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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