During left bundle branch block, electromechanical delay was prolonged in the late-activated lateral wall compared to the septum (39 vs 11 ms, P=0.002) due to higher dP/dt at the time of activation.
Prolonged electromechanical delay in late-activated myocardium during LBBB is caused by a higher dP/dt at the time of activation, suggesting that LV contractility modifies mechanical dyssynchrony.
Absolute Event Rate: 39% vs 11%
p-value: p=0.002
During left bundle branch block (LBBB), electromechanical delay (EMD), defined as time from regional electrical activation (REA) to onset shortening, is prolonged in the late-activated left ventricular lateral wall compared with the septum. This leads to greater mechanical relative to electrical dyssynchrony. The aim of this study was to determine the mechanism of the prolonged EMD. We investigated this phenomenon in an experimental LBBB dog model (n = 7), in patients (n = 9) with biventricular pacing devices, in an in vitro papillary muscle study (n = 6), and a mathematical simulation model. Pressures, myocardial deformation, and REA were assessed. In the dogs, there was a greater mechanical than electrical delay (82 ± 12 vs. 54 ± 8 ms, P = 0.002) due to prolonged EMD in the lateral wall vs. septum (39 ± 8 vs.11 ± 9 ms, P = 0.002). The prolonged EMD in later activated myocardium could not be explained by increased excitation-contraction coupling time or increased pressure at the time of REA but was strongly related to dP/dt at the time of REA (r = 0.88). Results in humans were consistent with experimental findings. The papillary muscle study and mathematical model showed that EMD was prolonged at higher dP/dt because it took longer for the segment to generate active force at a rate superior to the load rise, which is a requirement for shortening. We conclude that, during LBBB, prolonged EMD in late-activated myocardium is caused by a higher dP/dt at the time of activation, resulting in aggravated mechanical relative to electrical dyssynchrony. These findings suggest that LV contractility may modify mechanical dyssynchrony.
Russell et al. (Sat,) conducted a other in Left bundle branch block (n=22). Late-activated left ventricular lateral wall vs. Septum was evaluated on Electromechanical delay (EMD) (p=0.002). During left bundle branch block, electromechanical delay was prolonged in the late-activated lateral wall compared to the septum (39 vs 11 ms, P=0.002) due to higher dP/dt at the time of activation.