Atypical atrioventricular nodal reentrant tachycardia: prevalence, electrophysiologic characteristics, and tachycardia circuit

This study aimed at assessing the prevalence, electrophysiologic characteristics, and mechanism of atypical atrioventricular nodal reentrant tachycardia (AVNRT). We studied 925 consecutive patients with AVNRT. Atrial-His (AH) and His-atrial (HA) intervals were measured during atypical AVNRT (HA > 70 ms), and compared with measurements in 34 patients with typical (slow-fast) AVNRT. Assuming that conduction velocity over the fast pathway is similar in the anterograde and retrograde directions, the AH interval during the fast-slow form should be smaller than the HA during slow-fast. Atypical AVNRT was diagnosed in 59 patients (6.4%), median age 50 years (range 19-79 years), and 37 (59.7%) of them female. Fast-slow AVNRT was diagnosed in 44 patients (74.5%), and slow-slow AVNRT in 9 patients (15.2%). The remaining six patients (10.2%) could not be reliably classified due to inconsistent AH, and HA/AH patterns or variable intervals. Tachycardia induction with anterograde conduction jumps was seen in two patients with the fast-slow, and in three patients with slow-slow or intermediate forms. Atrial-His in the fast-slow group was significantly longer than HA in the slow-fast group, 99.7 ± 40.5 ms vs. 45.8 ± 7.7 ms, P < 0.001. Tachycardia cycle length was longer in fast-slow compared with slow-fast, 379.1 ± 68.5 ms vs. 317.1 ± 42.8 ms, P < 0.001. Of AVNRT cases, 6.4% are atypical and may display patterns that do not necessarily correspond to the fast-slow or slow-slow conventional types. Atypical fast-slow and typical AVNRT do not appear to utilize the same limb for fast conduction.