Stroke is the most common cause of disability in Western Countries, and its lifetime risk is up to 25%. While managing acute stroke patients in hyperacute stroke units is regarded as having benefits for short and long term outcome, specific therapeutic options are limited. The first major option for treatment of ischaemic stroke was intravenous thrombolysis, paralleling its previous development in acute myocardial infarction. However, while use in the latter indication was widespread in the 1990’s, it has only been widely for stroke in the last ten years. This is probably because of the narrower therapeutic window and the more severe consequences of haemorrhagic complications in the brain. In addition, its benefits are actually relatively modest. In randomised clinical trials on use within three hours (bearing in mind that in the first hour a stroke often spontaneously recovers – termed a TIA), using NICE data (June 2007) 15% of patients have an improved outcome, but with a brain haemorrhage risk of 7% greater, and a major haemorrhage rate actually considerably worsening the stroke (>= 4 points on the National Institute of Health Stroke Severity Scale) of 1.7% . When delivered between 3 and 4.5 hours after stroke onset the benefits were not even clearly significant.
So it is not surprising that there has been a move, just like in cardiology a decade or two earlier, away from intravenous thrombolysis and towards direct intra-arterial catheter treatment. This article discusses this new treatment and the ramifications for delivery of such a service.
The paper, Revolution in acute ischaemic stroke care: a practical guide to mechanical thrombectomy, summarises recent evidence in favour of this treatment and the infrastructure required to manage patients in this way.
While the first such devices were approved for use in 2004, technical developments and the improved expertise that comes with experience show in recent studies published since 2010 on new generation devices that they yield major improvements in outcome. The HERMES collaboration meta-analysis revealed that 46% of patients had a good outcome with functional independence (grades 0-2 on the Modified Rankin scale) compared with 26.5% on best medical treatment. Most of the patients in both groups received intravenous thrombolysis, since in most study protocols patients had iv thrombolysis before going on to have thrombectomy an hour or so later. Mortality and the risk of brain haemorrhage did not differ between the two groups. The benefit seemed still to be present in patients over 80, and still present when patients did not receive iv thrombolysis, though the numbers in this case were smaller. While the window for thrombectomy was within 6 hours, there may still be improved outcomes up to 7.3 hours after symptom onset, but in generation faster intervention leads to greater benefit.
The procedure involves a number of variations depending on the Neuroradiologist and the particular nature of the thrombus. It may be done under general anaesthesia or local anaesthesia and sedation with anaesthetic support. A large gauge catheter is directed to the internal carotid via a femoral puncture, and an intermediate catheter inside it is directed to the Circle of Willis. Then a microcatheter inside that serves as a guide wire to the actual clot. The microcatheter is then removed and a stent retriever is placed within the clot, and pulled back to draw the clot to the intermediate catheter. Suction is applied to this catheter to remove the clot entirely. Some techniques involve directly removing the clot by suction on the intermediate catheter. A balloon may be located on the distal end of the clot to prevent forward movement. When removing the clot reveals a tight lumen, there is the further option to perform angioplasty or stenting to open the vessel. The same can apply to a more proximal carotid stenosis occurring in tandem with the more distal thrombus.
The main complications are technical, including vessel perforation (1.6%), other symptomatic intrcranial haemorrhage (3-9%), subarachnoid haemorrhage (0.6 – 5%), arterial dissection (0.6 to 3.9%), or emboli distally (1-9%). In addition , there can be vasospasm or issues related to the puncture site. While the total incidence is 15%, not always is there any actual clinical adverse consequence.
- While the time window for thrombectomy is wider than for intravenous treatment, there are other selection criteria that are more strict.
- There should be a documented anterior circulation large vessel occlusion of the middle cerebral or carotid artery. (There is only limited evidence for efficacy in basilar occlusion.)
- There should be good collateral cerebral circulation.
- There should be relatively normal extracranial arterial anatomy from the technical viewpoint of passing the catheter.
- There should be significant clinical deficit at the time of treatment, but this parallels the criteria for intravenous treatment and a large vessel occlusion with minimal clinical deficit nevertheless incurs a significant risk of clinical deterioration.
- There should be a lack of extensive early ischaemic change on CT (according to ASPECTS score a threshold of 5). The role of more advanced imaging , eg CT perfusion to establish salvageable brain, is yet to be clarified.
- Consideration should be given to pre-stroke functional status and the potential of benefit.
- Patients should have had iv thrombolysis within 4.5 hours of symptom onset.