Chronic arterial responses to stent implantation: A serial intravascular ultrasound analysis of Palmaz-Schatz stents in native coronary arteries

Objectives. We used intravascular ultrasound (IVUS) imaging to evaluate the chronic vessel responses to Palmaz-Schatz stents. Background. Palmaz-Schatz stents have been shown to inhibit early elastic recoil and late arterial remodeling while triggering neointimal hyperplasia. However, changes occurring in native vessels surrounding stent struts have not been well studied. Methods. Postintervention and follow up (mean [+/-SD] 5.4+/-3.8 months) serial IVUS imaging was performed in 25 stents without restenosis and 24 with in-stent restenosis. Intravascular ultrasound imaging using automatic transducer pullback at 0.5 mm/s allowed measurement at 1-mm axial increments of external elastic membrane (EEM), stent and lumen cross-sectional areas (CSAs) and calculation of peristent plaque plus media (P+M=EEM-stent) CSA, intrastent plaque (stent-lumen) CSA, arterial remodeling (Delta EEM CSA), tissue growth outside the stelae (Delta P+M CSA) and tissue growth within the stent (Delta stent-lumen CSA). Volumes were calculated using the Simpson rule. Results. Mean EEM CSA increased significantly from 16.9+/-5.0 mm(2) after intervention to 18.4+/-4.9 mm(2) at follow-up (p <0.0001), reflecting an Increase in P+M CSA surrounding the stent (1.6+/-1.3 mm(2)). Greater tissue growth within the stent (2.4+/-2.2 mm(2)) correlated weakly, but directly with tissue growth surrounding the stent (r=0.356, p=0.0121). The ratio of peristent/intrastent tissue growth correlated weakly with arterial remodeling (r=0.282, p=0.0525). Restenotic stents had more tissue growth both within and surrounding the stent than did nonrestenotic stents. Volumetric measurements, which could be obtained in 15 lesions, showed similar results. Conclusions. After implantation there is a chronic increase in plaque mass both within and surrounding the stents, The increase in peristent plaque mass is associated with adaptive remodeling.