Association of secundum atrial septal defect and atrioventricular nodal dysfunction. A genetically transmitted syndrome.

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Abstract
Secundum atrial septal defect may occasionaly be transmitted as an autosomal dominant trait. Patients with this entity often show evidence of conduction system abnormalities by electrocardiogram. To define the nature of the conduction system disease in such patients, a family was studied in which 5 closely related members in 3 generations had the combination of atrial septal defect, syncope and 1st and/or 2nd degree atrioventricular (AV) block by electrocardiogram. Of these 5 patients, 3 required permanent pacing. Three other relatives without syncope also had conduction abnormalities, including 1 patient with atrial septal defect. Of the 8 family members, 3 were studied with His bundle electrocardiography. Two of these 3 patients had syncope preceding operative closure of an atrial septal defect and 1 had no history of syncope or evidence of an atrial septal defect; all 3 had 1st degree AV block. Intracardiac electrophysiological study showed that each patient had a long AH time (which decreased with atropine), normal HV time, and prolonged AV nodal refractory periods. Both secundum atrial septal defect and intrinsic AV nodal disease may be transmitted as autosomal dominant traits (probably as manifestations of a single mutant gene), and may occur together or separately in members of the same family.