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A transfer function model for AV conduction in the human heart

INTRODUCTION Contraction of cardiac muscIe is triggered by depolarization of the cell membrane. The depolar­ization front is spread in a rapid coordinated fashion through the myocardium [IJ and through a specialized conducting system of the heart. From the sinoatrial (SA) node, the normal pacemaker of the heart, the excitation wave spreads throughout the atria. At the base of the atria, the excitation wave enters a small group of specialized cells which form the atrioventricular (A V) node. This node and the bundie of fibres called the His bundie stemming from it, constitute the only conducting link between the atria and the ventricles. This ensures that excitation can only travel from atria to ventricles through the A V node. After leaving the A V node, the impulse travels along the bundie of His to the base of the papillary muscles and then spreads throughout the left and right ventricles. Little is known about the way the A V node con­ducts the impulses, about the possible influence of previous impulses and especially about the time intervals between these impulses. Earlier studies were done with isolated rat hearts (see Heethaar [2]) resulting in an empirical model that showed dependence of the time interval between a stimu­lus (S) and the resulting ventricular excitation (S-R interval) of, at most, five preceding stimulus intervals (S-S intervals). We made an effort to explain the conduction through the A V node during random stimulation by fitting a transfer function model to the S-S and S-R intervals.