Introduction: Ventricular pacing results in QRS widening and increased electromechanical latency. The present study has assessed whether these effects mimic a condition of left bundle branch block (LBBB).
Methods: Electrocardiographic and echo-Doppler evaluation was performed during routine follow-up checks in 20 pacemaker patients provided with intrinsic AV conduction (IAVC): 17 cases featured synchronous ventricular activation (QRS duration < 120 ms) and 3 were affected by LBBB. The time from the QRS onset to the start of pulmonary and aortic flow (Q-Po; Q-Ao) was measured in the presence of IAVC as well as with sequential right-ventricular apical pacing (RVAP).
Results: Mechanical interventricular desynchronization (Po-Ao delay > 40 ms) was demonstrated in all patients showing LBBB on the ECG. In contrast, RVAP acutely induced interventricular dyssynchrony in only 3/17 patients featuring synchronous IAVC (18%). When RVAP did not affect the interventricular synchronization, the electromechanical latency was increased in both right and left ventricle to a similar extent (Tab. 1).
Conclusions: Unlike LBBB, RVAP generally delays the aortic and pulmonary ejection as well, suggesting a bilateral activation delay in the basal region.