A COMPUTER HEART MODEL INCORPORATING ANISOTROPIC PROPAGATION .2. SIMULATIONS OF CONDUCTION BLOCK

This study describes the simulation of the more common types of conduc tion blocks with a computer model of the heart incorporating anisotrop ic propagation. The rationale was to test the model as to its ability to simulate these blocks by physiologically justifiable adjustments of the conduction system alone. The complete blocks were generated by si mply blocking conduction totally at selected sites in the proximal con duction system, and the incomplete blocks by slowing down the conducti on velocity in the proximal system. Also simulated were the left fasci cular blocks and the bilateral blocks. All simulated electrocardiogram s, vectorcardiograms, body surface potential maps, and epicardial isoc hrones for these blocks were similar to clinically observed data, with the exception of the left posterior hemiblock, which was slightly aty pical. This could be because such blocks are usually accompanied by ot her cardiac pathologies not included in our simulations. The model als o supports van Dam's observation that during left bundle branch block the passage of activation from right to left occurs via slow myocardia l activation with no evidence of a local delay due to a septal barrier . Finally, the model suggests that a left bundle branch block with a n ormal frontal plane QRS axis may simply represent a case of an incompl ete left bundle block, whereas one that exhibits a left axis QRS devia tion in the frontal plane represents a more severe complete left bundl e branch block.