Stage 3 Fontan Operation Liver Ultrasound Study

The Fontan repair for single ventricle congenital heart lesions consists of three stages. This surgery has enable pediatric patients who have the repair to live into adulthood. Stage 3 of the surgery introduces immediate congestion of blood in the liver by increasing central venous pressure (CVP). CVP is the blood pressure within the vena cava, a major blood vessel in the body. Many patients later develop progressive liver fibrosis (stiffness) possibly as a result of increased blood pressure. Liver stiffness is increased both by congestion and fibrosis. Liver fibrosis has significant health risks and may complicate the patient's future healthcare. There are no established, noninvasive means of detecting the liver fibrosis until it becomes severe. Acoustic radiation force impulse (ARFI) elastography, an ultrasound technique, can measure the stiffness of the liver safely from outside the body. The investigators hypothesize that liver stiffness will be increased by stage 3 of the Fontan operation due to onset of liver congestion. Using ARFI, the investigators will measure liver stiffness before and immediately after stage 3 of the Fontan operation, when congestion of blood is likely the only contributor to any change in liver stiffness. The investigators will follow the trend of liver stiffness at six months by repeating the ARFI imaging.