ICDs can Save Heart Patients

Patients with hypertrophic cardiomyopathy who are at high risk can benefit from implantable defibrillators. The devices can cut down their risk of sudden death, according to a new study published in the Journal of the American Medical Association.

Hypertrophic cardiomyopathy is a genetic disease that can lead to abnormal thickening of the heart muscles. The thickening can disrupt the electric system of the heart and lead to disturbances in the rhythm of the organ called arrhythmias, which can be fatal at times.

Implantable cardioverter-defibrillators (ICDs) can take care of these dangerous rhythm changes. As a result they have become routine treatment for patients at high risk due to hypertrophic cardiomyopathy. Now the new study has found that people benefiting from the ICDs face only a single risk factor for sudden cardiac death.

For the study, Dr. Barry Maron and colleagues at the Minneapolis Heart Institute Foundation analysed data gathered from an international, multi-center registry of defibrillators. The data covered 506 patients with hypertrophic cardiomyopathy who were fitted with ICDs between 1986 and 2003.

While all the patients were considered at high risk for sudden death, nearly 87% had only mild symptoms or none at all. The average age of the patients was 42 years and they were split between those who had never had a problem (the defibrillator was primary prevention) and those who already had a problem (defibrillators were secondary prevention).

The researchers found that the ICD terminated ventricular fibrillation (severely abnormal heart rate that results in cardiac arrest) or ventricular tachycardia (abnormally fast heartbeat) in around 20% of the patients. In patients who had the device for secondary prevention, the ICD corrected abnormal heart rhythms in 10.6% of patients annually. The same figure for patients with primary prevention was 3.6%.

It was also observed that there was nearly 25% probability of a defibrillator intervening up to five years after implantation. The device was also found to have intervened appropriately in over 40% of patients under the age of 40 years.

The analysis also revealed that a single risk factor was responsible for implantation of the defibrillator for primary prevention in nearly 35% of the patients. The researchers found that the chances of the device intervening in patients with one, two or three or more risk factors were just about the same.

“Hypertrophic cardiomyopathy is the most common cause of sudden death in young people, including athletes, and a defibrillator affords the opportunity, as it turns out, to change the natural course of the disease and prevent sudden death,” said Dr. Maron, Director of the Hypertrophic Cardiomyopathy Center at the Minneapolis Heart Institute Foundation.

“In a way, this highlights the use and effectiveness of the device in this genetic disease in these young patients and expands the number of patients that could be eligible at least for consideration of a defibrillator,” he added.

Medical experts however were not impressed with the findings and feel that it does not provide any new information. “Some of this data has been published in a smaller number of patients. This study confirms what has already been done,” said Dr. Jose Joglar, Director of Clinical Electrophysiology, and Associate Professor of Medicine at the University of Texas Southwestern Medical Center at Dallas. “This is not going to expand the use of defibrillators.”

The researchers however stand by their findings as they believe it is not always easy to identify which patients with hypertrophic cardiomyopathy would benefit from an ICD. “It’s traditionally difficult to determine precisely which patients among all with this disease are at high risk and would deserve consideration for an ICD, because HCM [hypertrophic cardiomyopathy] is a particularly heterogeneous disease,” Dr. Maron explained.

“Most of the patients at high risk have no symptoms or only mild symptoms and are younger than those who have coronary disease by, on the average, 25 years. And there is no one single risk factor that has emerged such as with coronary disease following a heart attack,” he said.

“Because the patients are younger, the decision for these ICDs is bigger because of the time period they will have them is longer,” he continued. And while the study might not be the first one to study ICDs for hypertrophic cardiomyopathy, it is the largest.

Additionally the researchers evaluated risk factors including a history of hypertrophic cardiomyopathy-related sudden death in one or more relatives under the age of 50; fainting; and abnormally rapid heart rhythm.

“This is a select patient population. The risk factors are pretty significant; the patients were probably sicker,” Dr. Joglar said. “The great majority of patients with HCM will have a better prognosis than that.”

Despite their findings, the researchers added a word of caution regarding defibrillators not being necessary for all patients with hypertrophic cardiomyopathy. In their opinion, the call for implanting a defibrillator should be given by individual doctors.

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