Measuring spatial waves of repolarization in canine ventricles using high-resolution epicardial mapping

The importance of the role of ventricular repolarization in arrhythmogenesis and defibrillation prompted the exploration of new methods for observing and measuring repolarization. Specifically, the authors' goal was to establish independent procedures for assessing activation-recovery intervals. Canine epicardial electrograms from high-resolution arrays (2-mm spacing, 25 x 21 electrodes) were recorded-during pacing from a variety of single or simultaneously paced epicardial locations in canine hearts. For each activation sequence, the activation and repolarization times were measured using timing of intrinsic QRS and T wave deflections (activation-recovery interval method) and timing of the peak magnitude of spatial derivatives (gradient method). Both methods should, theoretically, provide estimates of local activation and repolarization times, which reflect timing of local action potential upstrokes and downstrokes. Scattergrams comparing activation and recovery times for the two methods showed high correlation, slopes close to 1.0, and intercepts near the origin. For most activation sequences, observation of the potential and gradient distributions as dynamic, three-dimensional perspective displays, revealed a well-defined, rapidly propagating repolarization wave, superimposed on a slowly varying, high-amplitude distribution occurring during the T wave. These data suggest that repolarization times measured using temporal or spatial derivatives are consistent with theoretical predictions and reflect timing of local action potential downstrokes. They also suggest potential utility of combining spatial and temporal approaches for improving reliability in the measurements.