Written By: Joseph Marion, MD; Jacob Fleming; David Bamshad; Muhammad Noor; Jesus Conteras, MD, and Erica Alexander, MD

With Guidance From: David Sacks, MD, Martin Radvany, MD, and Geogy Vatakencherry, MD

It is no mystery that major changes impacting stroke therapy have taken place over the past several years. Mechanical thrombectomy of large vessel occlusive (LVO) ischemic strokes has changed guidelines, protocols, and lives since first published in 2015 (1-4). The need for such a therapy is real, with approximately 691,650 ischemic strokes every year, and an estimated 11% (or 24 per 100,000 person years) of those being LVOs (5,6). This patient population is further divided into patients that qualify for thrombectomy and those who do not. Contraindications to mechanical thrombectomy include unfavorable imaging findings as well as pre-stroke disability measured with the modified Rankin Scale score. The number of patients who are thrombectomy eligible is likely between 7 and 22 per 100,000 person years (6,7). This range of patients is derived from studies that relied on the then-current guidelines limiting thrombectomy to patients with LVO presenting within 6 hours of symptom onset. The recently published DAWN and DEFUSE 3 trials have expanded the indication for thrombectomy to select patients who present between 6 and 24 hours after symptom onset, and the latest AHA/ASA guidelines for 2018 have been revised to reflect these findings (8-10). While there are no published epidemiological analyses that take this new data into account, the number of indicated cerebral thrombectomies is certain to rise.

An estimated 10,284 mechanical thrombectomy procedures occurred in 2015 (6). This translates into three thrombectomy procedures per 100,000 person years, and leaves considerable room for growth in making this treatment available across the country. Currently, there is ongoing debate on how to best expand access to such a vital treatment. Gupta et.al showed that high volume centers performed better and had better patient outcomes from 2009 to 2011 and outlined areas for improvement (11). Both Zaidat et.al and Adamczyk et.al also argue for a centralized approach to stroke care (12,13). Although a centralized approach allows for careful resource utilization and greater experience for a small number of interventionalists, delaying treatment in order to transport patients to centralized stroke centers results in worse patient outcomes with fewer candidates for thrombectomy after transport (6,14). In response to this, The Joint Commission recently announced a new certification for “thrombectomy-capable stroke centers” which could allow smaller medical centers to establish thrombectomy services (15). Aside from the benefit of bringing thrombectomy to more patients quickly, this approach addresses disparities in care. Nationally, rates of mechanical thrombectomy are higher in whites and patients with higher socioeconomic status, while African Americans and patients with lower socioeconomic status are at equal or higher rates of stroke (16). Additionally, geographic distribution of stroke centers makes it difficult or impossible for patients to reach care, including in areas of the southeast where stroke rates are the highest in the country (17). Given these findings, it is best to establish thrombectomy-capable stroke centers that are accessible to more patients, and work to improve systems and outcomes at smaller stroke centers rather than centralizing and restricting access to mechanical thrombectomy.

The challenge of covering 24/7 thrombectomy call will be difficult for smaller stroke centers. At least 2 to 3 neurointerventionalists will be needed to cover the call schedule. The number of neurointerventionalists must increase if the number of thrombectomy capable stroke centers is to rise, although maintaining the number of neurointerventionalists has been a topic in the neurointerventional literature for several years. Jabbour et.al argued in 2013 that all neurointerventional fellowship training should be suspended until future need for neurointerventional services could be determined (18). Rai stated in 2015 that there could be an oversupply of neurointerventionalists in regards to endovascular aneurysm treatment, but an undersupply in regards to mechanical thrombectomy treatment with its expanded indication. This raises the large issue of maintaining an adequate supply of stroke interventionists, while also not saturating the neurointervention job market. One route to solve this is to increase the number of neurointerventionalists to meet the demand of mechanical thrombectomy in the hopes that neurointerventionalists will find enough work beyond stroke call responsibilities. The second option is to centralize resources, which risks worse patient outcomes and fewer patients able to undergo thrombectomy after transport, as already discussed. A third option would be to engage interventional radiologists who have training or amassed experience in stroke intervention, specifically cerebral angiography and mechanical thrombectomy. This option would also not diminish the number of cerebral aneurysm and neuro embolization cases performed by fellowship trained neurointerventionalists.
Interventional radiologists have training and experience with micro catheters and stent retriever devices in peripheral vessels and in many instances have extensive experience with neurovascular diagnostic and therapeutic procedures. Interventional radiologists who perform mechanical thrombectomy for LVO strokes have validated outcomes comparable to neurointerventional trained physicians (19-21). Most notably, data from interventional radiologists in the Czech Republic closely matched that from the HERMES collaboration data of the randomized control trials (22,23). Interventional radiologists have the skillset to perform mechanical thrombectomy and the training to interpret acute neurologic imaging used to diagnose cerebral infarction. Sacks argues that patient outcomes from approximately 1000 acute stroke cases performed by interventional radiologists who have received the appropriate additional training were similar to the patient outcomes of cases performed by neurointerventional physicians (24). Newly accredited interventional radiology residency programs have the opportunity to grow clinical experience for trainees as it relates to stroke care (25).

