What Is a Normal Heart Rhythm?
The heart has four areas, or chambers. During each heartbeat, the two upper chambers (atria) contract, followed by the two lower chambers (ventricles). This is directed by the heart's electrical system.
The electrical impulse begins in an area called the sinus node, located in the right atrium. When the sinus node fires, an impulse of electrical activity spreads through the right and left atria, causing them to contract, forcing blood into the ventricles.
Then the electrical impulses travel in an orderly fashion to areas called the atrioventricular (AV) node and HIS-Purkinje network. The AV node is the electrical bridge that allows the impulse to go from the atria to the ventricles. The HIS-Purkinje network carries the impulses throughout the ventricles. The impulse then travels through the walls of the ventricles, causing them to contract. This forces blood out of the heart to the lungs and the body. The pulmonary veins empty oxygenated blood from the lungs to the left atrium. A normal heart beats in a constant rhythm -- about 60 to 100 times per minute at rest.
What Is Atrial Fibrillation?
Atrial fibrillation (also referred to as AF or AFib) is the most common type of irregular heartbeat. It is found in about 2.2 million Americans. Its frequency increases with age. If you have AF, the electrical impulse does not travel in an orderly fashion through the atria. Instead, many impulses begin simultaneously and spread through the atria and compete for a chance to travel through the AV node.
The firing of these impulses results in a very rapid and disorganized heartbeat. The rate of impulses through the atria can range from 300 to 600 beats per minute. Luckily, the AV node limits the number of impulses it allows to travel to the ventricles. As a result, the pulse rate is often less than 150 beats per minute, but this is often fast enough to cause symptoms.
What Are the Symptoms of Atrial Fibrillation?
You may have atrial fibrillation without having any symptoms at all. If you have symptoms, they may include:
- Heart palpitations (a sudden pounding, fluttering, or racing feeling in the chest)
- Fatigue or lack of energy
- Dizziness (feeling faint or light-headed)
- Chest discomfort (pain, pressure, or tightness in the chest)
- Shortness of breath (difficulty breathing during normal activities or even at rest)
What Causes Atrial Fibrillation?
Atrial fibrillation is associated with many conditions, including:
- High blood pressure
- Coronary artery disease (blockages in the heart's arteries)
- Heart valve disease
- Previous heart surgery
- Chronic lung disease
- Heart failure
- Cardiomyopathy (disease of heart muscle that causes heart failure)
- Congenital heart disease (heart disease present at birth)
- Pulmonary embolism (blood clot in lungs)
Less Common Causes of Atrial Fibrillation
Less common causes of atrial fibrillation include:
- Hyperthyroidism (overactive thyroid)
- Pericarditis (inflammation of the outside lining of the heart)
- Viral infection
In at least 10% of people with AF, no underlying heart disease is found. In many of these people, AF may be related to alcohol or excessive caffeine use, stress, certain drugs, electrolyte or metabolic imbalances, or severe infections. In some people, no cause can be found.
The risk of AF increases with age, particularly after age 60. According to the CDC, AF affects roughly one in every 10 people ages 80 and older.
Why Is Atrial Fibrillation Dangerous?
Many people live for years with atrial fibrillation without problems. However, because the atria are beating rapidly and irregularly, blood does not flow through them as quickly. This makes the blood more likely to clot. If a blood clot is pumped out of the heart, it can travel to the brain, resulting in a stroke. The likelihood of a stroke in people with AF is five to seven times higher than in the general population. Although about half of all blood clots related to AF result in stroke, clots can travel to other parts of the body -- such as the kidney, heart, or intestines -- also causing problems.
AF can also decrease the heart's pumping ability by as much as 20%-25%. AF combined with a fast heart rate over a period of days to months can result in heart failure. Control of AF can then improve heart failure.
How Is Atrial Fibrillation Diagnosed?
Four tests are used to diagnose atrial fibrillation, including:
- Holter monitor
- Portable event monitor (also called a loop recorder)
- Transtelephonic monitor or wireless monitor (via the Internet)
These monitoring devices help your doctor learn if you are having irregular heartbeats, what kind they are, how long they last, and what may be causing them.
How Is Atrial Fibrillation Treated?
Many options are available to treat AF, including medication, lifestyle changes, certain medical procedures, and surgery. The choice of treatment for you is based on your heart rate and symptoms. The goals of AF treatment are to:
- Regain normal heart rhythm (sinus rhythm)
- Control the heart rate
- Prevent blood clots
- Reduce the risk of stroke
How Are Medications Used to Treat Atrial Fibrillation?
Medications are prescribed depending on the overall treatment goal. If the goal is to restore normal heart rhythm, a type of drug called an antiarrhythmic is prescribed. If it's not possible to achieve this goal, doctors will try to manage your condition by slowing down the heart rate. In both cases, your doctor will give you drugs called anticoagulants to decrease blood clot formation.
