Microvolt T-Wave Alternans, Peak Oxygen Consumption, and Outcome in Patients with Severely Impaired Left Ventricular Systolic Function
Received 14 December 2008; received in revised form 22 February 2009; accepted 7 April 2009. published online 15 May 2009.
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.
aDepartment of Cardiovascular Medicine of Cleveland Clinic, Cleveland, Ohio
cDepartment of Cardiothoracic Surgery of Cleveland Clinic, Cleveland, Ohio
bHeart and Vascular Research Center of the MetroHealth Campus of Case Western Reserve University, Cleveland, Ohio
dDivision of Prevention and Population Sciences of the National Heart, Lung, and Blood Institute (MSL), Bethesda, Maryland
Reprint requests: Michael S. Lauer, MD, FACC, FAHA, Director, Division of Prevention and Population Sciences (DPPS), National Heart, Lung, and Blood Institute (NHLBI), National Institutes of Health, Rockledge Center II, 6701 Rockledge Dr, Rm 10122, Bethesda, MD 20892. Telephone: 301-435-0422. Fax: 301-480-1864
This work was funded by National Heart, Lung, and Blood Institute grant CAN# 8324207.
ABSTRACT