Septal flash is a prevalent and early dyssynchrony marker in transcatheter aortic valve replacement-induced left bundle branch block.

New-onset left bundle branch block (LBBB) is a frequent complication after transcatheter aortic valve replacement (TAVR) and provides an opportunity to study dyssynchrony immediately following acute LBBB. This study aims to (1) assess echocardiographic dyssynchrony in acute TAVR-induced LBBB (TAVR-LBBB), and (2) compare dyssynchrony parameters among different patient groups with LBBB. The study enrolled all TAVR-LBBB patients at Ghent University Hospital between 2013 and 2019. First, acute TAVR-LBBB dyssynchrony was assessed by: (1) septal flash (SF); (2) interventricular mechanical delay (IVMD; cut-off ≥ 40 ms) and (3) presence of 'classical dyssynchronous strain pattern' assessed with speckle tracking. Secondly, acute TAVR-LBBB patients with SF (LBBBTAVR+SF) were compared to randomly selected LBBB-SF patients with preserved (LBBBSF+PEF) ànd reduced ejection fraction (LBBBSF+REF). In TAVR-LBBB patients (n = 25), SF was detected in 72% of patients, whereas only 5% of TAVR-LBBB patients showed a classical dyssynchronous strain pattern. IVMD in these TAVR-LBBB patients was 39 ms. In 90% of LBBBTAVR+SF patients, SF was observed within 24 h after LBBB onset. Among LBBB-SF patients, a classical strain pattern was more prevalent in LBBBSF+REF patients compared to LBBBTAVR+SF patients (80% vs. 7%; p < 0.001). IVMD was significantly longer in LBBBSF+PEF patients (52 ms; p = 0.002) and LBBBSF+REF patients (57 ms; p = 0.009) compared to LBBBTAVR+SF patients (37 ms). SF is an early and prevalent marker of LV dyssynchrony in acute TAVR-LBBB, whereas strain-based measures and IVMD do not appear to capture dyssynchrony at this early stage. Our findings from the comparative analysis generate the hypothesis that progressive LBBB-induced LV remodeling may be required for a 'classical dyssynchrony strain pattern' or significant IVMD to occur in TAVR-LBBB patients.