One-third of implanted heart devices may be
10 January 2007
A new study has found that a large number of patients with implanted
cardiac devices may not benefit from them and that a simple heart-rhythm
test can tell who will not benefit.
If the test were used on the majority of ICD candidates, as many as
one-third could be spared the operation to implant a device, without raising
their risk of sudden death. In the US this means that Medicare could be
spared the additional $90,000 lifetime cost of each device compared to best
The study, published in the January issue of the Journal of the
American College of Cardiology, is based on data from 768 patients who
were candidates for ICDs at Christ Hospital and the Ohio Heart and Vascular
Center in Cincinnati. All of the patients had survived heart attacks but had
permanent damage to their heart muscle caused by lack of blood flow — a
condition called ischemic cardiomyopathy.
Each patient received a test called microvolt T-wave alternans or MTWA,
along with a battery of other tests, during their evaluation. Half of the
patients went on to receive ICDs, although the MTWA test results weren’t
used in the decision-making process. The patients’ health and the causes of
any deaths were tracked for up to three years.
After that time, the data were analyzed by researchers from the
University of Michigan Cardiovascular Center and VA Ann Arbor Healthcare
System, in cooperation with the Ohio team.
In all, 67% of patients had positive or inconclusive MTWA test results.
Of them, the patients who went on to receive an ICD were 55% less likely to
die in the follow-up period than those who hadn’t gotten an ICD. They were
also 70% less likely to die suddenly due to a heart-rhythm disruption. But
at the same time, the one-third of patients who had negative MTWA tests and
then received ICDs were no less likely to die than those with similar test
results who didn’t receive ICDs.
“This is the first study to demonstrate that a subset of patients who
meet current criteria for defibrillator placement may not benefit at all
from ICDs,” says Paul Chan, M.D., M.Sc., senior author and a fellow in
cardiovascular medicine at the U-M Medical School. “Use of the MTWA test,
which has been covered by Medicare since spring of 2006, could truly help us
tell which ICD candidates will benefit most.”
In all, the authors calculate, one life could be saved every two years
for every nine ICDs implanted in people with positive or inconclusive MTWA
results. But it would take 76 ICD implantations in people with negative MTWA
tests to save one life every two years.
The reductions in death risk were present even after the authors
corrected for many other variables and differences between the two
MTWA-positive and MTWA-negative groups.
Chan and his Ohio colleagues, led by first author Theodore Chow, M.D.,
FACC, of the Lindner Clinical Trial Center at Christ Hospital and the OHVC,
have studied the use of MTWA in predicting patients’ risk for several years.
Last spring, they published results from the same group of ischemic
cardiomyopathy patients, showing that the MTWA test was able to predict the
risk of death from any cause, even after they adjusted the data for other
heart-rhythm test results and medical issues.
Also in 2006, Chan and his colleagues from U-M and the VA Ann Arbor
Health Services Research & Development Center of Excellence demonstrated how
MTWA testing could reap hundreds of millions of dollars in savings for the
Medicare system, and the taxpayers who support it. That analysis was based
on assumptions about MTWA testing’s ability to predict risk – assumptions
that can now be adjusted based on the new study results.
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
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
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.
Reference: Journal of the American College of Cardiology, January
2 2007, Vol. 49, No. 1.