Thyroid dysfunction in pediatric Fontan patients is associated with unfavorable hemodynamic status and severity of protein-losing enteropathy: A report from the Fontan care network.

Background: Thyroid dysfunction may have adverse effects on Fontan hemodynamics. Data on thyroid function in pediatric Fontan patients with or without protein-losing enteropathy (PLE) are limited. Methods: This retrospective multicenter study included 67 Fontan patients (median age 10.9 years; 35.8% female; 28.4% PLE) in whom thyroid function testing was performed. Results: Subclinical hypothyroidism (SHT) was present in 16 (23.9%) patients. Subjects with SHT had significantly lower systolic blood pressure (p = 0.014) and body weight z-score (p = 0.006), were in a worse New York Heart Association (NYHA) functional class (p = 0.004), were more often pacing dependent (p = 0.007), and were more likely to have PLE (p = 0.033, 8/19 (42.1%) patients). Serum thyroid stimulating hormone (TSH) levels were significantly higher in patients with NYHA class ≥ II (p = 0.005), significant atrioventricular valve regurgitation (p = 0.023), elevated serum natriuretic peptides (p = 0.031), and in those with PLE (p = 0.002). Patients with active PLE had significantly higher TSH levels than those in remission (p = 0.003). A strong inverse relationship was found between lower free triiodothyronine (fT3) levels and natriuretic peptides (r: -0.599, p = 0.040). Using binary logistic regression analysis we found that worse NYHA class was an independent predictor of SHT (OR 4.2; 95% CI 1.1-16.1, p = 0.036). Conclusions: Subclinical thyroid dysfunction is common in Fontan, particularly in patients with hemodynamic derangements and PLE. Future studies are needed to address the prognostic implications of thyroid dysfunction in the Fontan population.