: The murine FeCl3 model is a widely used model for studying arterial thrombosis, yet provides limited information from each mouse, often only a single time point for the onset of occlusion (defined as the time to occlusion; TTO). To optimize data from the murine ferric chloride model of thrombosis. FeCl3 injury was induced in the carotid arteries of wild-type and Factor IX (FIX) knockout mice, with infusion of recombinant FIX (rFIX) to normalize FIX deficiency at various times around FeCl3 injury. The TTO was recorded as a percentage of baseline flow as occlusion continued to zero flow, with identification of reflow events. The TTO among the treatment groups of FIX-deficient mice showed no statistical differences, except with physiological saline-treated FIX-deficient mice and those receiving delayed treatment. Incidences of occlusion were 100% for wild-type mice and FIX-deficient mice receiving slow infusions of rFIX at early times around the FeCl3 application. In contrast, only 68% of FIX-deficient mice achieved occlusion with preinfusion of rFIX and none occluded with delayed rFIX infusion. A majority of occluded vessels exhibited reflow events, with significantly lower incidence for slow infusion of rFIX starting 4 min after FeCl3 application in comparison with preinjury bolus, demonstrating characterization of a differential response to timing and infusion rates of treatment. Simple use of the time to occlusion may not maximize data available from the FeCl3 arterial thrombosis model. Inclusion of documenting reflow events can extend the useful data obtained with application of this model.

Background: The timing for initiation of effective antithrombotic therapy relative to the onset of arterial thrombosis may influence outcomes. This report investigates the hypothesis that early administration of heparin anticoagulation relative to the onset of thrombotic occlusion will effect a reduction in occlusion. Methods: A standard rat model of experimental thrombosis induction was used, injuring the carotid artery exposure with FeCl 3 -saturated filter paper, followed by flow monitoring for onset of occlusion and subsequent embolization events. Intravenous heparin administration (200 units/mL) was timed relative to the initiation of injury or onset of near occlusion, compared with controls (no heparin administration). Results: No occlusion was found for delivery of heparin 5 min prior to thrombus induction, whereas all vessels occluded without heparin. Unstable (embolic) thrombi were seen with heparin given at or shortly after initial occlusion. Only 9% (1/11) of the vessels had permanent occlusion when heparin was given at the time of thrombotic onset (p < 0.0001 vs. unheparinized), while 50% occluded when heparin was delayed by 5 min (p > 0.05). Conclusions: These findings provide evidence that antithrombotic therapy may need to be administered prior to the onset of anticipated loss of patency, with less effectiveness when given after occlusion has occurred.