Short QT Syndromes

The SQTS is a recently described genetic arrhythmogenic disorder, characterized by abnormally short QT intervals and a high incidence of sudden death during life, including the first months of life. Therefore, it should also be considered as a possible cause of the sudden infant death syndrome. Often a noticeable family history of cardiac sudden death is present. AF may be observed, also in young individuals. The inheritance is autosomal dominant, with genetic heterogeneity. Gain-of-function mutations in 3 genes encoding potassium channels have been identified, explaining the abbreviated repolarization seen in this condition: KCNH2 encoding IKr (SQT1), KCNQ1 encoding IKs (SQT2), and KCNJ2 encoding IK1 (SQT3). Some cases present with a double phenotype of SQTS and Brugada syndrome. Loss-of-function mutations in 2 genes encoding the cardiac L-type calcium channel, CACNA1C and CACNB2b, have also been found. At electrophysiologic study, short atrial and ventricular refractory periods are found, and AF and VF are easily induced by programmed electrical stimulation. The outcome of patients with SQTS becomes relatively safe when they are identified and treated. Currently, the suggested therapeutic strategy is the implantation of an ICD in patients with personal or familial history of sudden death. Concern exists for elderly asymptomatic patients and for children. In these categories, pharmacologic treatment with HQ, which has been shown to prolong QT and reduce the inducibility of ventricular arrhythmias, may be proposed.