Stroke

Stroke is the 4th most prevalent cause of death (7% of deaths registered) and it is the main cause of disability in adults, with 1.2 million stroke survivors currently living in the UK. Stroke mortality rates have fallen significantly since 1990, with a reduction in death of 46%, but it is still a major killer; 1 in 8 strokes lead to death in the first 30 days, and 1 in 4 strokes are fatal during the first year 1. Not only is the mortality rate high, but many stroke survivors are left with life-changing disabilities, which puts further stress on themselves, carers and families. The overall death rate after a stroke is 20-25% 2, but this number will continue to fall with further improvements in stroke management; time is key following a stroke, as the faster a stroke is diagnosed and treated the better the outcome is, with reduced death rates and less severe disability.

What is a Stroke?

A stroke is when there is a reduction or complete lack of oxygen (ischaemia) to an area of the brain, causing the death of neurones and therefore various deficits (disabilities) such as weakness in the arms, legs and face, slurred speech and confusion depending on the area of the brain affected. A stroke is defined as rapid onset of these deficits lasting >24 hours or causing death, with no other neurological explanation. A mini-stroke, or TIA (transient ischaemic attack) is a very brief episode of stroke symptoms, usually lasting seconds or minutes, but with rapid complete recovery 2.

A stroke can either be ischaemic (80% of cases), often caused by a thrombus (clot) forming in an artery and lodging in smaller vessels, or haemorrhagic (17%) which can be caused by small vessels bursting and bleeding into the brain. The other 3% of strokes include venous sinus thrombosis, where a thrombus forms in a sinus, a large vein that drains the brain 2.

Figure 1: a breakdown of stroke occurrence by percentage

Figure 2: a comparison of the two main causes of stroke 3

Although TIA usually leaves no lasting damage it is still a serious event; suffering from a mini-stroke can be a sign that thrombi are forming in the circulation, meaning the patient is at a higher risk of a major stroke in the next few years. Without treatment about 10-20% of people who suffer a TIA go on to have a major stroke within the next year, so TIA’s should be treated as soon as possible to prevent any further strokes 4.

Risk Factors for Stroke

As with many conditions, there are certain environmental and genetic factors that increase a person’s risk of suffering from a stroke. Modifiable risk factors include hypertension, smoking, heart disease (especially atrial fibrillation), diabetes mellitus, a history of a TIA, having a high blood lipid concentration (hyperlipidaemia) and a high alcohol intake; these factors can be seen in figure 3, and they can all speed up the process of atherosclerosis, thus increasing the risk of clots forming in the circulation 5.

Figure 3: the main risk factors contributing to a stroke

The heart condition atrial fibrillation (AF) causes a 5x increased risk of a major stroke; due to an electrical defect within the atria, the heart muscle fails to contract efficiently, meaning that blood can pool in the atria and clot. These thrombi can then be pumped into the circulation where they may block a cerebral artery and cause a stroke.

Aetiology and Pathophysiology

Most ischaemic strokes occur due to blockage of a cerebral artery by a thrombus; these clots can either form in slow-moving blood within the cerebral arteries themselves (thrombosis in situ) or they can travel from other parts of the circulation until they become stuck in the cerebral vessels. These thrombi often form on a background of atherosclerosis in an arterial wall, where a fatty deposit (an atheroma) grows creating a narrowing in the artery 2.

If the fibrous cap of an atheroma ruptures, which can happen when a patient is hypertensive and the atheroma is large, platelets stick to the exposed tissue and cause a thrombus to form. The clot becomes an embolus, which is a mobile thrombus, and moves through the blood stream until it becomes lodged in a small artery, blocking it. A stroke caused by AF is termed a cardio-embolic stroke; any condition that weakens the heart muscle and allows blood to pool increases the chance of a clot forming 2.

Being starved of oxygen causes neurones to dysfunction and eventually die. Time is of the essence following a stroke as the longer the patient waits without treatment, the more neurones die, causing more severe disability. In fact, with each minute without treatment around 1.9 million neurones die, and unlike some other cells in the body neurones do not regenerate 6. This means that often the functional deficits experienced by patients after a stroke are permanent and irreversible.

