Entrainment of typical AV nodal reentrant tachycardia using para-Hisian pacing: Evidence for a lower common pathway within the AV node

Lower Common Pathway Within the AV Node. Introduction: Despite the ability to cure atrioventricular nodal reentrant tachycardia (AVNRT) by radiofrequency catheter ablation with a high success rate, the exact localization of the tachycardia circuit is still not well established. The presence of AV nodal tissue between the typical AVNRT circuit and the His bundle, constituting a lower common pathway (LCP), remains controversial. Methods and Results: Entrainment of AVNRT during para-Hisian stimulation allows accurate measurement of the His- to- atrial (HA) interval which is part of the same circuit as that of the tachycardia. With an LCP, during tachycardia, there is simultaneous conduction from the low turnaround of the circuit to the atrium (via the fast pathway) and to the His bundle (via the LCP). However, during entrainment by para-Hisian pacing, the impulse has to retrogradely depolarize sequentially the LCP and the fast pathway. Therefore, in the presence of an LCP, the HA interval duration during tachycardia (HAt) should lye shorter than that of during entrainment by para-Hisian stimulation (HAe). We considered an LCP present when Hae - HAt was greater than or equal to 10 msec. Entrainment of typical AVNRT with para-Hisian stimulation was performed in 23 consecutive patients (21 females) with a mean age of 45 +/- 17 years. LCP was considered to be present in 18 of 23 patients (78%). In addition, transient His-bundle dissociation from the ongoing tachycardia occurred in semen patients (30%). Conclusion: These results support the presence of a LCP during typical AVNRT. (J Cardiovasc Electrophysiol, Vol. 10, pp. 655-661, May 1999).