A stroke occurs when a part of the brain gets damaged due to interruption of its blood supply.
Ischaemic stroke is the most common type of stroke and accounts for about 80% of strokes in Singapore. It occurs when a blood clot is lodged in an artery and cuts off blood supply to the brain.
Another type of stroke is haemorrhagic stroke, which occurs when there is a rupture of a blood vessel causing bleeding in the brain.
One of the factors affecting eventual outcome is how fast patients and their caregivers identify stroke symptoms, and present themselves at the nearest tertiary institution for treatment. Stroke symptoms using the acronym F.A.S.T was introduced through mass media and outreach programmes to educate the public in recognising early symptoms of stroke and calling an ambulance immediately for early diagnosis and treatment.
The emergent treatment of acute large vessel ischaemic stroke has advanced since 2015, after major clinical trials1 proved the effectiveness of
mechanical thrombectomy – a minimally-invasive endovascular procedure, where clots are extracted from larger brain vessels by a neurointerventional team - over non-intervention or conventional treatment methods using intravenous thrombolytics alone.
The innovative ideas behind the development of endovascular device-based methods have revolutionised the way clots lodged in larger brain vessels are extracted.
There are two main methods of clot extraction:
Aspiration (via large-bore catheters) - improvements in stent-retriever design have led to better clot-capturing efficacy.
Clot-capture (via stent-retrievers) - the increase in flexibility and calibre of the latest aspiration catheters have improved their reach and suction strength.
Used either alone or in synergy, these two methods can now result in recanalisation rates reaching as high as 80% to 90% of cases.
As mechanical thrombectomy can only be performed within a small therapeutic window, clinical assessment and imaging in the form of a CT scan or MRI should be performed urgently.
After confirming the blockage of a large vessel and presence of salvageable brain tissue, the patient is brought to the angiographic suite. A team comprising of a neurointerventionalist, anaesthetist, nurses and radiographers will perform the mechanical thrombectomy under X-ray guidance. Depending on the patient’s condition, mechanical thrombectomy may be performed under moderate sedation or general anaesthesia. Through a femoral artery puncture, the guiding catheter is advanced close to the site of occlusion. The microcatheter is then navigated past the clot, followed by deployment of the clot-removal device of choice. Once deployed, the device is retrieved and checked for any clot removed.
A clot in the brain vessel at the white arrow on CT (Figure 1) leading to eventual tissue death, marked by the bright area in the orange circle on MRI (Figure 2).
Two main issues affecting the selection of clot-removal device are the site of obstruction, and how easily that site can be accessed by the delivery catheters.
Depending on the outcome, additional adjuvant intraarterial thrombolytic therapy may be administered.
As with any procedure, there are complications that can take place.
Mechanical manipulations can result in damage to the vessel wall, leading to bleeding. As a result, further artery blockage or clots may occur.
As X-rays are used, there will be exposure to radiation though steps are taken to minimise the exposure. An X-ray dye will also be introduced to better visualise the blood vessels and some patients may experience an allergic reaction.
These risks are weighed against the benefit of removing the clot, to improve clinical outcome and odds of functional independence.
Without mechanical thrombectomy, the chances of reopening the blocked vessel are slim, leading to a loss of salvageable brain tissue, and subsequent large stroke territory with complications such as brain swelling and haemorrhagic transformation.
The 2015 clinical trials1 proved that mechanical thrombectomy benefits patients who present within 6 hours of symptom onset.
More recent studies2 show that in selected cases, patients may benefit from this procedure up to 16 hours of stroke onset.
However, the benefits remain greatest in patients who present to the hospital early. Brain tissue is sensitive to oxygen deprivation and cells start dying within minutes of a stroke onset. A core of damaged brain tissue forms, surrounded by salvageable “tissue-at-risk” which can be recruited into the core if blood flow is not restored.
Through improved devices and techniques for clot-retrieval, and stronger public awareness, more stroke patients can benefit from endovascular therapy, for improved clinical outcomes.
Dr Wickly Lee is a Senior Consultant at the Department of Neuroradiology. He
subspecialises in interventional neuroradiology and is also Director of the Joint
Neurovascular Service at the National Neuroscience Institute.
Zain Almuthar is a Senior Radiographer at the Department of Neuroradiology.
He is trained in Computed Tomography, Magnetic Resonance Imaging and
Neuroangiography. As the Head of the Angiography Suite, Zain leads and trains
his team of radiographers, as well as assists in the development of new facilities
and techniques. He was awarded the Ministry of Health Talent Development
Fund Award (Allied Health Professionals Category) in 2015.
GPs can call for appointments through the GP Appointment Hotline 6330 6363 for more
information about the department.
1. Goyal M, Menon BK, van Zwam WH, et al. Endovascular thrombectomy after large-vessel ischaemic stroke: a metaanalysis of individual patient data from five randomised trials. Lancet 2016; 387: 1723-31.
2. Nogueira RG, Jadhav AP, Haussen DC, et al. Thrombectomy 6 to 24 Hours after Stroke with a Mismatch between Deficit and Infarct. N Engl J Med 2018; 378: 11-21. By: Dr Wickly Lee is a Senior Consultant at the Department of Neuroradiology. He subspecialises in interventional neuroradiology and is also Director of the Joint Neurovascular Service at the National Neuroscience Institute. Zain Almuthar is a Senior Radiographer at the Department of Neuroradiology. He is trained in Computed Tomography, Magnetic Resonance Imaging and Neuroangiography. As the Head of the Angiography Suite, Zain leads and trains his team of radiographers, as well as assists in the development of new facilities and techniques. He was awarded the Ministry of Health Talent Development Fund Award (Allied Health Professionals Category) in 2015
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