Would you take an acute STEMI patient to a non-interventional catheter lab? If not, would you take a stroke patient with a high probability of large vessel occlusion (LVO) to a hospital that does not provide endovascular thrombectomy for clot removal? The conventional wisdom for EMS providers is to transport a stroke patient to a hospital within a certain time frame for tissue plasminogen activator (tPA) treatment to break up the clot. The advancement in endovascular thrombectomy techniques to remove clots are changing this paradigm, though. LVO is a blockage of one or several of the main cerebral arteries that supply the brain with blood, and they account for 40-50% of ischemic strokes. TPA given to patients with a LVO CVA has been shown to have little or no effect on recanalization and reperfusion, which is our ultimate goal. Around 80% of patient with a LVO who did not receive effective treatment will die within 90 days or become functionally disabled. Since tPA has little effect on LVO, the paradigm shift is to get these patients to a stroke center that provides mechanical and/or endovascular thrombectomy. The earlier the clot is removed, the better the neurological outcome.
Studies are still ongoing regarding what the optimal time frame is from onset of symptoms to mechanical recanalization. However, one study showed that patients who received recanalization within 8 hours after onset had a modified Rankin score of 2 after 90 days (0=no symptoms and 6=death). Most studies such as the MR CLEAN study used a 6 hour window of symptom onset to intra-arterial recanalization. At 90 days, they used the odds ratio of achieving a lower score on the modified Rankin scale (shift analysis) with endovascular therapy. This was achieved with an odds ratio of 1.67 (95% confidence interval, 1.21 – 2.30), which means having a reduced Rankin score is highly likely. Dr. Dipple, lead author of the MR CLEAN study, stated that “Standard treatment of stroke, including tPA if indicated, leads to 1 in 5 of these patients having a good outcome. With intra-arterial intervention, as in our study, 1 in 3 patients had a good outcome. That is a huge improvement.” The recent DAWN trial showed that there is hope for patients who had endovascular thrombectomy between 6 and 24 hours after the onset of symptoms. The rate of functional independence for the group that received endovascular thrombectomy at 90 days was 49% compared to 13% for the control group. Endovascular thrombectomy is a game changer in the treatment of stroke. The sooner it is performed, the better.
In the prehospital setting, clinicians have several scales to quickly assess their patients for stroke. Is there a stroke scale that helps determine a high probability of LVO specifically? Yes, the Rapid Arterial Occlusion Evaluation (RACE) stroke scale. The RACE scale is based on the National Institute of Heath Stroke Scale (NIHSS); the qualitative comprehensive scale used in most hospitals. The items on the NIHSS that had a high predictable value of LVO were used to create the RACE scale. The predictive value of the RACE scale and the NIHSS for detecting LVO had a high correlation of 0.93 (P.001). The RACE scale is a 6 item scale, and each item has a score that can be assigned. A score of 5 or above has an 85% probability of a LVO stroke. South Carolina EMS utilizes an excellent checklist/handout that describes how to perform and score the RACE stroke scale, as shown below:
The RACE stroke scale for detecting LVO is being compared to the 12-lead ECG in detecting myocardial infarction and early activation of the cardiac cath lab. Early detection of a LVO stroke can lead to an early endovascular thrombectomy. Memorial Health Care Systems in Florida is already doing this. When EMS calls in a stroke patient with a RACE score of 5 or higher, the cath lab is alerted of a possible mechanical thombectomy. As more research is published regarding advances in clot retrieval methods, I see changes to EMS triage protocols that include transportation of stroke patients to definitive care.
YouTube links for how to do the R.A.C.E. scale and mechanical thrombectomy:
Clot retrieval with mechanical thrombectomy
Actual stroke patient before, during, and after recanalization
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