An autosomal dominant defect of cardiac conduction that is characterized by an abnormal st-segment in leads v1-v3 on the electrocardiogram resembling a right bundle-branch block, high risk of ventricular tachycardia or ventricular fibrillation, syncopal episode, and possible sudden death. This syndrome is linked to mutations of gene encoding the cardiac sodium channel alpha subunit. A variant of mutations of scn5a gene encoding the cardiac sodium channel alpha subunit.