Introduction 

Cerebrovascular accidents, commonly known as strokes, are medical emergencies which cause a threat to life. Stroke is the second most common cause of mortality worldwide and the third most common cause of disability. Around 13.5% of stroke victims die within one month of an ischemic stroke, and around 40% die within the first year.^5,6 Strokes, along with heart attacks are the two main causes of mortality due to cardiovascular disease. 

What are strokes?

There are two main types of stroke: ischaemic and haemorrhagic. 

In an ischaemic stroke, a person may have a blood clot elsewhere in the body- usually in one of the heart valves. This blood clot breaks off and circulates through the blood and reaches the brain causing a stroke. The travelling blood clot is also known as an embolus. If it blocks an artery in the brain, it can prevent or significantly reduce blood supply to the areas that the particular artery supplies. 

A haemorrhagic stroke happens when a blood vessel in the brain bursts and causes a bleed inside the head. This can be incredibly painful - like a bullet entering the head. 

Ischaemic strokes are more common, around 60-80% of global cases and the remaining are haemorrhagic, although figures from individual countries can vary.⁴ 

What happens to the brain?

If the area of the brain that is further downstream to the area of the clot does not have adequate blood supplying it, the cells will be deprived of glucose and oxygen, both of which are essential for the cells to remain alive. The cells do not die straight away, they continue to live but at a reduced function. However, after some time (usually a few minutes), the cells will start to die and without prompt treatment, will not recover.³ 

The arteries that supply the brain are known as the carotid arteries (there are two- one on the left side of the body and one on the right), which begin from the neck and go upwards. The carotid arteries branch off into smaller arteries which supply different parts of the brain. The artery in the brain most commonly involved in ischaemic strokes is the middle cerebral artery. Strokes involving this artery will have the typical presentation of loss of limb function on one side(usually arm), unilateral facial paralysis and slurred speech. The person may not be able to see with f one eye or may be unable to speak altogether. This is because the middle cerebral artery directly supplies certain parts of the brain involved in these functions. Long-term, stroke victims may have motor or speech problems if they have had damage to these parts of the brain.³ 

Risk factors 

Cigarette smoking is a known risk factor for cardiovascular diseases including ischaemic stroke.² The other two major risk factors are high blood pressure and diabetes.⁴ 

Passive smoking also increases the risk of cardiovascular disease and stroke. According to the CDC, in the US, there is a 20-30% increase in stroke risk if a person is exposed to cigarette smoke as opposed to someone who isn’t,⁹ although this can increase up to 45% depending on how much smoke they are exposed to. For those who do smoke, for every 5 cigarettes smoked per day, the risk of stroke goes up by 12%].² 

Role of smoking in cardiovascular disease

Smoking has a complex role as a cause of cardiovascular disease. 

Nicotine causes the artery walls to narrow (known as vasoconstriction), and this in itself can increase blood pressure in individuals. Nicotine, carbon monoxide and other toxins can also lead to a process called atherosclerosis. When the cells lining the arteries (known as endothelial cells) are damaged cholesterol and fats can stick to the lining of the walls of the artery forming a plaque. These plaques narrow the lumen (hole in the middle) of the artery. They also harden the wall of the artery (muscle is normally smooth and can expand and contract, but the plaques make the artery walls thick). This process is shown in the image, (source). 

This plaque can also attract blood cells which can form clots. If these clots break off, they are known as emboli. These emboli can lodge themselves in other arteries and if it reaches the brain, it can cause an ischaemic stroke. The hardened artery walls also increase blood pressure, which is another risk factor for ischaemic stroke. In addition to this, the nicotine present in cigarettes increases platelet adhesion (platelets are the constituents of blood that aid in forming clots) within the blood. This also contributes to clot formation 

Thirdly, smoking cigarettes also leads to a process called oxidative stress. There are some byproducts of chemical reactions in the body called free radicals- namely oxygen free radicals. These are highly reactive, and an excess build-up of them can lead to damage of endothelial cells and a chronic state of inflammation within the cardiovascular system. The state of inflammation leads to the release of other molecules involved in the inflammatory process which can further damage the endothelial cells. 

High blood pressure is a risk factor for stroke as it can also facilitate the atherosclerotic process, harden artery walls and destabilise existing plaques on the walls, leading to the formation of emboli. Diabetes- particularly type 2 diabetes- is a risk factor for both hypertension and cardiovascular disease. It is often found in people who are obese, and obesity is also a main risk factor for cardiovascular disease. If blood sugar levels are high over a long period of time, this can damage the blood vessels and also facilitate oxidative stress and chronic inflammatory states. Diabetes can also disturb the blood flow and lead to a higher risk of blood clots and therefore an increased risk of stroke or heart attack. 

Prevention of strokes

Smoking cessation is one of the best ways to lower the risk of ischaemic stroke. According to evidence, the risk of stroke stopped increasing in those who stopped smoking- which in itself shows the benefits of smoking cessation. Another large study looked at smokers who had had a stroke and followed them up for 5 years following the stroke. The participants were divided into two groups- one group stopped smoking for 5 years of the study and the other group continued to smoke. The study found that there was a significant reduction in the risk of stroke following 5 years of smoking cessation compared to those that did not.⁷ Although quitting will not totally reverse or eliminate the damage that is already done, it is never too late to stop. Those who continue to smoke, especially after any treatment or surgery have notably worse outcomes than those who stop.⁸ 

Other preventative measures include maintaining a healthy body weight, controlling alcohol consumption and having a healthy diet. These will all lower the risk of cardiovascular disease.

Treatment of ischaemic stroke

Time is an important factor in the treatment of stroke. The main form of treatment is by giving a drug called tissue plasminogen activator which will help to dissolve a clot. The earlier this is given following the onset of symptoms, the better the chances of survival (and recovery). Long-term treatment involves taking medication to prevent new clots from forming (usually lifelong), along with physiotherapy and rehabilitation. In general, outcomes following a stroke are difficult to predict. Outcomes are very much dependent on how big the blood clot is, the baseline function (before the stroke), the location of the clot in the brain and the intensity of post-treatment rehabilitation.³ 

Summary 

Ischaemic strokes occur when an artery in the brain is blocked by a blood clot and the brain cannot receive blood supply in certain areas. Without the supply of blood, the brain is deprived of oxygen and glucose, both of which are needed for survival. The brain cells will not die straight away- they can remain vital for some time (around 15 minutes). Prompt treatment is one of the main requirements for survival. Still, strokes are often fatal- with around 40% of people dying within a year of having a stroke.

Smoking is one of the main risk factors for strokes- toxins such as nicotine and carbon monoxide damage the arteries, making it more likely for fat deposits and blood clots to form in the arteries, which blocks them. The other main risk factors for stroke are diabetes and hypertension. All three of them are linked, in that they all add up the risk of having a stroke. 

Smoking cessation is one of the best ways to reduce the risk of a stroke (along with other health benefits)- and it is never too late to stop smoking.