Thrombus formation and endothelial alterations in microarterial anastomoses.

The sequential hematological and endothelial responses in the postoperative period after end-to-side arterial anastomosis in 1- to 1.3-mm vessels were assessed by scanning electron microscopy. Two minutes after restoration of flow, an amorphous coating covered the vessel lumen around the suture line, and oozing of blood from the suture line ceased. Within 15 minutes, a partially occluding thrombus was present, which was maximal at the anastomotic bifurcation point. The thrombus underwent partial lysis or embolization within 30 minutes, and gross intraluminal thrombi did not recur. The initial thrombi that formed within 2 minutes were composed of platelets and erythrocytes in a loose reticular fibrin network, but the intraluminal thrombi present at the branch point 15 minutes after flow restoration appeared to be composed solely of platelets. Thrombi that did not undergo complete dissolution had a loss of distinct cellular elements at later time intervals. The fibrin-platelet matrix coating the lumen remained unchanged during the initial 24 hours. When examined at 9 days, normal endothelium was present throughout the vessel with the exception of the suture line, which remained covered by a smooth coagulum. This sequence of events suggest that if surgical manipulation is to result in complete occlusion of the anastomosis, it will likely occur in the initial 30 minutes after resumption of blood flow. Anticoagulant regimens were evaluated. Pretreatment with aspirin and intraoperative heparin irrigation of the vessel lumen were not beneficial in altering the quantity of thrombus. All systemic heparin regimes tested resulted in a quantitative decrease of thrombotic material. Five minutes of intravenous heparin therapy after resumption of blood flow was as effective as long-term heparin in decreasing the transient intraluminal thrombotic response.