A stethoscope in the shape of a heart on a heartbeat pulse graph.Source: Getty Images
Things to know about atrial fibrillation (AFib)
- Atrial fibrillation (also referred to as AFib or AF) is the most common type of abnormal heart rhythm.
- Atrial fibrillation is caused by abnormal electrical discharges (signals) that generate chaotically throughout the upper chambers of the heart (atria).
- It reduces the ability of the atria to pump blood into the ventricles and usually causes the heart to beat too rapidly.
- One-half million new cases of AFib are diagnosed every year in the U.S., and billions of dollars are spent annually on its diagnosis and treatment.
- Symptoms of the condition include:
- Some people have no signs or symptoms.
- Complications of atrial fibrillation include heart failure and stroke.
- Physical examination, electrocardiogram, Holter monitor, or patient-activated event recorder can make and confirm the diagnosis of atrial fibrillation.
- Treatment for the condition is directed toward controlling underlying causes, slowing the heart rate and/or converting the heart to a normal rhythm, and stroke prevention using blood-thinning medications.
- Medications are commonly used in the longer term to control or prevent the recurrence of AF, but medications may not be effective and may have intolerable side effects.
- Electrical cardioversion is successful in over 95% of individuals with AF, but 75% of them have a recurrence of the disease within 1 to 2 years.
- Some doctors may leave a patient in AF for the long term provided the rate is under control, blood flow is adequate, and blood is adequately thinned with medications.
- Non-medication treatments of atrial fibrillation include pacemakers, AV node ablation, atrial defibrillators, and the Maze procedure.
- Pulmonary vein isolation shows promise for the treatment of the disease and has a high rate of success; however, longer-term experience is necessary.
- The prognosis for a person with this condition depends upon the cause and extent of this type of heart disease.
What is atrial fibrillation?
Atrial fibrillation is an abnormal and irregular heart rhythm in which the electrical signals are generated chaotically throughout the upper atria (chambers) of the heart. Many people with this condition have no signs or symptoms (asymptomatic). It is the most common supraventricular tachycardia.
What is the normal function of the heart, and how does its electrical system work?
What is the normal function of the heart?
The heart has four chambers. The upper two chambers are the atria, and the lower two chambers are the ventricles: 1) the right atrium (upper right); 2) the left atrium (upper left); 3) the right ventricle (lower right); and 4) the left ventricle (lower left).
Blood returning to the heart from the body contains low levels of oxygen and high levels of carbon dioxide. This blood flows into the right atrium and then down into the adjacent right ventricle. After the right ventricle fills, contraction of the right atrium pumps additional blood into the right ventricle. The right ventricle then contracts and pumps the blood to the lungs where the blood takes up oxygen and gives off carbon dioxide. The blood then flows from the lungs to the left atrium, and then down into the adjacent left ventricle. Contraction of the left atrium pumps additional blood into the left ventricle. The left ventricle then contracts and pumps the blood to the aortic artery and then to the rest of the body via the vascular system.
The heartbeat (pulse) that we feel is caused by the contraction of the ventricles. The ventricles must deliver enough blood to the body for the body to function normally. The amount of blood that is pumped depends on several factors. The most important factor is the rate of contraction of the heart (the heart rate). As the rate increases, more blood is pumped. The heart pumps more blood with each beat when the atria contract and fill the ventricles with additional blood just before the ventricles contract.
How does the electrical system of the heart work?
With each beat of the heart, an electrical discharge (current) passes through the electrical system of the heart. This discharge causes the muscle of the atria and ventricles to contract and pump blood.
The electrical system of the heart consists of the SA node (sinoatrial node), the AV node (atrioventricular node), and special tissues in the atria and the ventricles that conduct the current.
- The SA node is the heart's electrical pacemaker. It is a small patch of cells located in the wall of the right atrium; the frequency with which the SA node discharges determines the rate at which the heartbeats. The current passes from the SA node, through the special tissues of the atria, and into the AV node.
- The AV node serves as a relay station between the atria and the ventricles. Signals from the atria must pass through the AV node to reach the ventricles.
The electrical discharges from the SA node causing the atria to contract and pump blood into the ventricles. The same discharges then pass through the AV node to reach the ventricles, traveling through the special tissues of the ventricles and causing the ventricles to contract. In a normal heart, the rate of atrial contraction is the same as the rate of ventricular contraction.
