Cineventriculographic Analysis of the Ventricular Septal Motion during Stimulation of Various Pacemaker Site

Abstract

By means of cineventriculography, contraction pattern of the ventricular septum was studied during electrical stimulation of the right atrium (RA), outflow tract (RVO) and apex (RVA) of the right ventricle and apex (LVA) and lateral wall (LVL) of the left ventricle.RA pacing produced a monophasic shortening of the septal hemiaxes after initial lengthening for about 40 msec from R wave of ECG. In contrast, ventricular stimulation near the septum (i.e. RVO, RVA and LVA) resulted in a biphasic and decreased contraction of the septal wall, in which an early preejection shortening was followed by a brief lengthening and second shortening.LVL pacing showed a monophasic and increased contrac tion of the septal wall. The biphasic motion of the septal wall was likely to be related to the abnormal mechanical contraction caused by the abnormal conduction sequence of ventricular depolarization.On the other hand, the lateral wall demonstrated a biphasic and decreased contraction during LVL pacing, and a monophasic and increased contraction during RVO, RVA and LVA pacing. Thus, the biphasic and diminished contraction at the site of electrical stimulation was compensated by the monophasic and forceful contraction of the contralateral wall. It is considered that the ventricular septum plays an important functional role in regulation of cardiac performance. ventricular septum; left ventriculogram; ventricular asynchrony; cineradiography; pacemaker siteIt has been known that cardiac output and systemic blood pressure during ventricular pacing are lower than those observed during right atrial pacing at the same rate.Our previous study, using two straingauge arches attached to the apical and lateral walls of the left ventricle, demonstrated that the decrease in cardiac performance during ventricular pacing was related to the severity of asynchrony rather than the change in regional myocardial tension (Miyazawa et al. 1977).The interventricular septum appears anatomically to be a part of the left ventricle, but relatively little is known about the functional contribution of the septum to the left ventricle.From this standpoint, the cineventriculographic and cineradiographic studies were designed to analyze the dynamic behavior of the septum to gether with that of contralateral free wall during atrial and ventricular rhythm