Congenital long QT syndrome with functionally impaired atrioventricular conduction: successful treatment by mexiletine and propranolol.

Congenital long QT syndrome (LQTS) with atrioventricular block is a rare and malignant arrhythmia, which usually responds poorly to traditional β-blocker therapy. We describe a male neonate with LQTS with ventricular tachycardia and 2:1 atrioventricular block. This patient's sister had similar presentation and died suddenly at the age of 8 months despite β-blocker and pacemaker therapy. Our patient responded to a combination of sodium channel blocker (mexiletine) and β-blocker (propranolol) therapy. He was asymptomatic during a 2-year follow-up period. This case suggests that propranolol combined with mexiletine might be useful in the treatment of patients with LQTS with atrioventricular block.