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Emergent Large Vessel Occlusion Screen Is an Ideal Prehospital Scale to Avoid Missing Endovascular Therapy in Acute Stroke

Originally publishedhttps://doi.org/10.1161/STROKEAHA.118.022107Stroke. 2018;49:2096–2101

Abstract

Background and Purpose—

The strong evidence of endovascular therapy in acute ischemic stroke patients with large vessel occlusion (LVO) is revealed. Such patients are required to direct transport to the hospital capable of endovascular therapy. There are several prehospital scales available for paramedics to predict LVO. However, they are time consuming, and several of them include factors caused by other types than LVO. Therefore, we need a fast, simple, and reliable prehospital scale for LVO.

Methods—

We developed a new prehospital stroke scale, emergent large vessel occlusion (ELVO) screen, for paramedics to predict LVO. The study was prospectively performed by multistroke centers. When paramedics referred to stroke center to accept suspected stroke patients, we obtain the following information over the telephone. ELVO screen was designed focusing on cortical symptoms: 1 observation; presence of eye deviation and 2 questions; paramedics show glasses, what is this? and paramedics show 4 fingers, how many fingers are there? If the presence of eye deviation or ≥1 of the 2 items were incorrect, ELVO screen was identified as positive. We evaluated between results of ELVO screen and presence of LVO on magnetic resonance angiography at hospital arrival.

Results—

A total of 413 patients (age, 74±13 years; men, 234 [57%]) were enrolled. Diagnosis was ischemic stroke, 271 (66%); brain hemorrhage 73 (18%); subarachnoid hemorrhage, 7 (2%); and not stroke, 62 (15%). One hundred fourteen patients had LVO (internal carotid artery, 33 [29%]; M1, 52 [46%]; M2, 21 [18%]; basilar artery, 5 [4%]; P1, 3 [3%]). Sensitively, specificity, positive predictive value, negative predictive value, and accuracy for ELVO screen to predict LVO were 85%, 72%, 54%, 93% and 76%, respectively. Among 233 patients with negative ELVO screen, only 17 (7%) had LVO, which indicated to be an ideal scale to avoid missing endovascular therapy.

Conclusions—

The ELVO screen is a simple, fast, and reliable prehospital scale for paramedics to identify stroke patients with LVO for whom endovascular therapy is an effective treatment.

Introduction

The strong evidence for the benefits of endovascular therapy (EVT) in patients with acute ischemic stroke (AIS) and large vessel occlusion (LVO) is changing the face of prehospital systems.1,2 EVT may offer a longer time window and higher rate of complete reperfusion than intravenous tissue-type plasminogen activator therapy.3,4 The efficiency of EVT depends on the interval between onset-to-reperfusion time.3–8 AIS patients with suspected LVO should be transported directly to a stroke center capable of EVT 24/7. A new simple, fast, and reliable prehospital scale based on cortical symptoms is needed to identify patients with LVO eligible for EVT. However, no stroke center has the capacity to accept all patients, and transport of patients without LVO is thus clinically unwise, time consuming, and expensive. In addition, recent reports have shown EVT eligibility for 10% of patients with AIS arriving at the hospital within 24 hours,9 whereas far fewer patients actually receive EVT. The reasons behind this disparity are the lack of hospitals capable of EVT and the undeveloped state of prehospital systems. Development of better emergency stroke transportation systems is thus imperative.

Past scales have focused on selecting AIS for intravenous tissue-type plasminogen activator therapy.10,11 A new scale is now required to detect EVT-eligible patients. Several dedicated clinical scores have been proposed to help predict LVO.12–25 However, these scales have shown problems in terms of complexity and unacceptable negative predictive value (NPV, representing the probability that an individual returning a negative result is actually negative for LVO), with at least 20% of patients with LVO missed when applying published cutoffs.26 Furthermore, paramedics must be able to easily apply scales for AIS as soon as possible before hospital arrival to enable transfer of suspected AIS cases with LVO to a stroke center capable of EVT. The ideal prehospital scale would thus satisfy the criteria of simplicity, ease of use, and a high NPV. We developed a new scale, the emergent large vessel occlusion (ELVO) screen, for paramedics to detect patients with LVO. The aim of this study was to evaluate the utility of the ELVO screen in predicting LVO among patients with acute stroke.

