The long QT syndrome with impaired atrioventricular conduction: a malignant variant in infants.

INTRODUCTION: The long QT syndrome (LQTS) is occasionally complicated by impaired AV conduction, mostly 2:1 AV block. This form of LQTS can manifest before birth or during neonatal life, and it is more sporadic than familial. It is usually an isolated disorder, although it can be accompanied by a variety of cardiovascular and other anomalies. In spite of different treatment modes, mortality is high. METHODS AND
RESULTS: The reported case presented not only with 2:1 AV conduction, but also with Wenckebach episodes with impaired right and left bundle branch conduction, and decremental conduction in the His-Purkinje axis. We also observed sinus pauses and accelerated AV junctional escape beats.
CONCLUSION: Our findings, and similar observations by others, suggest involvement of the sinus node and the distal conduction system in this form of the LQTS. Several histologic studies have documented abnormalities within the conduction system, including apoptosis. Because of the rare occurrence and poor prognosis of the LQTS with impaired AV conduction, international guidelines for diagnosis and treatment are needed. Development of an internal cardiac defibrillator for this young age group is necessary.