Determinants of neointimal strut coverage in bio-degradable polymer coated ultrathin strut stent

Abstract

Abstract Introduction Incomplete strut coverage (ISC) is the most important morphometric determinant of stent thrombosis. Determinants of ISC have been studied in thick and thin strut stents. Purpose To identify morphometric factors causing ISC in the biodegradable polymer-coated ultra-thin strut drug eluting stent (BP-UTS-DES) that are designed to encourage better strut coverage. Methods Patients undergoing implantation of a 65μm BP-UTS-DES had opportunistic OCT during staged PCI to assess strut coverage at 90 days. Images were analysed offline by experienced operators blinded to patient and procedural data. Neointimal thickness (NIT, μm) was measured as the minimum endoluminal distant between the strut and lumen border. All malapposed struts were considered uncovered. ISC was defined as <100% covered struts in a frame. Stepwise logistic regression using multiple morphometric variables was used to identify independent determinants of ISC including markers of circumferential distribution of neointimal growth (CVS,NUS,RUS), symmetry of stent expansion (SEI, AVS, MAS) in each cross section and the geographical location of the frame along the axis of the stent. Results We analysed 11652 frames of 65 stents (1976 mm) in 46 arteries of 40 patients. All stents were post dilated. 95.6% arteries had >20mm stents, 39.1% were overlapped and 15.2% were chronic total occlusions. Malapposition was seen in 2.6% of all struts and 39.2% of uncovered struts. The proportion of covered struts decreased as indices of circumferential uniformity of distribution of neointimal hyperplasia increased (CVS: r=0.37, p<0.001; RUS: r=0.36, p<0.001; NUS: r=0.52, p<0.001). As uniformity of stent expansion improved (SEI increased) strut coverage and circumferential uniformity of neointimal hyperplasia increased (CVS, NUS and RUS decreased) suggesting that distribution of neointimal growth becomes homogeneous as uniformity of stent expansion improves (Fig. 1). Determinants ISC is shown in Table 1. Conclusion SEI but not AVS or MAS determines ISC. Compared to the distal third of the stent frames in the middle third had lower and the proximal third had high risk of ISC. Funding Acknowledgement Type of funding sources: None.