Methods

ELVO Screen Design

We developed our scale with a focus on simplicity and convenience. Most patients with LVO show cortical symptoms, so we selected 3 items associated with cortical symptoms. These 3 items comprised 1 observation and 2 questions. When paramedics contact a stroke center to accept a patient with suspected stroke before hospital arrival, we obtain the following information over the telephone. The first item is the observation: does the patient show eye deviation? The second item is question 1: a paramedic shows the patient a pair of eyeglasses or a watch and asks “What is this?” The final item is question 2: a paramedic shows the patient 4 fingers and asks “How many fingers am I holding up?” (Figure).

Figure.

Figure. The 3 items of the emergent large vessel occlusion (ELVO) screen. We checked the following 3 questions through paramedics: (1) observation: “Does the patient show eye deviation?” Presence of eye deviation is defined as a positive result; (2) question 1: the paramedic shows the patient eyeglasses or a watch, and asks “What is this?” and (3) question 2: the paramedic shows 4 fingers to the patient and asks how many fingers there are. If the presence of eye deviation or ≥1 of the 2 items were incorrect, the result of the ELVO screen was positive.

Definition of a Positive Result

When we acknowledge eye deviation or at least 1 cortical symptom such as aphasia and unilateral spatial neglect, we can suspect such patients as having LVO. In addition, we stuck with simplicity: if eye deviation is present or either question is answered incorrectly, the ELVO screen is defined as positive. To ascertain whether the cutoff for an ELVO screen positive result was correct, we examined the relationships between the number of positive items and both sensitivity and specificity.

Validation of ELVO Screen in a Prospective Prehospital Cohort

Between September 2016 and July 2017, we studied results from the ELVO screen for emergency patients with suspected acute stroke at 4 stroke centers: Nippon Medical School Hospital, Tokyo; Jusendo General Hospital, Fukushima; Shioda Hospital, Chiba; and Kitamurayama Hospital, Yamagata. When paramedics contacted one of these stroke centers on transfer of a patient with suspected stroke, we asked the paramedic to apply the ELVO screen. A key point was that the ELVO screen was applied by paramedics, not doctors.

Baseline characteristics, onset-to-door (O2D) time, diagnosis on admission, and presence of LVO were recorded prospectively. Presence of LVO was documented on admission using magnetic resonance angiography at the time of hospital arrival. LVO was defined as occlusion of the internal carotid artery, intracranial cerebral artery, horizontal portion of the middle cerebral artery (M1), insular portion of the middle cerebral artery (M2), basilar artery, or P1 segment of the posterior cerebral artery. Vascular risk factors were identified as follows: (1) hypertension, as a history of using antihypertensive agents; (2) diabetes mellitus, as the use of hypoglycemics, random glucose level ≥200 mg/dL, or glycosylated hemoglobin test >6.4% on admission; (3) dyslipidemia, as the use of antihyperlipidemic agents or serum cholesterol level >220 mg/dL on admission; and (4) smoking, as any cigarette usage within the 28 days preceding admission. To detect arterial fibrillation, all patients underwent 12-lead electrocardiography on admission. Neurological severity was assessed using the National Institutes of Health Stroke Scale score. The institutional review board decided that informed consent to subjects in the study was not required because the study used emergency data and did not affect therapy of included patients.

Statistical Analysis

First, we clarified and calculated the rate of positive results for each of the 3 items in the ELVO screen. Second, we compared all patients regarding presence of LVO and results of the ELVO screen and evaluated sensitivity, specificity, NPV, positive predictive value, and overall accuracy. We then compared results according to the number of positive results to confirm whether a score of ≥1 for the 3 items as the optimal definition of a positive overall result for the ELVO screen. Next, all patients were classified into groups according to a positive or negative overall result from the ELVO screen. Clinical characteristics, neurological severity, and O2D time were compared between groups. Finally, we compared results according to O2D time to confirm whether results differed according to O2D time. Welch test was used to analyze differences in continuous variables, and the 2-tailed Fisher exact test was used to analyze differences in categorical variables. Data are presented as a median and interquartile range or as a frequency and percentage. All statistical analyses were performed using JMP version 11 software (SAS Institute, Cary, NC). In all tests, values of P<0.05 were defined as statistically significant.

