Endovascular Therapy for Acute Stroke: A Multidisciplinary Team Discussion

Robert Brown, MD; Alejandro Rabinstein, MD; David Kallmes, MD; Giuseppe Lanzino, MD

Disclosures

October 18, 2016

Editorial Collaboration

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Dr Robert Brown, MD: Greetings. I'm Dr Robert Brown, chair of the division of stroke and cerebrovascular disease at Mayo Clinic. During today's discussion, we'll be talking about stroke and endovascular therapy. I'm joined by my colleagues, Drs Alejandro Rabinstein, David Kallmes, and Giuseppe Lanzino, who are specialists in this area. Welcome.

Several recently published studies have demonstrated the effectiveness of endovascular therapy for acute ischemic stroke. Can you provide a general summary of these studies and what we have learned? Dr Rabinstein?

Recent Trials of Endovascular Therapy in Stroke

Alejandro Rabinstein, MD: That is correct. Last year, we were happy to see the publication of five randomized controlled trials comparing conventional treatment of acute ischemic stroke—which could include intravenous thrombolysis—vs acute endovascular therapy, primarily through mechanical thrombectomy using new devices called retrievable stents, which are more effective in achieving recanalization or reperfusion of major intracranial vessels.[1,2,3,4,5] The results of these five trials were consistently very positive. In essence, they demonstrated that acute endovascular therapy is very effective in improving functional outcomes in patients with major acute ischemic stroke.

The magnitude of the benefit was variable across the trials but very convincing throughout. To summarize those outcomes, one can say that the proportion of patients who achieved functional independence at 90 days varied between one-third and 71% of the patients treated endovascularly. That results in a number necessary to treat between 3 and 7, which one could say is spectacularly good. And this was compared against patients that could have received intravenous thrombolysis.

Now, one has to take into account that not every acute-stroke patient is a candidate for endovascular therapy. The good candidates are adult patients who have good prestroke function and who present with disabling neurological deficits from a proximal intracranial vessel occlusion and do not have any extensive acute ischemic changes on the head [computed tomography] CT scan. Time is also essential. The benefit was greatest when the endovascular treatment could be initiated within 6 hours of symptom onset. There was some variation across trials in regard to the method of identification of the best patients or the patients who could be randomized. But overall, the substantial benefit achieved by endovascular therapy in these trials has been a game-changer in practice.

Selecting Patients and Imaging

Dr Brown: Thank you. Dr Kallmes, Dr Rabinstein did allude to those patients who might be selected for this therapy. From your standpoint, what are the key factors in selecting patients who would be optimal candidates based on the data from these clinical trials?

David Kallmes, MD: [Dr Rabinstein] did hit the high points, but I would say that similar to acute [myocardial infarction] MI where time is of the essence, in acute ischemic stroke, time is brain. Among the three major factors he talked about—time since onset, degree of neurological deficit, and changes on CT scan—we've always got to focus on time. We are in a nonhurried rush to get the patient to the angiogram table, get the catheter in the artery, and get the clot out. There have been post hoc analyses from these same studies showing that even 15 minutes can yield substantial changes in outcome. So, time of onset is key. Get the patient to the angio table as soon as possible.

Second, degree of neurological deficit. While some of the trials allowed [National Institutes of Health] NIH Stroke Scale of just 2, generally it will be a more disabling NIH Stroke Scale—8, 9, or higher—that we want to target for endovascular therapy.

Last, you want to look very carefully at just the plain, old-fashioned 1980s noncontrast CT scan to look for subtle changes that suggest irreversible injury. We have a scale of 0 to 10 called the Aspects Scale, and if the patient's score is 6 or above, that means they have sufficient, probable salvageable tissue to be a candidate for endovascular therapy. Time, degree of neurological deficit, and findings on old-fashioned plain CT scan.

Dr Brown: Thank you. Dr Rabinstein, how have these studies changed the early evaluation and management of acute ischemic stroke and, in particular, what imaging studies can be used in the emergency-room setting to guide the next step in therapy? Dr Kallmes alluded to a CT scan without contrast, which has been in place for many, many years. Are there other imaging strategies that you and colleagues have found to be helpful as well?

