Microvolt T-Wave Alternans, Peak Oxygen Consumption, and Outcome in Patients with Severely Impaired Left Ventricular Systolic Function

Background: Abnormal microvolt T-wave alternans (MTWA) and low peak oxygen consumption (VO₂) both predict poor outcome in heart failure. However, their independent predictive properties have not been assessed in large-scale cohorts. Methods: This was an observational prospective cohort study of 303 consecutive patients referred for metabolic stress testing. All had an ejection fraction ≤ 40% and were considered candidates for transplantation. The exercise laboratory did not collect MTWA data from patients with implanted pacemakers or defibrillators. The primary end point was a composite of all-cause death or United Network for Organ Sharing status 1 transplantation. Results: During a 2.8-year period, there were 34 deaths and 17 transplantations. Patients with abnormal MTWA had a higher event rate of 23% (31 of 136) vs 12% (20 of 167), with an unadjusted hazard ratio (HR) of 1.90 (95% confidence interval [CI], 1.90-3.33; p = 0.03). The association remained significant after adjustment for 3 clinical variables (HR, 1.89; 95% CI, 1.05-3.39; p = 0.03). After adding peak VO₂ to the model, the association was no longer significant (adjusted HR, 1.18; 95% CI, 0.64-2.17, p = 0.60). After accounting for peak VO₂ and 28 other confounders in a matched propensity analysis, MTWA was not predictive (propensity-matched HR, 0.79; 95% CI, 0.37-1.66; p = 0.53). Conclusions: These results confirm the association of abnormal MTWA with poor outcome amongst patients with impaired left ventricular systolic function. However, this association is markedly attenuated after accounting for peak VO₂.