Blood flow and thrombus formation determine the development of stent neointima

To establish a relationship between flow, acute thrombus formation, and late intimal formation in implanted arterial stents, canine femoral arteries with normal blood flow were compared to contralateral femoral arteries with restricted blood flow. Thrombocyte activity over the stent segment was evaluated for 3 h after stent placement with nuclear scanning, following administration of In-111 labeled platelets. To evaluate long-term stent patency in relationship to arterial flow, an additional group of dogs were subjected to long-term observation. Matched, symmetrically implanted femoral stents with normal and restricted flow were explanted at 1, 12, and 24 weeks for histological analysis and comparative measurement of neointimal thickness. Angiographic studies were performed before and after nuclear scan in the acute animals and before explant in the chronic animals. Acutely, heparinization prevented subocclusive or occlusive thrombus, regardless of flow. In the absence of heparinization, normal arterial blood flow did not prevent thrombus formation on stents. Chronically, stents with flow restriction had significantly greater neointimal formation in comparison with unrestricted stents. Histological studies suggested that the stent neointima resulted from progressive replacement of stent thrombus.