Abstract WP293: A Prospective Validation of Stroke Network of Wisconsin (snow) Scale to Predict Large Vessel Occlusion (lvo) and Comparison With Other Stroke Scales

Abstract

Background: Prior retrospective analysis confirmed that the Stroke Network of Wisconsin (SNOW) scale was highly predictive of large vessel occlusion (LVO) in patients with Acute Ischemic Stroke (AIS). In this study, we prospectively validated the SNOW scale for the identification of LVO. We also compared its accuracy to other stroke scales retrospectively applied to the same dataset. Methods: The SNOW scale consists of 3 exam elements: expressive aphasia/Speaking difficulty (S), neglect (N) and Ocular deviation (O). The scale is positive if any one of these items is present. We prospectively evaluated all acute ischemic stroke (AIS) patients who presented within 24 hours after onset at Aurora St. Luke’s Medical Center between July 2017-February 2018 and calculated the SNOW score. We retrospectively calculated Rapid Arterial Occlusion Evaluation (RACE), the Field Assessment Stroke Triage for Emergency Destination (FAST-ED), the Vision Aphasia and Neglect Scale (VAN), the Cincinnati Prehospital Stroke Severity (CPSS), the Los Angeles Motor Scale (LAMS), the Prehospital Acute Stroke Severity Scale (PASS) for all patients. The predictive performance of all scales and National Institute of Health Stroke Scale (NIHSS) cut offs ≥6 were determined and compared. LVO was defined by total occlusions involving the intracranial internal carotid artery, middle cerebral artery (M1), or basilar arteries Results: Among 344 AIS patients, 283 (82%) had vascular imaging and were included in the analysis. LVO was detected in 43 (15%). Positive SNOW scale showed: sensitivity = 0.84, specificity = 0.63, positive predictive value = 0.29, negative predictive value= 0.96, and area under the curve =0.74. SNOW scale had comparable accuracy to predict LVO as other scales and NIHSS cut offs ≥6. If LVO includes M2, positive SNOW had sensitivity of 0.85, specificity of 0.70, positive predictive value of 0.49, negative predictive value of 0.93 and area under the curve of 0.77. SNOW had the highest sensitivity but lowest specificity among other scales. Conclusion: The SNOW scale is a simple and accurate tool to help identify AIS due to LVO, and it compares favorably to the other scales evaluated. A prospective validation study of the SNOW scale in the prehospital setting is underway. .