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Is There a Difference Between Balloon-Expandable and Self-Expanding Stents for Transapical Aortic Valve Replacement?
Bogdan Kindzelski, Ming Li, Dumitru Mazilu, Keith Horvath.
National Heart, Lung and Blood Institute, NIH, Bethesda, MD, USA.
OBJECTIVE: While both balloon expandable (BE) and self-expanding (SE) prostheses are used for transapical aortic valve replacement (TAVR), differences between these types of devices are unknown. Histopathology, aortic insufficiency (AI) assessment, and structural integrity of BE and SE stents in a preclinical model were analyzed up to 6 months post-TAVR.
METHODS: Real-time MRI guided TAVR was performed in 22 Yucatan Swine using BE (10) or SE (12) prostheses. Follow-up echocardiography and MRIs were performed at 1, 3, and 6 month intervals. Additionally high contrast radiographs were used to assess for any strut fractures. Pigs were sacrificed at 6 months for histopathologic analysis. Transverse sections of the aortic root and stent/valve assembly were examined by light microscopy for the presence of inflammation, calcification, thrombus and neointimal formation, endothelialization, aortic wall integrity, patency of coronary ostia, and valve apposition. AI was assessed by echocardiography and correlated with left ventricular hypertrophy or dilatation.
RESULTS: No statistically significant differences were noted in leaflet thrombus and fibrin deposition, pannus formation, neointimal formation, calcification, or hemorrhage between BE and SE groups. Stent malapposition was found in 7 BE (70%) and 3 SE (25%) prostheses (p=0.046). There were 3 (25%) specimens with partial coronary ostia obstruction in the SE group. In the BE group, 2 (20%) specimens had partially collapsed prosthetic leaflets. The incidence and severity of AI along with the mean heart weight upon fixation were similar between BE and SE groups. 3 BE (30%) and 1 SE (8.3%) prostheses had a gap between the stent frame and aorta. Strut fractures were 6.1 ± 3.45 and 1.17 ± 2.32 (mean ± SD) in the BE and SE groups, respectively (p=0.002). Additionally, 2 (20%) implanted BE prostheses had a compressed stent frame appearance as a result of the strut fractures.
CONCLUSIONS: Long-term pathology results from necropsy specimens in a preclinical model of rtMRI guided TAVR demonstrate that SE are superior to BE stent prostheses in terms of proper valve apposition and durability. These results may be attributed to differing deployment methods and associated expansion forces employed by BE and SE stents.
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