Acute Stroke Intervention and the Interventional Radiology Trainee

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.

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