See below for a video description of atrial fibrillation:
Atrial fibrillation (also known as AF or A Fib) is the most common abnormal rhythm of the heart, affecting 2.3 million adults in the United States. It is projected that by the year 2040. over 5 million Americans will be affected with atrial fibrillation. Atrial fibrillation is increasing in prevalence likely due to a combination of factors including the aging of the population, a rising prevalence of chronic heart disease, and more frequent diagnosis.
Atrial fibrillation increases in prevalence with age, increasing to nearly 1 in every 10 person older than age 80 years. It is more comon in men than women and more common among Caucasians than African-Americans. Very often atrial fibrillation is associated with underlying heart disease although a significant proportion of patients have no detectable heart disease whatsoever.
The Heart in Atrial Fibrillation
The heart is made up of four chambers: right atrium, left atrium, right ventricle, and left ventricle. At its essence, the heart is a pump which circulates blood throughout the body. Blood returning from the body via the superior and inferior vena cava flows into the right atrium and then into the right ventricle. The right ventricle acts to pump blood to the lungs by way of the pulmonary artery where it is oxygenated and then returns to the left atrium by way of the pulmonary veins. Blood then flows into the left ventricle and is pumped to the rest of the body by way of the aorta.
The heart is a muscle which is stimulated to squeeze by electrical impulses arising from a specialized area known as the sinus or SA node, the body's natural pacemaker. The normal rate of the sinus node is 60 beats per minute increasing as necessary with exertion to 110 to 120 beats per minute. After electrical impuses start in the sinus node, the impulse travels through the right and left atrium to the atrioventricular or AV node. From there the impuse travels through the right and left ventricles via the right and left bundle branches and the Purkinje fibers.
In atrial fibrillation, this orderly progression of an impulse from the body's natural pacemaker to the ventricle is replacd by many rapid and chaotic impulses. This leads to very chaotic squeezing of the atrial muscle at very fast rates (300 to 550 beats per minute). As a result, blood in the atria does not progress in an orderly fashion to the ventricles but rather becomes static and swirls around. This sluggish flow promotes the formation of blood clots in the atria.
As this rapid, chaotic activity progresses to the ventricles, the AV node fortunately cannot conduct all these impulses. However, the rapidity of the ventricles response to atrial fibrillation is poorly regulated and may be as fast as 150 to 200 impulses per minute and in a very irregular fashion. If the ventricles beat excessively fast, there may be inadequate flow of blood to the rest of the body.
Causes of Atrial Fibrillation
As discussed above, atrial fibrillation increases in frequency with age and occurs in people with underlying heart disease. However, atrial fibrillation is also associated with many non-cardiac conditions and may occur in people who are otherwise healthy.
Some important cardiac and non-cardiac conditions associated with atrial fibrillation include:
- Heart failure. Although heart failure is most commonly a result of a heart attack, there are many other causes of heart failure which can also lead to atrial fibrillation.
- A heart attack (also known as myocardial infarction or MI)
- Hypertension or high blood pressure
- Heart valve disease, most commonly mitral or aortic valve
- After heart or other surgery
- Congenital heart disease (heart disease that is present at birth but may not be hereditary)
- Lung disease such as emphysema or COPD
- Sleep apnea
- Alcohol use, particularly binge drinking
- Hyperthyroidism (a condition caused by an overactive thyroid gland resulting is excessive production of thyroid hormone)
Diagnosis of Atrial Fibrillation
Atrial fibrillation is readily diagnosed by obtaining an electrocardiogram (ECG or EKG) which records ongoing electrical activity of the heart.
In a person with atrial fibrillation, normal organized atrial activity depicted by a "p wave" (see purple arrow) is replaced by disorganized "fibrillatory waves" (see red arrow) and irregular electrical activity of the ventricles. Other tests are routinely performed with a first diagnosis of atrial fibrllation such as blood tests and ultrasound imaging of the heart (echocardiogram) to look for underlying conditions which may have predisposed a person to develop atrial fibrillation. Often a continous electrocardiogram (ECG) monitor is performed for several days to evaluate just how much of the time a person is having atrial fibrillation.
Consequences of Atrial Fibrillation
The consequences of atrial fibrillation can be life threatening in some people and must always be addressed. These life threatening problems arise as a result of a rapid heart rate and the formation of blood clots in the heart. In other people, atrial fibrillation is not life threatening but can severely diminish one's quality of life.
If the heart rate is rapid for an excessive period of time as a result of atrial fibrillation, a person can develop weakening of the heart muscle resulting in heart failure. Heart failure leads to such symptoms as shortness of breath at rest or with exertion, swelling of the legs, and weight gain. If left untreated, heart failure can even result in sudden death.
During atrial fibrillation, sluggish flow of blood can lead to blood clot formation in the heart, usually the left atrium. If a portion of a clot breaks off, this can migrate to other parts of the body and obstruct blood flow in a blood vessel (known as an embolus). One of the most worrisome places for an embolus to migrate is to the blood vessel in the brain. This results in a stroke, or "brain attack," which can result in permanent brain damage. A person suffering a stroke can permanently lose function of an arm or leg or lose the ability to speak. It can result in significant disability. The risk of blood clot formation in a person with atrial fibrillation is dependent on a number of factors such as age, the presence of other medical conditions, or a prior history of stroke.
Atrial fibrillation can also lead to a number of symptoms which may not be life threatening but can significantly diminish a person's quality of life. These symptoms may include:
- A sense of the heart racing (palpitations)
- An unpleasant sensation due to irregularity of the heart beat
- Lightheadedness or near fainting
- Shortness of breath that limits the ability to exercise
- Mild chest pain or tightness