This research has focused on patients with ischemic cardiomyopathy the most common form of heart-muscle damage that weakens the heart's pumping ability, leaves patients prone to sudden cardiac death and therefore makes them candidates for an ICD.

In recent years, ICDs have been shown to reduce the overall risk of sudden cardiac death well enough to be given approval by the Food and Drug Administration and to receive coverage by Medicare and other insurers.

In fact, in 2004 Medicare expanded the group of patients who were eligible for ICD therapy, leading to estimates that 50,000 new patients each year can qualify for the devices based on criteria relating to their heart rhythm and pumping capability. But if every Medicare participant who qualified for an ICD under current guidelines received one, it would cost the Medicare system an additional $2.9 billion to treat all of them for life.

The use of the MTWA test could potentially save a large part of those costs. But using MTWA testing to determine who will get the most benefit from an ICD is still not standard practice, despite Medicare coverage for one form of the test.

Chan, Chow and their colleagues hope that their study -- and larger studies now under way or planned -- will lead to routine use of MTWA testing, which is much like a standard treadmill "stress test" familiar to many heart patients.

In an editorial accompanying the paper, two University of Pennsylvania cardiologists note that the study adds more information to the issue of MTWA testing for ICD candidates, but that larger studies are needed.