This highly promising strategy for acute stroke management is sufficiently interesting from the exam standpoint that it should merit its own page, particularly as it had recently become the topic of Question 4 from the first paper of 2020. There, trainees were expected to briefly describe its "indications, post-procedure management and procedural complications". Though this question did not ask for a critical appraisal of the practice and the evidence behind it, that stylised approach to discussing it was felt to have some merit, as it in the event that such a question ever comes up its answer will already be available.
Systemic thrombolysis, which is still the standard of care in those Australian institutions which happen to be further from the beach, is sufficiently interesting to be discussed on its own in another chapter. Supportive management for stroke has also been discussed elsewhere. The topic here will be mechanical endovascular embolectomy.
- Systemic thrombolysis has a substantial bleeding risk
- The time window is often too narrow
- A targeted endovascular approach may have the effect of revascularising the culprit vessel without systemic bleeding complications, and with much greater effect than conservative therapy.
- Ischaemic stroke with large vessel occlusion
- Substantial neurological deficit, NIHSS ≥ 5
- Timeframe criteria:
- Less than six hours: "broad clinical and imaging criteria"
- 6-24 hour window: "significant volume of salvageable tissue"
- Good level of premorbid independence
- Bleeding (though the risk of symptomatic ICH is no higher)
- Cerebral oedema
- Vascular access site complications
- Post-procedure management:
- Extubate early, if able.
- Mechanical ventilation focuses on maintenance of normoxia and normocapnia
- Blood pressure control:
- Aim for SBP <140-160 for fully revascularised patients
- Aim for MAP 10-20% over normal baseline and SBP <185 for partially revascularised patients
- Minimise sedation and maximise the opportunity for regular reassessment
Also, scan their head after the first 24 hrs.
- Control of electrolytes to prevent AF
- Maintenance of neutral fluid balance
- Glucose control: hyperglycaemia is harmful
- Antiplatelets after 24 hrs (earlier if they had an endovascular stent)
- Fever is harmful: paracetamol is recommended
In terms of published evidence, there are several excellent articles which can be recommended to the time-poor trainees unwilling to wade through hundreds of pages of stroke literature. An excellent ICU-centric paper by Ma, Moynihan and Donaldson (2019) covers the post procedure management very well. Patient selection and technique is well described by Silva et al (2020), and the AAN has decided not to paywall it for now. Evidence regarding the efficacy of this method is analysed in a systematic review by Rodrigues et al (2016). These sources and others have been blended together into something that might look like a CICM Part II pass-level answer, if one does not look at it too closely.
The initial experience was very promising, but only applicable to a limited extent. The investigator's interest in endovascular stroke management was considerable. For instance, the MERCI trial investigators enrolled all-comers to receive embolectomy (within 8 hours!) by use of the Merci Retriever device. As a marketing exercise for this device, the trial was a success; in spite of a 7.1% serious complication rate the technique was viewed as "safe" in the conclusion. In fact there are numerous such devices, and the campaign to sell each one has yielded some equally promising propaganda material. Unfortunately, like in the MERCI trial, the outcomes of all these studies compared poorly with historical controls.
In 2009, the American Journal of Neuroradiology has published a summary of their opinions and experiences regarding endovascular stroke management.
"despite higher rates of recanalization, the mechanical thrombectomy studies have demonstrated substantially lower rates of good outcomes compared with IV and/or intra-arterial thrombolytic trials."
This was sad. There is something heroic and noble-sounding about accessing the cerebral vessels to suck out the clot and save the brain. In spite of this rather negative reception, as well as consistently depressing outcome data, enthusiasts continued to experiment, and the technology matured. Rather than attempting to dress it up as a viable alternative to thrombolysis, the investigators have recently focused on identifying a patient group which would derive the greatest benefit from the technique.
The discussion of "rationale" for getting rid of the clot in a disease state where an errant clot is doing all the harm seems somewhat indirect. Surely, the rationale is obvious. The real question is, what is the rationale for performing this interventional neuroradiology procedure, as opposed to the systemic thrombolysis?
