The Alternans Before Cardioverter Defibrillator (ABCD) Trial sought to determine if this non-invasive test could help predict the risk of sudden cardiac death (SCD) and thereby direct the therapy of implanted cardiac defibrillators (ICD) as good as, or better than current methods. Electrophysiology study (EP) is the prevailing method and involves threading a catheter through a patient's veins into the heart to induce an arrhythmia with an electric shock. This invasive technique requires a high degree of skill, which limits its availability, and exposes the patient to a certain degree of procedural risk. The Microvolt T-Wave Alternans (MTWA) Test™, however, involves only the topical placement of electrocardiogram sensors on the chest.

“The ABCD trial is the first to use MTWA to guide implantation of defibrillators,” said David Rosenbaum, MD, Professor of Medicine at Case Western Reserve University in Cleveland and lead author on the study.

The trial was initiated in May 2001 and enrolled 566 patients with ischemic cardiomyopathy from 43 centers in the United States, Germany and Israel. Participants were 18 years of age and older, had no prior arrhythmias and left ventricle injection fractions (LVEF) ≤40. Patients were placed into one of two groups according to initial test results. If either the EPS or MTWA test was positive, patients received an ICD; if both tests were negative, an ICD was optional but encouraged. Seventy percent of this later group chose to receive the defibrillator; 88% of the total population therefore received ICDs. The median follow-up time was 1.9 years with events adjudicated by an independent committee who were blinded to the screening methodology.

At one year, both EPS and MTWA strategies had similar positive and negative predictive values. The event rates for patients that had an indication for an ICD according to both tests were higher (12.6%) than those with negative predictor values (2.3%; p=0.017). Negative predictive values of both methods combined was better than that of either method alone.

“Another finding of the ABCD trial…is that risk stratification can improve the therapeutic efficacy of ICD implantation to a far greater extent than increases in risk. And, of course the appropriate level of acceptable risk must be individualized to specific patients,” said Dr. Rosenbaum. For example, 95% of patients who have an indication for ICD implantation by LVEF alone do not experience an event (representing therapeutic inefficiency), whereas only 65% of patients with an indication for a device by MTWA are event free. The therapeutic risk of each of these indicators (untreated patients who experience an event) increases only from 0% to 1.5%.

Finally, the predictive values of these tests appear to depend on timing. The EP study was not predictive until nine months or more and remained predictive for two years, whereas the MTWA test was predictive as early as 6 months, but lost its predictive value after 12 months. These findings suggest that periodic screening, combined with more than one risk test may be appropriate.