Results

A total of 413 patients (age, 74±13 years; 234 men [57%]) were enrolled (Nippon Medical School Hospital, 227 patients; Kitamurayama Hospital, 84 patients; Jusendo Hospital, 63 patients; Shioda Hospital, 39 patients). Final diagnosis for the 413 patients was ischemic stroke in 271 patients (66%), brain hemorrhage in 73 (18%), subarachnoid hemorrhage in 7 (2%), and a diagnosis other than stroke in 62 (15%). LVO was identified in a total of 114 patients (28%; internal carotid artery, n=33 [29%]; M1, n=52 [46%]; M2, n=21 [18%]; basilar artery, n=5 [4%]; P1, n=3 [3%]).

Results of the ELVO screen were shown as follows: positive eye deviation, 22% (90 of 413); positive response for question 1, 35% (146 of 413); and positive response for question 2, 25% (105 of 413). Among all patients, the percentages showing 1, 2, or 3 positive results for the ELVO screen were 44% (180 of 413), 29% (120 of 413), and 12% (48 of 413), respectively. As a result, a positive result for the ELVO screen (ie, ≥1 positive result for the 3 items) was seen in 44% (180 of 413) and a negative result in 56% (233 of 413). Table 1 shows the relationship between positive and negative results of the ELVO screen and presence or absence of LVO. Sensitivity, specificity, positive predictive value, NPV, and accuracy of the ELVO screen in detecting LVO were 85%, 72%, 54%, 93%, and 76%, respectively. Among the 233 patients with a negative result for the ELVO screen, only 17 (7%) showed LVO, suggesting this tool as ideal to avoid missing EVT in LVO patients. Regarding the 114 patients with LVO, results for the 3 items were as follows: 3 items positive, 34 (30%); 2 items positive, 37 (32%); 1 item positive, 26 (23%); and all items negative, 17 (15%).

Table 1. Association Between ELVO Screen and Large Vessel Occlusion (LVO)

ELVO Screen
PositiveNegativeTotal
LVOPresence9717114
Absence83216299
Total180233413

LVO contains ICA, M1, M2, BA, and P1 occlusion. BA indicates basilar artery; ELVO, emergent large vessel occlusion; ICA, internal carotid artery; and LVO, large vessel occlusion.

As an indicator to avoid missing EVT, we compared NPV according to positive answers on the 3 items to validate how many positive answers provided the optimal definition of an overall positive result for the ELVO screen. One or more positive items showed the highest NPV (93%) and was considered best (Table 2).

Table 2. Sensitivity, Specificity, PPV, NPV, and Overall Accuracy According to Different Cutoff Value of ELVO Screen

ELVO Screen ScoreSensitivity, %Specificity, %PPV, %NPV, %Accuracy, %
≥18572549376
≥26284598578
≥37195717877

ELVO screen score ≥1 show higher sensitivity and NPV rather than ELVO screen score ≥2 or ≥3. ELVO indicates emergent large vessel occlusion; NPV, negative predictive value; and PPV, positive predictive value.

Patients were divided into 2 groups according to a positive or negative result for the ELVO screen. Clinical characteristics of the 2 groups are shown in Table 3. Age (77±12 versus 71±14 years; P<0.001) and presence of hypertension (60% [108 of 180] versus 71% [166 of 233]; P=0.021) and atrial fibrillation (39% [70 of 180] versus 14% [33 of 233]; P<0.001) were higher in the positive group than in the negative group. In terms of neurological severity, National Institutes of Health Stroke Scale score on admission was higher in the positive group (16 [9–21] versus 4 [2–7]; P<0.001). No significant differences in sex, dyslipidemia, diabetes mellitus, or O2D time were identified between groups. In addition, no significant difference in positive rate for the ELVO screen was seen according to participating hospitals.

