Abstract 2522: Reentrant Circuit is Totally Confined to Atrioventricular Node in Half of Atypical Atrioventricular Nodal Reentrant Tachycardias
Background Although atypical AV nodal reentrant tachycardias (AVNRTs) are amenable to slow pathway ablation, there are still controversies as to the precise location of the reentrant circuit, especially whether or not the perinodal atrium is involved in the reentrant circuit.
Purpose This study was performed to assess whether the perinodal atrium is involved in the reentrant circuit of atypical AVNRT.
Methods Among 19 patients with 25 atypical AVNRTs (slow-slow: 11, fast-slow: 14) induced during electrophysiological study, overdrive pacing was performed from high right atrium during atypical AVNRT to assess whether the AVNRT was reset when the perinodal atrium (coronary sinus (CS) and His bundle site (HBS)) was antidromically captured by overdrive pacing. The AVNRT reset was defined as shortening of the H-H interval by >10 msec.
Results Fourteen atypical AVNRTs (56%, slow-slow: 7, fast-slow: 7) induced in 10 patients (53%) were not reset by overdrive pacing even when all the perinodal atrium, including the earliest retrograde atrial activation site during atypical AVNRT (CS ostium: 3, proximal CS: 10, HBS: 1), was antidromically captured and pre-excited 5–15 msec earlier than expected. Among them, 4 atypical AVNRTs (16%) induced in 4 patients (21%) presented ventriculo-atrial (VA) dissociations during atypical AVNRT, including transient VA block in 2 and variable H-A interval during constant H-H interval in the remaining 2 patients. In the other 11 atypical AVNRTs (44%, slow-slow: 4, fast-slow: 7, the earliest retrograde atrial activation site: CS ostium: 9, proximal CS: 2) induced in the other 9 patients (47%), the atypical AVNRT was not reset by atrial overdrive pacing when HBS was antidromically captured 5–15msec earlier than expected, but reset only when both HBS and the earliest retrograde atrial activation site were antidromically captured.
Conclusions All the atypical AVNRTs were not reset even when the atrium at the HBS was pre-excited, suggesting atrial myocardium near the HBS would not be involved in the reentrant circuit of atypical AVNRT. All the perinodal atrium could be pre-excited without tachycardia reset in 56% of atypical AVNRTs, suggesting intra-nodal reentry without participation of perinodal atrium in about half of atypical AVNRTs.