LAUSR

There exists an electrotonic interaction between the slow and fast AV node pathways that results Introduction Marked PR prolongation is an uncommon presentation of dual atrioventricular (AV) nodal physiology and may cause “pseudo-pacemaker syndrome.” The usual explanation for a prolonged PR interval in this context is persistent anterograde conduction over the slow pathway, perpetuated by retrograde concealed conduction into the fast pathway, but significant impairment in anterograde fast pathway conduction is also possible. An “electrotonic” interaction between the slow and fast pathways is the putative reason why the effective refractory period of the fast pathway decreases after ablation of the slow pathway, and this electrotonic effect may also impair fast pathway conduction velocity. from a voltage gradient between the 2 pathways related to the altered timing of conduction in each pathway. Elimination of this electrotonic interaction is thought to be the reason why the fast pathway refractory period improves after slow pathway ablation.