T-wave alternans could surpass LVEF as risk-stratifier for ICD
implantation
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May 11, 2005 |
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Steve Stiles |
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New Orleans,
LA - T-wave
alternans-(TWA) testing has a very low false-negative rate when stratifying cardiomyopathy
patients for risk of death or sustained ventricular arrhythmias, adds to risk
assessments with LVEF alone, and isn't muddled by prolonged QRS intervals,
according to post hoc analyses of a prospective, observational trial.[1,2]
The findings add to mounting evidence that the noninvasive TWA test, which
monitors shape variations in the electrocardiographic T-wave at exercise, can
sharpen the screening of candidates for a primary-prevention implantable
cardioverter-defibrillator (ICD).
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Dr J Thomas Bigger |
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In the T-wave
Alternans in Heart Failure (TWA in HF) trial, the TWA test "was at
least twice as strong in predictive value as ejection fraction, which is an
incredibly good risk stratifier," Dr J Thomas Bigger (Columbia
University, New York, NY), told heartwire. "Furthermore, if
you use both of them together, you can get a group with very high risk and a
group with very low risk approaching zero."
After presenting
the findings last week at the Heart Rhythm Society 2005 Scientific Sessions,
Bigger's Columbia colleague Dr Sarah B Levin sliced the trial's data
another way and found equal predictive values for TWA in patients with QRS
durations <120 ms compared with those with longer QRS intervals.
The Centers
for Medicare & Medicaid Services (CMS) had commented that TWA would be
worth exploring as a potential risk indicator for screening primary-prevention
ICD candidates when it proposed reimbursement criteria for such devices in
September 2004.[3,4] The official decision in January 2005 was
more expansive than the proposal, allowing reimbursement for ICD candidates in
NYHA class 2-3 with an LVEF <35% and class-4 patients if they are
also eligible for resynchronization therapy.
"CMS did
the medical community a big favor. It gave them very broad coverage for
prophylactic ICD implants
maybe broader than they might
have," said Bigger. The criteria leave a lot of the patient selection up
to the physician. "It's a wonderful position to be in, but I think we have
to use it responsibly."
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"There are
low-risk subsets among those identified under the coverage decision,"
perhaps a quarter to a third of the total, Bigger said, "that really don't
have much chance of benefiting from one." Society unnecessarily bears the
cost in such cases, and "as far as the patient's concerned, it's more of
an aggravation than a benefit."
It's the TWA
test's tiny false-negative rate "that makes it extraordinarily powerful in
identifying these low-risk groups among those covered by the CMS
decision," Bigger said. "I think it will give physicians the
confidence to use it and make a decision not to implant [an ICD] when the
impulse is to be safe and put one in."
If the test is
ever included within the reimbursement criteriaand "I think we're a long way
from that," Bigger saidit would be fairly easy to
implement. In the trial, patients were maintained on their drug therapy, which
included beta blockers in 81%, which "made it very convenient to use in
outpatients," he said. "Anybody who does exercise testing for
coronary disease in their office could do this."
TWA
compared with, combined with LVEF
The population
consisted of 549 mostly male patients in sinus rhythm and an LVEF <40%
(average 25%) who were in NYHA class 1-3, divided nearly evenly between those
with ischemic and nonischemic cardiomyopathy.
The baseline TWA
test was abnormal in 66% of patients. Over the next two years, the primary end
point, defined as all-cause mortality or nonfatal sustained ventricular arrhythmias,
occurred in 10.7% of patients. But event rates varied considerably by TWA
results and LVEF.
Predictive value of TWA vs LVEF
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*Abnormal LVEF <30%, normal LVEF >30%
On its own, TWA
surpassed LVEF as a predictor of the primary end point, Bigger observed when
presenting the findings. Patients with an LVEF of 31% to 40% had a high risk
"and, if risk-stratified with T-wave alternans, probably in the future
[many could] be candidates for ICD prophylaxis." He said the TWA test is
"dominant" when the two risk indicators are used together; still,
their combination can disclose "a group that's at very high risk relative
to the whole group or an ultra-low-risk group that is negative for both
variables." The latter group, he said, "probably can be managed
conservatively and don't have much to gain from having a prophylactic ICD
implantation."
Event rates by paired TWA and LVEF test results
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30%
Does QRS
interval influence the TWA test?
Although at
least one prior study has suggested that TWA isn't predictive of death and
ventricular arrhythmias among patients with a prolonged QRS interval,[5]
according to the common definition also used in Bigger's study, retrospective
data from the TWA in HF trial suggests the opposite.
"Regardless
of QRS duration, those with an abnormal T-wave-alternans test have a markedly
higher two-year event rate," Levin said during her presentation. Patients
with an abnormal TWA test by itself, she said, "had a 650% increased risk
of death or [nonfatal] sustained ventricular arrhythmia compared with those
with a normal test," suggesting its predictive value is "robust"
regardless of QRS duration.
Although QRS
prolongation alone similarly increased the risk, adding QRS to the TWA test
appeared to stratify the patients more precisely.
Hazard ratios (95% CI) for primary end point at
2 years, abnormal TWA vs QRS prolongation
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*Abnormal QRS >120 ms, normal QRS <120 ms
Event rates by paired TWA result and QRS
duration
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To download tables as slides, click on slide logo below
The findings
from both analyses should be explored in the context of ICD trials, in which
patients have TWA, LVEF, and QRS intervals assessed but receive ICDs
regardless, Bigger said when interviewed. A few such studies are ongoing, he
noted, including the international Alternans Before Cardioverter
Defibrillator (ABCD) trial.
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