EVIDENCE OF 3 CLINICAL SUBGROUPS IN PATIENTS WITH DUAL ATRIOVENTRICULAR NODAL PATHWAYS

We attempted to test the hypothesis that dual atrioventricular (A-V) n odal pathways with second-degree atrioventricular block (2nd A-V block ) present as a different clinical entity from those with A-V nodal ree ntranttachycardia (AVNRT). By evaluation with Holter monitoring (2.9 /- 2.5 recordings/patient) and 12-lead electrocardiogram (11.9 +/- 11. 6), 177 patients with dual A-V nodal pathways could be divided into th ree subgroups. Thirty-two patients had 2nd A-V block only (2nd A-V blo ck group), 57 had AVNRT only (AVNRT group), 88 had neither 2nd A-V blo ck nor AVNRT (silent group), and none had 2nd A-V block and AVNRT both . Electrophysiologic studies showed that the atrio-His interval was si gnificantly greater (P < 0.0001) and the maximal 1:1 atrioventricular conduction rate was lower (P < 0.0001) in the 2nd A-V block group than in the other two groups. These differences were nullified after the a dministration of atropine. These results suggest that patients with du al A-V nodal pathways can be classified into three clinical subgroups based on the presence of either 2nd A-V block or AVNRT. We suggest als o that patients of the 2nd A-V block group may have a more augmented v agal tone on the A-V node than the other two groups.