Atrioventricular nodal dysfunction in patients with atrial septal defect. Abnormalities of conduction and reciprocal rhythms.

Electrophysiologic studies were performed in 17 unselected patients (mean age, 20 years) with atrial septal defect (ASD) of the ostium secundum type. In nine (52.9 percent) signs were found of atrioventricular (A-V) nodal dysfunction, in seven (41.1 percent) prolonged A-H interval, and in three (17.6 percent) prolonged effective refractory period of A-V node and in five (29.4 percent) A-V nodal tachycardia and reentry. Three of the four cases showed anterograde conduction (Ae-H interval) faster than retrograde conduction (H-A3 interval) during the tachycardia. In one patient with reentry a similar phenomenon was observed. In the remaining patient the conduction time was reversed (Ae-H longer than H-Ae). In two patients infrahisian and intrahisian block (first and second degree) with persistence of the tachycardia was observed. Patent or latent abnormalities in A-V node function are a frequent finding in patients with ASD. In the sinus node, any kind of significant abnormality can be found.