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mG-FAST, A single pre-hospital stroke screen for evaluating large vessel and non-large vessel strokes

Original research article by: Roy El Koussa, Sarah Linder, Alicia Quayson, Shawn Banash, James J. MacNeal, Parshva Shah, Mariaelana Brenner, Ross Levine, Osama O. Zaidat and Vibhav Bansal

There are approximately 800,000 new ischemic strokes in the United States annually. Of these, close to 20% are the result of a large vessel occlusion (LVO). A large vessel occlusion is defined by a thrombus in one of the major cerebral vessels including the terminal internal carotid artery (ICA), middle cerebral artery (MCA), anterior cerebral artery (ACA), or basilar arteries. Studies have shown that pharmacologic thrombolytic therapy alone for LVOs is often ineffective for achieving artery recanalization.

Early revascularization improves outcomes of patients with LVO with research demonstrating an average of 90 minutes saved if patients are admitted directly to a comprehensive stroke center capable of mechanical thrombectomy. It is therefore imperative that patients who are suffering from an LVO are transferred to these hospitals without delay. To accomplish this, a simple and effective screening tool for EMS to use in the field is necessary to simultaneously identify stroke patients and LVO. This chosen tool should have a high sensitivity and negative predictive value to ensure that no LVO is missed, while maintaining a low false positive rate to avoid overwhelming endovascular capable centers.

Several LVO stroke scales have been implemented in communities to enhance early recognition of LVO. However, these scales necessitate a tiered approach requiring EMS to either utilize two separate stroke scales, or complete complicated physical exams, unfamiliar to EMS and difficult to perform in the field. In the emergent setting, it is inefficient for multiple scales to be used for a single disease process.

Ideally, a single stroke scale should be utilized by EMS to triage all strokes, including LVO. The scale should be validated in the pre-hospital setting in a suspected stroke cohort, inclusive of stroke mimics. EMS professionals around the country are familiar with the Cincinnati Stroke Scale (Face-Arm-Speech-Time, FAST) which has high sensitivity for stroke. A score to identify LVO, that builds on this well-known scale, would be readily utilized by EMS to simultaneously screen for stroke and LVO. The G-FAST scale incorporates gaze deviation in FAST to preserve the high sensitivity of FAST for stroke detection with the added benefit of allowing simultaneous evaluation for LVO. The presence of gaze deviation is the single best predictor of LVO on the National Institute of Health Stroke Scale (NIHSS). It has a sensitivity and specificity for LVO of 58 and 95%, respectively.

Utilizing a single stroke scale in the field improves EMS dispatch-to-stroke center time, EMS dispatch-to-groin puncture time, and EMS door-to-intervention time. Implementation of mG-FAST as a pre-hospital screening tool is an effective method of triaging patients to the appropriate facility.

mG-FAST differs from G-FAST by giving greater weight (2 points) to gaze preference, the best predictor of LVO. This study prospectively enrolled 150 consecutive patients identified by EMS as potential strokes using only the mG-FAST scale. Patients with a score of 1 or 2 were paged as a non-LVO code stroke and those with an mG-FAST ≥3 as an LVO code stroke.

An mG-FAST score of 3 was chosen as the threshold for LVO for two main reasons. First, the presence of gaze preference (2 points) and hemiparesis of an extremity (1 point) are very predictive of LVO, therefore yielding a score of 3. Secondly, prior studies have demonstrated that the presence of all 3 signs of the FAST scale, which would also result in an mG-FAST score of 3, as highly predictive of LVO even in the absence of gaze deviation

One hundred fifty consecutive patients were rated with this scale by EMS professionals in the pre-hospital setting and independently evaluated by a member of the stroke team upon arrival to the hospital. EMS dispatch-to-facility arrival time, EMS dispatch-to-arterial puncture time, door-to-arterial puncture time and door-to-intervention time were measured for the 15 months prior to and 18 months after implementation of mG-FAST.

Following implementation of mG-FAST, mean EMS dispatch-to-facility time decreased by 22 min; mean EMS dispatch-to-arterial puncture time decreased by 62 min; mean door-to-groin puncture time decreased by 27 min. Mean door-to-intervention time also decreased by 50 min.

Out of the 32 LVO patients with an mG-FAST of 3 or more, 10 were admitted to the comprehensive stroke center hospital and 12 were admitted to a non-comprehensive hospital. The mean EMS dispatch-to-facility time was 53.9 and 228.6 min, respectively. This resulted in a decrease of 174.7 min.

The use of mG-FAST drastically decreased the EMS dispatch-to-facility time, EMS dispatch-to-groin puncture time, and the EMS door-to-intervention time. Additionally, this study demonstrated that using mG-FAST as a pre-hospital LVO screening tool was an effective and efficient method in triaging patients to a comprehensive stroke center.

Utilizing a single comprehensive stroke assessment tool in the field improved EMS dispatch-to-facility time as well as EMS dispatch-to-groin puncture time in patients with LVO stroke. This study demonstrated that using mG-FAST as a pre-hospital stroke screening tool was an effective and efficient method in triaging patients into comprehensive stroke centers and non-comprehensive hospitals. mG-FAST is the only scale to our knowledge that has been prospectively validated in the pre-hospital setting in a suspected stroke cohort that allows the use of a single stroke scale to triage all strokes, including LVO. This scale has the highest sensitivity and highest negative predictive value of all stroke scales prospectively studied in the field. The utilization of this single scale for EMS to triage all stroke patients results in a simple, reliable, and effective tool ensuring a high level of compliance.

If you would like to read more about this study, click here.