CLINICAL RESEARCH: HEART RHYTHM DISORDER
Microvolt T-Wave Alternans Identifies Patients With Ischemic Cardiomyopathy Who Benefit From Implantable Cardioverter-Defibrillator Therapy
Theodore Chow, MD, FACC*,
Dean J. Kereiakes, MD, FACC*,
Cheryl Bartone, BS*,
Terri Booth, RN*,
Edward J. Schloss, MD, FACC*,
Theodore Waller, MD, FACC*,
Eugene Chung, MD*,
Santosh Menon, MD*,
Brahmajee K. Nallamothu, MD, MPH and
Paul S. Chan, MD, MSc,*,1
* The Lindner Clinical Trial Center at the Christ Hospital and the Ohio Heart and Vascular Center, Cincinnati, Ohio
VA Ann Arbor Health Services Research and Development Center of Excellence, and the University of Michigan Medical School, Ann Arbor, Michigan.
Manuscript received May 20, 2006;
accepted June 28, 2006.
* Reprint requests and correspondence: Dr. Paul S. Chan, VA Ann Arbor Health Services Research and Development Center for Excellence, Cardiology (111-A), 2215 Fuller Road, Ann Arbor, Michigan 48105. (Email: paulchan{at}umich.edu).
OBJECTIVES: This study sought to assess whether implantable cardioverter-defibrillators (ICDs) have different mortality benefits among patients with ischemic cardiomyopathy who screen negative and non-negative (positive and indeterminate) for microvolt T-wave alternans (MTWA).
BACKGROUND: Microvolt T-wave alternans has been proposed as an effective tool for risk stratification. However, no studies have examined whether ICD benefits differ by MTWA group.
METHODS: We developed a prospective cohort of 768 patients with ischemic cardiomyopathy (left ventricular ejection fraction  35%) and no prior sustained ventricular arrhythmia, of which 392 (51%) received ICDs. The mean follow-up time was 27 ± 12 months. Propensity scores for ICD implantation based on the variables most likely to influence defibrillator implantation were developed for each MTWA cohort. Multivariable Cox analyses that controlled for propensity score, demographics, and clinical variables evaluated the degree to which ICDs decreased mortality risk for each MTWA group.
RESULTS: We identified 514 (67%) patients with a non-negative MTWA test result. After multivariable adjustment, ICDs were associated with lower all-cause mortality in MTWA-non-negative patients (hazard ratio [HR] 0.45, 95% confidence interval [CI] 0.27 to 0.76, p = 0.003) but not in MTWA-negative patients (HR 0.85, 95% CI 0.33 to 2.20, p = 0.73) (for interaction, p = 0.04), with the mortality benefit in MTWA-non-negative patients largely mediated through arrhythmic mortality reduction (HR 0.30, 95% CI 0.13 to 0.68, p = 0.004). The number needed to treat with an ICD for 2 years to save 1 life was 9 among MTWA-non-negative patients and 76 among MTWA-negative patients.
CONCLUSIONS: In patients with ischemic cardiomyopathy and no prior history of ventricular arrhythmia, mortality reduction with ICD implantation differs by MTWA status, with implications for risk stratification and health policy.
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Abbreviations and Acronyms
| | CI = confidence interval | | CMS = Center for Medicare and Medicaid Services | | EPS = electrophysiological study | | HR = hazard ratio | | ICD = implantable cardioverter-defibrillator | | LVEF = left ventricular ejection fraction | | MTWA = microvolt T-wave alternans | | SCD = sudden cardiac death |
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