Stent Struts and Articulations

OBJECTIVES AND RATIONALE: To evaluate the hoop strength, the pushability, and the radiopacity of endovascular stents depending on their design. MATERIAL AND METHODS: The Palmaz Medium (rectangular stent struts, no articulation = RE-NA), the Palmaz-Schatz Long-Medium (rectangular stent struts, central articulations = RE-CA), and the 39 mm and 29 mm version of the Palmaz Corinthian Stent (arch-like stent struts, omega hinges = AR-OH 1 and AR-OH 2) were included in the study. Hoop strength, pushability, and radiopacity were assessed in-vitro. A radiopacity score (RS)-ranging from 0 = invisible, 1 = poor, 2 = average, 3 = good, and 4 = very good-was used. RESULTS: Mass adjusted hoop strength was nearly the same for the AR-OH 1 and the AR-OH 2 (AR-OH 1: 159.2 N/g*cm; AR-OH 2: 156.5 N/g*cm). Their hoop strengths per unit mass significantly exceeded that of a RE-NA (125 N/g*cm) and that of a RE-CA (75.3 N/g*cm). The most pushable stent was the AR-OH 2 (0.54 1/N) followed by the AR-OH 1 (0.47 1/N) and the RE-CA (0.169 1/N). Because of multiple stent dislocations, the RE-NA was considered nonflexible. At spotfilm mode the RE-NA was the most visible stent (RS 3.5) followed by the AR-OH 1 (RS 3.25), the RE-CA (RS 3.12), and the AR-OH 2 (RS 1.9). At continuous fluoroscopy the AR-OH 1 (RS 1.8) was better than the RE-CA (RS 1.125), the RE-NA (RS 1.0), and the AR-OH 2 (RS 0.6). At 7.5 pulses per second the RE-NA (RS 1.3) performed slightly better than the AR-OH 1 (RS 1.25), and clearly better than the RE-CA (RS 0.8), and the AR-OH 2 (RS 0.3). CONCLUSION: Overall, the ideal stent-having high hoop strength, a low profile, a good pushability, and a good radiopacity-still does not exist. However, by changing strut design (from rectangular to arch-like struts) and by inserting articulations, hoop strength and pushability can be improved without reducing radiopacity.