Introduction

The pandemic of SARS-CoV-2, more commonly known as COVID-19, was no longer declared a public health emergency on May 5 2023. However, the consequences of COVID-19 are still being studied to this day. Most people suffering from COVID-19 experience mild to severe respiratory problems, but there have been links to vascular complications as well. Recent studies have linked COVID-19 with ischaemic stroke, a life-threatening emergency caused by a compromised supply of blood to the brain, suggesting some mechanisms connect the two conditions. Understanding this connection will help improve patient care and public health knowledge. 

Understanding ischaemic stroke

Overview

A stroke is a life-threatening emergency where the blood flow to the brain is blocked or restricted, damaging and killing brain cells. Strokes are a type of cerebrovascular disease which is the 2^nd leading cause of death, right behind ischaemic heart disease. Ischaemic strokes are the most common type of stroke, accounting for roughly 87% of stroke cases. Hemorrhagic strokes are the other main type of stroke that involves a rupture or bleeding of a blood vessel. Both types of stroke can be life-threatening and will require medical attention.

Causes

The restricted blood flow in an ischaemic stroke is typically caused by a thrombus, also known as a blood clot. Blood clots can form as a result of a process known as atherosclerosis where fatty deposits called plaques build up in a person’s arteries, increasing the risk of a blockage. 

Symptoms

The symptoms of ischaemic stroke typically develop suddenly or within a short space of time. 

These can include:

• Numbness or weakness in the arms or legs, usually on one side of the body
• Problems seeing in one or both eyes
• Trouble speaking or hearing
• Being unable to walk properly
• Dizziness¹¹

Treatment

The standard form of treatment for an ischaemic stroke is an IV injection of a tissue plasminogen activator (tPA). tPA works by dissolving a blood clot and allowing blood flow to return to the brain. Other forms of treatment can involve direct delivery of medicines to the brain or removal of a clot with a stent.

Understanding COVID-19 

COVID-19 is a respiratory disease caused by a strain of coronavirus called SARS-CoV-2. COVID-19 causes similar illnesses such as the common cold, SARS and MERS. The symptoms of COVID-19 can be mild, symptomless, or severe depending on a person’s age, pre-existing illnesses, or other factors. 

Causes

COVID-19 is caused by infection with the SARS-CoV-2 virus. It is spread from person to person through airborne droplets.

Symptoms

Typical symptoms of COVID-19 can include:

• High temperature
• Chills
• New cough
• Change in smell or taste
• Issues breathing
• Exhaustion
• Body aches
• Diarrhoea 
• Nausea

Treatment

Most people can recover from COVID-19 through rest and keeping hydrated. Antiviral drugs such as nirmatrelvir plus ritonavir, molnupiravir, and remdesivir can be used if advised by a medical professional. If COVID-19 symptoms become more severe, hospitalisation and continuous medical attention may be needed. 

The relationship between COVID-19 and ischaemic stroke

The rate of stroke in COVID-19 patients

Despite being classified as different types of illnesses, research suggests that contracting COVID-19 can increase the risk of stroke and other cardiovascular illnesses.⁵ Patients admitted to hospitals with COVID-19 are known to have an increased rate of ischaemic strokes compared to those with similar conditions such as influenza (1.6% compared to 0.2%).⁶ The World Health Organisation (WHO) reported that the risk of ischaemic stroke with COVID-19 is approximately 5% and the mortality rate of stroke patients was around 38% more than stroke patients who did not have COVID-19.⁷ The Stroke Association states that having COVID-19 could increase your risk of a stroke by 20 times in the first few weeks of getting the disease.¹⁰

COVID-19 and thrombosis

In patients admitted with COVID-19, almost a third of patients (31%) may experience issues with blood clotting, also known as coagulation.³ COVID-19 is understood to put patients in a “hypercoagulable state” which means there is an increased risk of clots forming in the blood.¹³ One study found that COVID-19 increased the risk of deep vein thrombosis and pulmonary embolism up to 3 and 6 months after contracting COVID-19, respectively.⁸ This could imply that COVID-19 induces changes within coagulation pathways that increase the chance of a blood clot forming. An increased risk of blood clot formation also increases the risk of stroke.

Potential mechanisms that link COVID-19 to ischaemic stroke

One possible explanation for this increased risk of stroke could be due to the cytokine storm that can occur in COVID-19. Cytokines are a group of proteins released by cells in the immune system. These proteins are responsible for regulating inflammation by directing where immune cells should migrate. However, diseases such as COVID-19 can cause a cytokine storm where excessive amounts of cytokines are released in a short period of time.¹⁴ Specific cytokines such as interleukin-6 are found at significantly higher levels in COVID-19 patients and play a key role in blood coagulation. Elevated levels of these cytokines can lead to cell and tissue damage and increase the risk of a blood clot forming, suggesting COVID-19 increases the risk of stroke.

D-dimer is another protein that is found at higher levels in COVID-19 patients. D-dimer is a protein fragment involved in the formation of a blood clot, through a process known as hemostasis. Hemostasis is a necessary process that prevents a person from losing too much blood from an injury in a blood vessel. A protein called fibrin forms a protein net that surrounds a blood clot to anchor it as an injury heals. Once healed, the blood clot is degraded and D-dimer is a by-product of this degradation. Under normal conditions, D-dimer is undetectable or found at very low levels in a blood test. If higher levels of D-dimer are detected in the blood, this could indicate there is an issue with a person’s blood coagulation. COVID-19 patients have been found to have D-dimer levels twice as high as patients with pneumonia or other conditions. Patients with high D-dimer levels were more likely to require intensive care and had a higher risk of death than patients with normal D-dimer levels.⁹ This is another reason that could explain why COVID-19 sufferers are more likely to suffer from a stroke.

However, the mechanisms and pathways that directly link these two conditions are not fully understood. Further research is needed to determine exactly why COVID-19 increases the risk of an ischaemic stroke.

FAQ’s

What should you do if you’re concerned about your or someone else’s risk of contracting COVID-19 or a stroke?

Book a consultation with your GP or a medical professional if you’re concerned about your own or someone else’s health. They will be able to perform examinations and tests to determine your risk and offer any help if needed. 

The general advice for both illnesses is to focus on making healthy lifestyle changes such as eating a balanced diet, getting regular exercise and limiting smoking and drinking.

Since COVID-19 is passed from person to person, it would be best to stay away from large crowds where possible, wear face masks and practise regular hand washing to minimise the risk of contracting COVID-19.

Who is most at risk from COVID-19 or stroke?

Both illnesses can happen to anyone at any point in their life. However, those most at risk include newborn babies, the elderly, those with pre-existing conditions, and those who are immunocompromised. 

Risk factors such as having high blood pressure, eating a poor diet, being obese, or being exposed to air pollutants can increase the likelihood of both conditions.

Summary

COVID-19 and ischaemic stroke present as two very different illnesses, but research suggests that these conditions are more interlinked than previously thought. Specific proteins that are involved in the formation of blood clots are found at high levels in COVID-19 patients. High levels of these proteins can increase the risk of a blood clot blocking a blood vessel, therefore increasing the risk of an ischaemic stroke. The reasons why COVID-19 affects these coagulation pathways are not fully understood and require more research. Understanding the link between these diseases is crucial in understanding how to better care for patients who are at higher risk of stroke.