For local trainees preparing for their exam in the advanced medical thought incubator that is NSW Health, the Agency for Clinical Innovation had published an excellent document regarding patient eligibility for ECR. Their indications for referral include:
This NSW agency had got their recommendations from the Australian Stroke Foundation clinical guidelines, for which the most recent available version at the time of writing is 2019. These were influenced by the contemporary AHA guidelines (Powers et al, 2019) and the European guidelines (ESO / ESMINT, 2019).
The most interesting element of the indications for endovascular clot retrieval is the 6-24 hour window. The 6 hour window is pretty uncontroversial, and closely resembles the four hour window you have come to know and love from the IV t-PA stroke management protocol. The 6-24 hour window where some "volume of salvageable tissue" can still be rescued is a completely different animal. In support of this timeframe, the Stroke Foundation refers to Nogueira et al (2018) and Albers et al (2018), both of which are soiled with the grime of heavy industry involvement.
Nogueira et al (the DAWN trial) looked at a group of ICA or proximal MCA strokes who had a major difference between the severity of their clinical deficit and the radiological appearance; specifically, the clinical features of the stroke were very severe but the CT or MRI volume of the stroke was comparatively small, ~ 10ml. These patients, the investigators argued, have a large amount of threatened brain tissue (hence symptoms) which has not yet completely infarcted (hence radiology), and therefore these are the people who will benefit most from a cath. And if one were going to use a cath anyway, why not choose this lovely Trevo device from my very good friends at Stryker? Literally everybody among the investigators was on the payroll of a manufacturer who stood to gain from a positive result. The list of affiliation disclosures spans across most of the last page of this study.
Similarly, Albers et al (the DEFUSE-3 trial) was a study of large vessel strokes which happened to have occurred within mere minutes of a fully stocked highly advanced neurointerventional radiology lab with proprietary sponsor software installed into its imaging system. This trial was stopped prematurely when the DAWN trial was published, and data were analysed with a much smaller group of patients, mainly because equipoise was lost.
In short, the data collected by these trials was highly promising. Of their carefully selected patient population, with an overbearing abundance of interventional expertise and equipment available, functional independence at 90 days was achieved by 49% of embolectomised patient vs 13% of the conventional therapy group in DAWN, and by 45% vs 17% in DEFUSE-3. Though there are obviously serious concerns of impartiality raised by the taint of sponsorship, one cannot be dismissive of the methodology or the obviously promising results. Even bloggers who have no vested interest in protecting corporate whoring have spoken out in favour of these studies, and the changes in AHA guidelines which they have produced. The promise of rescuing at least a couple of people from perpetual hemiplegia is too good to pass by.
Bleeding: Hao et al (2017) looked through all the major publications on the outcomes following endovascular clot retrieval and reported that among the 1,499 reported patient cases, the risk of intracranial haemorrhage was substantially higher in the endovascular group. That's right, medical management actually carried a much lower risk of intracranial haemorrhage, only 19% - whereas with the endovascular approach the risk was 35%. However, this is only surprising if one assumes that "medical management" is systemic thrombolysis. In actual fact, Hao et al included trials which grouped "best medical therapy" together with intravenous t-PA, which probably dropped the risk of ICH somewhat. Moreover, even with this caveat, the extra intracranial blood in the interventional groups appears to have gone largely unnoticed by the patients and their families: when only "symptomatic" stroke was included in the analysis, the numbers were much lower, and very similar (5.6% vs 5.2%).
Cerebral oedema can develop, with an ensuing rise in the intracranial pressure and adverse effects of midline shift. Malignant MCA-like management, including decompressive craniectomy, is then floated as an idea. One might counter this enthusiasm by pointing out that, if the brain has swollen quite as bad as this, then one might make the argument that the volume of salvageable tissue was not rescued, and the outcome for this patient will be more like the outcome for untreated stroke (i.e. bad no matter what you do).
Vascular access site complications are seen in a substantial proportion of these patients as they are often full of antiplatelet agents at the time of interventional access sheath removal.