Cardiac Resynchronization
Therapy Successful for Heart Failure Patients
September / October 2004
 Penn
Cardiac Care recently participated in the MIRACLE (Multicenter
InSync Randomized Clinical Evaluation) study that evaluated
the safety and therapeutic benefits of the Medtronic InSync™
atrial synchronous biventricular pacing device and accompanying
software and pacing leads in delivering cardiac resynchronization
therapy (CRT) in patients with moderate to severe heart failure.
The results of the study showed that patients who used the
InSync system improved exercise capacity, their New York Heart
Association (NYHA) functional class and quality of life.
The FDA-approved device is surgically implanted under the
skin on the upper chest and is similar to a pacemaker. CRT
is delivered as tiny electrical pulses to the right and left
ventricles through three leads that are inserted through the
veins in the heart. In combination with standard drug therapy,
CRT is believed to resynchronize the heart, help the lower
chambers of the heart beat simultaneously in a normal sequence
and treat ventricular dysynchrony. The randomized, double-blind
parallel controlled study evaluated 453 heart failure patients.
Patients were implanted with the InSync system and then three
days later randomized to either have the CRT turned on or
off for six-months.
Patients who utilized the new system improved their exercise
capacity by an increase in six-minute hall walk distance of
fifty meters or greater. And, compared to baseline, 68 percent
of patients in the treatment group experienced an improvement
in NYHA functional class by one or more classes at six months,
versus 38 percent in the control group. Improvements of one
or more classes indicate an improved ability to perform the
activities of daily life. According to the Minnesota Living
with Heart Failure Questionnaire, patients receiving CRT (who
were already receiving standard drug therapy) felt better
as a result of treatment. Finally, improvements in cardiac
function were noted, including, reduction in systolic and
diastolic volumes, increase in left ventricular ejection fraction
(EF), and reduction in severity of mitral valve regurgitation.
“The MIRACLE trial showed for the first time that poor
heart function could be reversed and there was a relationship
between the EF changes, which measures the heart’s pumping
ability, and symptomatic improvement,” says
Martin G. St. John Sutton, MBBS, cardiovascular medicine
specialist and director of cardiovascular imaging at the Hospital
of the University of Pennsylvania and a principal investigator
for the MIRACLE study. “The study clearly shows the
heart reduces in size on therapy and improving heart function.
The unique aspect of this biventricular pacemaker is that
it coordinates the electric activation sequence and improves
inter and intra ventricular contraction,” adds Dr. St.
John Sutton.
There are more than 400,000 patients diagnosed with heart
failure in the United States each year. For many of these
individuals quality of life is severely limited and many are
too fatigued to participate in daily activities. The treatment
of heart failure has been primarily limited to pharmaceutical
interventions with ACE inhibitors, Beta adrenergic receptor
blockers, diuretics and vasodilators. And although these medications
have been very effective at relieving symptoms, they have
not reversed cardiac function. Other treatment options for
select patients with heart failure may include heart transplant
or destination therapy with mechanical devices.
As of April 2004, more than a hundred patients have received
the pacemaker at Penn and according to Dr. St. John Sutton
many more could find sustained improvement via biventricular
pacing. The best candidates are patients who are:
- not eligible for a heart transplant
- on maximum medical therapy and
- still symptomatic.
“The trial found that patients with non-ischemic coronary
myopathy improved significantly, but those with non-ischemic
coronary myopathy did even better, which was surprising because
these hearts are usually the largest with the worst function,”
explains Dr. St. John Sutton.
“For some patients the results have been extraordinary.
One patient who before receiving the pacemaker primarily went
from his bed to a chair, has since returned to work as a lawyer,
playing golf and traveling.”
Some people with heart failure are also at risk for extremely
fast and life-threatening heart rhythms. One answer to this
problem is a combination of CRT and an internal cardiac defibrillator
(ICD). Although still under investigation, the use of CRT
plus ICD is thought to help the lower two chambers of the
heart beat in a normal sequence and treat ventricular arrhythmias
by automatically detecting the life-threatening arrhythmias
and correcting the heart's rhythm.
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