A computer heart model incorporating anisotropic propagation. II. Simulations of conduction block

This study describes the simulation of the more common types of conduction blocks with a computer model of the heart incorporating anisotropic 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 simply blocking conduction totally at selected sites in the proximal conduction system, and the incomplete blocks by slowing down the conduction velocity in the proximal system. Also simulated were the left fascicular blocks and the bilateral blocks. All simulated electrocardiograms, vectorcardiograms, body surface potential maps, and epicardial isochrones for these blocks were similar to clinically observed data, with the exception of the left posterior hemiblock, which was slightly atypical. This could be because such blocks are usually accompanied by other cardiac pathologies not included in our simulations. The model also supports van Dam's observation that during left bundle branch block the passage of activation from right to left occurs via slow myocardial 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 normal frontal plane QRS axis may simply represent a case of an incomplete left bundle block, whereas one that exhibits a left axis QRS deviation in the frontal plane represents a more severe complete left bundle branch block.