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Biomechanics of Pulmonary Autograft Remodeling: Determining In Vivo Stresses on Autograft Roots at One Year Follow-up
Yue Xuan1, Matt Zweber1, Ismail El-Hamamsy2, Francois Pierre-Mongeon2, Richard L. Leask3, Alexander Emmott3, Aly Ghoneim3, Elaine E. Tseng1, Liang Ge1.
1UCSF Medical Center and San Francisco VA, San Francisco, CA, USA, 2Montreal Heart Institute, Montreal, QC, Canada, 3McGill University, Montreal, QC, Canada.

Biomechanics of Pulmonary Autograft Remodeling: Determining In Vivo Stresses on Autograft Roots at One Year Follow-up
1Yue Xuan, 1Matt Zweber, 2Ismail El-Hamamsy, 3Francois-Pierre Mongeon, 4Richard L. Leask, 4Alexander Emmott, 5Aly Ghoneim, 1Elaine E. Tseng, 1Liang Ge.
1Department of Surgery, University of California San Francisco Medical Center and San Francisco VA Medical Center, San Francisco, CA USA; 2Divison of Cardiac Surgery, and 3Department of Medicine, Montreal Heart Institute, Montreal, Canada; 4Department of Chemical Engineering and 5Faculty of Medicine, McGill University, Montreal, Canada
Objective: The Ross procedure has favorable long-term survival benefits while also providing excellent hemodynamics, freedom from oral anticoagulation, and living tissue for children and young adults. However, aneurysmal remodeling of autograft can require reoperation. To understand the biomechanics of autograft remodeling, we previously demonstrated elevated autograft wall stress without appreciable dilatation immediately after surgery. We also measured average wall stress in a single Ross patient. In this study, we used patient-specific models to investigate changes in autograft stress one year after surgery.
Methods: Five patients who underwent Ross procedure as full root replacement were included in this study. Cine magnetic resonance imaging (MRI) one year post-operatively was used to create the 3D geometry of aorta and pulmonary autograft for each patient. Material properties and wall thickness of autograft and aorta were measured from biaxial stretching and incorporated. The multiplicative Lagrangian formulation was used to calculate the prestress while anisotropic hyperelastic material model was used. Simulations were performed using LS-DYNA to determine autograft wall stress.
Results: Average thickness of pulmonary autografts was 1.190.11mm. Average peak first principal stress of autograft roots was 0.680.32MPa with range of 1.103MPa to 0.31MPa at 120mmHg (figure 1). Average peak second principal stress was 0.260.08MPa with range of 0.37MPa to 0.15MPa.
Conclusions: We determined the in vivo stress on 5 autograft roots from Ross patients one year post-operatively using in vivo MRI imaging and patient-specific material properties. Peak stresses were mainly located in sinotubular junction. Future studies will incorporate follow-up geometries of those patients and correlate the remodeling to peak stress distribution.


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