A COMPUTER HEART MODEL INCORPORATING ANISOTROPIC PROPAGATION .3. SIMULATION OF ECTOPIC BEATS

With the advent of catheter ablation procedures, it has become an impo rtant goal to predict noninvasively the site of origin of ventricular tachycardia. Site classifications based on the observed body surface p otential maps (BSPMs) during ventricular endocardial pacing, as well a s on the patterns of the QRS integrals of these maps, have been sugges ted. The goals of this study were to verify these maps and their QRS i ntegral patterns via simulation using a computer heart model with real istic geometry and to determine whether the model could improve clinic al understanding of these ectopic patterns. Simulation was achieved by initiating excitation of the heart model at different endocardial sit es and their overlying epicardial counterparts. This excitation propag ated in anisotropic fashion in the myocardium. Retrograde excitation o f the model's His-Purkinje conduction system was necessary to obtain r ealistic activation durations. Simulated BSPMs, computed by placing th e heart model inside a numerical torso model, and their QRS integrals were close to those observed clinically. Small differences in QRS inte gral map patterns and in the positions of the QRS integral map extrema were noted for endocardial sites in the left septal and anteroseptal regions. The simulated BSPMs during early QRS for an endocardial site and its epicardial counterpart tended to be mirror images about the ze ro isopotential contour, exchanging positive and negative map regions. The simulation results attest to the model's ability to reproduce acc urately clinically recorded body surface potential distributions obtai ned following endocardial stimulation. The QRS integral maps from endo cardial sites in the left septal and anteroseptal regions were the mos t labile, owing to considerable cancelation effects. Conventional BSPM s can be useful to help distinguish between endocardial and epicardial ectopic sites.