A haemorrhagic stroke occurs most often on a background of long-term hypertension; the high blood pressure weakens small arteries and can cause them to rupture. Bleeding into the brain not only starves neurones of oxygen, but also puts pressure on the brain tissue causing further neuronal damage. Depending on the size of the bleed, there can be catastrophic brain damage and distortion of the brain tissue. A patient on anti-coagulants, such as warfarin or heparin, is at a higher risk of haemorrhagic stroke as these drugs prevent clots forming. Warfarin can be given prophylactically to patients with AF to prevent a cardio-embolic stroke. Unfortunately this increases their bleeding risk, including from small arteries within the brain 7.

A TIA is normally caused by micro-thrombi breaking off a larger thrombus in an artery; because these thrombi are small they get broken down very quickly by clot-digesting molecules in the blood, but they still cause transient symptoms and are an important warning sign that the patient is in danger of a larger stroke.

Signs and Symptoms of Stroke

The immediate signs and symptoms of a stroke have been outlined in public health drives over the last decade; the aim has been to educate the public so that they can recognise the signs of a stroke in others, meaning that patients get prompt treatment when they need it. Public Health England’s Act FAST campaign was launched in February 2009, and it has been a fantastic educational tool, with posters and television adverts being used across the country to raise awareness of stroke 8. Figure 4 shows how Act FAST is a useful and memorable summary of the early signs and symptoms of a stroke, which include drooping of the face on one side, one-sided muscle weakness and slurred or unintelligible speech.

Figure 4: the F.A.S.T mnemonic is a succinct way of remembering the early signs of a stroke. The faster
the patient receives treatment, the better their prognosis after the stroke, so it is important that the public
know to call 999 as soon as possible 9

Figure 5: a diagram to show the different parts of the brain that can be damaged by a stroke, and the functions of each area that may be affected when the blood and oxygen supply is reduced 10

Overall, the symptoms caused by a stroke depend on the area of the brain affected. The arterial supply to the brain is complicated, and different arteries supply areas that have different functions. For example, as can be seen in figure 5, the motor cortex (the part of the brain that controls movement) is in the middle of the brain; the main blood supply here is via the middle cerebral artery (MCA), so a stroke in this artery almost always causes weakness on the opposite side of the body. In most people the speech centre for producing and understanding speech is found in the parietal lobe on the left side of the brain; this area is also supplied by the MCA, so if the affected artery is the left MCA then speech and movement deficits are common. In medical terms patients with a left MCA stroke tend to suffer from contralateral hemiparesis and dysphasia.

Because the left side of the brain controls the muscles on the right side of the body, and vice versa, if the left motor cortex is damaged there will be weakness on the right side of the body. This is called contralateral (opposite) weakness, whereas weakness on the same side would be ipsilateral. Contralateral hemiparesis down one side of the body is a classic MCA stroke presentation.

Management of Stroke

Stroke management depends on whether it is ischaemic or haemorrhagic, as the treatment pathways for both are very different. Either way, stroke is a medical emergency, and so treatment should be started as soon as possible.

Once the patient has been admitted to a stroke unit, the aim is to distinguish between an ischaemic and a haemorrhagic stroke. This is usually done by an urgent CT scan, as these are fast and readily available. On a CT scan blood shows as a brighter white than the surrounding tissues, and if blood is present this suggests a haemorrhagic stroke. An ischaemic stroke is more subtle; the early CT image may show some slight darkening and tissue disturbance, or even nothing at all. Ischaemic changes become more obvious on CT a few days later. Figure 6 compares ischaemic and haemorrhagic CT images 11.

Figure 6: head CT scans comparing the subtle changes of an early ischaemic stroke (left) to the bright white collection of blood marking a haemorrhagic stroke (right) 12

If a stroke is ischaemic, then immediate thrombolytic (clot-busting) therapy should be given if possible to break down the thrombus and restore blood flow. Thrombolysis is the best current therapy for ischaemic stroke, but because it affects clotting and increases the risk of major bleeding only about 20% of patients are currently eligible for thrombolysis and receive it. For example, it is contraindicated (should not be given) in pregnancy or if the patient has uncontrolled hypertension, has had recent surgery or trauma or if they have a clotting problem like haemophilia. For these people thrombolysis would do more harm than good 13.

