Atrial Fibrillation

What is atrial fibrillation?

The heartbeat is controlled by an electrical conduction system that sends impulses to the heart muscle causing it to rhythmically expand and contract. Sometimes the heart’s electrical conduction system loses its regular pattern, which can cause many different heart rhythm problems. One of these is atrial fibrillation (AF or Afib).

In AF, the electrical impulses are no longer coming from the heart’s natural pacemaker (the sinus node), but from the heart’s top chambers (atria). Compared to the typical impulses, which occur 60 to 70 times per minute, in AF the charges are very rapid, more than 300 times per minute. The rapid, uncoordinated muscle contractions that result prevent the heart from pumping effectively. The abnormal impulses in the atria also spill over to the heart’s main pumping chambers (the ventricles), causing them to beat rapidly and irregularly as well.

AF can be continuous (persistent AF), or episodes may alternate with periods of normal heart rhythm, a condition known as paroxysmal AF. When the rhythm disturbance has lasted for more than a week, it is considered persistent AF.

What are the symptoms of atrial fibrillation?

Symptoms of AF typically include a racing, irregular, or uncomfortable heartbeat, or a sensation of a “flopping” in the chest. Some people also experience dizziness, chest pain, and sweating. Not all people with AF experience symptoms.

How common is atrial fibrillation?

AF is the most common heart rhythm disorder, affecting an estimated 2.2 million Americans, or about 1 in 100 people. According to the US Census Bureau, the number of people affected by AF is projected to be more than 12 million by the year 2050.

Although men are 1.5 times more likely than women to develop AF, the actual numbers of women and men with AF are roughly the same because AF is more common in older people and women tend to live longer than men. As with many heart problems, women who develop AF tend to do so later in life than men, at an average age of 75 (compared to 67 in men).

AF itself is not usually deadly, but it can lead to other problems such as chronic fatigue, heart failure and, most importantly, stroke. There is no difference in the mortality rate between men and women with AF.

Atrial Fibrillation & Stroke

What does atrial fibrillation have to do with stroke?

In people with AF, the atria’s rapid, irregular beat moves blood inefficiently, and the blood inside the chambers tends to form clots. These clots can break loose and travel through the bloodstream to the brain, where they become lodged in an artery, causing a blocked-vessel (ischemic) stroke.

Illustration showing how atrial fibrillation can cause a blocked-vessel (ischemic) stroke. The blood clot travels from the heart to the brain where it blocks blood flow to part of the brain. Source: NHLBI

What impact does atrial fibrillation have on my stroke risk?

AF is responsible for 15% to 20% of all strokes. It increases the risk of a first stroke 3- to 4-fold, and doubles the risk of a recurrent stroke. The stroke risk is the same whether the AF is persistent or paroxysmal (comes and goes).

Several studies have found that AF is a more important stroke risk factor in women than in men. In one observational study of 1581 patients (half were women) who had experienced a first stroke, women were almost twice as likely to have had AF that preceded the stroke (31% versus 19% of men).

If you have AF, your personal stroke risk varies widely based on other conditions you may have: doctors use a formula called the CHADS2 score to determine your approximate risk.

To find out your stroke risk, add up all your CHADS2 points in Table 1 below, and then look up your corresponding yearly stroke risk in Table 2.

Table 1: CHADS2 Score
For Predicting Stroke Risk in Patients with AF
Risk Factor Points
Heart Failure +1
Systolic blood pressure higher than 160 mm Hg +1
Being 75 years or older +1
Diabetes +1
Previous Stroke or TIA +2
Table 2: Your Stroke Risk
CHADS2Score Risk Level Yearly Stroke Risk
0 Low 1.0%
1 Low to Moderate 1.5%
2* Moderate 2.5%
3 High 5.0%
4, 5, or 6 Very High More than 7%
*If you have had a stroke or TIA you are considered to be at high risk, even if you have no other risk factors

In addition to increasing your chances of stroke, AF also tends to make strokes more severe: one study found that people with AF who had a stroke were more than twice as likely to be bedridden than those who had strokes from other causes.

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