Blacks less likely to benefit from high-tech treatments for rapid heartbeat

June 23, 2003

DALLAS, June 24 - Testing to guide treatment of rapid heart rhythms leads to poorer survival in blacks than in whites, according to research published in today's rapid access issue of Circulation: Journal of the American Heart Association.

Lead author Andrea M. Russo, M.D., says blacks were much more likely to refuse implantable cardioverter-defibrillators or ICDs when doctors recommended the devices, which that may explain some of the survival difference.

The study analyzed data collected in the Multicenter UnSustained Tachycardia Trial (MUSTT), which enrolled a total of 1,884 whites and 231 blacks. Researchers analyzed data from black and white patients who had inducible, sustained ventricular tachycardia (VT) meaning the rapid heartbeat could be reproduced by performing electrophysiological (EP) testing. EP testing can detect problems with the heart's electrical system by provoking an irregular heartbeat or arrhythmia.

Researchers compared 337 (301 white and 36 black) patients randomly assigned to standard medical treatment with beta-blockers and ACE inhibitors but no antiarrhythmic drugs and 341 (316 white and 25 black) patients assigned to EP-guided therapy, which included both antiarrhythmic drugs and ICDs for patients who failed drug therapy.

Ventricular arrhythmias are life-threatening, rapid, irregular heart rhythms that can lead to sudden cardiac arrest, the sudden stopping of the heartbeat. EP testing is a valuable tool to diagnose and treat the condition because it can provoke known but infrequent arrhythmias and unmask suspected arrhythmias. Electrode catheters are threaded through veins in the groin into the heart to record electrical impulses during each heart beat. EP testing can pinpoint where problems originate. This testing can give immediate feedback on how a patient responds to antiarrhythmic drugs for treating these abnormal heart rhythms. If drugs are not effective, patients may be treated with devices, which are implanted surgically.

Many patients with heart rhythm problems benefit from ICDs, small electrical devices that can detect irregular heartbeats and automatically shock the heart back into normal rhythm.

In this study of patients with coronary artery disease, 78 percent of whites randomly assigned to EP-guided therapy survived without arrhythmias for five years compared to just 46 percent of blacks. Moreover, whites had a 38 percent reduction in sudden cardiac arrest or deaths caused by arrhythmias, while blacks had a nearly three-fold increase in cardiac arrest or deaths related to arrhythmias.

Whites in this study were slightly more likely than blacks to have VT. Although there was no difference in the likelihood of blacks being offered treatment with ICDs if the abnormal rhythm remained inducible at EP testing, they were less likely to accept the treatment. ICDs were implanted in 50 percent of whites versus just 28 percent of blacks. Results of the trial previously found that the only patients who benefited from EP-guided treatment were those who received ICDs, and there was no benefit from antiarrhythmic drugs in the overall population of patients studied.

"We aren't able to determine why blacks are more likely to refuse ICDs, but this is an important question to address in future studies," Russo says. "This might reflect a cultural difference - perhaps blacks might be more reluctant to agree to surgical intervention." Russo is a clinical associate professor of medicine, University of Pennsylvania Health System, Philadelphia, Pa.

There were no racial differences in survival among blacks and whites who were assigned to standard medical treatment with no EP guidance and no antiarrhythmic drugs. Moreover, among patients in the EP-guided arm there is evidence that blacks and whites respond differently to anti-arrhythmic drugs.

"All patients were tried on at least two antiarrhythmic drugs," Russo says. "For some reason, blacks generally responded better and more often to drugs than whites. But despite this initial better response, they did worse on drugs in the long term. We are hypothesizing that there may be some difference in the heart muscle that may predispose blacks to adverse effects with long term antiarrhythmic drug therapy."

Alternately, the ability of EP testing to predict long-term drug response may not be as good in certain patients with other heart muscle abnormalities, such as thickened heart muscle, the latter of which may be seen more often in blacks and may be related to high blood pressure changes on the heart.

Russo notes that the findings are based on a retrospective analysis, and should be considered with caution. They must be validated in a prospective study.

Sudden cardiac death is a significant public health problem in the United States with an estimated 685 people experiencing cardiac arrest each day in the United States. Every year, an estimated 250,000 Americans die of coronary heart disease without being hospitalized. Most of those deaths are sudden deaths caused by cardiac arrest.
Co-authors are Gail E. Hafley, M.S.; Kerry L. Lee, Ph.D.; Nicholas J. Stamato, M.D.; Michael H. Lehmann, M.D.; Richard L. Page, M.D.; Teresa Kus, M.D., PhD; Alfred E. Buxton, M.D.; and the MUSTT Investigators.

Contact: For journal copies only,
please call: 214-706-1396

For other information, call:
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American Heart Association

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