Abstract: Objective To investigate the etiology, clinical features and prognosis of left bundle branch block (LBBB) in children. Method The clinical data of children diagnosed with LBBB from January 2013 to December 2018 were retrospectively analyzed. Results There were 43 patients with LBBB ( 35 boys and 8 girls), and the median age was 36 months ( 9 - 72 months). There were 36 cases of complete LBBB and 7 cases of left anterior branch block. Cardiac enlargement occurred in 36 cases and cardiac function decreased in 16 cases. Twelve patients had a history of surgery for congenital heart disease (CHD), including ventricular septal defect (VSD) repair in 7 cases and complicated CHD in 5 cases. Closure of VSD was performed in 12 cases. There were 6 cases of cardiomyopathy, 4 cases of myocarditis, 4 cases of CHD before operation, and 3 normal children. There were 1 cases of craniocerebral trauma and 1 cases of drowning. LBBB occurred in 12 cases 1 - 7 days after the closure of VSD. After treatment with methylprednisolone and myocardial nutrition, 8 cases recovered immediately; 4 cases were not recovered after treatment, and sinus rhythm was restored after surgical removal of occluder and repair of VSD from 3 to 8 days after interventional occlusion. LBBB was found in 12 cases of CHD after surgery. After treatment with hormones, nourishing myocardium and other drugs, all 8 cases returned to sinus rhythm, 1 case still had LBBB; 3 cases developed LBBB after repair of VSD, which gradually progressed to degree III atrioventricular block, and permanent cardiac pacemakers were implanted. The median follow-up time was 24 months ( 12 - 49 months). One patient returned to normal early after VSD occlusion, but delayed LBBB appeared at 7 months follow-up. At the end of the follow-up, one patient still had LBBB after surgery for complicated CHD and one patient with fulminant myocarditis still had LBBB accompanied by cardiac enlargement and cardiac dysfunction. One case of dilated cardiomyopathy complicated with LBBB died due to aggravation of heart failure at the age of 2 months. The remaining children had no discomfort, no changes in electrocardiogram, no abnormalities in cardiac function and left ventricular ejection fraction. Conclusions The most common causes of LBBB in children are surgery for CHD and closure of VSD. Clinical diagnosis and treatment should be made as soon as possible, and close follow-up should be conducted.

Key words: left bundle branch block; treatment; prognosis; child