Atrial Fibrillation
In this condition factsheet:
The Facts on Atrial Fibrillation
The heart is divided into four chambers: two atria on top and two ventricles underneath. The role of the atria is to fill the ventricles with blood, which is then pumped to the lungs or to the rest of the body.
The normal beating of the heart is controlled by electrical signals sent from a particular segment of heart tissue called the sinus node. The sinus node acts as the heart's natural pacemaker. It is found near the top of the right atrium. Normally, the sinus node sends an electrical pulse that travels down the muscle tissue to the atrioventricular (AV) node (acting like a "toll booth"), which determines how many impulses are allowed to then pass to the ventricles.
An arrhythmia occurs when the heart's regular rhythm becomes irregular – it may speed up or slow down. Many arrhythmias exist, but those originating from the ventricles are generally more serious than from the atria.
Atrial fibrillation (AF) is one type of arrhythmia. Instead of the sinus node controlling the heart rate, different parts of the atria fire at the same time. This causes the atria to fibrillate, which is an uncoordinated quivering of the muscle. The atria pump blood less effectively but well enough to allow the ventricles to function. The irregular heartbeat is due to rapid beating of the atria (usually more than 400 beats per minute), and the irregular movement of the electrical signals through the AV node. Instead of every electrical signal being allowed through to the ventricles, only certain electrical signals are allowed to pass.
AF is potentially dangerous because blood can pool in the atrium, which increases the risk that a blood clot will form. If this clot travels to the brain, it will cause a stroke. AF is the most common form of all harmful arrhythmias, affecting approximately 200,000 Canadians. The risk of developing atrial fibrillation increases with age.
AF may be present in a number of different forms:
- paroxysmal AF: recurrent temporary condition that starts suddenly and then after a period of time (usually less than 7 days), the heart returns to a normal heartbeat without medical assistance
- persistent AF: the heart beats irregularly and requires medical assistance to return to a normal rhythm. This type of AF tends to last more than 7 days .
- long-standing persistent AF: the heart has an irregular rhythm that has lasted longer than 1 year, but there is still the possibility of restoring a normal rhythm
- permanent AF: the heart has an irregular rhythm that cannot return to normal with medication or other treatments
Causes of Atrial Fibrillation
The cause of AF is not always known, but possible causes can include any of the following:
- abnormal structure of the heart
- diseases that damage the valves of the heart
- high blood pressure
- cardiomyopathy (a disease affecting heart muscle)
- thyroid disease
- heavy drinking
- smoking
- obesity
- increasing age
Symptoms and Complications of Atrial Fibrillation
The symptoms of AF include:
- palpitations
- chest pain
- rapid and irregular heartbeat
- lightheadedness or, in rare cases, fainting
- extreme fatigue
- dizziness
- an overactive thyroid gland (hyperthyroidism)
- shortness of breath – this may occur at rest in more severe cases of AF
- weakness
Some people do not experience any symptoms. In this case, their doctor may recognize the condition during a regular medical examination.
Experiencing an occasional flutter of the heart does not usually mean anything on its own. See your doctor if you experience chest pains, feel faint, or notice your pulse to be faster than usual or irregular over a prolonged period.
AF is a progressive condition that can weaken the heart and its ability to pump blood, especially if it is not treated properly. Another possible complication of AF is the formation of blood clots that can cause a stroke. The risk of stroke depends on your age and other risk factors, but the presence of AF increases your risk of having a stroke by 3 to 6 times.
