The Long QT Syndrome: problem identification, diagnostic challenges

Abstract

The Long QT syndrome (LQTS) is inherited or acquired channelopathy resulting ventricular tachyarrhythmia torsade de pointes (TdP) which causes syncope and sudden death. The acquired LQTS might be drug-induced that is significant public health issue. The estimated prevalence of inherited LQTS in the USA is estimated at about 1:7000 or 1: 5000 individuals according to different sources. The article covers the most important issues of the syndrome, clinical and diagnostic challenges when QT interval prolongation is seen on ECG in order to assist doctors deal with the problem.

LQTS is caused by mutations of genes which encode for cardiac ion channels. Five genes, (LQT1,2,3,5,6) with over 200 mutations have thus far been discovered. Clinically, LQTS is identified by abnormal QT interval prolongation on the ECG. Genotype-phenotype studies of LQTS have provided new insights into risk mechanisms, electrocardiographicf eatures, and long-term clinical course associated with this inherited disorder. Individuals with LQTS are practically healthy people without structural problems of the heart. The first manifestation of the disorder may be a fainting episode or syncope and sudden cardiac death. These events are due to the ventricular tachyarrhythmia torsade de pointes (TdP). ECG is informative and practically the main tool for diagnosis. The characteristic signs are QT interval prolongation and T wave abnormalities.  Usually, the rate adjusted QT interval is calculated (QTc) using the Bazett formula (QTc = QT/√RR). In case of suspicion, the QTc ranges from about 410 to over 600 msec. the most difficult task is to asses the risk of further arrhythmic events. Several approaches are implemented in clinical practice with this purpose (Schwarts score, Priory criteria).  Management of LQTS includes mainly beta-blockers, education of patients to avoid triggers, pacemakers in case of bradycardia or ICDs.