Atrial Fibrillation

Atrial fibrillation is a disorder found in about 2 million Americans. It is the most common type of arrhythmia, affecting approximately 250,000 Canadians. While it is rare in people under 40, its prevalence increases with age. About 3% of the population over the age of 45 and 6% over age 65 have atrial fibrillation. After the age of 55, the incidence of AF doubles with each decade of life.

"Atrial" refers to the top two chambers of the heart known as the atria, where the irregularity in atrial fibrillation occurs. Atrial fibrillation falls under a larger category of illnesses called arrhythmias, which are electrical disturbances of the heart. Arrhythmias can also occur in the ventricles, the two chambers below the atria, and these tend to be more serious than arrhythmias affecting the atria.

The atria (the heart’s “collecting chambers”) are designed to send blood efficiently and rhythmically into the ventricles (the “pumping chambers”) by way of regular electrical signals. From there,blood is pumped to the rest of the body.In atrial fibrillation, the electrical signals are rapid, irregular and disorganized, and the heart may not pump as efficiently.

Stroke occurs if a piece of a blood clot in the atria leaves the heart and becomes lodged in an artery in the brain. About 15 percent of strokes occur in people with atrial fibrillation.

Read more about the anatomy of the heart.

Three types of atrial fibrillation (AF)

• Paroxysmal Paroxysmal AF is a temporary, sometimes recurrent condition. It can start suddenly, but the heartbeat usually returns to normal on its own, without medical assistance.
• Persistent If you have had atrial fibrillation for more than seven days, this is considered persistent AF. With this type of AF, the heart continues to beat irregularly, and will require either medical or electrical intervention to return the heart to a normal rhythm.
• Permanent With permanent AF, the irregular beating of the heart lasts for more than a year when medications and other treatments have failed. Some patients with permanent AF do not feel any symptoms nor do they require any medications.

What causes atrial fibrillation?

Quite often, the cause of atrial fibrillation is unknown. Here are a few conditions that might lead to AF:

• High blood pressure, the most common cause
• Abnormal structure of the heart
• Infection or inflammation of the heart (myocarditis or pericarditis)
• Diseases that damage the valves of the heart
• Overactive thyroid (hyperthyroidism)
• A blood clot in the lung (pulmonary embolism)
• Congenital heart disease
• Excessive use of alcohol

How do I know if I have atrial fibrillation?

Some people with atrial fibrillation may feel perfectly fine. They may not know they have the condition until they have a routine test called an electrocardiogram (described below). Others with atrial fibrillation may experience various symptoms including:

• Irregular and fast heartbeat
• Heart palpitations or a rapid thumping in the chest
• Chest discomfort, chest pain or pressure
• Shortness of breath, particularly with exertion or anxiety
• Fatigue
• Dizziness, sweating, or nausea
• Light headedness or fainting

How is atrial fibrillation diagnosed?

If your pulse is fast and your heartbeat is irregular, your doctor may have you checked for atrial fibrillation. Your doctor will take your medical history, and will ask youfor details about your condition and risk factors. Questions may include: How long have you had symptoms? Describe your symptoms. Do they come and go? Do you have other medical conditions? How much alcohol do you drink? Your doctor will also ask you whether anyone in your family has atrial fibrillation, and whether you have heart disease or a thyroid condition. Your age is also a factor to take into consideration, as AF is more common in older people.

Stethoscope Using a stethoscope, your doctor will listen for fast, irregular beats. Your doctor will also check your pulse and determine whether or not it is normal.

To hear what atrial fibrillation sounds like, listen to this sound file.

Electrocardiogram The main diagnostic test is an electrocardiogram (ECG), which is a painless procedure performed in a clinical setting. Small electrodes are attached to your arms, legs, and chest, and the machine charts the electrical activity of your heart. Your doctor can determine what type of arrythmia is causing an irregular heartbeat from the printout provided by the electrocardiogram. Read more about electrocardiogram.

Echocardiogram A painless procedure, an echocardiogram uses sound waves to create a picture of your heart. Read more about echocardiogram.

Holter monitor To test the rhythm of your heart while you do regular daily activities, you may be asked to wear a Holter monitor for 24 hours. This is a small, portable device that is strapped to your body. It records the electrical activity of your heart during physical activity and while at rest.

Event monitor This electrical device, which is strapped to your body, monitors your heartbeat only when you turn it on to record your symptoms. It is generally worn for one or two weeks at a time.

Read more about holter and event monitoring.

Blood tests Your doctor may also order blood tests to rule out thyroid disease or other blood chemistry abnormalities.Read more about blood tests.

