Beyond Aspirin - How will strokes be prevented in the 21stC?
It is a well known fact that Aspirin is associated with stroke prevention but how does Aspirin work? Can future treatments ever replace aspirin as our first point of call as an effective method of stroke prevention? In this essay I will discuss Aspirins current effectiveness as well as the effectiveness of both present and possible future preventative treatments.
Symptoms of a stroke
To begin my essay I will first discuss the symptoms and causes of stroke so we may see how Asprin can be used effectively. The signs and symptoms of a stroke vary from person to person, but they usually begin suddenly. As different parts of your brain control different parts of your body, your symptoms will depend upon the part of your brain that has been affected and the extent of the damage.
* Face. The face may have fallen on one side, the person may not be able to smile, or their mouth or eye may have drooped.
* Arms. The person with suspected stroke may not be able to raise both arms and keep them there because of arm weakness or numbness.
* Speech. There may be slurred speech. 1
Types of stroke
A stroke is when a part of the brain is deprived of oxygen through lack of a sufficient oxygenated blood supply. There are 3 main ways in which a stroke can occur:
This is caused by a build up of fatty deposits on the walls of blood vessels. Here Aspirin can help increase the blood flow to restore oxygen levels in the brain.
This is caused through a blood clot, obstructing the blood flow to the brain.
This is caused when a blood vessel ruptures, most commonly caused by hypertension (Weakened over time by high blood pressure).
The first type and the most common stroke is the Ischemic stroke. It is characterized by the presence of a blood clot that blocks the flow of blood to one area of the brain, depriving that area of oxygen. 3 In this case Aspirin can be used to support the treatment of the clot, thinning the blood and increasing the blood flow around the clot to try and restore oxygen levels in the brain. The second most common stroke type is a Hemorrhagic stroke. In hemorrhagic stroke, bleeding in the brain itself (intracerebral hemorrhage) or between the brain and the skull (subarachnoid hemorrhage) disrupts brain function. Bleeding usually occurs because of a rupture in arterial walls that are already weakened by high blood pressure. A pool of blood compresses brain tissue in its vicinity, preventing adequate amounts of fresh blood from reaching the area.2 In this case since Aspirin increases the blood flow by ‘thinning' the blood, Aspirin would only worsen the situation.
How does Aspirin work?
The chemical name for aspirin is acetylsalicylic acid (ASA). ASA binds to an enzyme called cylooxygenase-2 within the cells. This is produced in large quantities in cells which are damaged, causing us to feel pain. Without the presence of ASA this enzyme makes chemicals called prostaglandins which send messages to the brain that that part of the body is in pain. They also cause the area that has been damaged to release fluid from the blood so that it will swell up or inflame. This protects the damaged cells from further damage by creating a cushion. When aspirin is taken the enzyme is no longer able to make prostaglandins and some of the pain messages aren't initiated and so are not sent to the brain, resulting in us feeling less pain. Also the areas don't inflame as much and inflammation is reduced. 2
But how can it be used in stroke prevention?
Aspirin makes its way into the blood stream and blocks the production of prostaglandins wherever they are formed. This is mainly in areas of damaged cells, but they are also formed in other parts of the body. In the blood stream prostaglandins cause clotting. This is useful when we have a cut or a nose bleed for example, but blood clots also cause heart attacks. 2 However, The risk of gastrointestinal bleeding (0·1% per year with aspirin vs. 0·07% per year without) probably outweighs the small benefit in stroke prevention (0.51% aspirin vs. 0.57% control per year) unless the risk is particularly high.5
Prevention of stroke may be classified as primary prevention if there is no previous history of stroke or transient ischaemic attack (TIA) and secondary prevention when the patient has not suffered from a stroke previously.