At rest, the frequency of the discharges originating from the SA node is low, and the heartbeats at the lower range of normal (60 to 80 beats/minute). During exercise or excitement, the frequency of discharges from the SA node increases, increasing the rate in individuals who are in good clinical health.
What causes atrial fibrillation?
The cause of atrial fibrillation is an abnormal heart rhythm. During this rhythm, electrical discharges are not generated solely by the SA node. Instead, discharges come from other parts of the atria. These abnormal discharges are rapid and irregular and may exceed 350 discharges per minute. The rapid and irregular discharges cause ineffective contractions of the atria. The atria quiver rather than beat as a unit. This reduces the ability of the atria to pump blood into the ventricles.
The rapid and irregular discharges from the atria then pass through the AV node and into the ventricles, causing the ventricles to contract irregularly and (usually) rapidly. The contractions of the ventricles may average 150/minute, much slower than the rate in the atria. (The ventricles are unable to contract at 350/minute.) Even at an average rate of 150/minute, the ventricles may not have enough time to fill maximally with blood before the next contraction, particularly without the normal contraction of the atria. Thus, AFib decreases the amount of blood pumped by the ventricles because of their rapid rate of contraction and the absence of normal atrial contractions.
What is an abnormal heart rhythm, and what are the types?
An abnormal heart rhythm is a type of condition in which the electrical activity of the heart malfunctions. The most common type of abnormal heart rhythm is atrial fibrillation. Other types of heart rhythm disorders include:
- Premature atrial contractions (PACs)
- Sinus tachycardia
- Atrial fibrillation
- Tachycardia
- Paroxysmal supraventricular tachycardia
Click more about other heart rhythm conditions »
A woman explaining symptoms of shortness of breath and chest pain to her doctor.Source: iStock
What are the symptoms of atrial fibrillation?
Many patients with this condition have no symptoms (asymptomatic) and are unaware of the abnormal rhythm. When symptoms do occur, the most common one is heart palpitations, an uncomfortable awareness of the rapid and irregular heartbeat.
Other symptoms of the condition are caused by the diminished delivery of blood to the body. These symptoms include:
- Dizziness
- Fainting
- Weakness
- Fatigue
- Shortness of breath
- Angina (chest pain due to reduced blood flow to the heart muscles)
What happens to the heart rate during atrial fibrillation?
In a heart that is beating normally, the rate of ventricular contraction is the same as the rate of atrial contraction. In atrial fibrillation, however, the rate of ventricular contraction is less than the rate of atrial contraction. The rate of ventricular contraction in the condition is determined by the speed of transmission of the discharges through the AV node. In people with a normal AV node, the rate of ventricular contraction in untreated disease usually ranges from 80 to 180 beats/minute; the higher the transmission, the higher the heart rate.
Some older people have slow transmission through the AV node due to disease within the AV node. When these people develop the problem, their heart rates remain normal or slower than normal. As disease in the AV node advances, these people can even develop an excessively slow heart rate and require a permanent pacemaker to increase the rate of ventricular contractions.
How can I know if I am at risk for developing atrial fibrillation?
There are many risk factors for developing atrial fibrillation. They include:
- Increased age (1% of people over 60 years of age have the disease)
- Coronary disease (including heart attack)
- High blood pressure
- Abnormal heart muscle function (including congestive heart failure)
- The disease of the mitral valve between the left and right ventricle
- An overactive thyroid gland (hyperthyroidism) or overdose of thyroid medication
- Low amounts of oxygen in the blood, for example, as occur with lung diseases such as emphysema or chronic obstructive pulmonary disease (COPD)
- Inflammation of the lining surrounding the heart (pericarditis)
- Blood clots in the lung (pulmonary embolism)
- Chronic lung diseases (emphysema, asthma, COPD)
- Excessive intake of alcohol (alcoholism)
- Stimulant drug use such as cocaine or decongestants
- Recent heart or lung surgery
- Abnormal heart structure from the time of birth (congenital)
About 1 in 10,000 young adults in otherwise good health have the disease without any apparent cause or underlying cardiac problems. Atrial fibrillation of the heart in these individuals usually is intermittent but can become chronic in 25%. This condition is referred to as lone AFib. Stress, alcohol, tobacco, or the use of stimulants may play a role in causing this arrhythmia.
How do doctors diagnose atrial fibrillation?
