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Paul S. Chan, MD, MPH, Dean
Kereiakes, MD, Edward Schloss, MD, Theodore Waller, MD, Eugene Chung, MD and
Theodore Chow, MD. University of Michigan School of Medicine, Ann Arbor, MI,
Ohio Heart and Vascular Center, Cincinnati, OH
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Objective: To assess if
implantable cardioverter-defibrillators (ICDs) have different mortality
benefits among patients with ischemic cardiomyopathy who screen microvolt
T-wave alternans (MTWA) negative and non-negative (positive and
indeterminate).
Background: MTWA has been proposed as an effective tool for risk
stratification. However, no studies have examined whether ICD benefit
differs by MTWA subgroup.
Methods: We developed a prospective multi-centered cohort of 752
patients with ischemic cardiomyopathy (LVEF<35%) and no prior
history of ventricular arrhythmia, of which 392 (52%) received ICDs. Mean
follow up was 18+10 months. We assessed the degree to which ICDs
decreased mortality risk by MTWA subgroup with Cox proportional hazards
analyses that used a propensity score for ICD receipt based on
electrophysiologic variables (QRS duration, Holter, microvolt T-wave
alternans, and electrophysiologic study results) and which controlled for demographic,
clinical, and medication treatment variables.
Results: We identified 514 (67%) patients with a non-negative MTWA
test. C-statistics for the propensity scores showed good discrimination
[C=0.80 (MTWA non-negative); C=0.75 (MTWA negative)]. After multivariable
adjustment, ICDs lowered all-cause mortality in MTWA non-negative [hazard
ratio (HR)=0.54 (95% CI: 0.29, 0.99); p=0.045] but not in MTWA negative
patients [HR=1.03 (0.23, 4.59); p=0.97], with the mortality benefit in MTWA
non-negative patients largely mediated through arrhythmic mortality
reduction [HR=0.33 (0.12, 0.93); p=0.036].
Conclusion: Risk stratification with MTWA testing may allow one to
determine which patients benefit from ICD therapy. 
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