Echocardiographic demonstration of abnormal motion of the interventricular septum in left bundle branch block.

A characteristic abnormality of motion of the interventricular septum was recorded by echocardiography in 17 of 18 patients with left bundle branch block. Early and abrupt contraction of the septum occurs during the pre-ejection period before the delayed commencement of contraction of the posterior wall of the left ventricle. This abnormality can be explained by asynchronous contraction of the left ventricle with early activation and contraction of the septum but delay in activation and contraction of the left ventricular free wall due to a block in the left bundle branch or its peripheral branches.