Table 3. Characteristics of Positive or Negative ELVO Screen

Positive n=180Negative n=233P Value
Age, y77±1271±14<0.001
Male gender, n (%)107 (60)127 (55)0.319
Risk factors, n (%)
 Hypertension108 (60)166 (71)0.021
 Dyslipidemia50 (28)83 (36)0.111
 Diabetes mellitus31 (17)53 (23)0.177
 Atrial fibrillation70 (39)33 (14)<0.001
NIHSS score16 [9–21]4 [2–7]<0.001
Onset-to-door time, h4.0 [1.5–8.0]3.5 [1.7–9.5]0.563
Hospital0.231
 Nippon Medical School101 (44)126 (56)
 Kitamurayama34 (40)50 (60)
 Jusendo23 (37)40 (63)
 Shioda22 (56)17 (44)

ELVO indicates emergent large vessel occlusion; and NIHSS, National Institutes of Health Stroke Scale.

Finally, we compared the sensitivity, specificity, NPV, positive predictive value, and accuracy according to O2D time to clarify whether we could use the ELVO screen in patients within 4.5 hours, 8 hours, and all cases after onset. All target groups showed high sensitivity (≥80%) and high NPV (≥90%; Table 4).

Table 4. Sensitivity, Specificity, PPV, NPV, and Overall Accuracy According to Different O2D Time

SensitivitySpecificityPPVNPVAccuracy
All n=41385%72%54%93%76%
O2D time <8 h n=26383%71%54%91%75%
O2D time <4.5 h n=20180%70%50%90%73%

Any target group show PPV ≥50% and NPV ≥90%. NPV indicates negative predictive value; O2D, onset-to-door; and PPV, positive predictive value.

Discussion

This study was prospectively conducted at 4 stroke centers, and paramedics performed all tests before hospital admission. Here, we identified 2 major findings. First, our scale offered a simple tool compared with former scales and took only a few minutes for paramedics to administer. Second, our scale proved highly predictive for LVO because ELVO screen focused on cortical symptoms. The ELVO screen seems to help effectively in avoiding missed opportunities for EVT.

A desirable scale in the hyperacute setting would be one that can be performed easily and quickly with a high level of detectability. For rapid administration, the scale must be simple. On the one hand, for vascular neurologists, the National Institutes of Health Stroke Scale is the most familiar scale for use with stroke patients, but for prehospital paramedics, this scale may be difficult and time consuming, and thus has not been validated as far as we know.27–29 Our ELVO screen consists of only 3 items. Eye position can be used to check for eye deviation. Naming the items glasses or watch can detect aphasia and disturbance of consciousness. Counting the number of fingers can identify unilateral spatial neglect or half-blindness. All these factors are able to be examined immediately with no need for specialized skills or equipment. Although the simple 3-item stroke scale,15 the Los Angeles Motor Scale,16 the Cincinnati Prehospital Stroke Severity Scale,17 and the Prehospital Acute Stroke Severity scale18 are also simple, they use cutoff values unlike those of the ELVO screen. The 3-item stroke scale, Los Angeles Motor Scale, and Cincinnati Prehospital Stroke Severity Scale require a weighted scoring method and thus need additional time to determine the score. We emphasize that our ELVO scale features a simple, informative scoring method without any weighted or cutoff scoring.

The most important characteristic of the ELVO scale is that it places weight on cortical symptoms and does not include factors of facial palsy or hemiparesis. Our approach is different to previous scales, in that all 4 scales mentioned above, as well as the Rapid Arterial Occlusion Evaluation12 and Field Assessment Stroke Triage for Emergency Destination,19 include factors of hemiparesis and facial palsy (Table 5). We did not include those factors because hemiparesis is not a specific feature of LVO despite being a major symptom of stroke. For example, most patients with lacunar stroke show hemiparesis without cortical symptoms. Aphasia without hemiparesis should indicate embolic stroke with middle cerebral artery occlusion.30,31 Another advantage of the ELVO screen is that we considered multiple factors related to cortical symptoms, and the possibility of underestimation was thus reduced. Indeed, of the 114 patients with LVO in our study, only 34 (30%) showed positive results for all 3 items, whereas 26 (23%) got just 1 positive item. Other published scales may not be sensitive enough to catch some patients who show mild cortical symptoms. We, therefore, think that the ELVO screen specialized for cortical symptoms would offer an anatomically reasonable scale to detect patients with LVO.

