ELECTROCARDIOGRAPHIC IMAGING - NONINVASIVE CHARACTERIZATION OF INTRAMURAL MYOCARDIAL ACTIVATION FROM INVERSE-RECONSTRUCTED EPICARDIAL POTENTIALS AND ELECTROGRAMS

Background-A recent study demonstrated the ability of electrocardiogra phic imaging (ECGI) to reconstruct, noninvasively, epicardial potentia ls, electrograms, and activation sequences (isochrones) generated by e picardial activation. The current study expands the earlier work to th e three-dimensional myocardium and investigates the ability of ECGI to characterize intramural myocardial activation noninvasively and to re late it to the underlying fiber structure of the myocardium. This obje ctive is motivated by the fast that cardiac excitation and arrhythmoge nesis involve the three-dimensional ventricular wall and its anisotrop ic structure. Methods and Results-Intramural activation was initiated by pacing a dog heart in a human torso tank. Body surface potentials ( 384 electrodes) were used to compute epicardial potentials noninvasive ly. Accuracy of reconstructed epicardial potentials was evaluated by d irect comparison to measured ones (134 electrodes). Protocols included pacing from five intramural depths. Epicardial potentials showed char acteristic patterns (1) early in activation, central negative region w ith two flanking maxima aligned with the orientation of fibers at the depth of pacing; (2) counterclockwise rotation of positive potentials with time for epicardial pacing, clockwise rotation for subendocardial pacing, and dual rotation for midmyocardial pacing; and (3) central p ositive region for endocardial pacing. Noninvasively reconstructed pot entials closely approximated these patterns, Reconstructed epicardial electrograms and epicardial breakthrough times closely resembled measu red ones, demonstrating progressively later epicardial activation with deeper pacing. Conclusions-ECGI can noninvasively estimate the depth of intramyocardial electrophysiological events and provides informatio n on the spread of excitation in the three-dimensional anisotropic myo cardium on a beat-by-beat basis.