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July 31, 2003
News this month
Trial may widen use of cardiac defibrillators
Recent data from a landmark trial show that implantable cardioverter defibrillators (ICDs) help prolong the lives of people who have experienced previous heart attacks.
ICDs help prolong the lives of people who have experienced previous heart attacks.
Results of the trial, called the Multicenter Automatic
Defibrillator Implantation Trial (MADIT II), demonstrate a 31 percent drop in the mortality rate among heart attack survivors implanted with ICDs compared to those receiving medication only.
Dr. Arthur Moss from the University of Rochester who
lead the multicenter trial, said, “To get a 31 percent reduction in mortality is pretty unusual and dramatic. This study was done in 76 centers, so it was a very
representative population of the patients at risk.”
The findings were so dramatic that the trial's independent data and safety monitoring board stopped the study because of the overwhelming improvement experienced
by those implanted with ICDs.
Study population
Moss and his team of researchers studied 1,232 heart attack survivors in whom the heart’s ejection fraction — the percentage of blood in the main muscle-walled
chamber that is pumped out when the chamber contracts — was 30 percent or less.
It usually requires a very large heart attack, or multiple attacks, to reduce the ejection fraction to this range. People with low ejection fractions have more severe
muscle damage and higher mortality rates than those with normal ejection fractions. A normal ejection fraction is between 50 and 75 percent.
Damaged muscle tissue can cause
abnormal heartbeats placing one at risk for sudden cardiac death.
The damaged muscle tissue can cause abnormal
heartbeats, or arrhythmias, placing one at risk for sudden cardiac death. Implanted under the collarbone like a pacemaker, an ICD can detect irregular and potentially
fatal arrhythmias—known as ventricular tachycardia or fibrillation—and deliver a shock to restore normal rhythm.
The study participants’ average age was 64 and many had suffered multiple heart attacks. All received
similar medical treatment, but 742 were randomly assigned to have ICDs implanted in their chests; 490 were not given the devices. Both groups were similar in
all parameters, including the use of beta blockers and ACE inhibitors.
There was a significant 30% reduction in all causes of mortality in the ICD group.
After two years, there was a significant 30 percent
reduction in all causes of mortality in the ICD group. The pattern continued over the next four years, when the monitoring board stopped the study.
The mortality rate among participants with ICDs was 14.2 percent, compared with 19.8 percent among those
without them, according to results Dr. Moss presented at the 2002 annual meeting of the American College of Cardiology in Atlanta. The findings were later published in The New England Journal of Medicine.
Most of the difference in death rates was explained by a
reduction in cardiac arrests caused by abnormal heart rhythms among patients given the device, Moss said.
Forty-five percent of the deaths in the non-ICD group were caused by abnormal heart rhythms, compared with
23 percent of the deaths in the ICD group. In both groups, various complications of heart disease, especially heart failure, were still the most common causes of death.
ICD use to widen
The findings have significantly enlarged the population
considered eligible for ICD implantation.
Before the study, FDA guidelines identified about 300,000 Americans who were eligible each year to receive ICDs. Based on the new findings, the Medicare Coverage
Advisory Committee unanimously voted to recommend expansion of Medicare coverage for the use of ICDs in patients meeting the MADIT II criteria.
Dr. Moss estimates that over two million people in the U.S. could become eligible for implanted devices under
these new guidelines.
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New hope for heart attack survivors
A sudden unexpected death caused by loss of heart function
(cardiac arrest) is a common cause of death in the U.S., killing more people than lung cancer, breast cancer and AIDS combined.
It is usually due to a serious fast heart rhythm, called a ventricular tachycardia or ventricular fibrillation.
“Sudden unexpected death caused by loss of heart function. . . .is usually due to a serious fast heart rhythm.”
A history of heart attacks, coronary artery disease and poor ejection fractions are all risk factors for sudden cardiac death (SCD
). For many who have survived heart attacks, death can come quickly and without warning a few years later.
Victims of cardiac arrest often lose consciousness in seconds, and death follows shortly unless they receive an electric shock to
restore the heart's rhythm within minutes of the event. Approximately 95 percent of these patients who experience an out-of-hospital cardiac arrest die from the episode.
Preventing sudden cardiac death
To significantly reduce the large number of sudden deaths that occur annually in the U.S. (about 400,000), it is important to
intervene in high-risk patients prior to the event. That's where an ICD proves to be a lifesaver. The small oval device jumpstarts damaged hearts.
The difficulty has been in identifying those at risk for dying
suddenly from those fast heart rhythms. While many studies over the years have demonstrated the benefits of ICDs in other patient
groups, the MADIT II trial convincingly shows that ICDs make it possible for people with significant damage to their hearts from a
heart attack, and no prior fast heart rhythms, to live longer if an ICD is implanted.
How do ICDs work?
When a heart attack occurs, it damages the heart's left ventricle, the heart's main pumping chamber. The damaged muscle tissue can
cause abnormal heartbeats, or arrhythmias, placing one at risk for SCD. These abnormal heart rhythms can occur without warning, many years after the heart attack.
The ICD, like a pacemaker, is implanted under the skin and
monitors the heart's rhythm. When a dangerous rhythm is detected, it rapidly delivers a controlled electric shock to restore the heart's normal rhythm.
Know your “ejection fraction”
If you've had a heart attack, it's important to find out what your ejection fraction is. This is the measure cardiologists use to judge
how well your heart is pumping. Most people with heart disease know their cholesterol numbers, but very few are aware of their ejection fractions.
A normal ejection fraction is at least 50 percent; anything less
indicates a problem — it means the heart is pumping out less than half of the blood into the rest of the body — and the heart's
effectiveness as a pump is severely impaired. That person may be at risk for sudden death. In general, the lower the ejection fraction, the greater the risk of sudden death.
Heart attack survivors should know their ejection fraction, and
those with a low ejection fraction or symptoms of heart failure (such as shortness of breath or swelling of the legs) should consult
a cardiologist to see whether they might benefit from an ICD.
What's the downside?
Early ICDs were difficult to implant and had limited battery life. Advances in technology have improved ICDs, making them easier
to implant and safer for patients. They are smaller, much more complex and have improved battery life from the days of their inception in 1980 and approval by the Food and Drug
Administration in 1985.
“ICDs. . . .should be considered in all patients with prior
heart attacks and significant heart muscle damage.”
During surgery to implant an ICD, fine, insulated wire leads connected to the device are inserted into a vein in the chest and
threaded into the heart muscle. The ICD is implanted under the skin of the upper chest or the abdomen. The procedure takes about an hour. Complications are rare and are generally easily treated.
ICD recipients must see a cardiologist every three to six months to
have the device checked, and ICDs usually need to be replaced after six to eight years via an outpatient procedure.
The MADIT II trial clearly shows the potential dramatic benefit of ICDs for a large number of patients. Their use should be considered
in all patients with prior heart attacks and significant heart muscle damage. They can be implanted with minimal risk and discomfort and may truly be life saving.
Dr. Grubman is a partner with Cardiology Associates of New
Haven. He is an attending physician at Yale-New Haven Hospital and a clinical instructor of medicine and cardiology at the Yale University School of Medicine.
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