The immediate reproducibility of T wave alternans during bicycle exercise. 
A number of recent studies have demonstrated that the microvolt level T wave alternans measured during bicycle exercise can identify patients at high risk for developing malignant ventricular arrhythmias.  However, little is known about the reproducibility of T wave alternans measured during bicycle exercise.  The purpose of this study was to prospectively evaluate the immediate reproducibility of T wave alternans measured during bicycle exercise testing.  Thirty-five patients with congestive heart failure underwent two sequential bicycle exercise tests with the measurement of T wave alternans.  The T wave alternans tests were randomly sorted and then classified by two readers who were blinded to the patient and the sequence of the two tests.  Tests were classified as determinate (positive or negative) or indeterminate according to previously published criteria.  Of the 22 patients that had two determinate T wave alternans tests, 18 (82%) of 22 patients had concordant test results (kappa 0.58).  Of the four patients who had discordant test results on the two tests, three patients had one test that was borderline and difficult to interpret.  One patient had two sequential tests that were clearly different.  Of the ten patients whose initial test was indeterminate, five became determinate on the second test.  T wave alternans measured during bicycle exercise has an acceptable reproducibility when measurements are madefrom two sequential exercise tests performed within a short period.  This data suggests that the measurement of T wave alternans during exercise is reliable.  Repeating the exercise test with a second measure of T wave alternans during the same session can significantly reduce the proportion of patients with indeterminate test results.