Hemorrhagic Transformation in Focal Cerebral Ischemia: Influence of Time to Artery Reopening and Tissue Plasminogen Activator

We used an adaptation of a well‐established rat model of middle cerebral artery occlusion (MCAO) that is both minimally invasive and reproducible to determine the effects of time to reperfusion and administration of tissue plasminogen activator (t‐PA) on the development of hemorrhagic transformation (HT) in a rat model of acute stroke. Animals were randomized to receive either t‐PA 10 mg/kg (29 rats) or an equal volume of saline (29 rats) over 20 minutes, beginning 5 minutes before reperfusion. Time to artery reopening varied between 1 and 24 hours after MCAO in both groups. At 18–24 hours after ischemia, the animals were sacrificed and their brains were preserved for analysis of HT. Logistic regression was used to determine the influence of time on HT risk and calculate the time at which 50% of animals developed HT (HT50%). At 24 hours, HT was present in 17 of 29 animals in each group and was significantly influenced by the time of artery reopening: 3 (15%) of 20 animals reperfused less than 3 hours after onset of ischemia and 32 (84%) of 38 reperfused 3 or more hours after the onset of ischemia (p