Two:One atrioventricular block in infants with congenital long QT syndrome

Congenital prolongation of the QT interval is a rare but life-threatening disorder of the cardiac conduction system.^1-5 The disorder usually presents as syncope or sudden death due to complex polymorphic ventricular tachycardia (torsade de pointes) or ventricular fibrillation.⁶ The major hypothesis explaining the disorder is an imbalance of sympathetic discharge between the right and left stellate ganglia resulting in inhomogeneity of ventricular refractoriness and a substrate for reentrant ventricular arrhythmias.^4-6 Although sinus bradycardia may be associated with the syndrome, abnormalities in atrioventricular (AV) conduction are rare.⁴ In this report we present 3 infants with the congenital long QT syndrome and 2:1 AV block and provide support for the role of the long effective refractory period in producing the block.