Immediate mechanical effects of acute left bundle branch block by speckle tracked strain

Left bundle branch block (LBBB) is a known complication of transcatheter aortic valve replacement (TAVR) and has been shown to predict worsened outcomes in TAVR patients. A regional longitudinal strain pattern, termed the "classic" pattern of left ventricular (LV) dyssynchrony, which is thought to be due to LBBB, is highly predictive of response to cardiac resynchronization therapy. Whether LBBB causes this "classic" pattern is not known.

We retrospectively studied patients undergoing TAVR who also underwent pre- and post-TAVR strain analysis to determine if the "classic" pattern arose in those who developed TAVR-induced true LBBB. After removing patients with baseline conduction abnormalities or insufficient studies 9 patients had sufficient data for analysis. Six patients developed LBBB after TAVR and 3 patients did not develop LBBB after TAVR. ECGs were analyzed for the new onset of LBBB after TAVR. Global longitudinal strain (GLS) and regional longitudinal strain patterns were analyzed for changes between pre- and immediately post-TAVR examinations.

Patients who did not develop LBBB showed no significant changes in their regional longitudinal strain pattern. Those patients who did develop LBBB showed significant increase in their difference of time-to-onset of contraction between the septal and lateral walls post-TAVR (22 ± 14 ms vs 111 ± 49 ms; p=0.003) and in their difference of time-to-peak contraction between the septal and lateral walls post-TAVR (63 ± 56 ms vs 133 ± 46 ms; p=0.002). Early lateral wall pre-stretch and delayed lateral wall peak contraction emerged in all patients with LBBB but early septal peak contraction meeting the established criteria was present in only one patient.

The onset of LBBB led to acute, measurable changes in the regional longitudinal strain pattern consisting of early lateral wall pre-stretch and delayed lateral wall peak contraction. These represent 2 of the 3 findings in the "classic" pattern of LV dyssynchrony. Early termination of septal wall contraction meeting established criteria was not routinely found. Time and/or other factors may be required to develop the full "classic" pattern.