QT interval time lag in response to heart rate changes during stress test for Coronary Artery Disease diagnosis

Background: : Slow adaptation of the QT interval to abrupt changes in heart rate (HR) can enhance ventricular heterogeneity and has been suggested as a marker of arrhythmic risk. Most investigations on QT rate adaptation lag have been performed in response to step-like HR changes. However, abrupt HR changes are difficult to induce or observe in ECG recordings under ambulatory conditions. Objective: We aim to evaluate the power of indices related to the QT lag in response to ramp-like HR changes in stress test to assess CAD risk. Methods: We quantified the lag between the actual QT series and the memoryless expected QT series, which was obtained by fitting a hyperbolic regression model to the instantaneous QT and HR measurements in stages where their behavior could be assumed stationary. The proposed methodology was applied to analyze ECG stress tests of a subset of 448 patients presenting different risk levels for Coronary Artery Disease (CAD). The QT lag was estimated separately in the exercise and recovery phases. Results: An increase in the estimated QT lag during exercise (from 25 to 36 s) and a decrease during recovery (from 57 to 39 s) were associated with higher CAD risk. The difference between these lags showed significant capacity for CAD risk stratification. Conclusion: The QT lag in response to HR changes can be quantified from a stress test. QT lag values in response to ramp-like HR changes are in ranges comparable to those quantified from abrupt HR changes and show clinical significance to stratify CAD risk.