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

“Indeterminate” Microvolt T-Wave Alternans Tests Predict High Risk of Death or Sustained Ventricular Arrhythmias in Patients With Left Ventricular Dysfunction Elizabeth S. Kaufman, Daniel M. Bloomfield, Richard C. Steinman, Pearila B. Namerow, Ottorino Costantini, Richard J. Cohen, J. Thomas Bigger Jr We performed a microvolt T-wave alternans (MTWA) exercise test in 549 patients with left ventricular ejection fraction ≤0.40 and followed them for 2 years. Among MTWA tests classified as “indeterminate,” 94% were so classified owing to ventricular ectopy, unsustained MTWA, or low exercise heart rate. Patients with an indeterminate MTWA test were at least as likely to die or experience a non-fatal sustained ventricular arrhythmia (SVA) as those with a positive test. Therefore, patients with indeterminate and positive MTWA tests can be combined into a single “abnormal” group at high risk of death or SVAs. 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. 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. 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. 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. In patients with left ventricular dysfunction, an “indeterminate” MTWA test due to patient factors predicted death or SVA at