Vitamin D Deficiency and Secondary Hyperparathyroidism in Adult Fontan Patients

Background: The prevalence of vitamin D deficiency and secondary hyperparathyroidism (sHPT) in adult Fontan patients remains unstudied, and the role of vitamin D and parathyroid hormone (PTH) levels in assessing heart and circulatory failure in these patients is unclear.

Methods: We compared vitamin D deficiency and sHPT prevalence in adult Fontan patients (n = 35; mean age 33 ± 7.5 years) to adults with mild congenital heart disease (ACHD, n = 14). We analyzed associations between laboratory measurements, patient characteristics, and clinical events.

Findings: Vitamin D deficiency was highly prevalent in both Fontan patients and ACHD controls (76.5 % vs. 71.4 %, p = 0.726). sHPT was exclusively present in Fontan patients (31.4 %). PTH levels correlated with NYHA class (r = 0.412), O2 saturation (r = -0.39), systemic ventricular function (r = 0.465), and NT-proBNP levels (r = 0.742). 25-hydroxyvitamin D showed an inverse correlation with NYHA class and systemic ventricular function (both r ≤ -0.38). Fontan patients with sHPT had a higher incidence of prior hospitalization for worsening heart failure and atrial arrhythmias compared to Fontan patients without HPT or ACHD controls. (Hospitalization: Fontan with HPT vs. Fontan without HPT: OR 5.46 [95 % CI 1.25-23.86], p = 0.021; arrhythmia: Fontan with HPT vs. Fontan without HPT: OR 1.96 [95 % CI 1.13-3.4], p = 0.035; ACHD: OR 11.45 [95 % CI 1.7-77.28], p=<0.001). PTH showed significant correlation with inflammatory markers, particularly with GDF-15 (r = 0.8).

Conclusion: Our study is the first to demonstrate a high prevalence of vitamin D deficiency and sHPT in adult Fontan patients. As PTH strongly correlates with heart failure severity, it seems to be a promising biomarker in Fontan patients.