The normal range of QT interval is 0.32s-0.44s, while QT interval >0.45s in men and QT interval >0.46s in women is considered as prolonged QT interval. The length of QT interval is usually related to the heart rate, the faster the heart rate, the shorter the QT interval, and vice versa, the longer the QT interval. prolonged QT interval can be clinically classified into two types, one is caused by congenital disease, i.e., born with a disease of unknown etiology that prolongs the QT interval; the other is acquired, i.e., caused by various factors, mainly including the following: 1. the effect of drugs, amiodarone, quinidine, diisoproterenol, and other antiarrhythmic drugs, as well as tricyclic antidepressants; 2, electrolyte disorders, hypokalemia, hypocalcemia, hypomagnesemia; 3, patients with malnutrition and slow heart rhythm; 4, patients with sympathetic nerve surgery resulting in abnormal adrenaline secretion.