Atrial fibrillation can be chronic and sustained, or brief and intermittent (paroxysmal). Paroxysmal atrial fibrillation refers to intermittent episodes of AF lasting, for example, minutes to hours. The rate reverts to normal between episodes. In chronic, sustained atrial fibrillation, the atria fibrillate all of the time. Chronic, sustained atrial fibrillation is not difficult to diagnose. Doctors can hear the rapid and irregular heartbeats using a stethoscope. Abnormal heartbeats also can be felt by taking a patient's pulse and by a doctor's diagnosis.
Tests to diagnose atrial fibrillation
- EKG (electrocardiogram): An electrocardiogram (EKG or ECG) is a brief recording of the heart's electrical discharges. The irregular EKG tracings of AF are easy to recognize provided AF occurs during the EKG.
- Echocardiography: Echocardiography uses ultrasound waves to produce images of the chambers and valves and the lining around the heart (pericardium). Conditions that may accompany AF such as mitral valve prolapse, rheumatic valve diseases, and pericarditis (inflammation of the "sack" surrounding the heart) can be detected with echocardiography. Echocardiography also is useful in measuring the size of the atrial chambers. Atrial size is an important factor in determining how a patient responds to treatment for the disease. For instance, it is more difficult to achieve and maintain a normal rhythm in patients with enlarged atria.
- Transesophageal echocardiography (TEE): Transesophageal echocardiography (TEE) is a special echocardiographic technique that involves taking pictures of the atria using sound waves. A special probe that generates sound waves is placed in the esophagus (the food pipe connecting the mouth to the stomach). The probe is located at the end of a long flexible tube that is inserted through the mouth into the esophagus. This technique brings the probe very close to the heart (which lies just in front of the esophagus). Sound waves generated by the probe are bounced off the structures within the heart, and the reflected sound waves are used to form a picture of the heart. TEE is very accurate for detecting blood clots in the atria as well as for measuring the size of the atria.
- Holter monitor: If episodes of the disease occur intermittently, a standard EKG performed at the time of a visit to the doctor's office may not show AF. Therefore, a Holter monitor, a continuous recording of the heart's rhythm for 24 hours, often is used to diagnose intermittent episodes of AF.
- Patient-activated event recorder: If the episodes of atrial fibrillation are infrequent, a 24-hour Holter recording may not capture these sporadic episodes. In this situation, the patient can wear a patient-activated event recorder for 1 to 4 weeks. The patient presses a button to start the recording when he or she senses the onset of irregular heartbeats or symptoms possibly caused by AF. The doctor then analyzes the recordings later.
- Other tests: High blood pressure and signs of heart failure can be ascertained (determined) during a physical examination of the patient. Blood tests are performed to detect abnormalities in blood oxygen and carbon dioxide levels, electrolytes, and thyroid hormone levels. Chest X-rays reveal enlargement of the heart, heart failure, and other diseases of the lung. Exercise treadmill testing (a continuous recording of the EKG during exercise) is a useful screening study for detecting severe coronary disease in a doctor's office or hospital.
A doctor discussing medication and treatment options with a patient.Source: iStock
What are the treatment guidelines for atrial fibrillation?
The treatment of atrial fibrillation is multi-faceted and involves:
- Reversing the factors that cause atrial fibrillation.
- Slowing the heart rate with medications.
- Preventing strokes.
- Converting atrial fibrillation to a normal heart rhythm with medications or electrical shock.
- Preventing the recurrence of atrial fibrillation with medications.
- Using procedures (for example, pacemakers, defibrillators, surgery) to prevent episodes of the disease.
However, each individual is unique, so the treatments vary depending on the patient’s medical condition (for example, the presence of a pacemaker or compromised renal function). Those interested can see the extensive guidelines for various patients in the American Heart Association Journal, Circulation, published in 2019; these may change as new methods and drugs are approved in the future.
Reversing the risk factors (drugs or other diseases or conditions) that cause atrial fibrillation
An important first step in the treatment of AF is to uncover and correct health conditions (such as hyperthyroidism or the use of stimulant drugs) that can cause the disease. These steps include:
- Stopping the use of stimulant drugs and excessive alcohol intake
- Controlling high blood pressure
- Correcting hyperthyroidism (too much thyroid hormone) and low blood oxygen levels
- Controlling cardiac failure and treating the diseases of the heart and the lungs that can cause atrial fibrillation
Drugs that slow the heart rate
Having excluded or corrected the factors that cause the disease, the next step when the ventricles are beating too rapidly usually is to slow the rate at which the ventricles beat.
