Interlead Difference in QT Interval Rate Adaptation During Exercise in Coronary Artery Disease Patients Susceptible to Ventricular Fibrillation

Abstract

Background: Nonhomogeneity in ventricular repolarization predisposes to ventricular tachyarrhythmias. Rate adaptation of the QT interval parallels rate adaptation of the action potential, both of which reflect the repolarization phase in ventricular myocardium. The aim of this study was to examine in patients with coronary artery disease (CAD) the relation of interlead differences in QT interval rate-adaptation to arrhythmia vulnerability. Methods: We studied 29 CAD patients with a history of ventricular fibrillation (VF) not associated with acute myocardial infarction (VF group), and their 29 individually matched CAD controls without arrhythmic events (controls). Rate adaptation of the QT intervals in the 12 leads of the electrocardiogram were determined from QT intervals measured at rest and at the end of each 3 minute load step during exercise test. The relation between heart rate (HR) and QT interval (QT/HR slope) was calculated separately in each lead by the linear regression equation. The slopes of these equations were used to characterize spatial QT interval rate adaptation. Results: The steepest QTapex/ HR slopes in any lead were (mean ±mD SD) −2.45 ± 0.63 in the VF group and -1.97 ± 0.45 in controls (P = 0.008), whereas the smallest slopes showed no difference (P = NS). The standard deviations of QTapex/ HR slopes were 0.48 ± 0.23 in the VF group and 0.33 ± 0.12 in controls (P = 0.012). Conclusions: Rate adaptation of the QTapex interval is locally exaggerated, resulting in nonhomogenous exercise response of the QTapex intervals in CAD patients susceptible to life-threatening ventricular arrhythmias. A.N.E. 2000;5(4):346–353