Familial sick sinus syndrome in two siblings.

Two siblings with sinus node disease are presented. The patients were severely affected and required permanent pacing. A cardiac electrophysiologic study was conducted in Case 2, which revealed an atrioventricular conduction disturbance in addition to sinus node dysfunction. The parents and other siblings showed no evidence of sinus node disorder. The occurrence of this disease in these siblings suggests an autosomal dominant mode of inheritance with variable penetrance.