Timothy Malisch, MD
Despite recent advances in treating both hemorrhagic and ischemic stroke, stroke remains a leading cause of death and permanent disability worldwide. Endovascular stroke rescue thrombectomy was long considered a promising therapy for those strokes caused by thrombus occluding the proximal, larger intracranial arteries supplying the brain. It was not until late 2014 that a series of trials demonstrated convincing evidence of benefit. Based on these trials, endovascular stroke rescue thrombectomy was accepted as the standard of care and recognized in national and international guidelines. These earlier trials focused on patients who could undergo intervention within a relatively short window of time from stroke onset, or since last seen at their baseline. This window of time was generally defined to be 6 hours, with some nuances and/or exceptions.
Many professionals in the stroke community pointed out that applying a blanket time limit of 6 hours to all patients might be preventing treatment of subsets of patients who would have benefitted from treatment at a later time. Not all patients suffering sudden occlusion of an intracranial internal carotid artery or middle cerebral artery progress towards irreversible neuronal injury at the same rate. Imaging of stroke progression over time with advanced MRI or CT techniques showed that some patients have slower progression towards irreversible injury, which was theorized to reflect better collaterals and/or better local perfusion pressures. Other patients are “faster progressors,” likely representing less robust collateral circulation. Unfortunately, these latter patients have relatively shorter time windows for rescue strategies to achieve clinically effective reperfusion; however, the “slower progressors” may have extended time windows for treatment.
Two new trials have demonstrated great clinical benefit of endovascular thrombectomy in patients with occlusions of the intracranial internal carotid arteries and middle cerebral arteries out to 16 or 24 hours — specifically in subjects selected based on advanced imaging that allowed measurement of their core infarct volumes.
The DAWN trial used either CT perfusion (CTP) studies or diffusion weighted MRI (dMRI) to measure the core infarct volume, and defined patients as candidates for thrombectomy based on an age-adjusted “clinical core mismatch.” In short, DAWN required a limit on completed infarct volume, with that limit depending in turn on patient age and severity of stroke, as measured by the NIH Stroke Scale.
The DEFUSE 3 trial also used CTP and/or dMRI to measure core infarct volumes. But unlike DAWN, DEFUSE 3 did not depend solely on a “clinical core mismatch” but also required a mismatch ratio of volume of ischemic tissue to completed infarct volume.
Both trials showed that thrombectomy was associated with significantly better 90-day functional outcomes than control patients. In DAWN, the number of patients who had regained independence (defined as a modified Rankin Score of 0-2) at 90 days was 49% in the thrombectomy group and only 13% in the control group. In DEFUSE 3, the number of patients who had regained independence at 90 days was 45% in the thrombectomy group vs 17% in the control group.
Both trials used imaging postprocessing software called RAPID, provided by the company iSchemaView Inc. We are now using RAPID at many of our Primary Stroke Centers and Comprehensive Stroke Centers and hope to bring RAPID to all of our remaining AMITA Health acute care hospitals soon.
Please consider referring your patients to the AMITA Health Neurosciences Institute. To schedule a referral, call 847.981.3630.