Prevalence and risk factors for low bone density in adults with a Fontan circulation.

Abstract

This study aimed to characterize bone mineral density abnormalities and pathophysiological associations in young adults living with a Fontan circulation. Participants underwent bone mineral density measurement using dual-energy X-ray absorptiometry and serum biochemical analysis, cardiopulmonary exercise and strength testing and transthoracic echocardiography. In our cohort (n=28), 29% had osteopenic-range bone mineral density and one patient was osteoporotic (average hip t score: -0.6±1.1; spine t score: -0.6±0.9). Four patients (14%) had z scores<-2.0. Parathyroid hormone levels were increased compared with laboratory median (6.1±3.5 vs 4pmol/L, P=.01) and 27% had 25-hydroxy-vitamin D<50nmol/L. 25-hydroxy-vitamin D negatively correlated with parathyroid hormone (ρ=-0.53, P=.01) suggesting secondary hyperparathyroidism. Atrioventricular valve systolic to diastolic duration ratio, an echocardiographic measure of diastolic dysfunction, inversely correlated with hip t and z scores (P<.01). Hip t scores were positively associated with oxygen saturations (ρ=0.45, P=.05) and tended to be inversely associated with parathyroid hormone levels (ρ=-0.44, P=.07) and N-Terminal pro b-type natriuretic peptide (ρ=-0.42, P=.08). Many young adults with a Fontan circulation have abnormal bone mineral density. The underlying pathophysiology is likely multifactorial. Possible contributors include secondary hyperparathyroidism, hypoxemia, diastolic cardiac dysfunction and neurohormonal activation. As low bone mineral density is clinically relevant and potentially treatable, assessment of bone mineral density should be part of routine care in this cohort.