Reaction to injury following balloon angioplasty and intravascular stent placement in the canine femoral artery

Intravascular stents are used clinically as an adjunct to coronary and iliac angioplasty. This study was performed to evaluate the thrombogenicity and intimal hyperplasia incited by stents deployed in non-injured and in balloon-injured femoral arteries in the canine model. Medinvent stents (4 mm) were placed in the femoral arteries bilaterally in five mongrel dogs via cut down. This was preceded by balloon catheter angioplasty of the stent site on one side. Platelet deposition was measured at 30, 60, and 90 minutes and at 24 and 48 hours after stent placement, using gamma camera imaging of Indium¹¹¹ platelets. The animals were killed after 2 months using a pressure perfusion technique, and the stents harvested. All vessels were patent at the time of harvest. Neointimal thickness was measured by computer image analysis. Platelet deposition was significantly increased on the angioplastied side compared to the non-angioplastied side at 60 minutes (5.67 x 10⁹ ± 1.4 versus 2.17 x 10⁹ ± 0.5 platelets/cm; P < 0.05), at 90 minutes (8.13 x 10⁹ ± 1.8 versus 2.33 x 10⁹ ± 0.6 platelets/cm; P < 0.05), and at 24 hours (stent-to-blood ratio = 15.86 ± 6.3 versus 3.75 ± 1.5; P < 0.05). Neointimal thickness was also significantly greater on the side of combined angioplasty and stent placement (0.45 ± 0.21 mm versus 0.33 ± 0.09 mm; P < 0.05). These results demonstrate that placement of intravascular stents in normal arteries is associated with a certain degree of thrombogenicity and formation of neointimal hyperplasia. Combining balloon angioplasty with stent placement significantly augments both thrombogenicity and production of intimal hyperplasia. This can limit the clinical application of such devices in small caliber blood vessels.