Introduction

Ischaemic stroke is an acute condition where a blood clot blocks the flow to an area of the brain, leading to symptoms such as weakness of the limbs, facial drooping, and loss of speech.¹ It is a leading cause of death in the world.² There are certain risk factors and medical conditions that predispose people to get a stroke.¹

For someone with a new diagnosis of atrial fibrillation, a stroke may be the last thing on their mind. They are coming to terms with new medications that they must take and the explanation of symptoms that they may be experiencing. It is, however, important to note the serious risk of an ischaemic stroke in a patient with atrial fibrillation.

Atrial fibrillation is a condition where the heart beats irregularly - this can often cause symptoms such as palpitations(heart racing) and chest pain. There is a proven link between ischaemic stroke and atrial fibrillation, which is why people with a diagnosis of atrial fibrillation are started on early prevention management to help lower the risk.³

Please read this article further to learn more about ischaemic stroke, atrial fibrillation, and the connection between the two conditions. 

Understanding Ischemic stroke

Definition and causes

Stroke is an acute condition where the blood supply to the brain is either partially or completely blocked, causing brain cells to die. It can be classified into two broad categories depending on the cause: ischaemic and haemorrhagic stroke.⁴ Ischaemic strokes account for 85% of total strokes and occur due to a blockage to the blood supply in the brain. There are many potential causes of ischaemic stroke, including atherosclerosis (narrowing of the arteries) and small vessel disease (development of smaller, narrower arteries in the brain). Ischaemic stroke may also be caused by heart conditions such as atrial fibrillation.¹

Clinical presentation

Ischaemic stroke usually presents with a specific set of symptoms. These occur due to the restriction/blockage of blood supply to certain areas of the brain which control muscles, movement, speech, and vision. The death of these brain cells contributes to the loss of these functions either temporarily or permanently.⁴

To raise awareness in the community, this set of symptoms has been shortened into an acronym: F.A.S.T, which stands for:

• Facial drooping - where one side of the face droops or becomes numb; smiles can turn lopsided
• Arm weakness - where one arm is weaker than the other 
• Speech difficulty - slurring of speech
• Time to call for help - call immediately for help to get treatment as soon as possible⁵

Other symptoms and signs of stroke include:

• Numbness
• Confusion
• Vision problems
• Trouble walking 
• Severe headache⁵

Diagnostic methods

Ischaemic stroke is confirmed by imaging of the brain, usually by computed tomography (CT)scan due to its availability and speed. As this is an acute condition which needs to be treated as an emergency, urgent imaging is done and interpreted to start management as soon as possible. Further tests may include mapping out the blood vessels of the brain using special scans such as CT or magnetic resonance imaging (MRI).¹

Treatment and management

In the acute setting, treatment is undertaken to remove the blood clot which is blocking the blood supply to the brain. This is best done as early as possible once an ischaemic stroke is diagnosed. Blood clots are either broken down by thrombolysis therapy (medications) or by procedures such as a thrombectomy. Following acute treatment, medications are usually taken lifelong to keep the blood thin and reduce the risk of developing blood clots again. Medications and lifestyle management are also used to reduce other modifiable risk factors.⁴

Many find the recovery process from an ischaemic stroke to be distressing. It is important to note that the recovery takes time and various functions of the body, including movement, speech and vision, may not return completely back to normal. However, there are many services available to help guide people during their recovery process and how to adapt to life after recovery. These include therapy services, such as physiotherapy and occupational therapy, rehabilitation teams, support from peer groups and community services.¹

Understanding atrial fibrillation

Definition and types

Atrial fibrillation is a condition defined by an irregular and abnormally high heart rate. The types are often classified by the effect on the patient. These include paroxysmal (where episodes are sporadic and stop within 48 hours), persistent (episodes lasting longer than 7 days), and permanent (irregular rate and rhythm present all the time).³

Aetiology and risk factors

In a normally functioning heart, the heart muscles contract and relax to force blood out of the heart and distribute it throughout the body. However, In atrial fibrillation, the heart’s atria (the upper chambers) contract randomly and so quickly that the heart is unable to relax between the contractions. This occurs due to firing of abnormal electrical impulses disrupting the regulation of the rate of contractions to synchronise with the ventricles (the lower chambers). The loss of the heart’s natural pacemaker leads to an irregular rhythm and a faster heart rate which defines atrial fibrillation.³ 

The cause of atrial fibrillation is not fully understood, but there are several factors which put people at a higher risk of developing this condition. The risk factors include:

• Older age 
• Heart disease
• High blood pressure
• Obesity
• Chronic lung diseases such as asthma and COPD⁶

Certain situations can also trigger episodes of atrial fibrillation, especially in those with risk factors. These include excessive consumption of alcohol including binge drinking, drinking lots of caffeine, illegal drugs such as amphetamine or cocaine, and smoking.⁶

Clinical presentation

Common symptoms in those with atrial fibrillation include:

• Dizziness
• Shortness of breath
• Tiredness
• Heart palpitations - heart feels like it is pounding, fluttering or beating irregularly

Many with this condition may also not experience any symptoms at all.

Diagnosis

Diagnosis of atrial fibrillation includes a combination of clinical examination and further tests of the heart. While experiencing episodes, pulse rate and rhythm can be assessed by palpating the pulse (most commonly the radial pulse over the wrist). If the pulse is found to be irregular and higher than normal (greater than 100 beats per minute), a further electrocardiogram(heart tracing) may be ordered.

