Hereditary prolongation of QT interval . Study of two families.

A syndrome has previously been recognized, which is characterized by recurrent episodes of loss of consciousness, some of which end fatally. The electrocardiogram in affected subjects shows prolongation of the QT interval. In the present study, 2 unrelated families with a total membership of 82 were investigated; 30 living subjects were examined and 20 were found to be affected. A further 14 members, 11 of whom died suddenly, were presumed from their histories to have been affected. The condition seems to be much more common, at least in South Africa, than the small number of previously reported cases would suggest. In contrast to the similar syndrome in which congenital deafness is also a feature and in which the disorder is transmitted in an autosomal recessive manner, analysis of the present data reveals an autosomal dominant inheritance with variable penetrance. The fundamental nature of the disorder remains unknown. Though treatment is generally unsatisfactory, beta-adrenergic blocking agents may be of value.