Dual atrioventricular nodal pathways a common lectrophysiological response'

Evidence of dual atrioventricular nodal pathways (a sudden jump in H1-H2 at critical A1-A2 coupling intervals) was shown in 4I out of 397 patients studied with atrial extrastimulus techniques. In 27 of these 41, dual pathways were demonstrable during sinus rhythm, or at a cycle length close to sinus rhythm (CL1). In the remaining 14, dual pathways were only demonstrated at a shorter cycle length (CL2). All patients with dual pathways at cycle length1 who were also tested at cycle length2 (iI patients) had dual pathways demonstrable at both cycle lengths. In these II patients both fast and slow pathway effective refractory periods increased with decrease in cycle length. Twenty-two of the patients (54%) had either an aetiologicalfactor strongly associated with atrioventricular nodal dysfunction or one or more abnormalities suggesting depressed atrioventricular nodalfunction. Evaluation offast pathway properties suggested that this pathway was intranodal. Seventeen of the patients had previously documented paroxysmal supraventricular tachycardia (group I). Eight patients had recurrent palpitation without documented paroxysmal supraventricular tachycardia (group 2), and I6 patients had neither palpitation nor paroxysmal supraventricular tachycardia (group 3). Echo zones were demonstrated in I5 patients (88%) in group i, no patients in group 2, and 2 patients (I3%) ingroup 3.