Pathology of balloon-expandable and self-expanding stents following MRI-guided transapical aortic valve replacement

Balloon-expandable (BE) and self-expanding (SE) prostheses are both used for transcatheter aortic valve replacement (TAVR), but differences in long-term outcome using these types of device are unknown. The study aim was to monitor the histopathology, echocardiographic findings and structural integrity of BE and SE stents in a preclinical model for up to six months after TAVR.

Real-time magnetic resonance imaging (rtMRI)-guided TAVR was performed in 22 Yucatan pigs using either a BE (n = 10) or a SE (n = 12) prosthesis. Follow up echocardiography and MRI studies were performed at one-, three-, and six-month intervals. Additionally, high-contrast radiography was used to assess for strut fractures. The pigs were sacrificed after six months and tissues taken for histopathologic analysis.

Stent malapposition was found in seven BE prostheses (70%), and in three SE prostheses (25%) (p = 0.046). Three of the SE group (25%) had a partial left coronary artery obstruction. The incidence and severity of aortic regurgitation were similar between the BE and SE groups. Three BE prostheses (30%) and one SE prosthesis (8.3%) had a gap between the stent frame and aorta. The mean (±SD) number of strut fractures was 6.1 ± 3.45 and 1.17 ± 2.32 in the BE and SE groups, respectively (p = 0.002). In addition, two implanted BE prostheses (20%) had a consequential compressed stent frame appearance.

Long-term pathologic examination of necropsy specimens from a preclinical model of rtMRI-guided TAVR showed SE stent prostheses to be superior to their BE counterparts in terms of correct valve apposition and durability. These results may be attributed to the differing deployment methods and associated expansion forces employed by the BE and SE stents.