title: Retrograde block during dual pathway  atrioventricular nodal reentrant paroxysmal tachycardia.
abstract: There are limited reported data regarding the occurrence of retrograde block during dual pathway atrioventricular (A-V) nodal reentrant paroxysmal tachycardia. This study describes two patients with this phenomenon. The first patient had 2:1 and type 1 retrograde ventriculoatrial block during the common variety of A-V nodal reentrance (slow pathway for anterograde and fast pathway for retrograde conduction). Fractionated atrial electrograms suggested that the site of block was within the atria. The second patient had type 1 retrograde block (between the A-V node and the low septal right atrium) during the unusual variety of A-V nodal reentrance (slow pathway for retrograde and fast pathway for anterograde conduction). The abolition of retrograde block by atropine suggested that the site of block was within A-V nodal tissue. Both cases demonstrate that intact retrograde conduction is not necessary for the continuation of A-V nodal reentrant paroxysymal tachycardia. Case 2 supports the hypothesis that the atria are not a requisite part of the A-V nodal reentrant pathway.
mesh_terms: D001283:Atrioventricular Node / Q000503:physiopathology; D002036:Bundle of His / Q000503:physiopathology; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D005260:Female; D006327:Heart Block / Q000209:etiology* / Q000503:physiopathology; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013614:Tachycardia, Paroxysmal / Q000150:complications* / Q000503:physiopathology