Finite Element Modeling of the Pulmonary Autograft at Systemic Pressure before Remodeling Peter B. Matthews, Choon-Sik Jhun, Stephanie Yaung, Ali N. Azadani, Julius M. Guccione, Liang Ge, Elaine E. Tseng Department of Surgery, University of California at San Francisco Medical Center and San Francisco Veterans Affairs Medical Center, San Francisco, CA, USA Aortic valve replacement with the pulmonary auto- graft, though originally implanted via a subcoronary technique, has been most commonly been performed as a full aortic root replacement since the late 1980s (1). However, late failure from autograft dilatation requires reoperation, and this is a critical limitation of the procedure (2-6). Significant autograft dilatation leading to aortic regurgitation or aneurysm formation occurs after biological remodeling when the pul- monary root, which is accustomed to pulmonary pres- sures, is subjected to systemic pressures within the aorta. Biologic remodeling involves reduced elastin and elastin fragmentation in the media of the wall, increased collagen and fibrosis, and hypertrophy of the smooth muscle (7). Remodeling is thought to be triggered by increases in autograft wall stress from pulmonary to systemic pressure; however, the auto- graft wall stress that occurs on an initial exposure to aortic pressures is unknown. Wall stress may be deter- mined by computational simulations (8) of the auto- Presented in part at the 94th Annual Clinical Congress of the American College of Surgeons, Owen H. Wangensteen Surgical Forum, San Francisco, CA, 14th October 2008, and as a poster at the Fifth Biennial Meeting of the Society for Heart Valve Disease, 27th- 30th June 2009, Berlin, Germany Address for correspondence: Elaine E. Tseng MD, UCSF Medical Center, Division of Cardiothoracic Surgery, 500 Parnassus Avenue, Suite W405, Box 0118, San Francisco, California 94143-0118, USA e-mail: elaine.tseng@ucsfmedctr.org © Copyright by ICR Publishers 2011 Background and aim of the study: Pulmonary auto- graft dilatation requiring reoperation is an Achilles’ heel of the Ross procedure, as exposure to systemic pressure increases autograft wall stress, which may in turn lead to tissue remodeling and aneurysmal pathology. However, the magnitude of autograft wall stress with the Ross procedure is unknown. The study aim was to develop a realistic finite element (FE) model of the autograft, and to perform simula- tions at systemic pressure to determine wall stress distribution immediately after the Ross operation. Methods: The porcine pulmonary root geometry was generated from high-resolution microcomputed tomography (microCT) images to create a mesh com- posed of hexahedral elements. Previously defined constitutive equations were used to describe the regional material properties of the native porcine pulmonary root. The anterior and posterior pul- monary arteries, and each of the pulmonary sinuses, were best described by non-linear, anisotropic Fung strain energy functions, and input individually into the model. Autograft dilatation and wall stress dis- tribution during pulmonary and systemic loading prior to remodeling were determined using explicit FE analysis in LS-DYNA. Results: The autograft was highly compliant in the low-strain region, and the majority of dilation occurred with <30 mmHg of pressurization. During pulmonic loading, a typical inflation/deflation was observed between systole and diastole, but the auto- graft remained almost completely dilated throughout the cardiac cycle at systemic pressure. Although the systolic blood pressure was 380% greater in the aortic than in the pulmonary position, the peak systolic diameter was increased by only 28%. The maximum principal wall stress increased approximately 10-fold during systole and 25-fold during diastole, and was greater in the sinus than the distal artery for all sim- ulations. Conclusion: Under systemic loading conditions, the pulmonary autograft remained fully dilated and experienced large wall stresses concentrated in the sinus. The future correlation of this model with explanted autografts may lead to an improved under- standing of tissue remodeling following the Ross procedure. The Journal of Heart Valve Disease 2011;20:45-52