Paradoxical motion of interventricular septum in left bundle branch block.

Abnormal interventricular septal motion, with pre-ejection posterior motion and anterior motion away from the posterior left ventricular wall during ejection, was demonstrated by echocardiography in 14 out of 17 cases with complete left bundle branch block (LBBB). Two of 14 cases had intermittent LBBB and showed abnormal septal motion only during LBBB. Of the control group of 49 patients without LBBB but with cardiac disorders similar to the cases with LBBB, only two showed abnormal septal motion. However, pre-ejection motion was not seen in these two cases. During right ventricular pacing abnormal septal motion was observed in three out of ten cases. It is suggested that conduction abnormalities are responsible for abnormal septal motion in LBBB; normal septal motion in most cases with right ventricular pacing may be due to different c3nduction pathways not affecting the septum.