A person with the disease and healthy AV nodes usually have ventricles that beat rapidly. Drugs are necessary to slow down the rapid heart rate. Drugs to slow the heart rate include:
- digitalis (Digoxin)
- Beta-blockers such as propranolol (Inderal), atenolol (Tenormin), metoprolol (Lopressor), esmolol (Brevibloc)
- Calcium channel blockers such as verapamil (Calan), diltiazem (Cardizem)
These medications slow the heart rate by retarding the conduction of the electrical discharges through the AV node. These medications, however, do not usually convert AFib back into a normal rhythm. Other drugs or treatments are necessary to achieve a normal heart rhythm and improve health.
Benefits of controlling the rate: In patients with rapid ventricle contractions as a result of the disease, slowing the rate of ventricular contractions improves the heart's efficiency in delivering blood (by allowing more time between contractions for the ventricles to fill with blood) and relieves the symptoms of inadequate flow of blood — dizziness, weakness, and shortness of breath.
With chronic, sustained disease, doctors may decide to leave some patients in atrial fibrillation if their heart rates are under control, the output of blood from the ventricles is adequate, and their blood is adequately thinned to prevent strokes. This form of treatment is called rate control therapy (discussed in this article).
Limitations of medications for controlling the heart rate: In people with diseased AV nodes, ventricular contractions may be slower than in those who have normal AV nodes. Moreover, some elderly individuals with atrial fibrillation are extremely sensitive to medications that slow the rate of ventricular contractions, usually because of a diseased AV node. In these patients, the heart rate can become dangerously slow with small doses of medications to slow the heart. This condition is referred to as tachycardia-bradycardia syndrome, or "sick sinus syndrome." Patients with tachycardia-bradycardia syndrome need medications to control the fast heart rate and a pacemaker to provide a minimum safe rate.
Drugs used in slowing atrial fibrillation generally cannot convert atrial fibrillation to a normal rhythm. Therefore, these patients are at risk for the formation of blood clots in the heart and strokes and will need prolonged blood thinning with anticoagulants like warfarin (Coumadin, Jantoven).
Risks and candidates for cardioversion
What are the risks of electrical cardioversion?
The complications of cardioversion include stroke, burns to the skin, and in rare instances, death. However, these problems are very uncommon.
Who are candidates for electrical cardioversion?
Doctors usually recommend that all patients with chronic, sustained atrial fibrillation undergo at least one attempt at cardioversion. Cardioversion usually is attempted with drugs first. If medications fail, electrical cardioversion can be considered. Sometimes a doctor may choose to use electrical cardioversion first if AF is of short duration (onset within 48 hours) and the transesophageal echocardiography shows no blood clots in the atria.
Cardioversion is performed urgently (on an emergency basis) on patients with severe and potentially life-threatening symptoms caused by AFib. For example, some patients with rapid AF can develop chest pain, shortness of breath, and dizziness or fainting. (Chest pain in these patients is due to an insufficient supply of blood to the heart muscles. Shortness of breath indicates ineffective pumping of blood by the ventricles. Fainting or dizziness usually is due to dangerously low blood pressure.)
What is rate control therapy?
Recent studies have shown that an acceptable alternative to cardioversion (chemical or electrical) is rate-control therapy. In this therapy, the doctor will leave the patients in AF provided their rate of ventricular contractions is under good control, the output of blood from the heart is adequate, and their blood is adequately thinned by warfarin to prevent strokes. Heart rate in these patients can be controlled using medications such as beta-blockers, calcium channel blockers, or digoxin or AV node ablation with pacemaker implantation. Rate-control therapy is used to simplify therapy and avoid the side effects of anti-arrhythmic medications (medications used to treat and prevent atrial fibrillation).
Over long periods of observation, patients treated with rate-control therapy have similar survival and quality of life as compared to those who undergo repeated electrical or chemical cardioversions.
Suitable candidates for rate-control therapy include:
- People who have had atrial fibrillation for more than one year
- Individuals with a significant disease of the heart valves
- People with enlarged hearts as a result of heart failure or cardiomyopathy (heart muscle weakness)
- Patients with significant or intolerable side effects with drugs used for the condition.
