The syndromes of familial atrioventricular block with sinus bradycardia: prognostic indices, electrophysiologic and histopathologic correlates.

A family with adult onset heart block (AOHB) and sinus bradycardia (SB) was investigated 5 yr after previous study. A 44-yr-old female previously 'normal' presented ECG evidence of 1st-degree and 2nd-degree atrioventricular block (AVB) with normal intraventricular conduction and episodic 3rd-degree AVB. His bundle electrocardiography (HBE) demonstrated A--H prolongation (245msec) with normal H--V time during sinus rhythm and 3rd-degree AV nodal block with a His bundle escape rhythm. Sinus node function served in first-order relatives. HBE and sinus node function were normal in a 38-yr-old sister with new SB. 37 families with familial 3rd-degree AVB were reviewed with attention to prognostic indices and electrophysiologic-pathologic correlates. The incidence of conduction abnormalities supported an autosomal dominant transmission with variable penetrance. Subsidiary pacemaker rate and QRS morphology showed no discriminative value with respect to prognosis. HBS identified A--H prolongation in 2 patients with AOHB and 2 with AOHB and SB, with coexistent H--V conduction delay in 2 cases of AOHB and SB with abnormal QRS morphology. Histopathology was variable, but the finding of multiple lesions in 2 of 5 patients with congenital heart block and each of 2 with AOHB and SB suggests that mixed conduction system disease is prevalent in familial heart block.