Perceived Limits of Endovascular Treatment for Secondary Medium-Vessel-Occlusion Stroke

DISCUSSION

Our findings suggest that a physician’s willingness to treat secondary MeVOs endovascularly is limited and varies per occlusion location. Most participants were in favor of treatment of M2/3 (74.3%) and A3 (59.7%) occlusions, while less than one-third opted to proceed with EVT for the more distally located M3/4 occlusions (28.3%). These data suggest that there is a certain limit to what is perceived as safely achievable and accessible for EVT. Cases that were used to create illustrative scenarios in the survey were successfully achieved and treated endovascularly. Therefore, this finding of the limit based on occlusion location more likely reflects subjective operator experience. Indeed, a too-distal location of the thrombus was the second most frequent reason given by the survey participants for no EVT.

Physicians were less likely to pursue secondary MeVOs if the patient’s clinical status improved in the scenarios in which distal embolization occurred in the initially affected territory (M2/3, M3/4). This scenario is suggestive of a hesitation of physicians to pursue EVT in secondary MeVOs in cases of early neurologic improvement. Furthermore, studies suggest that achieving TICI 2b with fewer passes is associated with better outcome compared with TICI 2c/3 reperfusion achieved with more passes.⁶ The neurologic status had no impact on the participants’ decisions to treat the presented case of A3 MeVO. This might be due to the initially unaffected anterior cerebral artery territory being supplied by the contralateral ICA. Thus, this MeVO can be considered embolization into a new territory, which may have affected the physician’s willingness to treat.

Physician’s characteristics related to an increased likelihood of immediate EVT in secondary MeVOs were interventional specialty, more experience in neurointervention, and higher annual case volumes. These are likely because interventionalists encounter such cases on a more frequent basis because LVOs migrate distally and become secondary MeVOs.⁵ In contrast, an average stroke neurologist likely has a limited knowledge of interventional techniques and, therefore, is unable to decide whether a distally located occlusion is accessible for EVT and can be successfully retrieved. Nevertheless, even noninterventionalists and less experienced neurointerventionalists would consider EVT based on either persistent occlusion on repeat DSA or after neurologic reassessment (Online Supplemental Data).

The eloquence of the affected territory plays an important role in EVT decision-making in patients with MeVO stroke. Despite MeVO’s relatively smaller vascular territory in comparison with LVO, the impact of ischemia can be severely disabling,⁷ for example, the loss of language skills due to a left anterior M2/M3 occlusion. In secondary MeVO strokes, evaluation of a patient’s neurologic status can be challenging because the neurologic deficit might be influenced by the initial LVO stroke.⁴ In the presented cases of secondary MeVOs in our survey, the most frequent reason for no EVT was that the benefits are too small: The affected areas were not considered responsible for the patients’ neurologic deficits, or the potential risks of the procedure were perceived to be greater than the benefits of the treatment. For example, due to the perceived fragility of the more distal, smaller-caliber vessels, there may be a potential risk of higher complication rates in MeVOs (eg, perforation, intracranial dissection).

Another aspect of a physician’s decision-making is the presence/absence of collateral flow in the affected area. If collateralization behind the occlusion is insufficient, the willingness to pursue distally located occlusions will be higher than in the case of rapid retrograde filling of the vascular bed. As a part of each case presentation, we included an image demonstrating a parenchymal phase on DSA (Online Supplemental Data) to account for this factor; however, a single image cannot replace a complete DSA run, and participants may have thought that they did not have enough information to make a decision.

The accessibility of more distally located occlusions is highly dependent on the available material. In our survey, we did not imply what EVT technique should be used, and it was left to the physician’s own judgment and experience to decide whether the presented occlusion was accessible. The potential challenges of MeVO EVT lie in the progressively changing and generally smaller caliber of the vessels, as well as thinner vessel walls in comparison with the more proximal vessel segments.⁸ Based on a recent systemic review by Ospel and Goyal,⁴ the most commonly reported complication in MeVO EVT was symptomatic intracranial hemorrhage. The prevalence of symptomatic intracranial hemorrhage ranges from 0% to 11%, with most studies reporting symptomatic intracranial hemorrhage rates of <8%,⁴ ie, slightly higher than that reported in the major LVO studies.⁹ One of the hypothesized mechanisms of periprocedural complications is endothelial injury during stent-retriever expansion and thrombus retrieval.^10,11 This could possibly apply even more to fragile, smaller distal vessels, while it has been shown that the radial force of stent retrievers gradually rises as the vessel diameter decreases.¹⁰ Smaller and softer devices that can be delivered through smaller microcatheters with an optimized vector of force to avoid pulling the whole vessel along with it are, therefore, warranted.

The optimization of the vector of force can be accomplished using an appropriately sized distal access catheter in conjunction with a stent retriever; such an approach can also decrease the risk of embolization into new territories. With the recent development of longer microcatheters¹² that enable delivery of stent retrievers to desired target locations, the option of coaxial delivery of a distal-access catheter over the microcatheters, and recent progress in the development of smaller stent retrievers showing promising results in achieving successful recanalization in MeVOs,¹³ the perception of the thrombus accessibility is likely to be shifted beyond the M3 or A3 vessel segments, particularly as experience with the novel material further increases.

Our study has limitations. First, the included participants were contacted through personal and professional networks of the study authors, and most (92.1%) were working in teaching hospitals. Therefore, responses may not be representative of the entire stroke community, and ascertainment bias may have occurred while more experienced and skillful interventionalists from high-volume teaching centers were predominantly represented in the survey dataset. However, replies from all over the world were collected, and we particularly assessed differences between regions to support correct local interpretation of the results. Moreover, we believe that the clinical practice in rich countries and teaching institutions serves as exemplary care that is usually followed by the rest of the medical society. Second, survey data do not always reflect real-world clinical practice. Physicians’ choices may be different in practice when facing diverse practical obstacles. Third, participants may have expected that a certain answer to the question was desired from them, probably in favor of EVT, given that the survey is conducted and spread in a research network partly dedicated to improving EVT results. We tried to minimize this effect by making all responses fully anonymous. Fourth, we did not collect information regarding institutional standard stroke imaging protocols and, therefore, did not assess the impact of various imaging protocols on participant decision-making. Because the EVT decision-making was based on the findings of DSA images, the baseline imaging (either CT or MR) played only an illustrative role in the presentation of the secondary MeVO cases. Finally, physicians could have been biased by the vascular anatomy provided for a particular case; our results regarding the occlusion sites are, therefore, not generalizable.

Due to lack of high-level evidence, a decision toward continuing with EVT in secondary MeVOs is mainly made on an individual basis and involves thrombus accessibility, eloquence of the affected territory, a patient’s current condition, and potential risks of the procedure. Therefore, it is clear that physicians vary in their treatment preferences with respect to secondary MeVOs and that experience with such cases is likely to play a role. Despite increasing effort to conduct a randomized controlled trial of EVT in patients with MeVO stroke, it is unlikely that patients with secondary MeVO will be randomized because it is not feasible to randomize patients during an ongoing EVT procedure. However, more evidence on the safety and efficacy of EVT for MeVO stroke is needed, for which observational or survey data could be of great use.