Background: Intravenous tPA has a limited efficacy in large vessel occlusion strokes (LVOS). Thus LVOS patients may be better served by direct transfer to endovascular capable centers. We aimed to develop a field scale to identify LVOS.
Methods: The FAST-ED scale was designed based on items of the NIHSS with higher predictive value for LVOS: Facial Palsy (scored 0-1), Arm Weakness (0-2), Speech Changes (0-2), Eye Deviation (0-2), and Denial/Neglect (0-2). The scale was tested in the STOPStroke cohort, a prospective study of patients who underwent CT angiography (CTA) within the first 24 hours of stroke onset. LVOS were defined by total occlusions involving the ICA-T, MCA-M1, MCA-2, or basilar arteries. Patients with partial, bi-hemispheric, and/or anterior + posterior circulation occlusions were excluded. Receiver operating characteristic (ROC) curve, sensitivity, specificity, positive (PPV) and negative predictive values (NPV) of FAST-ED were compared with the Rapid Arterial oCclusion Evaluation (RACE) scale and Cincinnati Prehospital Stroke Severity Scale (CPSSS).
Results: LVO was detected in 240 out of the 727 qualifying patients (33%). FAST-ED had a strong correlation with NIHSS (r=0.92; P<0.001). FAST-ED had comparable accuracy to predict LVO to the more complex NIHSS and higher accuracy than RACE and CPSS (area under the ROC curve: 0.81, 0.80, 0.77 and 0.75 respectively). Better performance of FAST-ED could be shown at two distinct thresholds depending on the desired sensitivity/specificity trade-offs with scores ≥3 and ≥4 having sensitivity for LVO of 0.71 and 0.60, specificity 0.78 and 0.89, PPV 0.62 and 0.72, and NPV 0.84 and 0.82 versus RACE ≥5 of 0.55, 0.87, 0.68, 0.79 and CPSS ≥2 of 0.56, 0.85, 0.65, 0.78, respectively.
Conclusions: FAST-ED is a simpler field scale that can be used by medical emergency professionals to accurately identify LVOS in the pre-hospital setting enabling rapid triage of patients to primary vs. endovascular capable stroke centers.