MEASURING SPATIAL WAVES OF REPOLARIZATION IN CANINE VENTRICLES USING HIGH-RESOLUTION EPICARDIAL MAPPING

The importance of the role of ventricular repolarization in arrhythmog enesis and defibrillation prompted the exploration of new methods for observing and measuring repolarization. Specifically, the authors' goa l was to establish independent procedures for assessing activation-rec overy intervals. Canine epicardial electrograms from high-resolution a rrays (2-mm spacing, 25 x 21 electrodes) were recorded during pacing f rom a variety of single or simultaneously paced epicardial locations i n canine hearts. For each activation sequence, the activation and repo larization times were measured using timing of intrinsic QRS and T wav e 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 repol arization times, which reflect timing of local action potential upstro kes and downstrokes. Scattergrams comparing activation and recovery ti mes for the two methods showed high correlation, slopes close to 1.0, and intercepts near the origin. For most activation sequences, observa tion of the potential and gradient distributions as dynamic, three-dim ensional perspective displays, revealed a well-defined, rapidly propag ating repolarization wave, superimposed on a slowly varying, high-ampl itude distribution occurring during the T wave. These data suggest tha t repolarization times measured using temporal or spatial derivatives are consistent with theoretical predictions and reflect timing of loca l action potential downstrokes. They also suggest potential utility of combining spatial and temporal approaches for improving reliability i n the measurements.