Dr Rabinstein: Yes, and the trials actually require the use of a CT angiogram to select candidates. Trials before these five positive trials have randomized patients without proof that they had a proximal intracranial vessel occlusion. In these trials, there was a requirement that the CT angiogram be conducted, and it had to prove that there was an occlusion in the supraclinoid, most distal portion of the intracranial internal carotid artery, or the proximal segment of the middle cerebral artery.

Furthermore, the same CT angiogram can be used to evaluate, to some degree, the collateral flow, which is very important in maintaining viability of the brain tissue when there is a proximal occlusion. Alternatively, another trial and many centers across the US and other parts of the world, use perfusion scans—either CT perfusion or MRI diffusion/perfusion—to determine the mismatch between the core of the infarction that is presumably impossible to salvage vs the total area of hypoperfusion, the difference between these two being the number of our salvageable tissue. The big question at this point is whether doing this type of advanced imaging scans is a measure that can improve patient selection enough to account for the extra time that is required for their performance.

Acute Stroke Care in Resource-Poor Environments

Dr Brown: How should a medical center approach care of acute ischemic stroke—and, in particular, imaging and endovascular therapies—if the therapies are not available due to the rural location of that hospital?

Dr Rabinstein: That may depend on each center and the logistics of each region, but we have three types of places where acute stroke can be treated: stroke-ready centers where intravenous thrombolysis can be administered, but the patients then have to be transferred out for additional postthrombolysis care; primary stroke centers that can administer intravenous thrombolysis and keep the patients for postthrombolysis care; and then the comprehensive stroke centers, such as ours, where patients can receive both intravenous thrombolysis, all the subsequent medical treatment, and endovascular stroke therapy.

The current practice is that the patients are triaged to the nearest hospital where they can receive intravenous thrombolysis if the patients are suspected to have an acute ischemic stroke. They can arrive to the emergency department so that they can receive intravenous thrombolysis within the accepted window of 4 to 5 hours from symptom onset. From there, the rest of the evaluation can proceed.

The stroke-ready hospitals typically do not have CT angiogram or additional imaging capabilities. In those cases, we rely on the clinical syndrome and decide where the patient should be transferred, whether to a primary stroke center or to a comprehensive stroke center. Alternatively, if the patients are in the primary stroke center, we have the option of confirming the presence of a proximal intracranial vessel occlusion amenable to endovascular therapy. In such cases, we proceed with a CT angiogram before deciding on the transfer. If the CT angiogram confirms the presence of a proximal intracranial vessel occlusion, then the patient gets transferred to a comprehensive stroke center. Otherwise, the patient can stay in the primary stroke center.

Dr Brown: Thank you. And that's likely the case, too, that many hospitals in rural areas now have a connection with a larger medical center via telestroke that can provide an audio/video connection between the tertiary medical center, that is the comprehensive stroke center, and the rural hospital so as to assist with that acute care.

Dr Rabinstein: That's very true.

Key Issues and Complications in Endovascular Therapy

Dr Brown: Dr Lanzino, from your standpoint as one of the colleagues who performs this procedure, what are some of the key issues you face in using this procedure for acute ischemic stroke?

Guiseppe Lanzino, MD: I think the two main key issues are related to time to revascularization and selection of patients. As Dr Kallmes has stressed, it's extremely important to go fast. A full team should be mobilized within a few minutes, and that often requires a complete cultural change compared with traditional care of patients with acute ischemic stroke.

The other factor is selection of the correct patients. Despite advances in imaging, we still are not completely sure about the maximum time window to perform these procedures. We don't want to exclude patients who could potentially benefit from the treatment. But at the same time, we need to utilize resources so that, ideally, we intervene only on those patients who can benefit from these expensive and resource-consuming procedures.

Those are the two main areas where we can and should continue trying to improve. As far as time to revascularization, we have improved a lot, but any minimal change will allow us to gain even a few minutes, as Dr Kallmes mentioned. It's critical to maximize the benefit of the procedure.

