External Validation of a Risk Score Model for Predicting Major Clinical Events in Adults after Atrial Switch Operation for Transposition of the Great Arteries.

Background: A risk model has been proposed to provide a patient individualized estimation of risk for major clinical events (heart failure, ventricular arrhythmia, all-cause mortality) in patients with transposition of the great arteries (D-TGA) repaired by an atrial switch operation. The aim of this study was to externally validate the model. Methods: A retrospective, multicentric, longitudinal cohort of 417 patients with D-TGA (median age 24 years at baseline [interquartile range 18-30], 63% male) independent of the model development and internal validation cohort was studied. Data on risk model predictors (age >30 years, prior ventricular arrhythmia, age >1 year at the atrial switch, moderate or severe right ventricular dysfunction, severe tricuspid regurgitation, and at least mild left ventricular (LV) dysfunction) were collected from the time of baseline clinical evaluation. The performance of the prediction model in predicting risk at 5 years was assessed. Results: Twenty-five patients (5.9%) met the major clinical events endpoint within 5 years. Model validation showed good discrimination between high and low 5-year risk patients (Harrell's C-index of 0.73 (95% CI 0.65-0.81)) but tended to overestimate this risk (calibration slope of 0.20 (95% CI 0.03-0.36)). We separately evaluated predictors of major clinical events in our cohort. History of heart failure and at least mildly impaired sub-pulmonary LV function remained the strongest predictors of major clinical events. Conclusions: We reported the first external validation of a major clinical events risk model in a large D-TGA patient population. Although good discrimination, the model tends to overestimate the absolute 5-year risk. Subpulmonary LV dysfunction appears to be a key marker in the prognosis of patients with Senning and Mustard.