Abstract 3782: Does Regional Electromechanical Delay in the Left Ventricle Contribute to Dyssynchrony During Left Bundle Branch Block?
Background: Previous studies have suggested that the latest activated segments during left bundle branch block (LBBB) display prolonged electromechanical delay (EMD). In the present study we investigated EMD by two different methods in the septum and lateral LV wall during baseline, LBBB and biventricular pacing (BVP).
Methods: In 5 anesthetized dogs with LV micromanometers we measured intramyocardial electromyograms (IM-EMG) and myocardial segment lengths by sonomicrometry. As reference method for onset of mechanical activation we used onset of regional active force generation (AFG), defined as the time when the myocardial pressure-segment length coordinate deviated upward from its passive-elastic curve (Fig. 1⇓). In addition we measured onset of mechanical activation as first onset of shortening (FOS). EMD was calculated as time from regional electrical activation (onset R in IM-EMG) to onset AFG and FOS during baseline, LBBB and BVP.
Results: Electrical activation delay of the lateral wall relative to septum was 3±5 ms (±SEM) at baseline, 53±4 ms during LBBB, and −5±2 ms during BVP. EMD measured by AFG was essentially constant in both walls during all interventions (13±1ms Fig. 2⇓). EMD assessed by FOS showed an increase in the lateral wall from baseline (17±2 ms) to LBBB (43±8 ms, p<0.05) but was near normalized by BVP (25±24 ms).
Conclusions: Electromechanical delay assessed by onset AFG was constant during all interventions and did therefore not contribute to dyssynchrony. The large changes between interventions in electromechanical delay assessed by first onset of shortening in the lateral wall suggest that this is an inaccurate measure of mechanical activation.