LQT is caused by the loss of function of KCNQ1 channel encoding IKs (slow activation of delayed rectifier potassium channels), LQT2 is caused by the loss of function of KCNH2 channel encoding I (fast activation of delayed Kr rectifier potassium channels), and LQT3 is caused by the rapid activation of cardiac sodium channels caused by mutations in the SCN5Aa gene.[15,16] QT interval duration can not distinguish the types of LQTS, while T wave morphological changes can be used to describe different phenotypes of LQTS. Here, KCNH2 is linked to familial long QT syndrome.