ATRIOVENTRICULAR NODAL REENTRY TACHYCARDIA - ELECTROPHYSIOLOGIC COMPARISONS IN PATIENTS WITH AND WITHOUT 2 1 INFRA-HIS BLOCK/

Patients with atrioventricular nodal reentry tachycardia (AVNRT) occas ionally may demonstrate a 2:1 infra-His block during tachycardia. Howe ver, the electrophysiologic background of this phenomenon has not been established so far. In the present study we compared the electrophysi ologic parameters of 10 consecutive patients with a transient 2:1 infr a-His block during AVNRT of the common type (Group A) with those of 17 consecutive patients without this phenomenon during tachycardia (Grou p B). Transient 2:1 infra-His block occurred without termination of th e tachycardia in all 10 patients of Group A. The tachycardia sustained despite intermittent or permanent conduction disturbance of the infra hisian tissue in 8 of these 10 patients. In comparison, the electrophy siologic parameters of 17 patients without 2:1 block during AVNRT of t he common type (Group B) were analyzed. A significantly longer antegra de (318 +/- 58 ms vs. 259 +/- 50 ms) and retrograde (308 +/- 59 ms vs. 239 +/- 20 ms) AV conduction capacity could be demonstrated in these patients. The tachycardia cycle length did not differ significantly be tween the two groups, although the mean tachycardia cycle length was 4 8 ms longer in patients of Group B. These observations demonstrate an advanced conduction capacity in patients with a transient infra-His bl ock during AVRNT of the common type. This study underlines that the re entry circuit in AVNRT is not necessarily dependent on infrahisian tis sue.