Characterization of cardiac repolarization response to heart rate changes provoked by a tilt test

In predicting the risk of suffering from ventricular arrhythmias, the dynamics of QT and T-peak-to-T-end (T_pe) intervals after changes in heart rate (HR) provide richer information than their values themselves. In this study, QT/RR and T_pe/RR dynamics were investigated. Electrocardiogram (ECG) recordings of healthy subjects were analyzed during a head-up tilt test. ECGs were delineated using multi-lead (ML) and single-lead (SL) techniques and the QT and T_pe intervals series were obtained. QT/RR and T_pe/RR dynamics were modeled using a nonlinear system, from which the time constant of adaptation t₉₀ was derived. QT/RR dynamics is similar using SL or ML delineation, with adaptation times being: t^SL₉₀[s] = 49.7 +/-29.0, t^ML₉₀ [s] = 47.1 +/- 20.1. The T_pe interval responded more abruptly to HR when calculated using SL as compared to ML. Consequently, T_pe/RR dynamics were characterized by different adaptation time constants depending on whether SL or ML was used: t^SL₉₀ [s] = 25.6 +/- 37.3, t^SL₉₀ [s] = 56.4 +/- 48.3. QT dynamics can be invariantly characterized using either SL or ML delineation, while T_pe dynamics are highly sensitive to the delineation method. Differences arise from the way SL and ML delineation are affected by T-wave loop rotation. Care should be taken when electrophysiological interpretation is provided to measurements obtained from one or the other delineation methods.