Genesis of Electrocardiographic and Vectorcardiographic QRS Patterns in Left Bundle Branch Block : By Means of Simulation of Ventricular Propagation Process and Computational QRS Reconstruction

In order to elucidate the propagation process of ventricular activation in left bundle branch block (LBBB) and its resultant QRS patterns observed on the body surface, a number of experimental studies have been made. However, the site and the mechanism of block still remain a matter of debate among these reports. It is also under question whether the results obtained from animal experiments can be applied to explanation for the genesis of naturally developed LBBB within human ventricles. The purpose of this paper is to discuss the mechanism of LBBB observed with human subjects. Namely, the ventricular propagation process of excitation was simulated in a model of the human ventricles which was constructed using the human heart as a basis and stored in a computer. A variety of speculative for LBBB was provided to the model before the simulated propagation took place. The body surface QRS patterns were computational reconstructions based on these simulated ventricular propagation processes. The obtained QRS pat-terns were then compared with those of clinical cases of LBBB. Moreover QRS vector loop were obtained and they were examined correspondence with the obtained QRS patterns. Methods: 1. Simulation and QRS reconstruction By means of digital computer simulation, a number of propagation processes in excitation of the ventricles with LBBB were obtained. The scalar QRS patterns for the thus acquired propagation processes were obtained by the above means in the conventional twelve leads and X, Y and Z leads of Frank system. QRS vector loops of Frank system were plotted by hand from the scalar QRS patterns. within human ventricles. In order to provide the ventricular model with a mechanism of LBBB, the following five kinds of different assumptions (1-a, 1-b, 2, 3 and 4) were utilized respectively. In all of these five assumptions, a lesion was assumed on the left bundle branch running on the upper portion of the ventricular septum. For the remaining parts of the ventricle, a block of the excitation spread was provided to the model according to one of the following five assumptions. Each of these assumptions was pursued on the bases of various interpretation of LBBB advocated in the previous reports on animal experiments.