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CLINICAL RESEARCH: HEART RHYTHM DISORDER

"Indeterminate" Microvolt T-Wave Alternans Tests Predict High Risk of Death or Sustained Ventricular Arrhythmias in Patients With Left Ventricular Dysfunction

Elizabeth S. Kaufman, MD, FACC^_*,_*, Daniel M. Bloomfield, MD, FACC, Richard C. Steinman, AB, Pearila B. Namerow, PhD, Ottorino Costantini, MD^_*, Richard J. Cohen, MD, PhD and J. Thomas Bigger, Jr, MD

^_* Heart and Vascular Research Center, MetroHealth Campus of Case Western Reserve University, Cleveland, Ohio
Columbia University, New York, New York
Massachusetts Institute of Technology, Cambridge, Massachusetts.

Manuscript received January 5, 2006; revised manuscript received May 30, 2006, accepted June 5, 2006.

^_* Reprint requests and correspondence: Dr. Elizabeth S. Kaufman, Heart and Vascular Research Center, Hamann 3rd Floor, MetroHealth Campus, Case Western Reserve University, 2500 MetroHealth Drive, Cleveland, Ohio 44109-1998. (Email: ekaufman{at}metrohealth.org).

OBJECTIVES: This study tested the hypothesis that an "indeterminate" microvolt T-wave alternans (MTWA) test, when due to ectopy, unsustained MTWA, or low exercise heart rate (HR), has prognostic significance similar to a positive MTWA test.

BACKGROUND: MTWA testing, used to stratify risk of sudden or total mortality in patients with structural heart disease, has been limited by a substantial number of "indeterminate" tests. Indeterminate tests are due to patient factors—excessive ventricular ectopy during exercise, unsustained MTWA, or failure to achieve a HR of 105 beats/min for 1 min—or technical factors such as a noisy recording or an exercise protocol that causes an excessively rapid rise in HR.

METHODS: Patients in sinus rhythm with left ventricular ejection fraction 0.40 underwent MTWA exercise tests, analyzed with the spectral method and classified by a computerized interpretation algorithm. The primary end point was all-cause mortality or documented non-fatal sustained ventricular arrhythmia (SVA). "Indeterminate" tests were reviewed jointly by 2 readers blinded to subsequent events to determine the primary reason for indeterminacy.

RESULTS: Participants (N = 549) were 56 ± 13 years and 71% male; 49% had ischemic cardiomyopathy. There were 40 deaths and 11 non-fatal SVA. Most (94%) indeterminate results were due to patient factors. The 2-year rate for death or SVA was 17.8% in patients with an "indeterminate" MTWA test compared with 12.3% in those with a positive test.

CONCLUSIONS: In patients with left ventricular dysfunction, an "indeterminate" MTWA test due to patient factors predicted death or SVA at least as well as a positive test.

Abbreviations and Acronyms   ACE = angiotensin-converting enzyme   ARB = angiotensin receptor blocker   CI = confidence interval   HR = heart rate   ICD = implantable cardioverter-defibrillator   LVEF = left ventricular ejection fraction   MI = myocardial infarction   MTWA = microvolt T-wave alternans   SVA = sustained ventricular arrhythmia

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