Abstract 2373: QT Dynamics Early After Exercise as a Predictor of Mortality
Background: Both exercise and the QT response to changing heart rate (QT dynamics) during ambulatory monitoring impact mortality in a variety of populations. While heart rate recovery (HRR) from exercise is a strong predictor of mortalitiy, the prognostic significance of QT dynamics during recovery from exercise has not been assessed.
Methods: The cohort included patients referred for treadmill exercise stress over a 5 year period. Patients had to have at least 4 ECG 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 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 cutpoints were chosen. All-cause mortality was determined from either the Social Security death index or hospital records.
Results: 2,994 patients met inclusion criteria. 197 (6.6%) died during an average follow-up of 6.6±1.8 years. Abnormal QT-500 (>=315 ms) was the strongest univariate QT dynamics predictor in a Cox proportional hazards model (hazard ratio=2.19, p<0.001). It remained an independent predictor of mortality after adjustment for age, sex, exercise capacity, SPECT defects, and abnormal (<12 bpm) HRR (hazard ratio=1.58, p=0.003).
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 incorporates information on both repolarization and autonomic responsiveness, its role in risk prediction for sudden cardiac death should be further explored.