The natural history of large vessel occlusion (LVO) strokes is poor. Currently AHA guidelines recommend endovascular thrombectomy (EVT) upto 24 hours since time last seen well in highly selected patient populations. We aim to understand the frequency of guideline ineligible patients, reasons for ineligibility and the required sample size for a trial exploring the effect of EVT in ineligible subgroups.

Retrospective chart review of consecutive acute ischemic stroke discharges was performed at a single comprehensive stroke center between November 2014 and February 2017. Demographic, clinical (stroke severity, time from stroke onset and mode of presentation) and radiological imaging data (occlusion location, stroke burden- ischemic core volume and ASPECTS score) were collected and analyzed for eligibility for EVT per AHA 2018 guidelines.

17.5% of acute ischemic strokes in the 0-6-hour and 9.2% in the 6-24-hour time window were EVT candidates per AHA guidelines. Of the patients harboring an intracranial vessel occlusion (639 of total 2667), the most common reasons for ineligibility were a large stroke burden (17%, ASPECTS ≤5), non-proximal occlusions (MCA-M2- 17%, MCA-M3/ ACA/ PCA-4%), vertebra-basilar occlusions (17%) and mild stroke symptoms (9%, NIHSS score ≤5). Assuming a 10% treatment effect of EVT concerning relevant endpoints, a sample size of 712, 774 and 602 would be required to study the effect of EVT in LVO strokes with ASPECTS ≤5, NIHSS score ≤5 and MCA-M2 occlusions, respectively. 

The frequency of acute ischemic strokes due to LVO eligible for EVT per AHA guidelines is low with only one in eight patients meeting AHA eligibility.  Common reasons for non-guideline eligibility are distal location, posterior circulation location, large core and low NIHSS.  These data outline opportunities for indication expansion.