Bicuspidalization of the Native Tricuspid Aortic Valve: A Porcine in Vivo Model of Bicuspid Aortopathy

Abstract

Objective: To examine early histologic changes in the aorta exposed to bicuspid flow. Material and Methods: A porcine bicuspid aortopathy model was developed by suturing aortic cusps. Of nine pigs, eight underwent sham surgery (n=3) or bicuspidalization (n=5); one was used as an intact control. Wall shear stress (WSS) was assessed by computational fluid dynamics (CFD). Animals were exposed to normal or bicuspid flow for 48 h and were then euthanized for histologic examinations. Results: No animal died intraoperatively. One animal subjected to bicuspidalization died of respiratory failure during postoperative imaging studies. Echocardiography showed the aortic valve area decreased from 2.52±1.15 to 1.21±0.48 cm² after bicuspidalization, CFD revealed increased maximum WSS (10.0±5.2 vs. 54.0±25.7 Pa; P=0.036) and percentage area of increased WSS (>5 Pa) in the ascending aorta (30.3%±24.1% vs. 81.3%±13.4%; P=0.015) after bicuspidalization. Hematoxylin-eosin staining and transmission electron microscopy showed subintimal edema and detached or degenerated endothelial cells following both sham surgery and bicuspidalization, regardless of WSS distribution. Conclusion: A bicuspid aortic valve appears to increase aortic WSS. The endothelial damage observed might have been related to non-pulsatile flow (cardiopulmonary bypass). Chronic experiments are needed to clarify the relationship between hemodynamic stress and development of bicuspid aortopathy.

Keywords: bicuspid aortic valve; bicuspidalization; pig; wall shear stress.

Fig. 1 CFD contour plots of WSS at peak systole, and bar graphs comparing WSS data between the sham surgery and bicuspidalization groups. (A) Simulation for the intact control animal (anterior view). (B) Simulation for the three animals subjected to sham surgery (anterior view). (C) Simulation for the four animals subjected to bicuspidalization (anterior and posterior views). (D) Bar graph of maximum WSS in the sham surgery and bicuspidalization groups. (E) Bar graph of the percentage of increased WSS (WSS >5 Pa) in the ascending aorta in the sham surgery and bicuspidalization groups.

Fig. 2 Representative H&E-stained tissue sections from the greater and lesser curvatures of the proximal ascending and from the proximal descending aorta from the intact control animal (left panel) and animals subjected to sham surgery (middle panel) or bicuspidalization (right panel). The intimal layer is seen in the upper portion of each image. (A) Low-power field imaging shows subintimal edema in all three aortic areas of animals subjected to sham surgery and those subjected to bicuspidalization surgery. Bar=100 µm. (B) High-power-field imaging shows an irregular endothelial covering, with degeneration of endothelial cells in all three aortic areas of animals subjected to either sham surgery or bicuspidalization. Arrows: degenerated endothelial cells; Arrowheads: detached endothelial cells. Bar=10 µm.

Fig. 3 Transmission electron micrographs of tissues from the ascending (A, B) and descending aortas (C, D) of the intact control animal. The endothelial cell marked by an arrow on each of the low-power field images (A, C) is also marked by an arrow on the corresponding high-power field images (B, D). Flat endothelial cells with few nuclear deformities are seen in both areas of the thoracic aorta.

Fig. 4 Transmission electron micrographs of tissues from the ascending (A, B) and descending aortas (C, D) of an animal subjected to sham surgery. The endothelial cell marked by an arrow on each of the low-power field images (A, C) is also marked by an arrow on the corresponding high-power field images (B, D). Cell swelling, nuclear deformity, and irregularly protruding cell processes on the luminal surface are seen in both areas of the thoracic aorta.

Fig. 5 Transmission electron micrographs of tissues from the ascending (A, B) and descending aortas (C, D) of an animal subjected to bicuspidalization. The endothelial cell marked by an arrow on each of the low-power field images (A, C) is also marked by an arrow on the corresponding high-power field images (B, D). Cell swelling, nuclear deformity, and irregularly protruding cell processes on the luminal surface are seen in both areas of the thoracic aorta.