Shape Variations in Right Ventricular 3D Geometry Are Associated With Adverse Outcomes in Hypoplastic Left Heart Syndrome Patients: A Fontan Outcomes Registry Using CMR Examinations (FORCE) Study.

BACKGROUND: Assessment of the systemic right ventricle (RV) is critical for patients with hypoplastic left heart syndrome (HLHS). Traditional imaging metrics fail to capture the RV's complex geometry and remodeling in HLHS, limiting risk stratification. We aimed to apply statistical shape modeling to a large multicenter cohort of cardiac magnetic resonance data sets to define RV shape variants and evaluate associations with clinical outcomes.

METHODS: Cardiac magnetic resonance from the FORCE (Fontan Outcomes Registry Using CMR Examinations) was analyzed for patients with HLHS post-Fontan. Three-dimensional RV models were segmented at end-diastole and processed using statistical shape modeling (ShapeWorks). Shape modes were extracted via principal component analysis and correlated with RV function, tricuspid regurgitation, remnant left ventricular morphology, and clinical outcomes, including mortality, transplant, and a composite adverse outcome including heart failure.

RESULTS: The mean RV shape template of 329 patients with HLHS (mean age, 14.7±6.3 years) depicted a circumferentially dilated RV with loss of septal concavity. RV end-diastolic volume was independently associated with composite adverse outcome (odds ratio, 6.50; P=0.001). Distinct shape modes were identified, including an apical bulge phenotype that was independently associated with composite adverse outcome (odds ratio, 2.45; P=0.047) and mortality/transplant (odds ratio, 4.24; P=0.004). This variant also correlated with RV dilation, hypertrophy, and impaired regional strain. A spheroidal shape was associated with ≥moderate tricuspid regurgitation and tricuspid annular dilation. Remnant left ventricular morphology influenced RV shape and function but not transplant-free survival.

CONCLUSIONS: Our statistical shape modeling analyses provide novel insights into RV geometric remodeling in HLHS and identify specific shape phenotypes associated with dysfunction and adverse outcomes. Shape-based metrics offer additive prognostic value beyond conventional volumetric analysis, with potential implications for risk stratification and surgical decision-making in single-ventricle physiology.