MEDIUM-TERM RESULTS OF EXPERIMENTAL STENT IMPLANTATION INTO THE DUCTUS-ARTERIOSUS

Balloon dilation is disappointing in maintaining patency of the arteri al duct. In neonatal lambs, stent implantation in the arterial duct re sults in significantly larger ducts with greater pulmonary blood flow than balloon dilation. Little is known, however, about the duration of duct patency after stent implantation. The outcome of stent implantat ion into the arterial duct in 12 lambs was observed over a period of 1 to 24 months. Stents (Wallstent in 9, Tower stent in 3) were implante d after recanalizing the occluded duct at 2 to 7 days of age. Heparin was given only during the procedure, but no further anticoagulants wer e used. Angiographic or postmortem evaluations were made at 1, 1.5, 2, 3, 4, 6, 12, 16, and 21 months in a subgroup of 9 lambs who did not u ndergo reinterventions. The duct was patent in all these except for on e studied at 16 months. Neointima initially developed in the center of the stent before extending toward the orifices, eventually burying th e metal strands in contact with the wall. From 4 to 6 months onward st enoses were present inside some of the stents. When the stent did not protrude into the aorta, neointima extended over the duct orifice. Met al strands that were not in contact with the duct wall were incomplete ly covered with endothelial cells, platelets, and fibrin strands, but no thrombi were noted. Late balloon dilation of the stented duct was p erformed in two lambs increasing the pulmonary artery blood flow. In o ne lamb the neointimal lining was successfully removed at 14 months wi th an atherectomy catheter. Stent implantation into the arterial duct can maintain patency up to 21 months and could be considered as an alt ernative to neonatal systemic to pulmonary artery shunt operations. Ne ointimal proliferation and stenosis formation, however, is a major lim itation that may eventually lead to a reduction in the pulmonary arter y blood flow.