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 radiofreque ncy catheter ablation with a high success rate, the exact localization of t he tachycardia circuit is still not well established. The presence of AV no dal tissue between the typical AVNRT circuit and the His bundle, constituti ng a lower common pathway (LCP), remains controversial. Methods and Results: Entrainment of AVNRT during para-Hisian stimulation al lows accurate measurement of the His- to- atrial (HA) interval which is par t of the same circuit as that of the tachycardia. With an LCP, during tachy cardia, there is simultaneous conduction from the low turnaround of the cir cuit to the atrium (via the fast pathway) and to the His bundle (via the LC P). However, during entrainment by para-Hisian pacing, the impulse has to r etrogradely depolarize sequentially the LCP and the fast pathway. Therefore , in the presence of an LCP, the HA interval duration during tachycardia (H At) should lye shorter than that of during entrainment by para-Hisian stimu lation (HAe). We considered an LCP present when Hae - HAt was greater than or equal to 10 msec. Entrainment of typical AVNRT with para-Hisian stimulat ion was performed in 23 consecutive patients (21 females) with a mean age o f 45 +/- 17 years. LCP was considered to be present in 18 of 23 patients (7 8%). In addition, transient His-bundle dissociation from the ongoing tachyc ardia occurred in semen patients (30%). Conclusion: These results support the presence of a LCP during typical AVNR T. (J Cardiovasc Electrophysiol, Vol. 10, pp. 655-661, May 1999).