Atrioventricular node reentry with 'smooth' AV node function curves - A different arrhythmia substrate?

Background Some patients with otherwise typical AV node reentry do not manifest discontinuous AV node function curves. We examined the effects of an ablation in the slow-pathway region in patients with smooth AV node function curves. Methods and Results Fifteen patients with AV node reentrant tachycardia (AVNRT) and discontinuous AV node function curves were compared with 15 patients with AVNRT and smooth AV node function curves. In the group with a discontinuous curve, the ''net'' anterograde effective refractory period (AERP) of the AV node increased (270+/-28 versus 304+/-37 ms, P=.03) and AERP of the remaining fast pathway decreased (367+/-100 versus 304+/-37 ms, P=.026) after the ablation. In the group with a smooth curve, the AERP of the AV node increased (266+/-42 versus 299+/-76 ms, P=.07) and the anterograde Wenckebach cycle length increased (336+/-66 versus 379+/-86 ms, P=.008) after the ablation. Retrograde conduction over the AV node was similar in both groups and was unchanged after ablation. The longest attainable AH interval (AH(max)) measured during atrial extrastimulus testing was more prolonged in patients with a discontinuous curve than in patients with a smooth curve (326+/-48 versus 250+/-70 ms, P=.002). The AH(max) shortened in both groups after ablation (326+/-48 versus 173+/-34 ms, P<.0001, and 250+/-70 versus 179+/-34 ms, P<.0003, respectively) and were similar. Successful ablation in the slow-pathway zone in patients with a smooth AV node function curve resulted in the loss of the ''tail'' of the curve representing the slow pathway. Conclusions These data suggest that the smooth AV node function curve consists of two distinct components representing both fast and slow AV node pathways even when the typical discontinuity is absent.