[Arrhythmia and genetic background]

Recent studies have demonstrated that genetic abnormalities associated with the regulation of myocardial ionic channels, receptors, transporters, cell membranous proteins etc, can create an arrhythmogenic substrate in some patients with structurally normal hearts, and these are called hereditary arrhythmic diseases. Various arrhythmic diseases (such as congenital long or short QT syndrome, Brugada syndrome, catecholamine-sensitive polymorphic ventricular tachycardia, arrhythmogenic right ventricular cardiomyopathy, early repolarization syndrome etc.) are categorized as hereditary arrhythmic diseases. Among them, we focused on long QT syndrome and Brugada syndrome in this review. In congenital long QT syndrome, either attenuation of the net outward current or augmentation of the net inward current is responsible for prolonging the myocardial action potential duration and QT interval on ECG. Premature ventricular beats triggered due to early after-depolarization infringe on the large spatial dispersion of ventricular repolarization and initiate polymorphic ventricular tachycardia with a specific form (torsade de pointes). Currently, thirteen genotypes in Romano-Ward syndrome and two genotypes in Jervell-Lange Nielsen syndrome have been reported. In Brugada syndrome, large transient outward current (Ito) creates a deep phase 1 notch in the action potential, especially at the epicardial myocardium of the right ventricular outflow tract. In combination with the delayed completion of repolarization and loss of the phase 2 dome in some epicardial myocardium in this area, coved-type ECG abnormality and ventricular fibrillation due to phase 2 reentry are believed to be induced in Brugada syndrome. Eleven genetic abnormalities are presently listed as a possible cause of Brugada syndrome.