Dr Brown: Thank you. Dr Rabinstein alluded early to the remarkable effectiveness of this procedure in acute ischemic stroke, but we also recognize that any procedure can have complications associated with it as well. I'll ask both you and Dr Kallmes to comment, again, as colleagues who perform this procedure: what are some of the complications [reported] in the clinical trials, and what do you most worry about?

Dr Lanzino: The main complication is the issue of reperfusion hemorrhage, as there is always an established core that is already infarcted in these patients. Revascularization of that established core in a patient, who often receives thrombolytics, has a risk of reperfusion hemorrhage. To some extent, this complication is almost random. Besides trying to control patients' blood pressure within certain limits, there is very little that can be done to prevent that complication. Hemorrhage can also result from vessel perforation during some of these procedures, but that is fairly rare today given advances in imaging and the microcatheter techniques.

The other main neurological complication is distal emboli. As you try to retrieve the embolus, quite often, the clot fragments into smaller pieces that can embolize downstream. Quite often we do this procedure with a balloon inflated proximally to arrest flow and try to prevent this complication, but it is not infrequent for some degree of distal microemboli to occur that obstruct smaller vessels.

I would say those are the two main complications, but likely with improvement in technology and better understanding of the disease and more experience, these complications are relatively infrequent.

Dr Brown: Dr Kallmes, anything else you would like to add?

Dr Kallmes: I would only reiterate to take another look at the distal emboli. You can also, unfortunately, as you're pulling back clot, send a piece of clot to a new territory. Let's say your primary clot is in the [middle cerebral artery] MCA. As you're pulling back, it breaks off and goes to the [anterior cerebral artery] ACA: [infarct new territory (INT)], which can be pretty bad, because now you're infarcting territory that wasn't already at risk. In fact, some of the new trials are looking at INT as a primary outcome, and some of the new devices are being designed with avoiding infarct in new territory as a primary aim.

Who Is Using Endovascular Therapies?

Dr Brown: Thank you. Now that these procedures are increasingly utilized for acute ischemic stroke, can you comment on what specialty groups are performing these procedures?

Dr Lanzino: At this stage, the specialty groups involved with the procedures [mostly depend on] local regional organizations and logistics rather than a planned national effort. There are some required standards to meet to perform these procedures, but we don't have yet a well-organized plan to make sure that different specialists performing the procedures are equally prepared to be able to do so both safely and effectively.

Traditionally, interventional neuroradiologists and more recently neurosurgeons and neurologists have been involved with these procedures, and they have a lot of experience in the catheterization of the distal intracranial circulation. The vast majority of these procedures are done by these specialty groups. But there are other specialists, like peripheral interventional radiologists and cardiologists, who are also performing in some areas.

What About Posterior Circulation Occlusions?

Dr Brown: Very good. Thank you. As we finish up, I had one additional question. We've talked a lot today about endovascular therapies for acute ischemic stroke, particularly in the carotid distribution, internal carotid artery, middle cerebral artery, anterior cerebral artery. Any additional factors that you would like to add regarding posterior circulation, that is basilar artery thrombosis and our approach in that scenario?

Dr Rabinstein: Certainly, while true that patients with vertebrobasilar occlusions were not included in the trials that we mentioned before, they have been the vessels that have been historically the most often targeted by endovascular therapy, simply because medical therapy in those cases often fails but also because when medical therapy fails, the prognosis is ominous. The attempt to open those blood vessels with catheter-based therapies started decades ago, and these trials should not change that. If anything, the advent of better recanalization techniques should make us more aggressive with the management of posterior circulation occlusions by endovascular means.

Dr Brown: Thank you. Dr Kallmes, any additional thoughts on that?

Dr Kallmes: To compare and contrast anterior vs posterior circulation occlusions, we're much more aggressive in terms of a time window in the posterior circulation than in the anterior circulation. Going up to 24 hours or more since time of onset is not unusual. In terms of aggressiveness in getting the clot out, we will work a little harder to revascularize, given the dismal outcomes without revascularization.

Dr Brown: Thank you. Very good. Well, I'd like to thank my colleagues for their insights on this topic and thank you all for joining us on theheart.org on Medscape.

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