Advantages of right ventricular outflow tract pacing for congenital heart disease: 1. Protection of cardiac function and reduction of myocardial remodeling Because of the proximity of the pacing position to the normal conduction bundle, excitation is transmitted to the ventricles along the left and right bundle branches after pacing, resulting in bilateral ventricular excitation-contraction synchronization, thus avoiding mitral regurgitation and cardiac insufficiency due to interventricular asynchrony caused by RVA pacing. Studies in children have shown that both early and long-term postoperative follow-up have shown that septal pacing is significantly less likely to cause left and right ventricular dyssynchrony than apical pacing, with no significant changes in myocardial perfusion, left ventricular myocardial contraction, or cardiac function, and less mitral regurgitation and atrial fibrillation, and no myofibrillar disorganization on subendocardial myocardial biopsy. RVOT pacing is beneficial to the improvement of left heart function, especially for those with preoperative combined cardiac insufficiency, RVOT pacing can significantly improve cardiac function, reduce patients’ clinical symptoms and improve their quality of life. LVEF and activity tolerance are increased, while oxygen consumption is reduced. In contrast, RVA pacing worsens cardiac function, and although there are different reports, most studies have shown that long-term RVA pacing causes LV enlargement, increased mitral regurgitation, and worsened cardiac insufficiency, with a higher incidence in those with preoperative combined cardiac insufficiency. Inter-ventricular and intraventricular contraction asynchronization, reduced myocardial perfusion, disorganized subendocardial myocardial fiber arrangement and abnormal mitochondrial arrangement in cardiomyocytes are obvious phenomena, and mitral and tricuspid regurgitation lead to atrial enlargement, which significantly increases the incidence of atrial fibrillation. Right ventricular pacing in children is often used in patients with sick sinus syndrome (SSS) and severe atrioventricular block due to various causes. Due to their young age, they need to be paced for a longer period of time than adults, and there is a significant positive correlation between the occurrence of pacemaker complications and the duration of pacing. Therefore, a thorough evaluation should be performed before installation. Although there are conflicting reports on RVA pacing, most studies have shown that even in patients without preoperative cardiac insufficiency, long-term RVA pacing can lead to a decrease in left ventricular systolic function and heart failure, with a higher incidence in patients with preoperative combined cardiac insufficiency, which is mainly related to the excitation-contraction sequence disturbance caused by RVA pacing, resulting in asynchronous left and right ventricular and left intraventricular contractions. It was found that the QRS wave in the 12-lead EKG was narrowed during RVOT pacing, and tissue Doppler studies showed that the distance from the beginning of the QRS to the systolic flow of the pulmonary artery and the distance from the beginning of the QRS to the systolic flow of the aorta were shortened, indicating that the contractions between the right and left ventricles tended to be synchronized. At long-term follow-up, the cardiac function of children with RVOT improved significantly, their self-conscious symptoms decreased, the distance of 6-minute walk test increased, and their quality of life improved significantly. 3. Stable and reliable pacing The advantage of RVA pacing is that the electrode leads are easy to fix and the pacing parameters are stable. In the control study, it was found that the parameters of RVOT pacing, such as pacing threshold, perception and impedance, did not change significantly in the early postoperative period and long-term follow-up, and the pacing was stable and reliable. The pattern of parameter changes was the same as that of RVA pacing, i.e., an increase in impedance and a slight increase in pacing threshold 1 month after surgery compared with 1 day after surgery. However, with the widespread use of hormone slow release electrodes, this phenomenon is significantly reduced. Unlike RVA pacing, RVOT pacing electrodes, once fixed, are basically free of displacement and have a higher safety profile. IV. Complications of right ventricular outflow tract pacing 1. Postoperative electrode displacement: The incidence is small, because the active spiral electrode is used for septal pacing, and displacement rarely occurs after screwing into the ventricular septum. Only a few early postoperative electrode displacements requiring refixation have been reported in large scale studies. 2. Postoperative pulmonary hypertension: The cause is unknown, and only a few cases have been reported of pulmonary hypertension early after RVOT implantation of electrodes. 3.Aortic valve injury: The conical interval of the outflow tract is close to the aortic valve, so improper installation can cause aortic valve injury, but it has not been reported clinically. Mainly because the conical part of the septum is smooth, not easy to fix, and the resistance is high after implantation, generally the outflow tract installation are chosen supraventricular crest inferior septum [6]. 4. Interventricular and intraventricular systolic asynchrony: Although the incidence is less than that of RVA pacing, this phenomenon still occurs in about 1/3-1/2 of patients, and even if it occurs, the asynchrony interval is shorter (narrow QRS wave) and has less impact on cardiac function. 5. Cardiac insufficiency: Most studies have shown that RVOT pacing has no significant effect on cardiac function and can even improve cardiac insufficiency, especially in those with preoperative combined cardiac insufficiency, and clinical symptoms are significantly reduced. However, it has also been reported that some patients with RVOT pacing showed deterioration of cardiac function, which is considered to be mainly related to the preoperative cardiac function status and improper electrode installation position, which may cause an increase in pacing threshold, poor perception, and even an increase in ventricular asynchrony, thus affecting cardiac function. Although the present experimental results are contradictory and need to be further investigated, RVOT pacing should be chosen more often for pacemaker installation in children because septal pacing is closer to physiological conditions and subsequent electrode replacement is easier than RVA pacing.