Post-exercise assessment of cardiac repolarization alternans in patients with coronary artery disease using the
Michael P Slawnych1, Tuomo Nieminen, Mika Kähönen
1Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
Objectives:
We sought to evaluate the utility of T-wave alternans (TWA) assessment in the immediate post-exercise period to identify and validate cutpoints for the modified moving average (MMA) assessment method.
Background:
The presence of TWA is associated with an increased risk of cardiovascular death (CVD). The immediate post-exercise period, where increased physiologic stress and minimal surface artifact coexist, appears ideal to implement the MMA method.
Methods:
A test (n = 322) and validation cohort (n = 681) provided 1,003 patients with coronary artery disease (CAD). We assessed TWA immediately after exercise. The outcomes, CVD and mortality, were adjudicated independent of the TWA results.
Results:
During 48 months of follow-up 85 deaths, 54 categorized as CVD (64%), were observed. A linear relationship between the magnitude of TWA and the risk of CVD was identified. As a continuous measure TWA voltage was equivalent to ejection fraction in predicting the risk of CVD. To facilitate clinical application, a sensitive, modest predictive accuracy (20 microV) and a specific, greater predictive accuracy MMA cutpoint (60 microV) were identified and validated. Each cutpoint was associated with a 2.5-fold greater risk of CVD, independent of other important variables, including ejection fraction.
Conclusions:
Post-exercise assessment of TWA using the MMA method is a strong, independent predictor of risk in patients with CAD. The 20-microV cutpoint (87% sensitivity) appears to be most suitable in higher-risk patients, whereas the 60-microV cutpoint (95% specificity) appears more appropriate when TWA is used as a single screening test in those at lower risk. (Assessment of Noninvasive Methods to Identify Patients at Risk of Serious Arrhythmias After a Heart Attack; NCT00399503).
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