Treatments for atrial fibrillation

Several approaches are used to treat and prevent abnormal beating of the heart

• Medications are used to slow down rapid heart rate associated with atrial fibrillation. These treatments may include drugs such as digoxin, beta blockers (atenolol, metoprolol, propranolol), amiodarone, disopyramide, calcium antagonists (verapamil, diltiazam), sotalol, flecainide, procainamide, quinidine, propafenone, etc
• Electrical cardioversion may be used to restore normal heart rhythm with an electric shock, when medication doesn't improve symptoms
• Radio frequency ablation may be effective in some patients when medications don't work. In this procedure thin and flexible tubes are introduced through a blood vessel and directed to the heart muscle. Then a burst of radio frequency energy is delivered to destroy tissue that triggers abnormal electrical signals or to block abnormal electrical pathways
• Surgery (rarely performed) can be used to disrupt electrical pathways that generate atrial fibrillation.
• Atrial pacemakers can be implanted under the skin to regulate the heart rhythm

Your physician will decide what the best treatment approach is for your atrial fibrillation.He or she willwill customize the treatment to your needs, based upon your risks, medical profile and how much the symptoms are interfering with your quality of life.

Most patients with atrial fibrillation will likely have to take blood thinners in order to reduce the risk of stroke. The risk of stroke depends on several other risk factors, including the presence of heart muscle weakness, having high blood pressure or diabetes, being over 75 years of age, or having had a previous stroke or a mini-stroke(TIA).Accordingly, your doctor may prescribe blood thinners such as an anti-platelet like ASA (Aspirin®) or an anticoagulant such as warfarin (Coumadin)to prevent clots from forming and travelling to the brain.

There are two general strategies for the treatment of atrial fibrillation–rhythm controland rate control. Your doctor will decide which strategy is best for you based on your symptoms and other factors.

• Rhythm control These treatments attempt to prevent an irregular heartbeat by restoring and maintaining a normal, regular heart beat. The first approach to rhythm control involves taking medications that will attempt to prevent the atrial fibrillation from occurring. Occasionally, some patients will require a controlled electric shock to the heart (called electrical cardioversion) to restore a normal rhythm. In some cases, if medications fail or are not well tolerated, your doctor may refer you to a specialist, who will decide if you are a candidate for an electrophysiologic study (see below).
• Rate control Almost every patient with atrial fibrillation will be prescribed a medication that is designed to slow the heart rate during atrial fibrillation. For some, this type of medication is enough to control the symptoms of atrial fibrillation.

When taking medications of any type, it is important to follow your doctor or pharmacist’s instructions. Establish a routine for taking your pills, and keep to your daily schedule. Do not share medications with others, and do not stop taking your medication without consulting your doctor. Report any side effects to your doctor, because he or she may change the dosage or type of medication to prevent or reduce any side effects.

Electrophysiology Studies (EPS) and Catheter Ablation On rare occasions, patients with atrial fibrillation who do not respond to medications or electrical cardioversion require an EPS in order to stop atrial fibrillation from recurring. The objective of EPS testing is to locate the cause of irregular electrical impulses in the heart. Catheter ablation is then performed to destroy, through tiny burns, the electrically chaotic tissue in the heart. During EPS and catheter ablation, thin wires (or catheters) are introduced to the heart through veins in the leg and neck. Radio frequency energy is sent through the catheters to the parts of the heart where the irregular electrical impulses are located. Ablation essentially creates scars in the heart that stabilize any electrical short circuits.

Read more about electrophysiology studies.

Read more about heart disease treatment.

Atrial fibrillation in people under 60

If you develop atrial fibrillation and do not have any structural heart disease, this is considered idiopathic (or lone) AF. Idiopathic AF usually occurs before the age of 60. Researchers have so far identified a handful of genes that predispose families to atrial fibrillation. Once all these genes are identified, researchers may be able to develop new treatments for this condition. Those who have a genetic predisposition to Idiopathic AF may develop the disease in their 30s and 40s. It is also possible for young people who do not have AF in their family to develop the disease.

What can you do?

Healthy lifestyle changes are always a good idea. Your risk for developing many diseases can be reduced if your diet is lower in saturated and trans fats, and includes plenty of vegetables, fruit, fibre and lean protein. Quitting smoking, limiting alcohol intake and reducing stress as much as possible have been shown to improve health in numerous studies. Any lifestyle changes that lower blood pressure (such as maintaining a normal weight) are likely to reduce the chances of developing AF.

It may be possible to prevent atrial fibrillation by staying physically active. A large study of people over the age of 65 found that participating in light to moderate physical activities, particularly leisure-time activities such as gardening and walking, were associated with significantly lower AF incidence. Even if you have AF, it is important to stay physically active because doing so has a positive impact on your overall health. Consult your doctor before you become more physically active.

Visit your doctor regularly have your atrial fibrillation monitored. Do not attempt to monitor your own heart rhythm by using expensive, high-tech equipment you may find on the internet. Using such products may unnecessarily elevate stress.

If you have high blood pressure, ask your doctor about how you can monitor your blood pressure at home.

Atrial fibrillation and stroke

AF increases your risk of stroke. It is estimated that up to 15% of all strokes are caused by atrial fibrillation. This risk increases with age, so that after age 60, one-third of all strokes are caused by atrial fibrillation. Also, individuals with atrial fibrillation have 3 to 5 times greater risk for ischemic stroke.

With a normal heart rhythm, the heart receives electrical signals from the brain via the sinoatrial (SA) node. The SA node sends impulses to the atria which instructs them to beat. The impulses then make their way to the lower chambers of the heart (the ventricles), which pump blood to the rest of the body.

