Patients with repaired TOF fulfilling inclusion and exclusion criteria will be recruited from Queen Mary Hospital, Hong Kong.
Patients who fulfill the inclusion and exclusion criteria will be interviewed by research staff and given a detailed explanation of the clinical trial. Written informed consent will be obtained if the patient agrees to enroll in the trial.
Assessments will be performed at Visit 1 (week 1): Review of medical history and history taking, Physical examination of vital signs (including blood pressure, pulse rate, and oxygen saturation by pulse oximetry), and cardiovascular system (12-lead electrocardiography (ECG), Blood tests (if not already done within 3 months): Complete blood count, Renal function test, Liver function test, Calcium and phosphate levels, N-terminal pro b-type natriuretic peptide (Nt-pro-BNP), High sensitive troponin T, Creatinine kinase, Hemoglobin A1c (HbA1c), Fasting glucose, Lipid profile , Erythropoietin, Multi-omic studies including proteomics, metabolomics, and lipidomics, Genetic test and geneticist consultation, Echocardiography (if not already done within 3 years), Cardiopulmonary test (CPX), Urine pregnancy test in women of childbearing age.
Randomization will be performed on the day of recruitment. An allocation sequence will be generated prior to initiation of the clinical trial using random numbers generated by computer. After entering a subject's information on the clinical trial system, the allocated group for the subject will be revealed. If a subject found to be ineligible for the clinical trial after randomization, the original assignment will be allocated to the next eligible subject. Subjects will be randomized in a 1:1 ratio to 1 of the 2 treatment arms:
1. SGLT2 inhibitor Group: Dapagliflozin 10mg once daily orally from Visit 1 (Week 1) to Visit 3 (Week 12 ± 1)
2. Control Group: Routine care.
CPX will be performed on Visit 1 (week 4 ± 1) and Visit 3 (week 12 ± 1) under supervision of cardiologist blinded to randomization results. VO2 max, which represent the maximal amount of oxygen consumed during peak exercise, will be measured. In addition, other parameters including metabolic equivalents (METs) achieved, oxygen pulse, anaerobic threshold (VO2 AT), ventilatory equivalent for oxygen (VE/VO2) will be evaluated. Participant will concurrently be Apple Watch Series 9 (Apple, USA) smartwatch for pre- and post-SaO2 and VO2max assessment.
Echocardiography will be performed on Visit 1 and Visit 3 by independent echocardiographer blinded to randomization result. Right ventricular function will be assessed by measuring fractional area change (FAC), tricuspid annular plane systolic excursion (TAPSE), lateral tricuspid annulus peak systolic velocity (RVS'). Right ventricular diastolic diameter including basal (RVD1), mid ventricle (RVD2) and longitudinal (RVD3) will be measured. Tricuspid regurgitation severity will be graded using vena contracta with \<0.2 cm as mild, 0.2-0.6 cm as moderate, and ≥0.7 cm as severe. Pulmonary regurgitation severity will be graded using semi-quantitative approach using right ventricular outflow view and parasternal short axis view with pressure half time \<100 ms to be graded as severe.
