Multicenter InSync Randomized Clinical Evaluation (MIRACLE): Results of a Randomized, Double-Blind, Controlled Trial to Assess Cardiac Resynchronization Therapy in Heart Failure Patients
William T. Abraham
University of Kentucky College of Medicine, Lexington, Kentucky, USA

Cardiac resynchronization therapy via atrial-synchronized bi-ventricular pacing has appeared to be a promising therapy for heart failure patients with intraventricular conduction delays or ventricular desynchrony. Preliminary small-scale, uncontrolled clinical trials showed favorable results, and now the large-scale, placebo-controlled MIRACLE trial has demonstrated conclusively that this technique is extremely effective in patients with moderate to severe heart failure.

Cardiac resynchronization therapy using atrial-synchronized bi-ventricular pacing demonstrated improved quality of life and functional capacity among patients with chronic heart failure in studies done during the preliminary development phases. However, those studies were not controlled and involved only small numbers of patients. The Multicenter InSync Randomized Clinical Evaluation (MIRACLE) trial is the first large-scale, double-blind, placebo-controlled trial of this therapeutic approach, and the MIRACLE investigators announced extremely favorable results in their presentation at this meeting.

All patients entering the study had atrial-synchronized bi-ventricular pacing devices implanted; the implantation success rate of 93% exceeded investigators' expectations. The implanted devices were turned off in the132 patients randomized to the control group, whereas the devices operated throughout the 6-month study period in the 134 patients randomized to the active therapy group. The results were very dramatic. Use of the device in patients with Class III or IV heart failure resulted in improved quality of life, an average improvement of one class in New York Heart Association Functional Class status, an increase in exercise tolerance, and improvements in cardiac structure and function. These parameters were measured using several techniques including echocardiography and a standardized 6-minute hall-walk evaluation. Treated patients also showed improvements in a composite heart failure score.

Dr. Abraham said that there are about 5 million people with heart failure in the United States, and about 750,000 of them may be candidates for this procedure (in other words, they have Class III or IV heart failure and desynchrony). He noted that all of the patients who had been in the control group in the double-blind phase of the study elected to have the devices turned on at the end of the 6-month primary study period. His group intends at some point to publish the results of their "crossover" clinical courses. In response to a question about the long-term safety of these devices, Dr. Abraham said that their first patient has had the device implanted and working since 1998 and is doing fine. "In fact, not only is there no deleterious effect, but long-term use appears to be consistently beneficial."

Reporter: Andre Weinberger, MD


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