During atrial fibrillation, the atria contract chaotically and in a disorganized manner. Because the atria don’t move blood properly, blood pools and gets stuck in the grooves of the heart. This may result in the formation of blood clots, which could get pumped to the brain and result in an ischemic stroke. An ischemic stroke is caused when blood flow to the brain is interrupted by a clot in one of the blood vessels within, or leading to, the brain. Studies show that long-term use of the blood thinner warfarin in patients with AF can reduce the risk of stroke by 70 to 80%.

Recommendations for Stroke Prevention

Treating atrial fibrillation is an important way to help prevent stroke. For this reason, the American Heart Association recommends aggressive treatment of this heart arrhythmia

Drugs help reduce stroke risk in people with AF. Long-term use of anticoagulants (drugs that help prevent blood from clotting) in patients with AF and other stroke risk factors can reduce stroke by 68 percent. Aspirin and warfarin are now used for this purpose

• Physicians differ on the choice of drugs to prevent embolic stroke — stroke caused by a blood clot. It’s clear that warfarin is more effective against this type of stroke than aspirin. However warfarin has more side effects than aspirin
• Patients at high risk for stroke should probably be treated with warfarin rather than aspirin unless there are clear reasons not to do so. Examples include potential bleeding problems or ulcer. Patients over 75 should be monitored especially carefully
• Aspirin is the standard treatment for patients at low risk for stroke

Factoids

• “Atrial fibrillation patients with prior TIA participating in the EAFT and SPAF III trial had lower rates of subsequent stroke during aspirin therapy than those with ischemic stroke, but the observed stroke rate was still substantial (7% per year) and halved by the use of warfarin. The absolute rate reduction in stroke by anticoagulation was particularly large for atrial fibrillation patients with prior ischemic stroke. These observations were consistent for atrial fibrillation patients with recent cerebral ischemia enrolled in the EAFT and for those with remote TIA and stroke participating in the SPAF III trial.”

• Medscape Resource Center
• Atrial fibrillation — Evidence Based Information
• Atrial Fibrillation website
• Research Articles of Interest

• Results - On average, the study patients were older (71.6 [standard deviation 9.3] years) and had a higher prevalence of underlying heart disease (52.0%) than those in the randomized trials. Nineteen patients had a first stroke: 4 in the ASA group, 4 in the warfarin group, 4 in the blended-treatment group and 7 in the no-treatment group, for rates of 5.2, 1.8, 5.3 and 5.9 per 100 person-years, respectively. Only warfarin was associated with a significantly lower risk of stroke compared with no anticoagulant therapy (RR 0.31, 95% CI 0.09—1.00). A similar protective effect of warfarin was found for stroke and TIA combined (2.3 v. 6.7 per 100 person-years; RR 0.34, 95% CI 0.12—0.99); the effect of ASA and blended treatment was not significantly different from no treatment. The rate per 100 person-years of any bleeding was not significantly higher for any treatment group (ASA 2.5, warfarin 3.4 and blended treatment 3.5) compared with the no treatment group (1.9). Patients receiving warfarin had a significantly greater risk of any bleeding event than patients not receiving anticoagulant therapy (RR 1.79, 95% CI 1.07—3.00)
• Interpretation - The relative effect of anticoagulant therapy with warfarin in preventing stroke in these practice settings was equivalent to that in the randomized trials, although these patients were older and sicker. This preventive treatment is likely to confer additional benefit as it is more widely prescribed. For more information see Anticoagulant prophylaxis against atrial fibrillation.pdf
• Warfarin has been in routine clinical use for more than 50 years; however, it was not proven to be of benefit in both primary and secondary prevention of stroke for patients with non-valvular atrial fibrillation (AF) until about a decade ago. Despite its efficacy in reducing the risk of stroke in patients with AF by about 60%, with an absolute reduction of about 3% per year, there have always been barriers to its use. These barriers have included the need for monitoring the degree of anticoagulation with blood tests to measure the international normalised ratio, frequent dose adjustments to maintain this ratio within quite a narrow therapeutic range, and the risk of bleeding should the upper limits of this range be exceeded. Aspirin has also been used but is less effective
• Recent developments - New oral drugs are being tested; these may be as effective at reducing stroke risk as warfarin in patients with AF. Direct thrombin inhibitors such as ximelagatran are not inferior to warfarin and, based on results from the SPORTIF III and V trials, are perhaps safer, with no need for long-term monitoring and dose adjustment. However, the side-effect of raised amounts of the liver enzyme alanine amino-transferase in 6% of patients needs to be resolved. In the ACTIVE trial, the efficacy of a combination of antiplatelet drugs (aspirin plus clopidogrel) is being tested against dose-adjusted warfarin; and in AMADEUS, the factor-Xa inhibitor and pentasaccharide idraparinux is being assessed in a similar way. Several surgical procedures and devices are also being developed to control AF rhythm and prevent stroke. For more information see Atrial fibrillation Warfarin.pdf

References

Information by the American Heart Association

Hart, Pearce, Koudstaal Transient Ischemic Attacks in Patients With Atrial Fibrillation Stroke (2004;35:948-951)