DYNAMIC RELATIONSHIP BETWEEN THE Q-AT INTERVAL AND HEART-RATE IN PATIENTS WITH LONG QT SYNDROME DURING 24-HOUR HOLTER ECG MONITORING

The purpose of this study was to investigate the dynamic relationship between heart rate and the Q-alpha T interval (the interval from the Q wave to the T wave apex) in patients with long QT syndrome. The QT to heart rate relation is useful for evaluating abnormalities of the ven tricular repolarization, but its clinical application to the long QT s yndrome requires accurate computer aided measurement of the QT interva l and the sampling of a large number of beats. Therefore, the Q-alpha T interval was used on the basis of some reports that the heart rate d ependency of the QT interval was concentrated in the Q-alpha T interva l. Recent advances in the computer technology have allowed analysis of the relationship between the Q-alpha T and RR intervals on Holter ECG recordings. However, in addition to a prolonged QT interval, most pat ients with long QT syndrome have bizarre and variable T waves and the influence of this T wave morphology on the Q-alpha T to heart rate rel ation has not been clarified. We investigated the dynamic relationship between the Q-alpha T interval and heart rate in 10 patients with lon g QT syndrome and 11 control subjects using our original computer algo rithm for the analysis of 24-hour Holter ECG recordings. The patients showed morphological T wave changes associated with heart rate changes during Holter recordings and these affected the Q-alpha T interval. T he patients showed the following characteristics in the relationship b etween the major T wave peak and the RR interval: (1) a modestly decre ased correlation between Q-alpha T and RFI than in the control subject s (alpha median r value of 0.87 vs 0.93; P = 0.001); and (2) a steeper Q-alpha T/RR slope than in controls (alpha median slope of 0.24 vs 0. 16; P < 0.05). Abnormal and variable T wave morphology in the long QT patients was closely related to a modestly decreased correlation betwe en Q-alpha T and RR than in the control subjects. The steep Q-alpha T/ RR slope might reflect unstable repolarization of the ventricle, which could act as a substrate for ventricular tachyarrhythmias.