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.