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

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Abstract
Using cineventriculography, the ventricular septum contraction pattern of dogs 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 ms from R wave of ECG. Ventricular stimulation near the septum (i.e RVO, RNA and LVA) resulted in a biphasic and decreased contraction of the septal wall, in which early preejection shortening was followed by a brief lengthening and second shortening. LVL pacing showed a monophasic and increased contraction of the septal wall. The biphasic motion of the septal wall could be related to abnormal mechanical contraction caused by abnormal conduction sequence of ventricular depolarization. The lateral wall demonstrated a biphasic and decreased contraction during LVL pacing, and a monophasic and increased contraction during RVO, RVA and LVA pacing. The biphasic and diminished contraction at the site of electrical stimulation was compensated for by the monophasic and forceful contraction of the contralateral wall. The ventricular septum may be functionally important in cardiac performance regulation.

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