Stroke diagnostic pathway and patient selection A neurological examination is performed on all patients with suspected hyperacute stroke. National Institutes of Health Stroke Scale( NIHSS) score is performed at the time of admission by the stroke team. Patients presenting with NIHSS ≥6 and within six hours of symptom onset for anterior circulation stroke or 12 hours for posterior circulation strokes are considered for mechanical thrombectomy.
As per the NCCCC guidelines, 9 plain CT of the brain is performed immediately to exclude patients with contraindications to treatment, such as acute haemorrhage or significant established ischaemia. For middle cerebral artery territory symptoms, the Alberta Stroke Program Early CT Score( ASPECTS) is performed to assess the degree of established ischaemia. Patients with a lack of extensive early ischaemic change( those with ASPECTS more than 5 on plain CT) are selected. 8
If there are no contraindications to treatment, then a CT angiogram is performed from aortic arch to the vertex. This helps to delineate the vascular anatomy and assess the patency of the intracranial arterial system, as well as the degree of collateral supply. In patients with uncertain time of symptom onset, brain perfusion imaging( CT or MRI) may be employed. 8 The decision to proceed with mechanical thrombectomy is made in conjunction with a stroke physician considering the patient’ s clinical condition, age and co-morbidities.
Neuro-interventional pathway Once the decision is made to proceed with mechanical thrombectomy, patients are consented and taken to interventional theatre. Intravenous tissue plasminogen activator( TPA) is given as a bridging therapy, which is then followed by intra-arterial thrombolysis and mechanical thrombectomy. MT is performed under general anaesthesia or conscious sedation. In our institution, we use a Philips Allura Xper FD20 / 20 biplane X-ray system for image guidance, as it enables FAST acquisition and 3D planning of the Circle of Willis.
Arterial access is gained by using Seldinger catheterisation of the right common femoral artery. A target vessel diagnostic angiography is performed to localise the level of occlusion.
The main two basic thrombectomy techniques involve the use of suction with a pump and / or a stentriever as described below. 1 Suction is performed using a large bore( 5F or 6F) catheter, which is engaged with the thrombus and suction is applied either directly with a syringe or a suction pump. 2 A stentriever is a retrievable stent, which is deployed across the thrombus and then pulled back to remove the thrombus. The most common stentrievers used are the Solitaire™ FR Revascularization Device( Covidien, ev3 Neurovascular, USA) and the Trevo Pro( Stryker Neurovascular, Kalamazoo, MI).
The precise mechanical thrombectomy technique is tailored for each patient based on the following factors: 1 Vascular tortuosity of the aortic arch, internal
Figure 1
Summary of mechanical thrombectomy techniques
scenario No
No vessel tortuosity, short segment occlusion in MCA or PCA
No
Long segment occlusion
No
Tortuous ICA / VBA No
Steep angled MCA occlusion
No
Tandem occlusion No
Anchored thrombus causing ball-valve effect
No
Proximal ICA or BA occlusion
No
Adherent thrombus in terminal ICA or MCA
No
Re-occlusion following thrombectomy
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes technique
Basic stentrieve technique
Ballon guide suction
Distal access catheter +/- tri-axial system
Proximal stenting and mechanical thrombectomy
Distal access catheter with suction
Plain suction thrombectomy
Intracranial balloon angioplasty and suction thrombectomy
Intracranial stent
carotid artery( ICA) or vertebrobasilar artery( VBA) 2 The level of occlusion – This may occur at the internal carotid artery( ICA), vertebral artery( VB), basilar artery( BA), middle cerebral artery( MCA, 1st segment M1) or posterior cerebral artery( PCA, 1st segment P1)
Length of the thrombus – This can be measured from the CT angiogram.
Using these criteria, a number of techniques of performing mechanical thrombectomy are described 8 and summarised in Figure 1.
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