Rigorous training guidelines must be created to establish clear standards for residency programs. Current standards put forth by the Committee for Advanced Subspecialty Training (CAST) make clear recommendations for neurointerventional fellowships that are available to neurosurgeons, neurologists and neuroradiologists (26). At the completion of a CAST accredited fellowship, trainees are able to perform the full spectrum of neurointervention. The CAST guidelines do not, however, take into account the disparity of a tight neurointerventional job market with the growing demand of mechanical thrombectomy.

The Society of Interventional Radiology is stepping up to answer the call and put forth rigorous training guidelines. In 2009, Connors et.al published training guidelines to specifically address stroke intervention training, which were adopted by SIR as a standard of practice (27). These guidelines include cognitive, brain imaging, technical, stroke and facility requirement topics related to endovascular stroke therapy training and provide a comprehensive pathway for interventional radiologists to safely and effectively offer mechanical thrombectomy services. Much has happened in the field of stroke intervention since 2009 and SIR is in the process of revising the training guidelines. Implementing these training guidelines into interventional radiology residencies and extending training after residency will create highly competent interventionalists capable of meeting the nationwide demand for interventional stroke therapy.

It must be noted that challenges still exist for interventional radiologists that offer stroke therapy. For example, The Joint Commission has made CAST fellowship completion an eligibility requirement for establishing a thrombectomy capable center. By doing this, a substantial group of physician leaders are excluded from establishing capable centers with appropriate support, and disregards patient outcomes. SIR is actively taking steps to amend these requirements to include appropriately trained interventional radiologists. Additionally, neurointerventionalists will continue to make efforts to centralize stroke care, and interventional radiologists will be tasked with proving their outcomes at smaller medical centers.

