Aims: Because sudden cardiac death (SCD) is due to cardiac electrical instability, we postulated that prediction of this mode of death by exercise capacity will be enhanced by combined assessment with T-wave alternans (TWA), an index of repolarization abnormality.
Material and methods: The Finnish Cardiovascular Study enrolled consecutive patients (n=2,044) with a routine clinically indicated exercise test. Exercise capacity was measured in metabolic equivalents (METs) and TWA by time-domain modified moving average method.
Results: During 47.2+/-12.8-month follow-up (mean+/-SD) 120 patients died; 58 were cardiovascular deaths, and 29 were SCD. In multivariate analysis after adjustment for sex, age, smoking, use of beta-blockers, as well as other common coronary risk factors, the relative risk of patients whose exercise capacity was depressed (MET < 8) was 8.8 (95% CI 2.0-38.9, P=0.004) for SCD. The combination of low exercise capacity (MET < 8) and elevated TWA (> or =65 microV) yielded relative risks for SCD of 36.1 (6.3-206.0, P<0.001), for cardiovascular mortality of 21.1 (6.7-66.2, P<0.001), and for all-cause mortality of 7.8 (3.5-17.4, P<0.001) over patients with neither factor.
Conclusions: Reduced exercise capacity, particularly in combination with heightened TWA, indicating enhanced cardiac electrical instability, powerfully predicts risk for SCD in patients referred for exercise testing.