An electrocardiogram is an electrical tracing of the heart and can pick up the abnormal electrical impulses in this condition. It can also help differentiate from other heart conditions which may cause higher heart rates and other symptoms. Further testing such as an echocardiogram (ultrasound scan of the heart) and a chest x-ray may be carried out.But they are not necessary to diagnose the condition.⁷

Relationship between ischemic stroke and atrial fibrillation

Atrial fibrillation is a significant risk factor associated with ischaemic stroke. Those with atrial fibrillation are 4 times more likely to have a stroke.⁸ In general terms, atrial fibrillation can cause an ischaemic stroke depending on the heart rate(fast) and rhythm(irregularity). Due to this, the heart does not completely empty itself of blood after a heartbeat and can cause the remaining blood to form a clot (a thickened piece of blood). If the blood clot travels to the brain, it can block the narrow blood vessels supplying blood to brain cells, and cause an ischaemic stroke.¹ 

Other mechanisms include structural abnormalities and vascular risk factors which are common in those with atrial fibrillation, predisposing people to blood clot formation and narrowing of blood vessels. For example, atrial fibrillation is sometimes associated with an aortic arch atheroma, which is a narrowing of the aorta (a large blood vessel associated with pushing blood out of the heart) by fatty tissues. Narrowing of blood vessels can block the blood flow, allowing pools of blood to thicken and form a clot.⁹

The risk of ischaemic stroke in those with atrial fibrillation is often measured using clinically proven tools such as the CHA₂DS₂‐Vasc score. This takes into account other risk factors including age, sex, and other vascular disease. The higher the score, the higher the risk of occurrence of an ischaemic stroke. This helps clinicians decide on the implementation of preventive therapy and further monitoring and care for people with atrial fibrillation.¹⁰

Prevention and management strategies

There are multiple ways to help prevent and manage the risk of stroke in patients with atrial fibrillation. Most patients are on lifelong anticoagulant(blood thinners) therapy to mitigate this risk. Types of anticoagulation therapy which may be started include vitamin K antagonists, such as warfarin, and new oral anticoagulants, such as apixaban and rivaroxaban.¹⁰ There are various side effects to anticoagulative therapy; the most important to note is the increased risk of bleeding, which affects the body’s healing process after an injury or after major surgical procedures.⁴ 

While anticoagulation therapy directly reduces the risk of an ischaemic stroke, there are other management strategies to help with atrial fibrillation, thus reducing the risk of stroke as well. Management of atrial fibrillation is divided into rate and rhythm control - targeting the two separate components which define it. Medical management can be used to slow the heart rate and to revert it back to a normal rhythm. Sometimes a controlled electric shock of the heart or surgical procedures such as ablation or pacemaker insertion can also improve the irregular rhythm of the heart.³ The overall benefit is to control atrial fibrillation and reduce the risk of blood clot formation.

Stroke prevention strategies in atrial fibrillation also include reducing the risk of developing comorbidities such as high cholesterol, high blood pressure, and high blood sugar. These are managed with lifestyle modification and/or medical therapies. These conditions can also contribute to other causes of ischaemic stroke such as atherosclerosis and small vessel disease.⁴

There are other proven modifiable risk factors for ischaemic stroke out of which high blood pressure and tobacco use are the most significant.¹¹ Therefore, lifestyle management to help reduce these, such as following a healthy, well-rounded diet, regular exercise, and smoking cessation.These are equally important and effective as medical therapies.⁴

FAQ’s

What is ischaemic stroke?

Ischaemic stroke is a serious and acutely life-threatening condition where there is a loss of blood supply to the brain. This is specifically caused by a blockage to the blood supply due to a blood clot. It impairs the brain’s ability to control the body, affecting muscle movements, speech, and vision. Urgent treatment is needed to remove the blood clot and restore normal blood supply.

What is atrial fibrillation?

Atrial fibrillation is a heart condition where the heart beats very fast and irregularly due to abnormal electrical impulses. The exact cause is unknown, and those with the condition may or may not experience associated symptoms with it. It is treated using medication to lower the heart rate and revert the rhythm back to normal.

How does atrial fibrillation cause ischaemic stroke?

Atrial fibrillation is defined by an abnormally fast heart rate and an irregular heart rhythm. Both of these contribute to the heart not being able to completely empty the blood stored inside during its contraction. Pools of remaining blood are at risk of thickening and forming clots. If these spread through the bloodstream into the narrow and smaller blood vessels supplying the brain, the clot can get stuck and restrict blood supply to the brain tissue, causing an ischaemic stroke.

How likely is it to have an ischaemic stroke if you have atrial fibrillation?

Atrial fibrillation increases your risk of having an ischaemic stroke by about 4 times. Individual risk can also be assessed using tools like the CHA₂DS₂‐Vasc score. 

What is the treatment for ischaemic stroke caused by atrial fibrillation?

Acute treatment for any ischaemic stroke is the same: thrombolysis treatment or possible thrombectomy. Medications are started afterwards for anticoagulation therapy (to thin blood and prevent clots) and to reduce the risk factors like high cholesterol and high blood pressure. Early prevention therapy with anticoagulation and reducing risk factors may be implemented before having a stroke in those with atrial fibrillation, since it is a known risk factor of ischaemic stroke.

Summary

There is a strong link between ischaemic stroke and atrial fibrillation. It is important to recognise and acknowledge this acutely life-threatening condition(Ischaemic stroke) to reduce the risk early on. There are many prevention strategies which can be implemented to avoid having an ischaemic stroke. This includes treating medical conditions such as atrial fibrillation and incorporating lifestyle modifications like regular exercise and smoking cessation.