Unique Systemic Vasodilatation of Post-fontan Physiology Compared with Biventricular Physiology: How Different is it on the CI-SVRI Plot?

Fontan circulation is characterized by elevated central venous pressure (CVP) and reduced preload, resulting in low perfusion pressure (PP). Maintaining adequate PP and low CVP may prevent multi-organ failure in post-Fontan patients. Vasodilatation, characterized by low systemic vascular resistance index (SVRI) and high cardiac index (CI), is a poor prognostic predictor. CI–SVRI plots have been proposed to visualize Fontan hemodynamics; however, direct comparisons with biventricular physiology are limited. We compared catheterization data between post-Fontan and repaired tetralogy of Fallot (TOF) patients, focusing on PP, and visualized hemodynamic differences using CI–SVRI plots. This single-center retrospective study included 45 post-Fontan patients and 28 with repaired TOF aged ≥ 18 years who underwent cardiac catheterization and cardiopulmonary exercise testing between 2017 and 2023. Patients were stratified by the percentage of normal peak oxygen uptake to account for exercise tolerance. Hemodynamic data were plotted on CI-SVRI plots. Logistic regression was used to identify independent correlates of Fontan physiology. Despite similar CI, post-Fontan patients had significantly higher CVP and lower systemic arterial pressure, resulting in lower PP and SVRI, than those with repaired TOF. These differences persisted after adjusting for similar exercise capacity. In CI-SVRI plots, patients with post-Fontan physiology occupied the lower-left area more frequently, indicating low PP and vasodilated systemic circulation. PP was independently associated with Fontan physiology after adjusting for confounding variables. Reduced PP due to systemic vasodilatation, even with a preserved CI, represents a distinct feature of Fontan physiology and may define hemodynamic targets beyond low CVP.