Parahisian pacing: Technique, utility, and pitfalls

Several observations and maneuvers in the electrophysiology (EP) laboratory are employed to identify whether retrograde ventriculoatrial conduction is via the atrioventricular (AV) node or an accessory pathway. Parahisian pacing is a unique maneuver where there is no change in the position of the catheter, the position of the stimulating electrode, nor the cycle length for pacing, but rather the pacing output is varied. The primary value for parahisian pacing is to distinguish between a septal accessory pathway and AV nodal conduction. However, more nuanced but just as reliable interpretation is possible to also help identify free-wall accessory pathways, intermittently conducting pathways, multiple accessory pathways, and various combinations of pathway and AV nodal retrograde conduction. In this review, we discuss the importance of correct technique and explain with examples some uncommon, yet instructive, findings when performing parahisian pacing.