Endovascular clot retrieval (ECR)

Endovascular clot retrieval (ECR), also known as mechanical thrombectomy (MT) or endovascular thrombectomy (EVT), is increasingly performed in patients presenting with large vessel occlusion (LVO), especially those with a large ischaemic penumbra that is likely to progress to ischaemic stroke. To be successful, careful patient selection and dedicated training and equipment are necessary. 

History

ECR and its efficacy in ischaemic stroke have been explored since 2005, initial trials revealed disappointing results. This was attributed to an inability to confirm large vessel occlusions radiologically combined with insufficiently developed devices and treatment delays ¹⁸. In 2015, multiple randomised controlled trials were published showing improved clinical outcomes in patients with acute ischaemic stroke due to large vessel occlusion undergoing ECR compared to medical (conservative) treatment alone ^3-5. As a result of these trials, ECR has now become the standard of care for large vessel occlusion strokes involving the anterior circulation.

Patient selection

• acute ischaemic stroke due to large vessel occlusion in the anterior circulation

  • robust evidence to support use within 6 hours of symptom onset ²⁴

  • growing evidence to support use beyond 6 hours ^6,13, including up to 24 hours and in patients with large ischaemic core volumes ^20,21

• acute ischaemic stroke due to large vessel occlusion in the posterior circulation remains an area of uncertainty and selection (c.2024) is dependent on clinician judgement in accordance with local guidelines, although there are several positive randomised clinical trials supporting its use ^22,23

• acute ischaemic stroke due to medium vessel occlusion (MeVO) in either the anterior or posterior circulation does not have robust randomised control data (c.2024) and thus no consensus recommendation can be made regarding endovascular clot retrieval in this setting ²⁵

Contraindications

• intracranial haemorrhage on initial non-contrast CT

• large infarct core with no significant penumbra (i.e. no salvageable brain)

  • note that large infarct cores by themselves may not be a contraindication, with two randomised clinical trials utilising core volumes of >50 mL ^20,21

• various patient factors (e.g. premorbid functional status, advanced directives, etc.)

Procedure

Preprocedural evaluation

Non-contrast enhanced CT is used to exclude haemorrhage and CT angiography to determine large vessel occlusion. Alternatively, MRI and DSA may also demonstrate the occlusion although the former is less commonly utilised for this due to difficulty with timely access to MRI in most institutions. CT perfusion is also important to determine the infarct core and penumbra size, especially in cases performed beyond 6 hours ^6,13,20,21.

Angiographic imaging can also:

• assess collateral vessels which contribute to predicting outcome in some settings ⁸

• assess the thrombus occlusion pattern (e.g. presence of the clot meniscus sign, a tapered appearance suggestive of underlying intracranial atherosclerotic disease, a cut-off appearance, a tram-track appearance) ²⁶

Positioning/room set up

Equipment

• stent retrievers

• aspiration devices

• balloon guiding catheter

• microcatheters

Technique

{{youtube:wY3fMI7LcCY}}

Postprocedural care

Although successful technical clot retrieval is essential, appropriate postprocedure care is also critical to avoid complications. 

Blood pressure control

Avoiding excessively high blood pressure is important in reducing the risk of secondary haemorrhage. In the acute post-ECR/thrombolysis period a target BP <185/110 mmHg is recommended ¹⁴, however, intensive blood pressure lowering (e.g. to <140 mmHg systolic) may be harmful ²⁷.

If critical carotid stenosis (i.e. tandem lesion) has been treated then more aggressive blood pressure control is probablymay be warranted to avoid the possibility of cerebral hyperperfusion as well as haemorrhage ¹⁶. There are, however, few universally agreed-upon guidelines and chosen targets will vary according to pre-procedure blood pressure, anticoagulation, pre-ECR thrombolysis, size of the expected infarct and a variety of other factors. 

Puncture site

Groin site neurovascular observations and bed rest are required as usual. There is an increased move towards radial artery access for lower complication rates ¹⁷. 

Anticoagulation

In a variety of settings, anticoagulation may need to be restarted shortly after clot retrieval (e.g. antiplatelet agents for stenting, anticoagulation for atrial fibrillation). The timing of this is on a case by case balance and involves balancing the risk of thromboembolic complications from delaying anticoagulation versus the increased risk of a cerebral haemorrhage.

Complications

The overall complication rate is about 15% ¹. Complications include ^2,9:

• intracranial haemorrhage (<8%)

  • parenchymal (5%)

  • subarachnoid

• emboli to new territories

• vessel perforation (1-5%)

• arterial dissection

• vasospasm

• vascular access site complications

  • groin haematoma (2-11%)

  • retroperitoneal haematoma (<6%)

• mortality

Outcomes

The technical outcome is graded using the mTICI score. ECR is a highly effective treatment for ischaemic strokes affecting the anterior circulation, with a number needed to treat (NTT) of 2.6 for an improved functional outcome. In a meta-analysis of anterior circulation ECR performed within 6 hours, 46% of patients treated with ECR achieved functional independence (modified Rankin scale (mRS) 0–2 at 90 days) compared to 27% for best medical treatment ². Outcomes of ECR in posterior circulation strokes are mixed, with trials demonstrating both positive and negative functional outcomes compared to best medical therapy ^19,22,23.