cardiovascular disorders
Short QT Interval Syndromes
Introduction
The short QT interval syndromes (SQTS) are extremely rare congenital or very rarely acquired disorders of cardiac ion channel function or regulation that shorten ventricular myocyte action potential duration as reflected by shortening of the rate-corrected QT interval on the ECG. (See also Overview of Arrhythmias and The cardiac ion channel dysfunction may involve Gain of function of repolarizing potassium current channels OR Loss of function of depolarizing sodium or depolarizing calcium current channels Note the changes in channel function (ie, gain or loss) are the opposite of those occurring in Long QT Interval Syndromes . The shortening of the action potential duration is most marked in the ventricular epicardium and may lead to polymorphic ventricular tachycardia (VT) or ventricular fibrillation (VF) often leading to sudden death. The likelihood of ventricular tachyarrhythmias increases with the degree of QTc interval shortening. Some patients with SQTS are also prone to Atrial Fibrillation . Short QT interval syndromes are classified based on the specific gene that has mutated. Abnormal genes includeKCNH2,KCNQ1, andKCNJ2. Patients are asymptomatic unless atrial fibrillation or VT/VF occurs, which may cause palpitations, near syncope, syncope, or cardiac arrest. 