Well-documented and modifiable risk factors for stroke include hypertension, exposure to cigarette smoke, diabetes, atrial fibrillation (AF), dyslipidaemia, carotid artery stenosis, sickle cell disease, postmenopausal hormone therapy, poor diet, physical inactivity, and obesity - especially truncal obesity.3
* Less well-documented or potentially modifiable risk factors include the metabolic syndrome, alcohol abuse, drug abuse, oral contraceptive use, obstructive sleep apnoea, migraine headaches, hyperhomocysteinaemia, elevated lipoprotein(a), elevated lipoprotein-associated phospholipase, and hypercoagulability.1
After a stroke or TIA, there is a high risk of stroke and of other serious vascular events. Medical treatments with clear evidence of benefit include:4
* Lowering blood pressure (BP) after all types of stroke or TIA
* Lowering blood cholesterol with a statin after ischaemic stroke or TIA
* Antiplatelet treatment after ischaemic stroke or TIA
* Warfarin instead of antiplatelet treatment in patients with ischaemic stroke or TIA who have atrial fibrillation (AF) and no contra-indications to anticoagulation 5
A key measure to prevent strokes is just to live a healthy lifestyle. Eating a diet high in saturated fats will only increase the risk of an Ischemic stroke since an increased in take of saturated fat can lead to heightened levels of cholesterol in the blood. This increases the chance of ‘fatty deposits' building up inside the vessels, leading to a blockage. Diet preventative measures;
* Total fat intake is 30% or less of total energy intake.
* Saturated fats are 10% or less of total energy intake.
* Dietary cholesterol is less than 300 mg/day.
* Saturated fats are replaced by monounsaturated and polyunsaturated fats. 5
Hypertension (elevated blood pressure can cause a hemorrhagic stroke due to an increase in blood pressure, weakening of the arteriol walls through constant high pressure.):
* Screen for hypertension and treat appropriately according to British Hypertension Society guidelines.
Antithrombotic treatment (prevents the formation of thrombi which contain platelets and fibrin usually responsible for obstructions within the blood vessels.):
* Following acute MI: anticoagulation is appropriate in those who are at increased risk of thromboembolism, including those with a large anterior MI, left ventricular aneurysm or thrombus, paroxysmal tachyarrhythmias, chronic heart failure or a history of thromboembolic events.
* Anticoagulation is indicated for other cardiovascular risk factors for thromboembolism, e.g. prosthetic valves, rheumatic heart disease and AF.
Drugs that act on fat production in the liver
These alter the way in which the liver makes fats, and can lower cholesterol and triglyceride levels. There are two main drug types - fibrates and statins.
Statins are the most potent cholesterol-lowering drugs, and are the most widely used treatment to tackle a high cholesterol level. Research has shown their positive effect in reducing the risk of heart disease and stroke, but they're less effective than fibrates in reducing triglyceride levels. Although statins work by stopping the body from making cholesterol, they also seem to reduce the risk of heart disease in other ways, such as keeping the lining of the blood vessels healthy and preventing the formation of blood clots.
Drugs that act on bile salts
Some drugs reduce cholesterol levels by acting on bile salts. Bile is a liquid produced by the liver and released into the intestines to aid digestion. It's rich in cholesterol, which is reabsorbed into the body once it's done its job in the intestines. These drugs prevent the cholesterol from being reabsorbed, leading to it being lost from the body through the gut. 6
To conclude I believe, on its own, Aspirin is not the future of preventative stroke treatment since the beneficial effects are out-wayed by the negative effects and since Aspirin ‘thins' the blood it could raise the patients blood pressure, worsening their condition if they suffer from hypertension leading to a greater risk of a Hemorrhagic stroke. In primary prevention I believe treatments such as Statin which target and prevent the build up of fats that cause strokes are a far more effective method of stroke prevention in patients who have a hereditary conditions or who have suffered from a stroke in the past which lead to heightened cholesterol levels. However, I believe just using Aspirin in combination with other anti-stroke medication as well as maintaining a healthy lifestyle through a balanced healthy diet and exercise will be the future preventative measure against strokes in the 21stC.
GBBB - Resource booklet - Week 7 - Prof Morrison › Neurological disorders - an overview - Slide 24
(2)http://everyday-chemistry.suite101.com/article.cfm/how_does_aspirin_work (how aspirin works)
(3)http://heart-disease.health-cares.net/different-stroke-types.php (types of stroke)
(4) http://www.strokesurvivors.ca/new/mi.php ( diagram)
(5) http://www.patient.co.uk/doctor/Stroke-Prevention.htm (stroke prevention)
(6) http://www.bbc.co.uk/health/ask_the_doctor/lipidloweringdrugs.shtml (Effects of lipid lowering drugs)
Define thrombus: http://www.mondofacto.com/facts/dictionary?thrombus