References:
1. Berkhemer OA, Fransen PS, Beumer D, et al. A randomized trial of intraarterial treatment for acute ischemic stroke. N Engl J Med. 2015;372(1):11-20.
2. Campbell BC, Mitchell PJ, Kleinig TJ, et al. Endovascular therapy for ischemic stroke with perfusion-imaging selection. N Engl J Med. 2015;372(11):1009-1018.
3. Goyal M, Demchuk AM, Menon BK, et al. Randomized assessment of rapid endovascular treatment of ischemic stroke. N Engl J Med. 2015;372(11):1019-1030.
4. Saver JL, Goyal M, Bonafe A, et al. Stent-retriever thrombectomy after intravenous t-PA vs. t-PA alone in stroke. N Engl J Med. 2015;372(24):2285-2295.
5. Benjamin EJ, Blaha MJ, Chiuve SE, et al. Heart Disease and Stroke Statistics-2017 Update: A Report From the American Heart Association. Circulation. 2017;135(10):e146-e603.
6. Rai AT, Seldon AE, Boo S, et al. A population-based incidence of acute large vessel occlusions and thrombectomy eligible patients indicates significant potential for growth of endovascular stroke therapy in the USA. J Neurointerv Surg. 2017;9(8):722-726.
7. Chia NH, Leyden JM, Newbury J, Jannes J, Kleinig TJ. Determining the Number of Ischemic Strokes Potentially Eligible for Endovascular Thrombectomy: A Population-Based Study. Stroke. 2016;47(5):1377-1380.
8. Albers GW, Marks MP, Kemp S, et al. Thrombectomy for Stroke at 6 to 16 Hours with Selection by Perfusion Imaging. N Engl J Med. 2018.
9. Nogueira RG, Jadhav AP, Haussen DC, et al. Thrombectomy 6 to 24 Hours after Stroke with a Mismatch between Deficit and Infarct. N Engl J Med. 2018;378(1):11-21.
10. Powers WJ, Rabinstein AA, Ackerson T, et al. 2018 Guidelines for the Early Management of Patients With Acute Ischemic Stroke: A Guideline for Healthcare Professionals From the American Heart Association/American Stroke Association. Stroke. 2018.
11. Gupta R, Horev A, Nguyen T, et al. Higher volume endovascular stroke centers have faster times to treatment, higher reperfusion rates and higher rates of good clinical outcomes. J Neurointerv Surg. 2013;5(4):294-297.
12. Adamczyk P, Attenello F, Wen G, et al. Mechanical thrombectomy in acute stroke: utilization variances and impact of procedural volume on inpatient mortality. J Stroke Cerebrovasc Dis. 2013;22(8):1263-1269.
13. Zaidat OO, Lazzaro M, McGinley E, et al. Demand-supply of neurointerventionalists for endovascular ischemic stroke therapy. Neurology. 2012;79(13 Suppl 1):S35-41.
14. Froehler MT, Saver JL, Zaidat OO, et al. Interhospital Transfer Before Thrombectomy Is Associated With Delayed Treatment and Worse Outcome in the STRATIS Registry (Systematic Evaluation of Patients Treated With Neurothrombectomy Devices for Acute Ischemic Stroke). Circulation. 2017;136(24):2311-2321.
15. The Joint Commission. Certification for Thrombectomy-Capable Stroke Centers. 2018; https://www.jointcommission.org/certification/certification_for_thrombectomycapable_stroke_centers.aspx. Accessed Feb 3, 2018.
16. Attenello FJ, Adamczyk P, Wen G, et al. Racial and socioeconomic disparities in access to mechanical revascularization procedures for acute ischemic stroke. J Stroke Cerebrovasc Dis. 2014;23(2):327-334.
17. Schieb LJ, Casper ML, George MG. Mapping Primary and Comprehensive Stroke Centers by Certification Organization. Circ Cardiovasc Qual Outcomes. 2015;8(6 Suppl 3):S193-194.
18. Jabbour P, Fiorella D. Are we training too many neuroendovascular fellows? World Neurosurg. 2013;79(1):9-10.
19. Belisle JG, McCollom VE, Tytle TL, et al. Intraarterial therapy for acute ischemic strokes. J Vasc Interv Radiol. 2009;20(3):327-333.
20. Burkart DJ, Day JS, Henderson K, Borsa JJ. Efficacy of peripheral interventional radiologists performing endovascular stroke therapy guided by CT perfusion triage of patients. J Vasc Interv Radiol. 2013;24(9):1267-1272.
21. Fjetland L, Roy S, Kurz KD, Larsen JP, Kurz MW. Endovascular acute stroke treatment performed by vascular interventional radiologists: is it safe and efficacious? Cardiovasc Intervent Radiol. 2012;35(5):1029-1035.
22. Goyal M, Menon BK, van Zwam WH, et al. Endovascular thrombectomy after large-vessel ischaemic stroke: a meta-analysis of individual patient data from five randomised trials. The Lancet. 2016;387(10029):1723-1731.
23. Volny O, Krajina A, Belaskova S, et al. Mechanical thrombectomy performs similarly in real world practice: a 2016 nationwide study from the Czech Republic. J Neurointerv Surg. 2017.
24. Sacks D. Interventional Radiologists and Endovascular Therapy for Acute Ischemic Strokes. J Vasc Interv Radiol. 2017;28(8):1137-1140.
25. Kaufman JA. The interventional radiology/diagnostic radiology certificate and interventional radiology residency. Radiology. 2014;273(2):318-321.
26. Day AL, Siddiqui AH, Meyers PM, et al. Training Standards in Neuroendovascular Surgery: Program Accreditation and Practitioner Certification. Stroke. 2017;48(8):2318-2325.
27. Connors JJ, 3rd, Sacks D, Black CM, et al. Training guidelines for intra-arterial catheter-directed treatment of acute ischemic stroke: a statement from a special writing group of the Society of Interventional Radiology. J Vasc Interv Radiol. 2009;20(12):1507-1522.