Inferior Vena Cava Diameter Predicts Nephropathy in Patients Late After Fontan Palliation

Single ventricle congenital heart defect patients have improved survival with Fontan palliation. However, they remain at risk for nephropathy, as indicated by pathologic microalbuminuria. We sought to investigate whether echocardiographic measures of the inferior vena cava diameter (a surrogate for elevated CVP) indexed to the body surface area (iIVC) or cardiac index (CI) can predict the presence of nephropathy in Fontan patients. We performed a single-center case-control study, including 39 asymptomatic Fontan (age 14.8 ± 7.9 years) and 29 healthy controls (age 12.7 ± 2.7 years). The primary outcome was abnormal microalbumin-creatinine ratio (MCR) from the first-morning void urine in Fontan patients. Measurements of iIVC and CI were derived using transthoracic echocardiography by two investigators with a high intra-class correlation coefficient (ICC = 0.97). Group comparison between Fontan and controls as well as between Fontan with normal and abnormal MCR was performed using Fisher's exact and t tests. Pearson and Spearman's correlations and multivariate regressions were performed to analyze the relations between the MCR, iIVC, and CI. Abnormal MCR was noted in 13/39(33%) of Fontan patients. The mean iIVC was larger in the Fontan compared to controls (p < 0.0001) and in Fontan with abnormal MCR compared to those with normal MCR (p = 0.0006). A positive correlation (r = 0.62; p < 0.001) was noted between MCR and iIVC. All patients with abnormal MCR had the iIVC > 1 cm/m². There were no significant relations between the CI and MCR. Significant prevalence of nephropathy late after Fontan palliation warrents screening. Echocardiographic measurement of iIVC could serve as one of the screening measures. The finding of the iIVC diameter > 1 cm/m² should prompt further renal evaluation.