Information about atrial fibrillation
(a common form of an irregular heartbeat)
What is atrial fibrillation and is it serious?
Atrial fibrillation (AF) is an irregular heartbeat. It is caused by a failure of the heart’s natural pacemaker, which is responsible for managing the contractions of the heart. Under normal circumstances the pacemaker first makes the two chambers at the top of the heart (the atria) contract, squeezing blood into the two lower chambers (the ventricles). These in turn are triggered to contract, squeezing blood out into the arteries.
In atrial fibrillation, a malfunction of the pacemaker interrupts this sequence of contractions causing the atria to twitch erratically – known as fibrillation – and the ventricles to contract more often and irregularly.
Not surprisingly the heart works less effectively as a pump in atrial fibrillation, resulting in symptoms like a rapid heart rate, difficulty breathing, tiredness and light-headedness. Now there are also areas within the heart where blood flow is slow or stagnant. Where this happens blood clots can form and it is these that account for the increased risk of stroke associated with atrial fibrillation.
Why atrial fibrillation increases your stroke risk
The problem with a blood clot in the heart is that some or all of it can break away and travel along major blood vessels directly into the brain.
As these very large blood vessels branch and get smaller / narrower in size, at some stage the clot or piece of clot is going to be too large to travel any further and will block the blood vessel in which it is travelling.
This means that the area of the brain beyond the clot can no longer receive the oxygen and nutrients that the blood normally delivers, causing the nerve cells to stop working and ultimately die.
This is what happens in a stroke – or more specifically in an ischaemic stroke (meaning one caused by an interruption in the blood supply). Because clots forming in the heart may be quite big they can block the larger blood vessels that supply large areas of the brain. Consequently, strokes arising from an irregular heartbeat or atrial fibrilation can be very serious, which is why it is so important to prevent clots forming in the heart.
How to avoid a stroke from atrial fibrillation
If you have atrial fibrillation you are at an increased risk of stroke due to the formation of blood clots in the heart. So what can be done to reduce this risk?
Clots are formed in a process known as coagulation. This is a complex series of steps that must occur in a specific order. By interrupting one or more of these steps it is possible to reduce the likelihood of a clot forming and, thereby decrease the risk of stroke. Medicines that block the coagulation process in this way are known as anticoagulants.
For many years the most commonly used anticoagulants for stroke prevention in patients with atrial fibrillation have been the vitamin K antagonists. Medicines in this class, such as warfarin, are affected by interactions with a number of common foods and with other medicines. As a result, frequent blood tests are needed to find the appropriate dosage – a process known as monitoring.
Recent developments have resulted in new oral anticoagulants that can be used as alternatives to vitamin K antagonists. These new drugs are largely free from interactions and consequently do not require monitoring. Currently these include an oral direct thrombin inhibitor and an oral, direct Factor Xa inhibitor. Ask your doctor what treatment is right for you.
References – Further Reading:
• American Heart Association/American Stroke Association. Let’s Talk About Lifestyle Changes To Prevent Stroke. 2007.
• Ansell J, Hirsh J, Poller L, et al. The pharmacology and management of the vitamin K antagonists: The Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Chest 2004; 126(3 suppl):
• Camm AJ, et al. European Heart Rhythm Association; European Association for Cardio-Thoracic Surgery,Guidelines for the management of atrial fibrillation: the Task Force for the Management of Atrial Fibrillation of the European Society of Cardiology (ESC). Eur Heart J 2010; 31(19): 2369–2429.
• CDC. Atrial Fibrillation Fact Sheet. National Center for Chronic Disease Prevention and Health Promotion, Division for Heart Disease and Stroke Prevention. 2010.
• Global Atlas on Cardiovascular Disease Prevention and Control. Mendis S, Puska P, Norrving B editors. World Health Organization, Geneva 2011.