The ABCD Trial shows that risk for sudden cardiac death can be as effectively determined with computer analysis of an electrocardiogram as with invasive electrophysiologic testing, according to a presentation at a late-breaking clinical trial session at the American Heart Association meeting.

The Alternans Before Cardioverter Defibrillator (ABCD) Trial was conducted to compare the T-wave alternans (TWA) test, which measures beat to beat variability on an electrocardiogram, with electrophysiological study (EPS).

The two diagnostic tests appear to be equally predictive, and the two tests together clearly identify patients at very low risk for sudden cardiac death; they are least likely to benefit from defibrillator therapy. However, the TWA test prediction of outcomes was limited to 15 months, suggesting that risk screening should be repeated at least every year and as a patient’s cardiac condition changes.

Unlike typical stress testing, the TWA uses a special computer program that analyzes subtle differences in the electrocardiogram’s T-wave from one beat to the next. Physicians first noticed the association between difference in T-wave patterns and risk of sudden death more than a century ago, but the availability of computers made it possible to analyze them to predict sudden cardiac death.

The 566 ABCD trial patients (average age 65 years; 84 percent male) were treated at 42 medical centers in the United States, Germany and Israel. All patients had previous heart damage from coronary artery disease, but none had previously experienced a cardiac arrhythmia. The patients underwent both tests and received a device if either or both tests were positive, making the current trial the first in which patients received active therapy based only on a positive TWA test.

If both tests were negative, patients and their physicians decided whether to proceed with implantation. The goal was to determine if TWA testing could be used in a strategy to identify patients most likely to benefit from preventative device therapy.

Over two years, doctors checked the patients every six months to see if the devices had discharged. Researchers found that the overall rate of arrhythmic events was low: 7 percent the first year and 13 percent over two years.

The event rate was highest if the two tests were both abnormal, lowest if both tests were normal, and intermediate if one of the two tests was abnormal, suggesting an additive predictive value of using both.

The other intriguing finding was an unexpected time dependency of risk markers for sudden death, Robert Rosenbaum, MD, said “We found that the EPS study was not predictive until nine months or more and then remained predictive for two years, while the TWA test was predictive as early as six months out but was no longer predictive of outcomes around the 12- to 15-month mark. The findings suggest the abnormalities in heart disease that increase the risk of arrhythmia are highly dynamic and change over time, which suggests annual screening may be beneficial.”