People with atrial fibrillation have an increased risk of stroke and venous thromboembolism (VTE). These are the two most common health conditions which are managed with anticoagulation treatments. As both disorders have a similar pathophysiologic base for clot formation, it may suggest that the risk factors for the occurrence of thrombosis might be similar. 

Background information about atrial fibrillation

Atrial fibrillation (AF) is defined as an irregular or very fast heartbeat. An abnormal heart rhythm is called an arrhythmia and AF occurs when this chaotic heartbeat affects the upper chambers of the heart – the atria.

Atrial fibrillation places a heavy burden on both patients and doctors as it represents both the cause and result of chronic conditions associated with cardiovascular diseases such as hypertension, atherosclerosis, stroke and thromboembolic events.

Statistics

• The Lancet Regional Health (Europe) study of 3.4 million people in England found the incidence of AF increased by 30% from 1998-2017.
• In the US, between 3-6 million individuals had AF in 2020, and this number is estimated to reach 6-12 million by 2050.
• In Europe, there are currently 8 million affected by AF and is also expected to drastically increase over the next few decades.
• Results from the Global Burden of Disease Study 2017 (195 countries) for prevalence of AF between 1990-2017 found that cases increased from approximately 19 million to 37 million.
• In 2020, 2.2% of Australians were recorded to have AF; 15% of acute hospitalisations for stroke were also diagnosed with AF; and AF related deaths nearly doubled from 4.6% to 9.0% from 2001-2018.

Symptoms - for many people, AF may not produce any symptoms, however the following may present:

• Fast, pounding, fluttering heartbeat, also known as heart palpitations.
• Chest pain.
• Shortness of breath.
• Light-headedness or dizziness.
• Feeling fatigued or have a reduced ability to exercise.
• Weakness.

Causes - the most common cause of AF is when there is a problem with the heart’s structure:

• Congenital heart defect.
• Sick sinus syndrome – an issue with the heart’s natural pacemaker.

Other causes include:

• Sleep apnoea.
• Heart attack.
• Heart valve disease – one or more of the four heart valves do not work properly.
• High blood pressure – over a long period time high BP may result in the heart becoming stiff and thick, which can affect the signals travelling through the heart.
• Lung diseases such as pneumonia.
• Narrowed or blocked arteries (coronary artery disease).
• Thyroid conditions such as hyperthyroidism (an overactive thyroid).
• Infections from viruses.
• Heart surgery or stress due to surgery.

Some lifestyle habits can also cause AF:

• Excessive intake of alcohol or caffeine.
• Smoking tobacco or illegal drug use.
• Some medications which contain stimulants (over-the-counter cold and allergy medicines).

There are also some additional circumstances which can increase the risk of AF:

• Age – worldwide prevalence is approx. 1%; >75 it is approx. 9%; ≥80 it increases to 22%.
• It is more common in males.
• Minerals – electrolytes in the blood (potassium, sodium, calcium and magnesium) assist the heart to beat. When these minerals become imbalanced (too high or low), irregular heartbeats can occur.
• Family history.
• Obesity.
• Chronic health conditions – diabetes, chronic kidney disease, or lung disease.
• Hypertrophic cardiomyopathy (HCM) - this is a condition where the heart muscle becomes thickened which can make it difficult for the heart to pump blood. One of the complications associated with HCM is atrial fibrillation, as a thickened heart muscle or changes to the heart’s structure can cause alterations in the heart’s electrical system and heartbeats. The global prevalence is approximately 1 in 500 adults.

Atrial fibrillation and thromboembolism

Atrial fibrillation is shown to increase the risk of thromboembolism, with a high association towards thrombus formation in the left atrium. There is also an elevated possibility of systemic embolism (blockage in an artery or vein of the limbs and the main internal organ cavities such as the abdomen).

A 16-year follow-up study (concluding in 2010) included 29,975 participants and investigated the association between atrial fibrillation and venous thromboembolism (VTE). During the study period 1604 subjects were diagnosed with AF, and 614 with incident VTE. The risk of VTE also increased significantly throughout the initial 6 months after AF diagnosis and persisted at this level during the entire study. The findings also showed there was a higher risk for pulmonary embolism than deep vein thrombosis.

Treatment options

To prevent ischaemic strokes, anticoagulation is a key and critical factor in the management for this chronic condition. It has been well documented that warfarin is used in the prevention of stroke and to reduce the risk of systemic embolism among AF patients. However, studies including people over the age of 80 is limited.

A 2023 review looked at the safety and efficacy of oral anticoagulants among patients aged ≥80 years of age with atrial fibrillation. The study found that compared to warfarin, non-vitamin K antagonist oral anticoagulants (NOACs) reduced the risk of stroke; and systemic embolism and all-cause mortality were lower. Warfarin can reduce the risk of stroke however has a slender therapeutic range, requiring constant coagulation observations with food and drug interactions. NOACs can tackle this somewhat, by dispensing fixed doses without monitoring and there are less issues with food and drug contraindications.

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References

• Atrial fibrillation - Symptoms and causes - Mayo Clinic
• Heart valve disease - Symptoms and causes - Mayo Clinic
• Atrial-fibrillation-in-Australia.pdf.aspx (aihw.gov.au)
• Atrial Fibrillation - StatPearls - NCBI Bookshelf (nih.gov)
• Epidemiology of Atrial Fibrillation in the 21st Century (ahajournals.org)
• Atrial fibrillation, a contemporary sign of multimorbidity and irregular social inequity (thelancet.com)
• Andersen, L.V., Vestergaard, P., Deichgraeber, P., Lindholt, J.S., Mortensen, L.S., & Frost, L. (2008). Warfarin for the prevention of systemic embolism in patients with non-valvular atrial fibrillation: a meta-analysis. Heart. 94(12):1607-1613. doi: 10.1136/hrt.2007.135657.
• Dai, H. et al. (2021). Global, regional, and national prevalence, incidence, mortality, and risk factors for atrial fibrillation, 1990–2017: results from the Global Burden of Disease Study 2017. European Heart Journal. Quality of Care & Clinical Outcomes, 7(6), 574–582. https://doi.org/10.1093/ehjqcco/qcaa061.
• Enga, K. F. et al. (2015). Atrial fibrillation and future risk of venous thromboembolism: the Tromsø study. Journal of Thrombosis and Haemostasis, 13(1), 10–16. https://doi.org/10.1111/jth.12762.
• Kang, F., Su, L., Fan, S., Lv, L., & Luo, B. (2023). Efficacy and safety of non-vitamin K antagonist oral anticoagulants in patients (≥80 years of age) with atrial fibrillation: systematic review and meta-analysis. Intern Med J. 53(9):1524-1532. doi: 10.1111/imj.16101.
• Morillo, C.A., Banerjee, A., Perel, P., Wood, D., & Jouven, X. (2017). Atrial fibrillation: the current epidemic. J Geriatr Cardiol;14(3):195-203. doi: 10.11909/j.issn.1671-5411.2017.03.011
• Shariff, N., Aleem, A., Singh, M., Li, Y.Z., & Smith S.J. (2012). AF and venous thromboembolism - pathophysiology, risk assessment and CHADS-VASc score. J Atr Fibrillation;5(3): 649. doi: 10.4022/jafib.649.