Background: As endovascular (EV) thrombectomy is a proven highly effective treatment for acute ischemic stroke due to large vessel occlusion (LVO), there is an urgent need for validated tools for paramedic use to identify likely LVO patients for direct routing to EV-capable centers. A deficit score ≥4 on the Los Angeles Motor Scale (LAMS) performed well in identifying such patients when administered by physicians in the ED. We now report a prospective validation with LAMS performed by paramedics in the field.
Methods: We analyzed all acute cerebral ischemia patients in the NIH FAST-MAG prehospital treatment trial who had LVO on first vessel imaging (CTA, MRA, or cath angio) done within 6h of last known well and prior to start of IV tPA. Prehospital LAMS was performed by paramedics prior to field enrollment. Hospital arrival (HA) LAMS and NIHSS were subsequently done by trained study nurses after ED arrival. LVO in a proximal cerebral artery (ICA, MCA M1 & M2, Basilar) was determined by 3 vascular neurologists with expertise in neuroimaging.
Results: Among 190 patients, age was 68 (±13), 45% female. Paramedic (PM) prehospital LAMS were done 21 (IQR 14-38) mins after last known well (LKW), and 33 (27-39) mins before ED arrival. The HA LAMS and HA NIHSS were done 154 (121-180) mins after LKW. On PM LAMS, median score was 4 (3-5) and 57% had score ≥4. Vessel imaging was done 41 (SD 97) mins after ED arrival. Overall, 95 (50%) patients had LVO, including MCA (n=62), ICA (29) and basilar (4). PM LAMS scores were higher in LVO patients, 5 vs. 3, p<0.001. When performed simultaneously with the NIHSS, HA LAMS ≥ 4 showed similar accuracy to HA NIHSS ≥ 10 in identifying LVO, c statistics 0.73 vs 0.77. The PM LAMS showed similar accuracy (c statistic 0.70) (slightly less discrimination is expected because of dynamic stroke evolution in the first 60 mins). For LVO, prehospital PM LAMS≥4 showed sensitivity 74%, specificity 58%, positive likelihood ratio 1.76 and negative LR 0.46.
Conclusions: The Los Angeles Motor Scale score identifies LVO in acute cerebral ischemia patients as well as the current gold standard NIHSS. In prospective field validation testing, a positive paramedic LAMS increased the likelihood of LVO by 76% and a negative cut the chance of LVO by more than half.