QT dynamics early after exercise as a predictor of mortality

Background: Exercise and QT dynamics during ambulatory monitoring impact mortality in a variety of populations. Heart rate recovery (HRR) after exercise is a known strong predictor of mortality. Objective: This study assessed the independent prognostic significance of the QT response to changing heart rate (QT dynamics) during recovery from exercise. Methods: The cohort included patients referred for treadmill exercise stress testing over a 5-year period. Patients had to have at least 4 electrocardiographic tracings within 5 minutes of peak exercise. One had to be recorded 60 seconds into recovery to calculate the HRR. Linear regression of the QT-RR relation during recovery was used to predict the QT interval at cycle lengths of 500 and 600 ms (QT-500 and QT-600). Only studies with an R² < 0.9 (72%) were retained. Optimal binary cut points were chosen. All-cause mortality was determined from either the Social Security Death Index or hospital records. Results: A total of 2,994 patients met inclusion criteria; 228 (7.6%) died during an average follow-up of 7.6 ± 1.9 years. Abnormal QT-500 (>316 ms) was the strongest univariate QT dynamics predictor in a Cox proportional hazards model (hazard ratio = 2.13, P <.001). It remained an independent predictor of mortality after adjustment for age, exercise capacity, medications, single photon emission computed tomography defects, and abnormal (<12 beats/min) HRR (hazard ratio = 1.46, P = .014). Conclusion: An abnormal predicted QT interval at 500 ms (120 beats/min) during recovery from exercise independently predicts all-cause mortality. Because QT dynamics in recovery incorporate information on both repolarization and autonomic responsiveness, its role in risk prediction for sudden cardiac death should be further explored.