Beat-to-beat QT variability and cardiac autonomic regulation

摘要

modern electrocardiographic (ECG) equipment allows easy collection of large volumes of digital signals. Their computer processing facilitates a number of ECG measurements that were previously unobtainable. Among such measurements, beat-to-beat QT interval variability has attracted some popularity and has been investigated in a varietyof physiological and clinical conditions (3, 9, 11, 15-17, 21). Different numerical quantifiers of the beat-to-beat QT variability have been proposed, but perhaps most frequently the so-called QT variability index (QTVI) has been used. Together with QT/RR variability coherence, QTVI was initially proposed by Berger et al. (3). Since the initial publication, it has been assumed that QTVI is an indirect measure of autonomic regulation of cardiac ventricular electrophysiology. The well-established capabilities of investigation of cardiac autonomic regulation by heart rate variability are restricted to the autonomic influence on sinus nodal periodicity (4, 5). Thus the possibility of assessing the autonomic influence at the ventricular level has an obvious appeal. Ventricular abnormalities rather than anomalies of sinus periodicity are responsible for ventricular arrhythmias. Also, diagnosis of the early stages of impaired ventricular regulation might help in identifying hearts at risk of failure. Thus any test, and in particular an easily applicable noninvasive test, assessing ventricular autonomic regulation would cover presently unmet diagnostic needs.