and there are 6 million individuals with the diagnosis of heart failure.
Discussant Dr. Gerasimos S. Filippatos of the University of Athens declared that the BLOCK-HF results will certainly lead to a reconsideration of current European Society of Cardiology and joint American College of Cardiology/AHA/Heart Rhythm Society guidelines for heart failure patients with heart block.
As a heart failure specialist and nonelectrophysiologist, Dr. Filippatos said he found the procedure-related complication rates notably high: 33% in recipients of CRT pacing-only devices and 17% in those who got a CRT/defibrillator.
Dr. Curtis replied that complication rates are always higher when putting in a left ventricular lead because it’s a more difficult procedure than putting in a right ventricular lead. One of the key points of BLOCK-HF, she added, was to look at whether or not putting patients through the added difficulty of implanting a biventricular pacing device has clear benefits – and the answer is yes.
The BLOCK-HF trial was sponsored by Medtronic. Dr. Curtis reported serving as a consultant to that company and to Biosense Webster, Sanofi-Aventis, and Bristol-Myers Squibb. Dr. Filippatos is a consultant to Novartis.