Abstract 823: Mechanisms of Septal Flash in Left Bundle Branch Block
Objective: Septal beaking or flash (SF) is seen in LBBB as abrupt leftward preejection displacement of septum, and has been suggested as predictor of successful CRT-treatment. Similar septal motion has been observed during RV pacing and has been attributed to end-diastolic reversal of the LV-to-RV transseptal pressure gradient (TSG). This study explores mechanisms of SF during LBBB.
Methods: In 6 anesthetized dogs with LV and RV micromanometers we measured myocardial segment-lengths by sonomicrometry and M-mode echocardiography, and intra-myocardial bipolar ECG. LBBB was induced by RF-ablation and load changes were performed by caval (CC) and aortic constriction (AC). SF was defined as shown in Figure⇓ and quantified as percent shortening of end-diastolic septal-to-lateral diameter (ED).
Results: QRS duration increased from 72 ± 2 to 122 ± 2 ms (± SEM p <0.01) after induction of LBBB. SF was minor at baseline, but became distinct during LBBB (Table⇓), and remained relatively constant during interventions despite marked changes in TSG. This was confirmed by M-mode. SF occurred after septal electrical activation, with a relatively constant time delay (t-SF).
Conclusions: Septal flash was present in LBBB, remained relatively constant during a wide range of TSG and was tightly coupled to septal electrical activation. These findings indicate that regional contraction plays an active role in SF.