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What is Atrial Fibrillation?

Atrial fibrillation is the most common type of irregular heart rhythm. Each beat that your heart takes requires a coordinated series of electrical impulses, with precise timing to allow the four chambers of the heart to receive and send blood to all areas of the body. Let’s start by exploring the basic anatomy of the heart, and how it works to understand exactly how atrial fibrillation affects this process. 

The heart has four chambers, 2 of which (called the atria) receive blood from either the body or the lungs. The other 2 (called ventricles) send blood to either the lungs or the rest of the body. One of the main functions of circulation and blood movement throughout the body is to carry oxygen to all tissues including muscles and organs. When blood the is filled with oxygen reaches it’s target destination, the oxygen is removed and used by the tissue and the blood returns to the heart to get more oxygen from the lungs. 

As you can appreciate, the process of receiving and directing blood flow through the heart needs to be managed. In the same way that roundabouts and traffic lights help to reduce congestion and manage the flow of traffic, the organisation of the different chambers and the coordinated contraction of the different chambers helps to direct blood to the right areas at the right times.

 Blood enters the heart on the right side into the right atrium. When this chamber is full, it contracts to push the blood into the next chamber which is called the right ventricle. When this chamber is full, it contracts to push blood into the lungs where the blood collects oxygen. Once the lungs have exchanged oxygen with the blood, the blood is then sent to the atrium on the left side of the body. When this chamber is full, blood is then pushed into the left ventricle and from here, it begins it’s journey into circulation. The chambers assist in maximising the exchange of blood. If too much blood is pushed into the heart at once, the amount of oxygen that is available in the blood relative to the volume of blood is low. Another important reason for the different chambers is the different pressures and forces required in different areas. The pressure to pump blood out of the left ventricle to the working tissues is higher than is needed in the other chambers. 

For this entire process to work well the atria need to contract at a different time to the ventricles. When the atria contract they do so together (ie left and right)which pushes blood into the ventricles. At the same time, both ventricles relax so that they can fill completely. When the ventricles are full, the atria then relax and re-fill with blood, and the ventricles contract to push blood on to it’s next destination. The ba-boom sound that makes up a heart beat reflects the contraction of these chambers, with the initial “ba” being contraction of the atria, and the “boom” being contraction of the ventricles.

So what happens in Atrial Fibrillation?

The electrical system that co-ordinates heart muscle contraction has a problem. The impulse that causes the atria to contract is affected making the contraction less forceful and out of sync with the ventricles. This results in less blood entering each chamber and ultimately less blood and oxygen pushed throughout the body with each heart beat. This means the heart has to work harder to provide the body with the blood and oxygen supply it demands. Over time, this additional stress can lead to an increased risk of heart attack and also to the development of heart failure. 

Another consequence of atrial fibrillation is that at times, blood flow is stagnant. When the co-ordination of heart chamber contraction is normal, the blood is constantly moving from one area to the next efficiently without any hold ups. When blood flow is altered, as is the case in a traffic jam, the likelihood of clot development significantly increases. As a result, atrial fibrillation is associated with a five fold increase in the risk of suffering a stroke. 

Luckily, in addition to any medications or medical interventions, exercise is an important part of management. Research indicates that aerobic exercise such as walking, swimming or cycling, is the most effective type of exercise to assist in the management of atrial fibrillation. This should be performed at a moderate intensity, or at a rating between 4-6 on a scale of 1-10 (with a score of 10 being extremely intense). You should measure your heart rate before you exercise, and ideally it should be under 120 beats per minute at rest. If your heart rate is above this value, then it is safest to reduce the intensity of your session for the day. 

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