O1005: Does Lack of Respiratory Variation in Inferior Vena Cava (IVC) Pressure Waveform Predict Fontan Conduit Obstruction?

Background: The Fontan operation is the final surgical step in single ventricle palliation. Optimal hemodynamics in this type of circulation require unobstructed blood flow from the systemic venous circulation to the pulmonary vascular bed. Due to low-velocity venous flows, assessing Fontan conduit patency can be difficult, and conventional pressure gradients may not accurately reflect the degree of conduit obstruction. We aim to investigate whether blunted respiratory variation in the inferior vena cava (IVC) pressure can predict significant Fontan conduit obstruction.

Methods: We conducted a retrospective study review of patients with extracardiac (EC) Fontan who underwent transcatheter Fontan conduit rehabilitation between 2010 and 2022. Pressure recordings were obtained in the superior vena cava (SVC) and IVC at peak inspiration and expiration before and after conduit rehabilitation. Blunted respiratory variation was defined as a difference between the maximum (expiratory) and minimum (inspiratory) pressure of less than 3 mmHg. Significant cath gradient was defined as a difference greater than 2 mmHg between mean pressure below and above the Fontan conduit. Descriptive statistics and two-tailed t-tests were performed. Pooled data are reported as median (IQR).

Results: A total of 31 patients met the inclusion criteria, with 65% males and a median age at intervention of 22 (17-25) years. 22 patients had EC fenestrated Fontan conduits. Twelve patients (40%) had EC homograft conduits; Gore-Tex grafts were used in the remaining 19 patients (60%). Half of the patients (n=16) had Fontan-associated liver disease (FALD) at the time of intervention. The median Fontan conduit diameter at implant was 18 (17-20) mm, and the median minimum conduit diameter at the time of intervention was 13 (11-14) mm. Blunted respiratory variation in the IVC waveform was present in 83% of the patients before stent implantation while only 25% of the patients had a gradient >2 mmHg prior to intervention. There was significant improvement in respiratory variation following stent implantation (p= 0.001). Utilizing both methods together (i.e., presence of blunted respiratory variation and/or a pressure gradient ≥ 2 mmHg) correctly predicted significant obstruction in 90% of the patients. Half of the patients with significant conduit obstruction had no measurable pressure gradient between the proximal IVC and the rest of the Fontan pathway.

Conclusion: Our study demonstrates that lack of respiratory variation in the IVC pressure more reliably predicts Fontan conduit obstruction than conventional pressure gradients. Based on these findings, we hypothesize that non-invasive Doppler surrogates of respiratory variation may help identify EC Fontan conduit obstruction and lead to earlier treatment and improved outcomes for patients.