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ObjectiveThe Ross procedure is an excellent option for children or young adults who need aortic valve replacement because it can restore survival to that of the normal aged-matched population. However, autograft remodeling can lead to aneurysmal formation and reoperation, and the biomechanics of this process is unknown. This study investigated postoperative autograft remodeling after the Ross procedure by examining patient-specific autograft wall stresses.MethodsPatients who have undergone the Ross procedure who had intraoperative pulmonary root and aortic specimens collected were recruited. Patient-specific models (n = 16) were developed using patient-specific material property and their corresponding geometry from cine magnetic resonance imaging at 1-year follow-up. Autograft ± Dacron for aneurysm repair and ascending aortic geometries were reconstructed to develop patient-specific finite element models, which incorporated material properties and wall thickness experimentally measured from biaxial stretching. A multiplicative approach was used to account for prestress geometry from in vivo magnetic resonance imaging. Pressure loading to systemic pressure (120/80) was performed using LS-DYNA software (LSTC Inc, Livermore, Calif).ResultsAt systole, first principal stresses were 809 kPa (25%-75% interquartile range, 691-1219 kPa), 567 kPa (485-675 kPa), 637 kPa (555-755 kPa), and 382 kPa (334-413 kPa) at the autograft sinotubular junction, sinuses, annulus, and ascending aorta, respectively. Second principal stresses were 360 kPa (310-426 kPa), 355 kPa (320-394 kPa), 272 kPa (252-319 kPa), and 184 kPa (147-222 kPa) at the autograft sinotubular junction, sinuses, annulus, and ascending aorta, respectively. Mean autograft diameters were 29.9 ± 2.7 mm, 38.3 ± 5.3 mm, and 26.6 ± 4.0 mm at the sinotubular junction, sinuses, and annulus, respectively.ConclusionsPeak first principal stresses were mainly located at the sinotubular junction, particularly when Dacron reinforcement was used. Patient-specific simulations lay the foundation for predicting autograft dilatation in the future after understanding biomechanical behavior during long-term follow-up.

Introduction: Ross operation provides young adult and pediatric patients a living valve with excellent hemodynamics and no lifelong anticoagulation. However, autograft dilatation is a concern when it leads to aneurysm formation and autograft insufficiency requiring reoperation. Computational simulations of autograft remodeling are potentially effective to predict autograft dilatation, but require zero-pressure geometry and patient-specific material properties for accuracy. Hypothesis: We hypothesized that pulmonary autograft wall stresses estimated from computational simulations using in-vivo imaging would reasonably correlate with the gold standard, wall stresses determined computationally using ex-vivo autograft specimens at zeto-pressure. We recently showed that autograft wall stresses significantly increased immediately after the Ross operation. Our goal was to compare autograft wall stresses based on in-vivo geometry to those based on ex-vivo autografts. Methods: Magnetic resonance imaging (MRI) was obtained in pre-operative Ross patients and used to reconstruct in-vivo autograft geometry. Pre-stress (zero-pressure) geometry was determined. As controls, pulmonary autografts explanted from normal donor hearts underwent micro-computed tomography scans for reconstruction of ex-vivo geometry. Biaxial stretch testing was performed on both intraoperative tissue from Ross patients and on ex-vivo autografts to determine patient-specific material properties. Finite element simulations using LS-DYNA were performed to determine wall stresses. Results: Imaging from ex-vivo pulmonary autografts (n=6) and Ross patients (n=6) were obtained. Peak stresses were 93 kPa for ex-vivo vs. 113 kPa for in-vivo autografts at 25mmHg and 448kPa vs. 558 kPa, respectively at 120mmHg. Conclusions: Wall stresses at pulmonary and systemic systolic pressure predicted by in-vivo MRI imaging reasonably correlated with wall stresses based upon ex-vivo autograft tissue. Computational simulations using in-vivo imaging provides a suitable surrogate for the gold standard simulations using ex-vivo tissue specimens and broadens clinical applicability of computational simulations for patient-specific outcomes. [ABSTRACT FROM AUTHOR]