Table 5. Comparison of Clinical Scales for Prehospital Prediction of LVO

ELVORACE123I-SS15LAMS16CPSSS17PASS18FAST-ED19ASTRAL20VAN21LEGS22LVOS23sNIHSS-EMS24FPSS25
TypeProspProspRetroRetroRetroRetroRetroRetroProspProspRetroRetroRetro
Sample size4133571711193031104727848621811663741856
StateJapanSpainGermanyUnited StatesUnited StatesDenmarkUnited StatesSwitzerlandUnited StatesUnited StatesUnited StatesEuropeFinland
Sensitivity, %858566818361618410069757054
Specificity, %72689289408389689081508191
PPV, %54427492796672417460157047
NPV, %939489744680829410086958193
No. of test363333517*44575
Test performerPD/PND/N/PND/NND/PD/NN/D/PN/D
Item
 Consciousness
 Gaze
 Hemineglaet
 Visual
 Facial palsy
 Motor arm
 Motor leg
 Grip strength
 Ataxia
 Sensory
 Language
 Dysarthria
 NIHSS score
 Sex
 mRS ≤2

3I-SS indicates 3-item stroke scale; ASTRAL, the Acute Stroke Registry and Analysis of Lausanne; CPSSS, Cincinnati Prehospital Stroke Severity Scale; D, non-neurologist doctors; ELVO, emergent large vessel occlusion; FAST-ED, Field Assessment Stroke Triage for Emergency Destination; FPSS, Finnish Prehospital Stroke Scale; LAMS, Los Angeles Motor Scale; LEGS, Texas Stroke Intervention Pre-Hospital Stroke Severity Scale; LVO, large vessel occlusion; LVOS, large vessel occlusion prediction scores; mRS, modified Rankin Scale; N, neurologists; NIHSS, National Institutes of Health Stroke Scale; NPV, negative predictive value; P, paramedics; PASS, Prehospital Acute Stroke Severity Scale; PPV, positive predictive value; RACE, Rapid Arterial Occlusion Evaluation; sNIHSS-EMS, the shortened NIH Stroke Scale for emergency medical services; and VAN, stroke vision, aphasia, neglect assessment.

*ASTRAL is performed by NIHSS score, modified Rankin Scale, atrial fibrillation, hemineglect, and sex.

Statistically, our ELVO screen achieved a high sensitivity of 85% and a specificity of 72% to detect patients with LVO, resulting in a high NPV of 93%. The ELVO screen showed better results than the 3-item stroke scale, Los Angeles Motor Scale, Cincinnati Prehospital Stroke Severity Scale, Prehospital Acute Stroke Severity scale, or Field Assessment Stroke Triage for Emergency Destination. Although Rapid Arterial Occlusion Evaluation results were comparable to those of the ELVO screen, our scale is simpler. The ELVO screen is thus the only scale satisfying both effectiveness and simplicity.

It is important for prehospital screening to avoid missing the opportunity for EVT in LVO patients. The most unfavorable situation in the prehospital phase is if a screen does not identify a stroke patient with potential LVO and therefore the patient is transferred to a primary stroke center where EVT is not available. In our ELVO screen, among 233 patients with a negative ELVO screen result, only 17 (7%) had LVO. The ELVO screen should thus be able to avoid missing EVT to great majority of patients having LVO.

This study has some limitations. First, the ELVO screen did not readily detect LVO patients without cortical symptoms. In the present study, however, such patients only comprised 4% (17 of 413), and most such patients may not be adaptable to EVT. Second, we did not evaluate interlayer validation between paramedics. Finally, we did not compare the ELVO screen with previous scales. In the future, a prospective validation study comparing the ELVO screen with other useful scales in the same field is warranted.

In conclusion, the ELVO screen is a simple, fast, and reliable prehospital screen allowing paramedics to properly identify patients with LVO. The ELVO screen will greatly help to avoid missed opportunities for EVT in patient with LVO.

Acknowledgments

We thank Nedu fire department, Tokyo Fire Department, Higashine city fire department, Murayama fire department, Obanazawa city fire department, Koriyama city fire department, Motomiya city fire department, Shirakawa city fire department, Katsuura fire department, and Ohara fire department for applying emergent large vessel occlusion screen.

Footnotes

Correspondence to Kentaro Suzuki, MD, Department of Neurological Science, Nippon Medical School Hospital, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113–8603, Japan. Email

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