M-mode and cross-sectional echocardiographic study of the left ventricular wall motions in complete left bundle-branch block.

Abstract

M-mode and cross-sectional echocardiograms of 37 patients with complete left bundle-branch block were compared with those of 5 patients with complete atrioventricular block during right ventricular pacing, 20 patients with anteroseptal infarction and 20 normal subjects. Of 37 patients with complete left bundle-branch block, 35 showed 3 types (A, B and C) of abnormal septal motion and 2 patients showed normal septal motion. In types A and B, early and abrupt posteriorly directed motion of the septum occurred during the pre-ejection period. After this early abnormal motion, the septum moved anteriorly in type A and posteriorly in type B. Type C exhibited akinetic or dyskinetic septal motion throughout systole. The onset of posterior wall contraction was delayed in all patients with complete left bundle-branch block. These patterns of abnormal septal motion were observed in almost all portions of upper- to mid-septum that could be recorded by cross-sectional echocardiography. Abnormal septal motion of types A and B was also observed during right ventricular pacing. Abnormal septal motion of types A and B could be due to asynchronous contraction of the left ventricle, with delayed activation of the left side of the septum and of the left ventricular free wall. The septal motion of type C is almost the same as that seen in patients with extensive septal infarction. Most patients having abnormal septal motion of type C had ECG and vectorcardiographic findings which were compatible with extensive septal infarction. Patients with complete left bundle-branch block and type C motion may have sufficient septal damage to prevent the early posterior motion seen in type A and B patients. A different sequence of ventricular activation will be responsible for the difference between type A and B. Some patients with type A septal motion may have septal damage to some degree, in contrast to type B. Normal septal motion recorded in 2 patients with complete left bundle-branch block might be the result of a peripheral block of the left bundle-branch.