KCNH2 and familial long QT syndrome: The algorithm was based on the combination of information about the presence of genetic variants on one of the three main LQTS genes (KCNQ1, KCNH2, and SCN5A defining LQT1, LQT2, and LQT3), gender, and QT interval duration (≥500 or <500 ms), which are known independent risk predictors in LQTS.