Late Positive Remodeling and Late Lumen Gain Contribute to Vascular Restoration by a Non-Drug Eluting Bioresorbable Scaffold: A Four-Year Intravascular Ultrasound Study in Normal Porcine Coronary Arteries

BACKGROUND—The interplay between mechanical dilatation, resorption, and arterial response following implantation of bioresorbable scaffolds is still poorly understood. METHODS AND RESULTS—Long-term geometric changes in porcine coronary arteries in relation to gradual degradation of bioresorbable scaffolds were assessed in comparison with bare metal stents (BMS). Intravascular ultrasound (IVUS)-derived lumen, outer stent/scaffold, and reference vessel areas were evaluated in 94 polymer scaffolds and 46 BMS at 5 days and 3, 6, 12, 18, 24, and 55 months, in addition to polymer scaffold radial crush strength and molecular weight (MW) at 3, 6, and 12 months. BMS outer stent area and lumen area remained constant through 55 months (P=0.05, but within 1 standard deviation of 100%, and P=0.58, respectively), while significant increases were exhibited by polymer-scaffolded vessels with the maximum late lumen gain at 24 months, paralleled by the outer scaffold area increase, and then remaining at that increased level at 55 months (P