Feasibility and Safety of Unzipping Small Diameter Stents in the Blood Vessels of Piglets.

Objectives: This study sought to determine the feasibility and safety of unzipping small-diameter stents (SDS) in a growing animal model.

Background: SDS implanted to relieve stenosis of blood vessels in infants may result in refractory stenosis as the child grows. If stents can be longitudinally fractured-unzipped-then the target vessel can potentially be redilated to the eventual adult vessel diameter.

Methods: Fifty stents (diameter 4 to 7 mm) were implanted in 5 neonatal piglets (mean age and weight = 1.5 weeks and 3.4 kg). Pre-mounted coronary (CS) (n = 24), biliary (BS) (n = 14), nitinol (NS) (n = 3), and renal stents (RS) (n = 9) were implanted in pulmonary arteries (n = 13), systemic arteries (n = 25), and systemic veins (n = 12). Three months later (median weight = 32 kg), unzipping was attempted by dilating the stents.

Results: All CS and RS unzipped at twice their nominal diameter with <20% shortening. None of the NS unzipped. The BS shortened the most (∼40%), with only 69% of the stents unzipping. Stainless steel CS and RS with an open cell design were significant predictors (p ≤ 0.01) for unzipping. On histopathology, unzipping of the BS caused the most medial dissection and vessel wall injury, while unzipping of the CS caused the least.

Conclusions: Unzipping of small-diameter CS and RS implanted in systemic and pulmonary vessels is more feasible than the BS and NS. This study may encourage the implantation of small stents in infant blood vessels and aid in selection of appropriate stent type.