Adults with congenital heart disease who underwent Fontan palliation are at increased risk of premature death and heart transplantation. Identifying factors associated with these events is essential to improve risk stratification and guide timely referral for advanced heart failure management. The Brompton score has been proposed as a risk stratification tool in Fontan patients, but its external validity remains uncertain.

We conducted a retrospective, observational, single-center study including all consecutive patients with a Fontan circulation followed at a tertiary referral center. The primary endpoint was a composite of all-cause death and heart transplantation. Event-free survival was assessed using Kaplan–Meier analysis, and factors associated with the primary endpoint were evaluated using Cox proportional hazards models. The secondary objective was to assess the external validity of the Brompton score through calibration analyses.

A total of 163 patients were included. Median age at baseline was 25 years (IQR 21–30), and median follow-up in the validation cohort was 7.40 years (IQR 3.60–13.59). Thirty-one patients reached the primary endpoint. Freedom from death or transplantation was 88.6% (95% CI 83.5–94.1) at 5 years, 78.7% (95% CI 71.6–86.6) at 10 years, and 77.0% (95% CI 69.4–85.5) at 15 years ( Fig. 1 ). In univariable analysis, age > 30 years (HR 3.23; 95% CI 1.57–6.62; P = 0.0014), history of supraventricular tachycardia (HR 2.57; 95% CI 1.27–5.22; P = 0.0086), history of heart failure requiring chronic diuretic therapy (HR 3.68; 95% CI 1.78–7.61; P = 0.00045), severe ventricular dysfunction (HR 35.25; 95% CI 10.10–123.01; P < 0.001), moderate-to-severe atrioventricular valve regurgitation, reduced peak VO ₂ , and abnormal liver biomarkers were associated with worse outcomes. After exclusion of patients with protein-losing enteropathy, the Brompton score showed limited discrimination (Harrell's C-index 0.30; 95% CI 0.20–0.41) and imperfect calibration (slope 0.62), although each 1-point increase in the score was associated with a higher risk of death or transplantation (HR 1.87; 95% CI 1.36–2.56; P < 0.001).

In this adult Fontan cohort, simple clinical, functional, and echocardiographic markers identified patients at higher risk of death or transplantation. The Brompton score showed limited external validity, highlighting the need for prognostic tools better suited to contemporary Fontan patients.