Large Vessel Occlusions

Podcast: Matt Mendes MD NR–P, Ross Orpet MD NR–P, Daniel Willner MD FACEP

Show Notes: Ross Orpet MD NR-P

Dan Willner breaks down the latest and greatest endovascular therapy since PCI.

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Ep. 2 Large Vessel Occlusion (LVO)

First and foremost we would like to thank all prehospital providers for the work you do. You are all underpaid, understaffed, and under appreciated. However, the unsung work you do now more than ever matters. We go to work every day in order to be there when the public needs us. Much of the focus as of late has been on COVID. And probably rightfully so. But that being said, patients continue to have MI’s, strokes, overdoses and many other emergencies. And these emergencies too still deserve our excellent care and diligence not to miss. So although we plan to have another special edition COVID update episode soon we don’t want to neglect these other emergencies. This month we talk Large Vessel Occlusions.

• Endovascular Stroke therapy (EST) for large vessel occlusion (LVO) – This is the hottest therapy since PCI – 12 studies since 2013, 5 studies in 2015 alone 
  • For a nice review of all of the studies and evolution of endovascular therapy visit:
    • https://rebelem.com/endovascular-therapy-for-acute-ischemic-stroke-the-new-shiny-toy-in-stroke-care/

• How is EST performed? 
  • A catheter is guided through one of the femoral arteries and up through the carotid and into the distal internal carotid, anterior cerebral artery or the middle cerebral artery
  • A clot retrieval device is fed through the catheter in order to retrieve the clot
  • Unlike tPA which has only shown very marginal benefit in just a few studies that were admittedly methodologically flawed. EST has recently had multiple strongly positive trials showing impressive benefits (although these benefits are likely over estimated, see the link above for a deep dive on the researches strengths and weaknesses)

• Who Qualifies for EST?
  • Initially studies for all comers with stroke receiving EST found no benefit
  • It wasn’t until they identified a subset of patients with Large Vessel Occlusions (LVO) that they began to see these impressive benefits
  • An LVO is defined as clot located in either the distal internal carotid, proximal anterior cerebral artery (ACA), or the proximal middle cerebral artery (MCA)
  • Not every stroke center has the capability to perform EST
    • Similar to the early days of PCI for myocardial infarctions when cath lab centers were farer and fewer between
  • What is the timeline to qualify for EST
    • Will likely vary based on your stroke center and may change with future studies so make sure you stay up to date with your local protocols.
      • Initial studies looked at less than 6 hour time window and is what the American stroke guidelines currently recommend. 
      • A lot of places have started pushing this time window further out and locally here we us a cut off of less than 24 hours
• So do we need to start re-organizing our transport priorities and transporting all of our suspected strokes to EST centers similarly to how we transport all of our STEMI’s to cath centers?
  • No, here’s where we don’t wanna get ahead of ourselves
    • With STEMI we have a clear diagnostic tool with our EKG to determine if somebody needs the cath lab. 
      • In order to know for sure if our patient would need EST we would need a CT scanner. And not just CT but also the ability to do CT with contrast in order to see which vessel the clot is in.
      • If there is even a clot at all. Given so many mimickers of stroke on a very small percentage of patients evaluated for concern for stroke actually end up having a stroke
    • Which brings us to the second point of why we don’t want to start transporting to only EST centers: Only a select number of stroke patients, those with clots in the large proximal vessels, will benefit from this therapy. 
      • Early trials from 2013 looked at utilizing this therapy for all comers with stroke and found no benefit when compared to tPA alone. 
        • It wasn’t until later trials when they narrowed the patients they were treating to those with identified LVO in the arteries mentioned before: distal internal carotid, proximal ACA, and proximal MCA that they started finding benefit. 
      • So even if we were sure our patient was having a stroke based on our exam they still would only benefit from transport to an EST if it was in one of these specific large and proximal vessels.
        • It turns out that only 1 in 770 of stroke patients will have an occlusion meeting criteria for EST. 
        • And that’s in patients who WE KNOW are having a stroke. Can you imagine what that number would be if we included everyone we just suspected of having a stroke? We would overwhelm the hospital. 

