Effects of Chronic Right Ventricular Pacing in Children With Advanced Atrioventricular Block

This is a prospective cohort study that will include patients younger than 18 years-old at initial pacemaker implantation due to advanced AVB. The design of the study will involve the following stages: 1. Screening and enrollment: patients will be selected consecutively during ambulatory care at our Institution or by the database of the Surgical Unity of Cardiac Pacing; 2. Clinical and laboratory evaluation: patient history, clinical evaluation, serum levels of neurohormonal and inflammatory biomarkers of heart failure, clinical and laboratory investigation of autoimmune rheumatic diseases, quality of life (SF-36, CHQ-PF50) and six-minute walk test; 3. Evaluation of ventricular function and cardiac synchronicity: Tissue Doppler (TDI) and real-time three-dimensional echocardiography (RT3DE); 4. Follow-up: patients will be monitored during 24 months. The main end-points are: * Clinical and functional changes (NYHA functional class) * Heart failure hospitalization * Quality of life * Overall and cardiac mortality * Cardiac resynchronization therapy and heart transplantation