Biomechanics of Failed Pulmonary Autografts Compared to Native Aortic Roots

Background Progressive autograft dilatation after a Ross operation suggests that remodeling does not effectively reproduce native aortic root biomechanics. In the first of this two-part series, we compared mechanical properties of explanted autografts to pulmonary roots at pulmonary pressures. The goal of this study was to compare mechanical properties of explanted autografts to native aortic roots at systemic pressures. Methods Autograft specimens were obtained from patients undergoing reoperation after Ross operation. For comparison, native aortic roots were obtained from unused donor hearts. Biaxial stretch testing was performed to determine tissue mechanical properties. Tissue stiffness was determined at patient-specific physiologic stresses corresponding to systemic pressures (80 and 120 mm Hg) and hypertensive state (200 mm Hg). Results Nonlinear stress-strain curves were present for both failed autografts and native aortic roots. Explanted autografts were significantly more compliant than native aortic roots at 80 mm Hg (1.53 ± 0.68 versus 2.99 ± 1.34 MPa; p  = 0.011), 120 mm Hg (2.54 ± 1.18 versus 4.93 ± 2.21 MPa; p  = 0.013), and 200 mm Hg (4.79 ± 2.30 versus 9.21 ± 4.16 MPa; p  = 0.015). Autograft tissue stiffness at 80, 120, and 200 mm Hg was not correlated with age at the time of Ross operation ( p  = 0.666, p  = 0.639, and p  = 0.616, respectively) or time in the systemic circulation ( p  = 0.635, p  = 0.637, and p  = 0.647, respectively). Conclusions Failed pulmonary autografts retained a nonlinear response to mechanical loading typical of healthy arterial tissue. Despite similar wall thickness between autografts and aorta, autograft stiffness in this patient population was significantly reduced compared with native aortic roots. We demonstrated that biomechanical remodeling was inadequate in these specimens to achieve native aortic mechanical properties, which may have resulted in progressive autograft root dilatation.