Abstract 4139930: Low Ventricular Stiffness is Associated with Suboptimal Outcomes in Single Right Ventricle Patients after the Fontan Operation: A Novel Phenotype

Introduction: Despite a rigorous screening process, including cardiac catheterization, a subset of single right ventricle (SRV) patients demonstrate suboptimal short-term outcomes after the Fontan operation. The goal of this study was to perform a comprehensive assessment of diastolic function in pre-Fontan SRV patients using invasive reference-standard measures and determine their associations with post-Fontan outcomes. Methods: Children 2-6 years old with SRV physiology undergoing pre-Fontan heart catheterization were recruited prospectively. SRV patients were divided into those who had an optimal or suboptimal outcome. A suboptimal outcome was defined as length of stay ≥14 days or heart transplant/cardiac death in first year after Fontan. Patients with hemodynamically insignificant patent ductus arteriosus referred for catheterization closure were recruited as controls. Patients underwent pressure-volume loop analysis using reference-standard methods. The measure of ventricular stiffness, β, was obtained via preload reduction. Cardiac magnetic resonance imaging for extracellular volume (ECV) and serum draws for matrix metalloproteinase (MMP) activity were performed. Results: Of 19 SRV patients, 9 (47%) had a suboptimal outcome. 15 controls were included. Demographic and catheterizations are shown in Table 1. Echocardiographic and MRI data are shown in Table 2. Patients with suboptimal outcomes had lower ventricular stiffness, lower ECV, and lower MMP-2 compared to patients with optimal outcomes (Figure 1). Patients with suboptimal outcomes had similar stiffness to biventricular controls. Patients with optimal outcome had less total fluid in the first 24 hours than the suboptimal group (1107 (IQR 953, 1303) vs. 1482 (IQR 1305, 1598) mL, p = 0.03). The only invasive measure that had an association with suboptimal outcome was β, p=0.038. Conclusion: SRV patients with suboptimal outcome after Fontan had lower ventricular stiffness compared to patients with optimal outcome. Lower stiffness led to an increased need for fluid resuscitation and higher chest tube output after Fontan. The usual response in chronically increased RV afterload is for the RV to hypertrophy and stiffen over time in order to maintain cardiac output. This is not seen in low SRV stiffness patients and may represent a maladaptive extracellular matrix response to chronic afterload elevation. This novel phenotype that may have important clinical implications and requires further study.