October 20, 2014
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Stroke Risk Reduction

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Atrial Fibrillation



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 350 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 6% of those over the age of 65, and the risk increases to 10% to 15% in people over 80.

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, 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
  • permanent AF: the heart has an irregular rhythm that cannot return to normal with medication or other treatments

All three situations carry equal risk of blood clot formation.

Are you at risk for a stroke?

Every 10 minutes on average, a Canadian has a stroke. Could you be next? There are many things that increase your risk of a stroke (called stroke risk factors).


Stroke risk factors

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Some people may have other risk factors for stroke. Talk to your doctor to find out if you're at risk of a stroke, and what you can do to reduce your risk.


To find out your risk of a stroke in the next 10 years, use the stroke risk assessment calculator.

Other resources about stroke risk reduction:



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
  • thyroid disease
  • binge drinking
  • increasing age




Symptoms and Complications of Atrial Fibrillation

The symptoms of AF include:

  • palpitations
  • chest discomfort
  • rapid and irregular heartbeat
  • lightheadedness or, in rare cases, fainting
  • dizziness
  • shortness of breath
  • weakness

Some do not experience any symptoms. In this case, their doctor may recognize the condition during a regular medical examination.

Everyone knows what it feels like to experience an occasional flutter of the heart, and usually it does not mean anything. 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 at least 5 times.

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