Association between the inferior vena cava collapsibility index and Fontan pressure in patients with Fontan physiology: a two-centre prospective pilot study

INTRODUCTION: Patients with functional single ventricle anatomy undergo staged surgical palliation in early childhood culminating in the Fontan procedure whereby the inferior vena cava is connected to the pulmonary artery. Fontan circulation inherently requires elevated central venous pressure to maintain adequate pulmonary blood flow; however, excessive elevation is associated with morbidity and mortality. In adults, a key component of echocardiographic evaluation is the use of a "sniff test" as a surrogate of downstream right atrial pressure. This technique has not yet been validated as a measure of pressure assessment in patients with Fontan circulation. METHODS: This was a two-center prospective study of patients with functional single ventricle physiology who had undergone the Fontan procedure and were undergoing previously scheduled transthoracic echocardiogram and cardiac catheterization as part of their standard clinical care. We correlated collapsibility index on echocardiogram with directly obtained Fontan pressure measurements from cardiac catheterization performed the same day. RESULTS: 15 patients were enrolled and analyzed for the study. Collapsibility index demonstrated an inverse correlation with Fontan pressure, (Pearson r = -0.72, R2 = 0.51, p = 0.003). Collapsibility index was significantly higher for patients with non-elevated Fontan pressure (45% vs 30%, p = 0.0005). Using a collapsibility index threshold of 35.0% demonstrated a 100% positive predictive value for detecting elevated Fontan pressure (greater than 14 mmHg). CONCLUSIONS: There was a significant inverse relationship between the collapsibility index and Fontan pressure. These findings may suggest a possible association between collapsibility index and Fontan pressure, warranting further investigation in larger studies.