DISPERSION OF VENTRICULAR REPOLARIZATION IN THE VOLTAGE DOMAIN

Dispersion of ventricular repolarization, assessed as QT dispersion in the ECG or by multiple monophasic action potential (MAP) recordings, is defined as the difference between the earliest and latest repolariz ation. It is thus measured in the time domain. However, myocardial ref ractoriness is primarily a function of the membrane potential during p hase 3 repolarization, The purpose of this study, therefore, was to me asure dispersion of ventricular repolarization in the voltage domain a nd to study its relation to SIF inducibility. To further validate this concept, the effects of chronic amiodarone treatment on the voltage d ispersion were assessed. MAPs were recorded simultaneously at 10 epica rdial and endocardial sites in isolated rabbit hearts, both under base line conditions (n = 8) and after chronic amiodarone treatment (n = 8) . Repolarization dispersion in the voltage domain n as calculated as t he difference between the highest and lowest repolarization level of a ll 10 MAPs at 10-ms steps, starting from the MAP plateau level to comp lete repolarization. Plotting these voltage differences along the time axis resulted in a dispersion curve, which rose during early repolari zation, reached a peak during phase 3 repolarization, and thereafter d eclined toward zero. There was a close correlation between VF vulnerab ility in response to electrical field stimuli and the time during whic h voltage dispersion was maximal (r = 0.828, P < 0.0001). Amiodarone c aused a rightward shift of both the dispersion curve (P = 0.007) and V F vulnerability (P = 0.025), but did not change the magnitude nor the shape of the voltage dispersion curve and its relation to VF vulnerabi lity. Repolarization dispersion in the voltage domain describes an alt ernate approach for evaluating the heterogeneity of ventricular repola rization and may help to characterize arrhythmia susceptibility under experimental conditions.