• So are there any physical exam findings to help us determine those likely to have a LVO and thus should be transported to one of these centers?
  • There’s not strong enough evidence to suggest such a protocol yet so for now keep transporting to your nearest local stroke center per your protocol 
  • But there are researchers looking at some prehospital scores to help with this question and we should be aware of and keep on the lookout for future data and research on this. See some of the prehospital scores and their associated ealy research below.
• VAN score – vision, aphasia, neglect
  • About the data: https://jnis.bmj.com/content/neurintsurg/9/2/122.full.pdf
    • 62 patients, 31% (19) were VAN positive
    • 90% of those had an LVO and no LVO’s occured in the VAN neg group. 
    • This is a small feasibility study. This means it was a smaller study done solely to determine if a larger more robust trial should be completed. Feasibility trials should not be used to change current care.
  • How do you do the exam?
    • Start with bilateral arm raise for 10 seconds
      •  if any drift then proceed with the VAN assessment, 
    • If any of the following are positive in a patient with arm drift then they are considered VAN positive
      • Visual fields
        • Check all 4 quadrants one eye at a time
        • I cover one eye and ask 1 or 2 fingers in each quadrant. 
        • If the patient is having difficulty cooperating you can blink to threat in all quadrants. 
          • Blink to threat
            • Move your hand quickly towards their eye from the quadrant you are testing (but don’t actually hit them).
            • If they blink you assume the vision is intact.
      • The next component is Aphasia
        • Aphasia either expressive or receptive. 
          • Expressive
            • Can’t say words or doesn’t say the right words 
          • Receptive
            • Unable to understand what you are saying. 
        • Important: 
          • Aphasia is different from dysarthria which is slurred speech.
          • Dysarthria is not what we are testing or scoring here.
      • Finally Neglect
        • Have the patient close both eyes and then you touch both of their arms with your fingers and ask which arm you are touching, if the patient fails to identify the weak arm (the arm you identified with a drift earlier) this is considered neglect. 
        • Other signs of neglect are an inability to track your finger beyond midline or a forced gaze deviation to one side. 
  • The pathophysiology behind why this should predict an occlusion in one of the large vessels amenable to EST:

Image courtesy of rebelem: https://rebelem.com/does-it-take-a-van-to-identify-emergent-large-vessel-occlusion-elvo-in-ischemic-stroke/

• Cincinnati pre-hospital severity stroke scale
  • About the data:
    • In the original derivation study it was found to have a sensitivity 83% and specificity 40% for identifying patients with a LVO. 
      • Katz BS, Mcmullan JT, Sucharew H, Adeoye O, Broderick JP. Design and validation of a prehospital scale to predict stroke severity: Cincinnati Prehospital Stroke Severity Scale. Stroke. 2015;46(6):1508-12.
      • However, in an externally it was found to have a sensitivity of 70% and specificity of 86%. 
        • Kummer BR, Gialdini G, Sevush JL, Kamel H, Patsalides A, Navi BB. External Validation of the Cincinnati Prehospital Stroke Severity Scale. J Stroke Cerebrovasc Dis. 2016;25(5):1270-4.
  • See MDcalc for the scoring details: https://www.mdcalc.com/cincinnati-prehospital-stroke-severity-scale-cp-sss#next-steps
• RACE
  • About the data:
    • In the original study a RACE Scale value of ≥5 had a sensitivity 85% and a specificity of 68% for identifying an LVO. 
      • Pérez de la Ossa N, Carrera D, Gorchs M, et al. Design and validation of a prehospital stroke scale to predict large arterial occlusion: the rapid arterial occlusion evaluation scale. Stroke. 2014;45(1):87-91.
    • A second study was designed to assess whether or not bypassing patients to a Comprehensive Stroke Center with a RACE Scale ≥5 would improve outcomes. 
      • Zaidi SF, Shawver J, Espinosa morales A, et al. Stroke care: initial data from a county-based bypass protocol for patients with acute stroke. J Neurointerv Surg. 2016; Jun 24. pii: neurintsurg-2016-012476. doi: 10.1136/neurintsurg-2016-012476. [Epub ahead of print]
      • The results of this study showed an increased treatment rate, improved door-to-CT times, and improved door-to-needle times. 
      • The rate of mechanical thrombectomy also increased with improved arrival-to-puncture and arrival-to-recanalization times as well. 
      • However, there was only a small trend toward improved outcomes that did not reach statistical significance.
  • See MDcalc for the scoring details: https://www.mdcalc.com/rapid-arterial-occlusion-evaluation-race-scale-stroke
• FAST ED
  • The data:
    • Lima FO, Silva GS, Furie KL, et al. Field Assessment Stroke Triage for Emergency Destination: A Simple and Accurate Prehospital Scale to Detect Large Vessel Occlusion Strokes. Stroke. 2016;47(8):1997–2002. doi:10.1161/STROKEAHA.116.013301 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4961538/
  • There’s an app for that
    • https://www.ahajournals.org/doi/full/10.1161/strokeaha.116.016026
• ELVO screen 
  • The data:
    • Kentaro Suzuki , Nobuhito Nakajima, Kenta Kunimoto, et. al. Emergent Large Vessel Occlusion Screen Is an Ideal Prehospital Scale to Avoid Missing Endovascular Therapy in Acute Stroke.. Stroke. 2018;49:2096–2101.
• American stroke algorithm for when to bypass and transport to an EST capable facility
  • Algorithm: https://www.heart.org/-/media/files/professional/quality-improvement/mission-lifeline/2_25_2020/ds15698-qi-ems-algorithm_update-2142020.pdf?la=en&hash=A0AB5E209AC78933C54E41C3FF235B60F9CC4A7C
  • Complete reference: https://www.heart.org/en/professional/quality-improvement/mission-lifeline/mission-lifeline-stroke

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