Lysis rates with rt-PB vary between different human emboli in a rat model of cerebral embolism

In apparently similar conditions lysis rates of cerebral emboli treated with thrombolytic drugs are quite variable. We used this model of rat embolism with human emboli to investigate whether this was, at least partially, dependent on the characteristics of the embolus. Sixty-two male Wistar rats were embolized via the external carotid artery. Emboli obtained from peripheral vessel embolectomies of two different patients were trimmed to a standardized length and diameter. Subgroups of the 9 animals in the two emboli groups (labeled groups 1 and 2) were randomly assigned to i.v. treatment with either saline, 1 mg/kg rt-PA or 10 mg/kg rt-PA. Only cases with internal carotid artery occlusion were included. Histology of both emboli was assessed by hematoxylin and eosin and trichromic Masson stainings. Recanalization rate was assessed by means of sequential angiograms, classified by TIMI grades, performed from 30 to 120 min after embolization. Complete recanalization rate in treated animals 2 h post-embolization was 88% for group 1 and 44% for group 2 (P < 0.05 chi-square test). The difference was based on the higher rate of recanalization in cases treated with 1 mg/kg rt-PA: 8/9 cases in group 1 and 2/9 cases in group 2. Both emboli had a similar structure of fibrin with blood cells, Different human emboli of similar size and apparently similar structure can show an unequal response to thrombolytic therapy. This finding could explain some of the variation in recanalization rates in cerebral embolism.