AHA: Non-Invasive Office-Based Test Could Increase Appropriate Use of ICDs

CHICAGO, Nov. 15 -- A noninvasive outpatient test can improve the chance that implantable cardioverter defibrillators (ICDs) will go to the patients most likely to benefit from them, researchers reported today.

The T-wave alternans test, which would supplant electrophysiology lab evaluations, uses a computer to interpret subtle differences in electrocardiogram tracings and can be done for in a physician's office. said David S. Rosenbaum, M.D. director of MetroHealth Heart and Vascular Center in Cleveland,

Moreover, it could sharply reduce the number of ICDs that are implanted but never fire, said Dr. Rosenbaum, who reported results of the Alternans Before Cardioverter Defibrillator (ABCD) trial during a late-breaking clinical trials session at the American Heart Association meeting. The trial evaluated the Microvolt T-Wave Alternans test.

With the average ICD carrying a price tag of ,000 and most implanted devices never fired, both clinicians and health economists have been searching for a better way to select patients for ICDs, and a T-wave alternans may be that better way, he said.

When the decision to implant an ICD is based solely on a left ventricular ejection fraction of less than 40%, about 93% of the devices will never fire, he said, "but if the device is implanted on the basis of an abnormal alternans test, only about 65% will never fire,"

Also, he said that the Microvolt T-Wave Alternans test was as effective as an invasive electrophysiological study for predicting ventricular tachycardia events at one year in patients at risk for sudden cardiac death.

The ABCD trial randomized 566 patients with ischemic cardiomyopathy with an ejection fraction of less than 40% and nonsustained ventricular tachycardia.

Patients who had either a positive electrophysiological study or a positive T-wave alternans finding were required to have an ICD implanted. Those with a negative electrophysiological study and negative T-wave alternans were encouraged to have the device implanted.

The endpoint was appropriate ICD therapy or sudden cardiac death. The patients were followed for up to two years.

Among the findings:

• 99 patients had a normal T-wave alternans test and a negative electrophysiological study.
• 245 had abnormal T-wave alternans results and negative electrophysiological study.
• T-wave alternans was normal in 66 patients who had positive electrophysiological study.
• 156 patients had an abnormal T-wave alternans and a positive electrophysiological study.
• At one year negative predictive value of electrophysiological study was 96% versus 95% for the T-wave alternans test.
• One year positive predictive value for EPS was 11% for electrophysiological study versus 9% for T-wave alternans.

Dr. Rosenbaum said the electrophysiological study was not "predictive for sudden cardiac death until nine months or more, but remained predictive for two years."

By contrast, the T-wave alternans results were predictive as early as six months but were no longer predictive of outcomes at 12 months.

The findings suggest that the abnormalities that increase the risk of arrhythmia "are dynamic and are subject to change over time, which means that periodic screening may be beneficial."

Dr. Rosenbaum said that in terms of reducing inappropriate use of ICDs, yet reducing the risk of sudden cardiac death in this population, "combining T-wave alternans and EPS would be the best strategy since the combination was synergistic in predicting events."

An electrophysiological study costs about ,000 and is done on an in-patient basis, "so one strategy might be to use T-wave alternans in the office and follow-up with the invasive procedure when results warrant."

St. Jude Medical sponsored the study and Dr. Rosenbaum disclosed that he is a consultant to Cambridge Heart Inc., which makes the Microvolt T-Wave Alternans test.