Abstract WP244: How Many Potential Mechanical Thrombectomy Patients Are Missed Because of Emergency Medical Systems Transport Windows of 4.5 Hours or Less Since Last Known Normal in the Field?

Abstract

Intro: Many EMS transport protocols exclude patients last known normal (LKN) >4.5 or >6 hours from transport to Comprehensive Stroke Center (CSC) as acute stroke codes. Because recent Mechanical Thrombectomy (MET) studies enrolled few patients last known normal (LKN) > 6 hours prior to imaging, the incidence of CTP or ASPECTS suggesting possible benefit from MET in this time window for Large Vessel Occlusion (LVO) ischemic stroke is unclear. Method: Through retrospective review of a prospective database, the percentage of LVO patients with ASPECTS or CTP suggesting possible benefit from MET, defined as ASPECTS score >5 or salvageable penumbra and <70ml ischemic core on CTP, was compared between a group of 42 patients imaged > 6 hours since LKN and 106 patients imaged <6 hours since LKN. Results: 33% (14 of 42) of LVO patients LKN > 6 hours at time of CTP imaging (median 8 hours, range 6-20 hrs) received MET based on favorable CTP imaging and disabling clinical deficits. This was not statistically significantly different than the 40.5% (43 of 106) of LVO patients LKN < 6 hours at time of CTP imaging (median 128 min) that received MET based on same criteria (OR 95% CI, 0.73 0.34 – 1.55; P=0.42). The LKN > 6 hour MET patients (median NIHSS 18) had a trend towards less frequent favorable home or rehab discharge destination than the LKN < 6 hour MET patients (median NIHSS 16) (29% vs 57%, OR 0.3040, 95 % CI: 0.08 to 1.12, P = 0.07). There were no significant differences between the > 6 hour and <6 hour groups in factors associated with poor outcome after intervention or poor collateral circulation: median ASPECTS score (9 for both), percentage of ASPECTS scores >5 (80% vs 90%, p=0.31) median age (74 for both), ED glucose >150 mg/dl (16.6% vs 23.5%, p= 0.51), Atrial fibrillation (38% vs 37%). With a 30 minute door-to-CTP time, a < 4.5 hour LKN EMS transport policy would have excluded 24.5% of patients who received MET at our CSC. 6, 8, 10 and 13 hour LKN EMS transport windows would have excluded 11%, 9%, 2% and 0% MET intervention patients respectively. Conclusion: < 4.5 hour LKN EMS transport protocols may exclude a significant number of LVO patients with CTP and ASPECTS results possibly suitable for MET. These data need to be confirmed with a prospective multicenter study.