Thrombolytic therapy has been proven to be beneficial if given in the first 4.5 hours after the onset of symptoms; after this time restoring blood flow to the affected area does not effectively prevent cell death 5. Some examples of thrombolytic drugs are tenecteplase and alteplase. All patients are then put on anti-hypertensive and anti-coagulant therapies in the aim of preventing any further strokes. The anti-platelet drug aspirin is given at a high dose straight after the stroke, then continued at a low dose, sometimes for the rest of the patients life 11.

In a haemorrhagic stroke, nothing should be given that would interfere with blood clotting, so here thrombolysis is strongly contraindicated. If the bleed is large, neurosurgery may be necessary to relieve pressure on the brain 11.

Stroke Prevention

The most effective way of preventing stroke is to avoid any risk factors and lead a healthy, active lifestyle; reducing fat intake, exercising regularly, lowering blood pressure, stopping smoking and not drinking to excess reduces stroke risk significantly. Even if a patient has had a major stroke or TIA before, it is important for them to understand that it is never too late for them to make these lifestyle changes and reduce their stroke risk.

Prognosis

The effects of a stroke vary hugely depending on the size and site of the damage. A large proportion of stroke survivors are left with long-term symptoms such as hemiplegia, loss of sensation, incontinence, speech and cognitive deficits, depression and difficulty carrying out daily activities for themselves. This can leave people dependent on others and sometimes needing 24 hour care, putting huge emotional and financial strain on patients and their families, carers and services.

Multidisciplinary specialist stroke units in hospitals provide a good environment for adjustment and rehabilitation, with physiotherapists, occupational therapists and speech and language therapists there to work with patients following their stroke, but once a patient is discharged it can be difficult and expensive to access these services. It is the duty of healthcare professionals who work with these patients to help improve motivation and quality of life wherever they can, and to support patients and their families and carers through such a life-changing event.

References:

1. Stroke.org Stroke Statistics 2015 https://www.stroke.org.uk/sites/default/files/stroke_statistics_2015.pdf Accessed: 29/07/15
2. Kumar P, Clark M, Kumar and Clarks Clinical Medicine 8th Edition (2012). Sunders Elsevier, pp. 1096-1097
3. Ischaemic vs Haemorrhagic http://www.webmd.com/stroke/ischemic-versus-hemorrhagic-stroke Accessed: 31/07/15
4. Transient Ischaemic Attacks http://patient.info/health/transient-ischaemic-attack Accessed: 29/07/15
5. Longmore M, Wilkinson IB, Baldwin A, Wallin E. Oxford Handbook of Clinical Medicine, 9th Edition (2014) Oxford University Press pp. 474
6. Saver, J. L. (2006). Time is brain—quantified. Stroke, 37(1), 263-266.
7. AF Treatment http://www.nhs.uk/Conditions/Atrial-fibrillation/Pages/Treatment.aspx Accessed: 31/07/15
8. Act FAST Campaign https://campaigns.dh.gov.uk/category/act-fast/ Accessed: 31/07/15
9. Act FAST Image http://www.wales.nhs.uk/sites3/home.cfm?orgid=840 Accessed: 31/07/15
10. Areas of Brain Affected by Stroke https://brooksbroadstrokes.wordpress.com/2013/04/18/stroke-warning-signs/ Accessed: 31/07/15
11. Kumar P, Clark M, Kumar and Clarks Clinical Medicine 8th Edition (2012). Sunders Elsevier, pp. 1103
12. Ischaemic and Haemorrhagic CT http://health-fts.blogspot.co.uk/2012/04/ischemic-stroke.html Accessed: 31/07/15
13. Thrombolytic Therapy http://www.nlm.nih.gov/medlineplus/ency/article/007089.htm Accessed: 31/07/15

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