Genotype-specific ECG patterns in long QT syndrome.

Different genetic types of the long QT syndrome (LQTS) are associated with distinct ECG manifestations, which relate to the type and magnitude of ion channel dysfunction. The QTc duration does not differentiate LQTS types, and therefore other static and dynamic ECG parameters reflecting changes in T wave morphology are used to describe phenotypic expression of different LQTS genotypes. LQT1 carriers usually have broad-based T waves, LQT2 carriers show low-amplitude T waves with high incidence of notches, and LQT3 carriers frequently have extended ST segment with relatively narrow peaked T wave. This phenotypic differentiation could be enhanced by quantifying additional ECG parameters reflecting components of repolarization morphology as well as to evaluate dynamics of repolarization parameters. Heart rate dependency and dynamic behavior of repolarization parameters differ by genotype and further show that genotype indicates ECG phenotype in patients with LQTS. However, there is a substantial variation in repolarization abnormalities observed in the same subject and in the members of the same family indicating large differences in gene penetrance. In conclusion, comprehensive analyses of static and dynamic features of repolarization provide unique opportunity to understand electrophysiology of cardiac repolarization.