Of the thousands of heart attack survivors each year, half remain at risk for sudden death -- despite the best medical care. Yet in this group of patients, preventive therapy with an implantable cardioverter defibrillator reduces the death rate by a remarkable 31 percent, according to research presented at the American College of Cardiology’s 2002 meeting in Atlanta, March 17 to 20.
Led by Arthur J. Moss, M.D., professor of Medicine, Division of Cardiology, at the University of Rochester Medical Center, the results of the major, four-year study are also reported in the March 21 issue of The New England Journal of Medicine. The study enrolled 1,232 patients at 76 sites around the world, but the enrollment criteria would apply to 3 to 4 million Americans with heart disease today, and about 400,000 new patients annually, Moss estimates.
The research is the first to show the preventive value of the implantable cardioverter defibrillator (also known as an ICD), a medical device about the size of a pager that is surgically implanted in the chest under local anesthesia. The device detects irregular and potentially fatal heartbeats and shocks the heart back into a normal rhythm. Introduced about 20 years ago, ICDs had been prescribed only for a small group of patients who had survived a cardiac arrest.
But after additional research and improvements to the device itself during the past decade -- with Moss at the forefront -- the most recent trial reaches the broadest group of patients ever and demonstrates the life-saving value of the ICD. “This is an important and major contribution to the field, as it sets new standards for therapy to save lives and improve survival,” says Moss, principal investigator of the study. “Currently there is no other preventive treatment for people at risk of dying suddenly from heart rhythm disorders.”
The high-tech device became more widely known after Vice President Dick Cheney had an ICD surgically implanted last summer. The ICD works internally in the same way that an external defibrillator can save someone, by delivering an electrical shock to the heart to restore its normal function.
“It’s like having your own personal coronary care unit,” Moss says. The research team recommends the device be used as standard, preventive therapy in patients with heart failure after a heart attack.
Sudden death from cardiac arrest is less understood than other forms of heart disease. It occurs most often in men in their 60s, when the heart stops abruptly, usually as a result of an electrical malfunction due to rapid and chaotic rhythms from blockage of coronary arteries or scarring from a prior heart attack. Young adults with heart disease are also prone to unexpected cardiac arrest, when an adrenaline surge during intense physical activity sets off an irregular heart beat. Certain drugs can also trigger abnormal rhythms and death.
Those who could benefit the most from an implantable defibrillator may not know they are at high risk for sudden death. These are patients with a low “ejection fraction,” a measurement of how much blood is pumped from the heart with each beat. Physicians measure a patient’s EF with a routine echocardiogram, a non-invasive procedure, or with a nuclear cardiology technique. The normal ejection fraction of the heart is 60 percent or more. Patients with an ejection fraction of 30 percent or less have a form of heart disease that increases their risk for sudden death, Moss says.
“Our study supports the idea that people should know their ejection fraction in the same way they know what their blood pressure and cholesterol values are,” Moss says. “It’s also an educational opportunity for physicians to encourage their heart patients to know their ejection fraction, for this information may lead to the use of life-saving treatment. ”
In the latest study by Moss and his team, they enrolled 1,232 heart patients into a clinical trial at 76 national and international medical centers. Each patient had suffered at least one prior heart attack and had been diagnosed with a low ejection fraction. Of the total, 742 patients were randomly assigned to ICD therapy and 490 did not receive an ICD. Both groups received optimal standard therapy, such as cholesterol-lowering drugs, beta-blockers and other appropriate medications.
An independent safety-monitoring group stopped the trial earlier than expected, on November 20, 2001, when data showed the survival rates were substantially better for those receiving ICDs. A detailed analysis showed that after following each patient for an average of 20 months, the death rate for patients with an ICD was 14.2 percent, versus 19.8 percent for those who did not have an ICD. Statistically, this survival difference translates into a 31-percent reduction in mortality for the group that received defibrillators.
Indianapolis-based Guidant Corp., a maker of cardiovascular medical devices, funded the $7 million trial. Guidant is awaiting FDA approval for use of preventive ICD therapy in patients with heart failure. Two other companies, St. Jude Medical Inc. and Medtronic Inc., also manufacture implantable defibrillators.
However, with a price tag of about $20,000 each, the researchers note in the New England Journal article that “the cost to the health care system would be substantial,” if large numbers of patients began using ICDs prophylactically. They hope market forces bring the cost down. Moss also maintains that other therapies, particularly surgery, are just as costly but have not always demonstrated through objective research that they save lives.
“We want doctors to be vigilant,” Moss says. “Just because you have one therapy that prevents death doesn’t mean you should ignore other therapies. The significant thing, though, is that no other single therapy for this population has been shown to reduce mortality by nearly one-third. The last breakthrough of this magnitude was the introduction of beta-blockers in the 1970s.”
The study found infrequent serious complications from an implanted defibrillator, but the incidence of new or worsened heart failure in the ICD group was slightly higher. Concerned by that finding, Moss says the research team investigated how often the device shocked a patient’s heart back to a normal rhythm, as well as what type of heart malfunction was occurring when the device fired. They found no evidence that the device itself worsens an existing heart condition. It’s more likely, Moss says, that by prolonging the life of patients with serious heart disease, the patients with ICDs were more apt to develop additional problems that could not be helped by the defibrillator.
Journal
New England Journal of Medicine