Implantable cardioverter defibrillators (ICDs) are devices designed to correct arrhythmias, electrical malfunctions that throw the heart out of rhythm and cause many of the 330,000 sudden cardiac deaths each year in the United States. Most fatal arrhythmias in the aging are caused by scar tissue left behind by heart attacks that interferes with the heart's electrical system. The connection has caused some to confuse sudden cardiac death with heart attack, which is brought when a blocked artery kills heart muscle. Many also confuse heart attack with heart failure, where heart becomes too insufficient to pump enough blood to meet the body's needs.
ICDs have been used more widely since studies found that the devices could reduce sudden death by up to 54 percent in those patients most at risk for arrhythmia: heart attack survivors. Led out of the University of Rochester Medical Center, the 2002 MADIT II study (Multicenter Automatic Defibrillator Implantation Trial II) in particular changed medical guidelines nationwide and made a hundred thousand heart attack survivors eligible for ICD therapy. The newly published study, from the MADIT II data, found that those same people who live longer are at increased risk of developing heart failure later on.
"Our results show that cardiologists and ICD patients nationwide because need to pay much greater attention to heart failure," said Ilan Goldenberg, M.D., research assistant professor at the University of Rochester Medical Center and lead author of the new re-analysis of MADIT-II. "Otherwise, effective treatment for arrhythmia may transform the risk of sudden death into a subsequent heart failure risk. If we could ramp up heart failure prevention along with implantation of ICDs, this will improve the quality of life in patients who live longer."
The original MADIT-II trial included 1,232 patients with an ejection fraction of 30 percent or less who had a heart attack at least a month before enrollment. Ejection fraction is a measure of the heart's pumping strength, and is reduced in patients in some stage of heart failure. With a healthy ejection fraction being about 60, the hearts of patients in MADIT-II were pumping blood with about half the force of healthy hearts.
In the newly published sub-analysis, patients who had ICDs implanted were 39 percent more likely to have a first hospitalization for heart failure than those who received only medical therapy after a heart attack, and 58 percent more likely to be hospitalized for recurrent heart failure during an average 20-month follow up.
The Next Step
A preventive strategy to reduce the risk of heart failure in ICD patients is currently being evaluated in yet another follow-up study to MADIT-II: The Multicenter Automatic Defibrillator Implantation Trial With Cardiac Resynchronization Therapy (MADIT-CRT). MADIT-CRT is designed to determine if the combination of ICD and resynchronization therapies can reduce the risk of mortality and heart failure events by approximately 25 percent.
A standard ICD includes one lead, a wire inserted into the heart that stands ready to shock the heart back into normal rhythm should an arrhythmia occur. Patients with both risk of arrhythmia and heart failure, however, have a second problem, a timing delay in the pumping signal as it passes between the right and left parts of the heart. The delay can accelerate heart failure and a single-lead ICD cannot address the problem. A new generation of ICDs designed with two leads has the potential to both stop arrhythmias and re-synchronize the heartbeat when necessary, reducing heart failure, according to theory and preliminary studies.
"Now that we are have had some success in preventing sudden cardiac death, it is imperative that we do more as a nation to address heart failure," said Arthur J. Moss, M.D., professor of Medicine in the Division of Cardiology and Director of the Heart Research Follow-up Program. "Future studies will need to address the best combination of treatment to stop both sudden cardiac death and heart failure, to improve the quantity and quality of life."