Noninvasive Electrocardiographic Imaging

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Abstract
Background The goal of noninvasive electrocardiographic imaging (ECGI) is to determine electric activity of the heart by reconstructing maps of epicardial potentials, excitation times (isochrones), and electrograms from data measured on the body surface. Methods and Results Local electrocardiac events were initiated by pacing a dog heart in a human torso–shaped tank. Body surface potential measurements (384 electrodes) were used to compute epicardial potentials noninvasively. The accuracy of reconstructed epicardial potentials was evaluated by direct comparison to measured ones (134 electrodes). Protocols included pacing from single sites and simultaneously from two sites with various intersite distances. Body surface potentials showed a single minimum for both single- and double-site pacing (intersite distances of 52, 35, and 17 mm). Noninvasively reconstructed epicardial electrograms, potentials, and iso-chrones closely approximated the measured ones. Single pacing sites were reconstructed to within ≤10 mm of their measured positions. Dual sites were located accurately and resolved for the above intersite distances. Regions of sparse and crowded isochrones, indicating spatial nonuniformities of epicardial activation spread, were also reconstructed. Conclusions The study demonstrates that ECGI can reconstruct epicardial potentials, electrograms, and isochrones over the entire epicardial surface during the cardiac cycle. It can provide detailed information on local activation of the heart noninvasively. Its uses could include localization of cardiac electric events (eg, ectopic foci), characterization of nonuniformities of conduction, characterization of repolarization properties (eg, dispersion), and mapping of dynamically changing arrhythmias (eg, polymorphic VT) on a beat-by-beat basis.