Electrophysiologic Factors Responsible for the Induction of AV Nodal Reentrant Tachycardia

Cho, Jeong Gwan; Shin, Soon Chul; Rhew, Jay Young; Bae, Youl; Kim, Jun Woo; Kim, Sung Hee; Kim, Ju Han; Seo, Jeong Pyeong; Cha, Gwang Su; Park, Jong Chul; Jeong, Myung Ho; Park, Jong Chun; Kang, Jung Chaee

Abstract

OBJECTIVES
Although a subtle balance between conduction time of the antgrade slow pathway and refractory period of the retrograde fast pathway is known to play the most critical role in the induction of AV nodal reentrant tachycardia(AVNRT), other electrophysiologic factors such as concealed conduction in to the fast pathway have been suggested to be responsible. The present study was performed to determine the electrophysiologic factors responsible for the induction of AVNRT.
METHODS
Total 34 subjects undergoing electrophysiologic study(EPS) including 9 normal subjects(SAVNP), 7 subjects with dual AV nodal pathways(DAVNP) but no inducible AVNBT, and 18 inducible AVNRT patients were included in this study. EPS was performed using the conventional technique. To evaluate the presence of concealed conduction into the fast AV nodal pathway(FP) and its effects on the effective refractory period(ERP) of the FP (FP-ERP) to a subsequent impulse, single(A2) and double atrial extrastimuli(A2A3) were given. FP-ERP of conducted A2 [FP-ERP-A2(+)] was measured with a second atrial extrastimulus(A3) following a first atrial extrastimulus(A2), which was delivered at a coupling interval 20-30ms longer than FP-ERP. ERPs of non-conducted A2 [FP-ERP-A(-)] was measured with A3 following A2 at coupling intervals 20 ms shorter than FP-ERP. Concealed conduction was considered to be present when A1A3 interval of A3 blocked at the FP with a longest A2A3 interval was longer than FP-ERP. Concealment index(CI)-1 and CI-2 were calculated by dividing FP-ERP-A2(-) by FP-ERP-A2(+) and FP-ERP, respectively. In addition, relationship between antegrade slow pathway conduction time(A2H2) and retrograde fast pathway conduction time(HA), retrograde AV conduction system block cycle length(VA-BCL), and retrograde AV conduction system EBP(VA-ERP) was evaluated by a regression analysis.
RESULTS
Concealed conduction was present in all the subjects. CI-1 was 0.63 +/- 0.04 and CI-2, 0.79 +/- 0.04 in SAVNP and 0.67 +/- 0.11, 0.68 +/- 0.07 respectively, in AVNRT patients in whom the antegrade slow pathway(SP) was ablated with catheter ablation, showing no significant difference in CI between 2 groups. At the time of induction of AVNRT with A2, A2H2. was significantly correlated with FP-ERP and FP-CT(r=OA43, p=0.04; r=0.507, p=0,02, respectively). By multivariate regression analysis, it was derived that A2H2 should be greater than "0.79 FP-ERP+1.57 FP-CT-0.44 HA-190(ms)" (r=0.71, p<0.05).
CONCLUSION
Induction of typical AVNRT with A2 is determined by conduction time of the slow pathway, refractory period and conduction velocity of the fast pathway, and concealed conduction into the fast pathway.