Dynamic Response of Electrocardiographic Indices During Abrupt Heart Rate Changes - Comparison between Young and Middle-aged Subjects

Abnormal modifications in ventricular repolarization dispersion (VRD) have been shown to constitute a substrate for malignant arrhythmias. In this work, we have induced abrupt heart rate (HR) changes to young and middle-aged healthy subjects through a Tilt-test and have analyzed the evolution of several VRD indices. Duration ones, based on electrocardiogram intervals; energy ones, developed through a Principal Components Analysis (PCA) in T-wave; and the morphology ones, extracted feature from an absolute T-wave. In both groups, results have shown significant decreases in early repolarization duration. These changes are responsible for the alterations in the total repolarization duration, because T-wave peak-to-end has not shown statistical significance. Moreover, we have found significant decreases in total, early and late repolarization energy, and in the T-wave amplitude. In another sense, we have observed that the repolarization energy obtained by PCA jointly with early T-wave slope and amplitude have been able to reflect VRD differences between young and middle-aged subjects. Finally, this work provides the range of values for VRD in normal conditions during abrupt HR changes. Outside this range, we could assume that it exists a cardiac risk.