Restore normal heart rhythm. These drugs help return the heart to normal rhythm and maintain that rhythm.
- Many drugs are available to restore and maintain a normal heart rhythm, including: amiodarone (Cordarone), dofetilide (Tikosyn), flecainide acetate (Tambocor), propafenone (Rythmol), and sotalol (Betapace AF. You may have to stay in the hospital when you first start taking these drugs so that your heart rhythm can be carefully monitored. These medications are effective 30%-60% of the time, but may lose their effectiveness over time. You may need to try several medications so your doctor can find the best one for you.
- Some rhythm control drugs may actually cause more arrhythmias, so it is important to discuss symptoms and any changes in your condition with your doctor.
- The FDA wants patients to be aware that a clinical trial of dronedarone(Multaq), called PALLAS, was halted when the drug doubled the risk of death, stroke, and heart failure hospitalization in heart patients with permanent atrial fibrillation.
- Heart rate control. Heart rate control drugs, such as digoxin (Lanoxin), metoprolol (Toprol XL, Lopressor), other beta-blockers, and calcium channel blockers, are used to help slow the heart rate during atrial fibrillation. You may need to take two different medications to keep your heart rate controlled.
- Blood thinners or anticoagulation drugs. Anticoagulant drugs -- such as apixaban (Eliquis), dabigatran (Pradaxa), edoxaban (Lixiana, Savaysa), rivaroxaban (Xarelto), and warfarin (Coumadin). Although anticoagulant drugs reduce the risk of stroke, they do not eliminate the risk. Regular blood tests are required when taking warfarin to evaluate the effectiveness and minimize the risks of the drug. Talk to your doctor about the anticoagulant drug that is right for you.
Until recently, the only anticoagulant approved by the FDA for AF was warfarin. While warfarin is highly effective and relatively inexpensive, there are problems associated with its use. For instance:
- Someone taking warfarin needs regular blood tests to adjust the dosage based on the way the blood clots.
- Proper dosage depends on a number of factors such as body size and age.
- Warfarin interacts with a wide range of foods as well as other drugs. So people taking warfarin need to make adjustments in their diet and have to be careful about what other medications they take.
Dabigatran (Pradaxa) is approved by the FDA to treat AF. Studies show it's at least as effective as warfarin at preventing strokes and perhaps even more effective at higher dosages.
The main advantage of dabigatran is that it works in a different way than warfarin does. As a result, it does not have the same kind of problems that are associated with warfarin. For example:
- People do not need to have regular blood tests to determine whether the dosage needs adjustment.
- There are no dietary changes required.
- Dabigatran does not interact with a large number of drugs the way warfarin does.
The differences between the two drugs may make dabigatran an attractive alternative for people who have difficulty taking warfarin. But there are also issues associated with the use of dabigatran that need to be considered. For example:
- Cost may be the biggest issue. Because it is only available as a brand-name drug, dabigatran is significantly more expensive than warfarin, which can be bought as a generic.
- In some studies, the higher dosage that produced greater protection against stroke also increased the risk of heart attack.
- The drug may not be appropriate for someone with kidney problems without regularly monitoring its effect on kidney function.
- Dabigatran produces more stomach pain and upset than warfarin.
Both dabigatran and warfarin carry a risk of serious bleeding. So if you take either medication, be sure to discuss the risks with your doctor and to follow the doctor's instructions for taking it.
Rivaroxaban (Xarelto) is also approved to prevent stroke in patients with AF not caused by a heart valve problem. It also increases the risk for bleeding. But rivaroxaban can also increase the risk of stroke if people stop taking it without medical supervision. That's the main warning in the "black box" on the rivaroxaban label. A black box warning is the FDA's strongest warning. Rivaroxaban had previously been approved to prevent blood clots in patients receiving hip and knee replacements and in those with deep vein thrombosis.
The usual dose of apixaban is 5 milligrams, taken twice a day with or without food. In a study of more than 18,000 patients comparing apixaban with warfarin, those on apixaban were less likely to have a stroke. In another study of people with AF who could not or chose not to take warfarin, apixaban was more effective than aspirin at preventing stroke.
Edoxaban (Lixiana, Savaysa) is another anti-clotting drug FDA-approved to reduce the risk of stroke in patients with atrial fibrillation (not caused by a heart valve problem). Edoxaban given at the higher dose level was found to be equal to warfarin in preventing stroke, while demonstrating less major bleeding.
Since anticoagulants lower clotting in patients, they carry a risk of causing excessive bleeding during non-stroke related injuries. The drug idarucizumab (Praxbind) can be used in emergencies to reverse the blood-thinning effects of the Pradaxa and thereby help stop the bleeding.
Lifestyle Changes for Atrial Fibrillation
In addition to taking medications, there are some changes you can make to improve your heart health.
