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Presentation Start/End Time:
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Monday, Mar 31, 2008, 10:00 AM -11:00 AM
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Author Block:
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Guy
Amit, Otto Costantini, Dennis M. Super,
David S. Rosenbaum, MetroHealth Campus of Case Western Reserve University,
Cleveland, OH
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Background:
Although microvolt T-wave Alternans (MTWA)
and electrophysiological study (EPS) are both markers for sudden
cardiac death (SCD), the ABCD trial, found the combination to be more
predictive than each alone. Therefore, we hypothesized that the two tests
measure elements of the arrhythmogenic substrate, which lead to different
arrhythmic outcomes.
Methods: The ABCD Trial included 566 patients with ischemic
cardiomyopathy, left ventricular ejection fraction (LVEF) ≤ 0.40, and
documented non-sustained ventricular tachycardia. All patients underwent both
MTWA test and EPS at enrollment. Implantable cardioverter defibrillators
(ICD) were implanted in 87% of patients. The primary end-point was first
appropriate ICD therapy or SCD. MTWA and EPS Core Laboratories blinded to
outcomes adjudicated the tests, and an Events Committee blinded to the
results of the tests adjudicated all events. Using Kaplan-Meier event rates
and the log rank test, we analyzed the performance of MTWA and EPS in
predicting distinct arrhythmic outcomes: 1. monomorphic ventricular
tachycardia (MVT) vs. 2. the combination of polymorphic ventricular
tachycardia (PVT) or ventricular fibrillation (VF) or SCD.
Results: MTWA was normal in 29% and abnormal in 71%, and EPS was
negative in 61% and positive in 39% of patients. There were 42 MVT events and
24 PVT/VF/SCD events, (8.8% and 5.6% 2-year event rate, respectively). At
1-year, MTWA predicted PVT/VF/SCD (event rate: 2.7% vs. 0% for MTWA abnormal
vs. normal; p=0.04), but not MVT. In contrast, EPS predicted MVT (event rate
9.7% vs. 2.2% for EPS + vs. EPS -; p<0.01), but not PVT/VF/SCD. At 2 years MTWA was
not a significant predictor of either arrhythmia outcome, but a positive EPS
remained predictive of MVT (14.7% vs. 4.7%; p<0.01). Finally, LVEF
(dichotomized by LVEF ≤ 0.30) was not predictive of either arrhythmia
outcome.
Conclusions: MTWA and EPS differ in the arrhythmic outcome they
predict, and the time frame of prediction, suggesting that they identify
different arrhythmogenic substrates. These data further suggest that multiple
risk markers used in combination may better define and predict the complex
electro-anatomical substrates which underlie the risk of SCD.
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