Hypertrophic cardiomyopathy complicated by severe bradycardias: a pedigree report.

We describe four patients with nonobstructive hypertrophic cardiomyopathy (HCM) from an extended Chinese family. The patients had remarkably similar physical and echocardiographic findings including a harsh localized systolic murmur and apical left ventricular hypertrophy. All four had severe sinus bradycardia and atrial-ventricular conduction block (AVB) manifest by recurrent syncope. Two died suddenly due to bradycardia. Holter monitoring showed no tachycardias. Late potentials were not present. We conclude that this unusual form of HCM may be caused by a new and as yet unknown gene mutation.