ARE SELF-EXPANDING STENTS SUPERIOR TO BALLOON-EXPANDED IN DILATING AORTAS - AN EXPERIMENTAL-STUDY IN PIGS

Objective: To study the stent/vessel interaction and distensibility fo llowing the natural increase in vascular diameter using self-expanding and balloon-expanded stents. Design: Open experimental study. Setting : Animal laboratory, university hospital. Materials and Methods: Eight Palmaz (P) and eight Gianturco (G) stents were transluminally placed in the infrarenal aortas of 16 pigs. Pulsatile diameter changes above, at and below the stents were non-invasively monitored with an ultraso und phase-locked echo-tracking system before and immediately after ste nting and at 4 and 18 weeks. Blood pressure was registered intra-arter ially and stiffness (beta) was calculated. Intravascular ultrasound (I VUS) Tons performed at 18 weeks. Results: Median weight increased from 20 kg (19-26) to 93 kg (62-130). Diameter of the aorta increased 60%. In group P no pulsatile diameter change could be measured at the sten t (beta = infinity). In group G stenting increased stiffness from beta 20.7 (9.2) to 43.2 (8.0) (p < 0.05). After 18 weeks stiffness returne d to beta 20.1 (12.4). Expanded, median diameter of the P stents was 7 .4 (0.8) min, not increasing after 18 weeks. Initial diameter of the G stents tons 7.8 (1.0) mm, increasing 56% to 12.2 (2.3) mm (p < 0.05). IVUS revealed the G stents to be well attached to the vascular wall, but five P stents were detached within half of the circumference. Conc lusion: Self-expanding stents follow the pulsatile diameter change of the vessel wall, not adversely affecting distensibility after 18 weeks . They show good attachment despite 56% dilation. In contrast, the bal loon-expanded stents do not show pulsatile movement and may detach dur ing vessel diameter increase. This may be of importance when choosing stents for endovascular treatment of abdominal aortic aneurysms.