DYNAMICS AND LOCALIZATION OF PLATELET DEPOSITION ON A SYNTHETIC VASCULAR GRAFT: CONTINUOUS IMAGING

The in vivo dynamics of thrombus formation have not been extensively studied, mainly due to technical limitations. We assessed the dynamics and localization of platelet deposition on a prosthetic vascular graft for the first 24 hours after implantation in swine, with continuous monitoring during the initial 6 hours, and the effect of heparin. Polytetrafluoro-ethylene (PTFE) grafts (5cm. L × 0.5 cm. ID) were inplanted in one of the common carotids of 13 normal pigs; 8 received iv heparin (150uAg) perioperatively. 111 In-labelled autologous platelets were injected 5 min before reperfusion of the graft. From 10 min to 24 hrs after unclamping the vessel sequential gamma camera images of the neck were taken and stored in an on-line computer. Pinpoint analysis of the platelet deposition was performed by creating seven regions of interest of 5 × 5 pixels over both graft and contralateral carotid territories. We obtained the ratio of the ¹¹¹ In-activity in each region of the graft, including both anastomoses, with respect to its contralateral homologous region. The ratios differed along the graft in both groups of animals, with maximal values at the anastomosis. Peak ratios were reached within 1 to 3 hrs, and were significatively lower in heparinized pigs (anastomosis: 1.95±0.36; graft: 1.3±0.66) than in rion-heparinized-pigs (anastomosis: 3.23±0.66; graft: 2.16±0.41; p<0.05). Heparinized pigs showed a progressive decrease of the ratios up to 24 hrs. In contrast, platelet deposition in non-heparinized-pigs continued up to 6 hrs. Patency at 24 hrs was 88% in heparinized-pigs versus 20% in non-heparinized-pigs. We conclude that computer assisted pinpoint analysis of platelet deposition may help to a better understanding of the thrombotic process differentiating platelet-graft interaction from platelet anastomosis interaction. The deposition of platelets and graft patency is strongly influenced by the stabilizing effect of procoagulant moieties, and the presence of the anastomosis (release of vessel wall procoagulant and platelet activating products and induction of blood flow disturbances) induces localized activation and deposition of platelets.