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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 following 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 ultrasound phase-locked echo-tracking system before and immediately after stenting and at 4 and 18 weeks. Blood pressure was registered intra-arterially and stiffness (beta) was calculated. Intravascular ultrasound (IVUS) was 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 stent (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 returned to beta 20.1 (12.4). Expanded, median diameter of the P stents was 7.4 (0.8) mm, not increasing after 18 weeks. Initial diameter of the G stents was 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.
Conclusion:
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 balloon-expanded stents do not show pulsatile movement and may detach during vessel diameter increase. This may be of importance when choosing stents for endovascular treatment of abdominal aortic aneurysms.