title: Limitation of tachycardia zone resulting from longitudinal dissociation of the atrioventricular node in concealed pre-excitation.
abstract: Two cases with a concealed left-sided accessory atrioventricular bypass tract are described. In both, functional longitudinal dissociation of the atrioventricular node narrowed the range of atrial premature beat coupling intervals which could initiate re-entry using the accessory pathway. In case 1 early premature atrial beats were followed by an atrioventricular nodal re-entrant echo. The atrial echo pre-empted retrograde conduction over the Kent bundle and thus limited the development of paroxysmal supraventricular tachycardia. In case 2 atrioventricular nodal conduction showed typical features ascribed to dual atrioventricular nodal pathways. In addition there was a bradycardia-related retrograde block in the concealed accessory pathway. Early premature atrial beats, because of exclusive "slow pathway" anterograde conduction, arrived at the ventricles during the period of bradycardia-dependent retrograde block and failed to initiate a macro re-entrant tachycardia. This study shows that (1) longitudinal dissociation within the atrioventricular node may limit the ability to initiate tachycardia in patients with concealed pre-excitation; and (2) discontinuous atrioventricular nodal conduction curves occasionally help to reveal bradycardia-related retrograde block in a concealed accessory pathway.
mesh_terms: D001145:Arrhythmias, Cardiac / Q000503:physiopathology*; D001283:Atrioventricular Node / Q000503:physiopathology*; D001919:Bradycardia / Q000503:physiopathology; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D005260:Female; D006327:Heart Block / Q000503:physiopathology; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013610:Tachycardia / Q000503:physiopathology