Mechanisms of Abnormal Systolic Motion of the Interventricular Septum During Left Bundle-Branch Block

Abstract

Background-In a majority of patients with left bundle-branch block (LBBB), there is abnormal leftward motion of the interventricular septum during the preejection phase. This motion was considered to be passive, caused by early rise in right ventricular (RV) pressure, and has therefore been excluded from most indices of left ventricular (LV) dyssynchrony. If considered active, however, the leftward motion reflects onset of septal activation and should be included. We therefore investigated if the motion was a passive response to pressure changes or caused by active contraction. Methods and Results-LBBB was induced in 8 anesthetized dogs with micromanometers. Cardiac dimensions were measured by sonomicrometry and echocardiography. Induction of LBBB resulted in preejection leftward motion of the septum, simultaneously with shortening of septal segments (PϽ0.01). In each experiment, preejection septal shortening occurred against rising LV pressure, consistent with active contraction. Furthermore, the LV pressure-segment length relationships were shifted upward (PϽ0.01) relative to the passive elastic curve, indicating stiffening of septal myocardium, confirming an active mechanism. Initially, RV pressure increased faster than LV pressure, suggesting that the leftward septal motion may have a passive pressure component. However, the passive component appeared to play a minor role. The magnitude of preejection septal shortening was modified by load alterations. Conclusions-Leftward preejection motion of the septum during LBBB is mainly a result of active septal contraction, whereas alterations in diastolic ventricular pressures modulate the amplitude of this motion. The findings imply that the preejection phase should be included when assessing LV dyssynchrony. (Circ Cardiovasc Imaging. 2011;4:264-273.)

Cardiopulmonary Exercise Testing in Patients With Left Bundle Branch Block and Preserved Ejection Fraction

“…11,12 In LBBB patients, LV shape is distorted during pre-ejection, as a result of the flattening of the septal curvature and simultaneous stretching of the lateral wall activated late. 21 The present work showed that the LBBB group reached peak PO 2 > 85% of the predicted value, and presented ascending behavior of the PO 2 curve during effort. Even though there are structural alterations in the LV, LVEF was preserved, without cardiovascular performance deficit.…”

The Speckle Tracking Imaging for the Assessment of Cardiac Resynchronization Therapy (START) Study

“…Pre-ejection septal shortening reflects active contraction, suggesting that the pre-ejection phase should be included when assessing LV dyssynchrony. 22 Moreover, because of the complex mechanical interactions between different parts of the LV wall, maximum peak measurements by STE mislead by misidentifying apparent dyssynchrony with complete left bundle branch block as no dyssynchrony. 23 Thus, first peak is more related to the electrical activation that can be treated by CRT than mamixum peak.…”

Mechanism of prolonged electromechanical delay in late activated myocardium during left bundle branch block

“…In addition, pacemaker leads were attached epicardially on the LV lateral wall and right atrium and endocardially in the right ventricular outflow tract close to the septum. LBBB was induced by radiofrequency ablation as previously described (6). Inflatable cuffs were placed around the aorta, and inferior and superior vena cava, allowing for controlled vascular constriction.…”