Hereditary bundle branch system defect. A new genetic entity?

A familial survey demonstrated mendelian inheritance in three large kindreds with conduction abnormalities and heart block. The trait was autosomal dominant, with varying expressivity and penetrance, apparent male preponderance, and congenital onset. Manifestations included right bundle branch block, left axis deviation, and right bundle branch block associated with left axis deviation. Complete heart block proved almost always to be a late event, and developed in all documented cases from bilateral bundle branch block. An r' pattern, most likely representing a right ventricular conduction delay, is discussed.