Abstract 5728: Abrupt Early Intraventricular Septal Motion In Not Passive But Active In Left Bundle Brunch Block
Abnormal early septal motion observed in patients with left bundle brunch block (LBBB) has been explained as a difference in right-to-left ventricular pressure. The interventricular septum was thought to be displaced passively into the LV because the right ventricle contracts prior to the LV and the right ventricular pressure exceeds the LV pressure during early systolic phase. Assuming that this theory is right, the interventricular septal wall would be stretched and shown positive strain value in circumferential and longitudinal directions during early systolic phase. We investigated the mechanism of the early septal motion with LBBB using speckle tracking imaging (STI).
Methods: Systolic septal motion on the middle LV portion level was analyzed in 44 patients with complete LBBB (mean QRS duration 166 ± 35 ms) using M-mode echocardiography and speckle tracking imaging (STI). Time from onset of QRS configuration to peak circumferential strain and longitudinal strain were measured in parasternal short axis and apical views by STI. Furthermore, 20 healthy individuals (mean QRS duration 84 ± 6 ms) were also analyzed. Changes in LV pressure and septal strain were simultaneously measured to evaluate the relationship between them in 6 patients with LBBB.
Results: Septal displacement into the LV was early and abrupt on M-mode echocardiograms from all patients with LBBB. During this displacement, the STI of the interventricular septum of all patients showed negative strain in both the circumferential and longitudinal directions. Furthermore, early septal displacement almost coincided with peak negative strain. Time to peak septal strain in LBBB patients was significantly shorter than in normal controls in the circumferential (296 ± 80 vs. 356 ± 30 ms; p < 0.05) and longitudinal (317 ± 104 vs. 369 ± 17 ms; p < 0.05) directions. The peak of septal negative strain was followed by an increase in LV pressure in all patients.
Conclusion: Early motion of the interventricular septum is provoked by its active contraction in LBBB. The septal contraction starts very early and almost isotonically toward a very low load. However, further shortening is suppressed by a subsequently increased load of pressure elevation due to the contraction of other LV segments.