Simultaneous dual fast and slow pathway conduction upon induction of typical atrioventricular nodal reentrant tachycardia: electrophysiologic characteristics in a series of patients.

Introduction: Simultaneous dual atrioventricular nodal conduction (SDNC) through slow (SP) and fast pathway (FP) is a rare phenomenon observed upon the induction of atrioventricular nodal reciprocating tachycardia (AVNRT). The aim of this study is to report the electrophysiological features of patients showing typical AVNRT induced through SDNC. Methods and Results: Among 461 consecutive patients with typical AVNRT submitted to radiofrequency catheter ablation (RFCA), seven patients (1.5%) with SDNC at tachycardia onset (group I: 6 female; age 60–72 years, mean 65.2 ± 3.8 years) and 118 age-matched controls (group II: 60 female; age 60–88 years, mean 68.4 ± 6.8 years) were considered. Controls were further subdivided into two subgroups according to age: subgroup A (94 patients, age 60–75 years) and subgroup B (24 patients, age >75 years). The value of the following parameters was significantly higher in group I than in group II and in subgroup A: A–H interval [113 ± 26 vs. 89 ± 27 (P < 0.01) vs. 84 ± 19 (P < 0.001)], ventriculoatrial conduction effective refractory period [355 ± 85 vs. 293 ± 87 (P < 0.05) vs. 281 ± 82 (P < 0.05)], SP conduction time upon AVNRT induction [444 ± 104 vs. 350 ± 72 (P < 0.01); vs. 345 ± 67 (P < 0.001)], AVNRT cycle length [484 ± 103 vs. 396 ± 71 ms (P < 0.05); vs. 384 ± 69 (P < 0.05)], and rate of AVNRT induction from ventricle [71% vs. 10% (P = 0.001); vs. 6% (P = 0.001)]. Differences were mostly not significant between group I and subgroup B. SP location and RFCA success rate were similar in all groups. Conclusion: In a population of AVNRT patients, SDNC at AVNRT induction is infrequent and it prevails beyond the fifth decade of life and in females. SDNC is associated with peculiar AVN conduction features, which resemble the age-related modifications of AVN conduction.