- If you notice that your irregular heart rhythm occurs more often with certain activities, you should avoid them.
- Quit smoking.
- Limit your intake of alcohol. Moderation is the key. Ask your doctor for specific alcohol guidelines.
- Some people are sensitive to caffeine and may notice more symptoms when using caffeinated products (such as tea, coffee, colas, and some over-the-counter medications). Consider limiting caffeine intake if you feel that it increases your symptoms.
- Beware of stimulants used in cough and cold medications. Some of these types of drugs contain ingredients that promote irregular heart rhythms. Read the label and ask your doctor or pharmacist what type of cold medication is best for you.
Procedures for Atrial Fibrillation
When drugs do not work to correct or control atrial fibrillation, or when medications are not tolerated, a procedure may be necessary, such as electrical cardioversion, pulmonary vein isolation ablation, catheter ablation of the AV node with a pacemaker, or device therapy.
What Is Electrical Cardioversion?
Electrical cardioversion frequently restores a normal rhythm, although its effect may not be permanent. After a short-acting anesthesia is given, a machine is used to deliver an electric shock through electrode patches placed on the chest to synchronize the heartbeat and restore a normal rhythm. Although this procedure only takes a few seconds, several attempts may be needed to restore a normal rhythm. A patient may need to be on warfarin for at least three weeks before this procedure is performed. This decreases the risk of a stroke that can occur with the cardioversion.
What Is Ablation Therapy?
Catheter ablation therapy is an option for people who cannot tolerate medications or when drugs fail to maintain the normal heart rhythm.
Pulmonary vein isolation: During this procedure, special catheters are inserted into the heart. Research has shown that most atrial fibrillation signals come from the four pulmonary veins as they enter the left atrium.
A specialized viewing device called intracardiac echocardiography is used to visualize the left atrium during the procedure. One catheter in the left atrium is used to map or locate the abnormal impulses coming from the pulmonary veins. The other catheter is used to deliver the radiofrequency energy to create lesions outside the pulmonary veins. The procedure is repeated for all four pulmonary veins.
The lesions heal within four to eight weeks and form a circular scar around the pulmonary veins. The scar blocks any impulses firing from within the pulmonary veins, thereby "disconnecting" the pathway of the abnormal rhythm and curing atrial fibrillation.
Ablation of the AV node: During this procedure, the doctor applies radiofrequency energy to injure the AV node. The end result is a permanent, very slow heart rate, since the electrical impulses from the top chamber of the heart cannot travel down to the lower chamber. Therefore, the patient needs a permanent pacemaker to maintain an adequate heart rate.
What Is a Permanent Pacemaker?
A pacemaker is a device that sends electrical impulses to the heart muscle to maintain a specified heart rate. Pacemakers may be implanted in people with AF who have a slow heart rate. The pacemaker has a pulse generator (which houses the battery and a tiny computer) and leads (wires) that send impulses from the pulse generator to the heart muscle, as well as sense the heart's electrical activity.
Newer pacemakers have many sophisticated features designed to help with the management of arrhythmias and to optimize heart rate-related function as much as possible.
What Surgeries Are Performed?
Patients with chronic atrial fibrillation not relieved by medication or procedures, or patients who have other conditions requiring heart surgery, may be candidates for surgical treatment of AF. These procedures are types of open-heart surgery that require general anesthesia (you are put to sleep) and a hospital stay.
During the Maze procedure, a series of precise incisions are made in the right and left atria to confine the electrical impulses to defined pathways to reach the AV node.
Surgical pulmonary vein isolation is a modification of the Maze procedure in which the surgeon uses alternative energy sources instead of incisions to create lesions. The alternative energy sources used during surgical pulmonary vein isolation include: radiofrequency, cryothermy, and laser. The goal of all four energy sources is to produce lesions and ultimately scar tissue to block the abnormal electrical impulses from being conducted through the heart and to promote the normal conduction of impulses through the proper pathway.
Many of these approaches can be performed with minimally invasive (endoscopic or "keyhole") surgical techniques.
- Radiofrequency ablation: A special radiofrequency energy catheter is used to heat the tissue and produce lesions on the heart similar to the lesions of the Maze procedure. There are a variety of surgical techniques related to the type of catheter used, the dose of energy, and the types of lesions created.
- Cryothermy (also called cryoablation): Very cold temperatures are transmitted through a probe (called a cryoprobe) to create lesions. This technique is used commonly during arrhythmia surgery to replace the incisions made during the Cox Maze procedure.
- Laser: Lasers rapidly create the lesions or lines of conduction block. Laser technology offers promise for the development of additional minimally invasive approaches.
Some patients may have atrial fibrillation in addition to other heart problems (such as valve or coronary artery disease) which require surgery. In these cases, the surgeon may combine the surgeries to correct the atrial fibrillation and the coexisting heart condition at the same time.