Biomechanical Analysis of the Ross Procedure in an Ex Vivo Left Heart Simulator

Abstract

Background Neo-aortic pulmonary autografts often experience root dilation and valve regurgitation over time. This study seeks to understand the biomechanical differences between aortic and neo-aortic pulmonary roots using a heart simulator. Methods Porcine aortic, neo-aortic pulmonary, and pulmonary roots (n = 6) were mounted in a heart simulator (parameters: 100 mm Hg, 37 °C, 70 cycles per minute, 5.0 L/min cardiac output). Echocardiography was used to study root distensibility (percentage change in luminal diameter between systole and diastole) and valve function. Leaflet motion was tracked with high-speed videography. After 30 min in the simulator, leaflet thickness (via cryosectioning), and multiaxial modulus (via lenticular hydrostatic deformation testing) were obtained. Results There were no significant differences between aortic and neo-aortic pulmonary leaflet motion, including mean opening velocity (218 vs 248 mm/s, P = .27) or mean closing velocity (116 vs 157 mm/s, P = .12). Distensibility was similar between aortic (8.5%, 1.56 mm) and neo-aortic pulmonary (7.8%, 1.12 mm) roots ( P = .59). Compared to virgin controls, native pulmonic roots exposed to systemic pressure for 30 min had reduced leaflet thickness (630 vs 385 µm, P = .049) and a reduced Young's modulus (3,125 vs 1,089 kPa, P = .077). In contrast, the aortic roots exposed to pressure displayed no significant difference in aortic leaflet thickness (1,317 vs 1,256 µm, P = .27) or modulus (5,931 vs 3,631 kPa, P = .56). Conclusions Neo-aortic pulmonary roots demonstrated equivalence in valve function and distensibility but did experience changes in biomechanical properties and morphology. These changes may contribute to long-term complications associated with the Ross procedure.

Invited Commentary: Will we work out the Ross dilemma in 30 minutes?—Or 30 years?

“…9 The principal changes they observed in the autograft group with simulation were twofold. (1) The closing velocity of the noncoronary leaflet was increased compared to that of the native aortic valve group. This finding may be related to the difference in compliance between the coronary and noncoronary sinuses due to the implanted coronary buttons.…”

“…In this issue of the World Journal for Pediatric and Congenital Heart Surgery , Bryan and coworkers from Stanford report results of mechanical testing of cadaver porcine aortic, pulmonary and “neoaortic,” or “autograft” roots using a “left heart simulator.” 1 They constructed the neoaortic roots by suturing porcine coronary button tissue into 2 of the pulmonary root sinuses, then suturing a cuff of aortic tissue to the distal portion of the pulmonary root, thus mimicking the Ross root. They subjected roots to 30 min of simulated left heart pressures, during and after which they measured a few solid and fluid mechanical characteristics.…”