Virtual electrode polarization
Virtual electrode polarization (VEP) effect refers to the fact that when a depolarized and hyperpolarized region is created surrounding the tip of the electrode, increased output would create a larger virtual electrode surrounding the tip, which results in larger volume of myocardium being depolarized 13-15. In bipolar pacing, the anodal right ventricular ring might pre-excite a portion of the right septum. When right ventricular anodal capture occurs, QRS duration is minimized, presumably because in this situation there are at least 2 depolarization waves fronts activating the ventricles, shortening conduction time from the left ventricle to the right ventricle.16 High output bipolar pacing would produce a narrower QRS duration as the right ventricular delay during LBBP is compensated by pre-exciton of a portion of the right septum12. To sum up, a fusion of right ventricular septal excitation along with ventricular excitation will be caused by the VEP. That is why the paced morphology of the typical RBBB changes, including the isoelectric interval fainted, the R wave disappeared in V1 and the QRS complex duration minimized.