Comparison of Echocardiographically-Calculated Fontan Fenestration Gradient and Catheter-Based Measurement

Background: Patients born with single ventricle anatomy typically undergo surgical palliation in three stages, culminating in the Fontan procedure. Assessment of flow across a Fontan fenestration by Doppler ultrasound theoretically allows for non-invasive estimation of the transpulmonary gradient (TPG). Our objective was to determine the relationship between Doppler-derived mean fenestration gradient (mFG) and direct catheter-based measurements of TPG in patients with fenestrated Fontans.

Methods: We performed a single-center retrospective cohort study of 59 patients with fenestrated Fontans completed between 2000 and 2022. The primary outcome was catheter-based measurement of TPG and the primary predictor was mFG from echo performed within 6 months of the catheterization. Linear regression and R² were used to determine the relationship between predictors and outcomes.

Results: Catheter-based measurements of TPG and mFG were weakly correlated (R² = 0.382, p < 0.001); the regression coefficient was 0.550, with a standard error of 0.09 for every increase in mFG (Cath TPG = 0.55 [mFG] + 1.92). mFG had a slightly better predictive relationship with cath-derived TPG in patients with systemic left ventricles with R² of 0.47, p < 0.004.

Conclusion: mFG accounts for approximately 38% of the variance in catheter-derived TPG. Although mFG is non-invasive and intuitive, mFG in Fontan patients should be interpreted with caution and direct measurement by cardiac catheterization should be considered.