Characterization of QT-Interval Adaptation Time Lag in Response to Sport-Induced Heart Rate Changes Measured From Wearable ECG Recordings

Objectives: Elevated heterogeneity in ventricular repolarization can promote malignant ventricular arrhythmias. During exercise, distinct ventricular cells may present different repolarization adaptation to heart-rate (HR) changes potentially increasing ventricular repolarization dispersion. An electrocardiographic descriptor of the temporal adaptation of action potential duration to HR changes is the time delay the QT interval takes in accommodating to abrupt acceleration and deceleration in HR. Previous investigations have been performed on standard electrocardiograms acquired during stress tests. The present work aims to characterize the time delay of QT-interval accommodation to HR changes for a healthy trained population during real training. Methods: The time delay was estimated through an optimally derived, model-based time-delay estimator as the lag between the actual QT series and an HR-derived expected memoryless QT series. The last one was obtained by fitting a logarithmic regression model to the instantaneous QT and HR measurements in assumed stationary time windows. The QT lag was estimated separately in HR acceleration, and HR deceleration, of single-lead ECG acquired through a chest strap while practicing sport. Results: The QT-adaptation time lag estimated during HR deceleration is longer than during HR acceleration, especially after intense physical exertion of athletes when they have overcome their theoretical maximal HR 14.5[2.4;28.0] s or they have been involved in dynamic sports 9.9[5.8;24.9] s. Conclusion: Higher repolarization dispersion can be captured by the proposed time delay biomarker in a distinctive way to the HR acceleration. Significance: Eventually the time lag is a biomarker for exacerbated increase of ventricular repolarization dispersion while exercising.