Medications used for converting atrial fibrillation carry a small risk of causing other abnormal heart rhythms…and can be more life-threatening than atrial fibrillation.Source: MedicineNet
Cardioversion with medications
Before prescribing medications for cardioversion, the doctor usually controls the rate of ventricular contractions and thins the blood, usually with warfarin.
Available medications for cardioversion
Drugs used in cardioversion usually work by blocking the channels in the walls of cells through which ions travel (sodium channels, potassium channels, beta-adrenergic channels, and calcium channels). Some examples of these medications include:
- quinidine (Quinaglute) — rarely used
- procainamide (Procan SR) — rarely used
- disopyramide (Norpace) — rarely used
- sotalol (Betapace)
- flecainide (Tambocor)
- amiodarone (Cordarone)
These drugs are capable of converting AFib to a normal rhythm in about 50% of patients. They often are used long-term to maintain a normal rhythm and prevent recurrences of AFib, and increase the person's health.
Disadvantages of using medications for cardioversion
Drugs used for converting atrial fibrillation carry a small risk of causing other abnormal heart rhythms — they are said to be proarrhythmic — especially in patients with diseases of the heart muscle or coronary arteries. These abnormal heart rhythms can be more life-threatening than atrial fibrillation. Therefore, treatment with these medications often is initiated in the hospital while the patient's rhythm is continuously monitored for 24 to 72 hours.
These medications may not be effective in the longer term. Many patients eventually develop a recurrence of atrial fibrillation despite the medications.
Drugs used in treating atrial fibrillation often have important side effects. Many patients discontinue them because they cannot tolerate these side effects. For example:
- Amiodarone commonly is used to treat atrial fibrillation because it is less proarrhythmic, and has been shown to maintain a normal rhythm in up to 75% of patients. However, amiodarone may cause side effects and drug interactions. Amiodarone can interact with other medications such as tricyclic antidepressants — for example, amitriptyline (Elavil, Endep) — or phenothiazine antipsychotics — for example, chlorpromazine (Thorazine) — and cause abnormal heart rhythms.
- Amiodarone interacts with warfarin (Coumadin, Jantoven) and increases the risk of bleeding, which can occur as early as 4 to 6 days after the start of both drugs or can be delayed by a few weeks. Thus, doctors prescribing both warfarin and amiodarone will adjust the dose of warfarin to avoid excessive blood thinning.
- Amiodarone also can cause thyroid disturbances in the fetus when administered orally to the mother during pregnancy. Amiodarone also may affect thyroid function in adults.
The most severe side effect of amiodarone is lung toxicity that potentially can be fatal. Because of this lung toxicity, patients should report any symptoms of cough, fever, or painful breathing to their doctors.
A doctor performs electrical cardioversion on a patient.Source: iStock
What is electrical cardioversion?
Other methods of converting AFib to a normal rhythm include electrical cardioversion and rate control therapy.
Electrical cardioversion is a procedure used by doctors to convert an abnormal rhythm (such as AFib) to a normal rhythm (sinus rhythm). Electrical cardioversion requires the administration of an electrical shock over the chest. This electrical shock stops the abnormal electrical activity of the heart for a brief moment and allows the normal rhythm to take over. Although electrical cardioversion can be used to treat almost any abnormal fast heartbeat (such as atrial flutter and ventricular tachycardia), it is used most frequently to convert atrial fibrillation to a normal rhythm.
Warfarin usually is given for 3 to 4 weeks before cardioversion to minimize the risk of stroke that can occur during or shortly after cardioversion. Warfarin is continued for 4 to 6 weeks after successful cardioversion. For some patients requiring urgent electrical cardioversion, warfarin may not work fast enough to thin the blood. Therefore, these patients may be given heparin before electrical cardioversion. Heparin is faster-acting blood thinner than warfarin, but it must be administered as a continuous intravenous infusion or as injections under the skin. After successful cardioversion, these patients can be switched from heparin to warfarin.
Method of cardioversion
Electrical cardioversions (urgent and elective) usually are performed in a hospital. For elective (nonurgent) electrical cardioversion, patients usually arrive at the hospital without eating in the morning. Necessary medications can be taken with small sips of water. Patients are given supplemental oxygen via nasal catheters, and an intravenous infusion of fluids is started. Electrodes (pads) are placed on the skin over the chest, which continuously monitors the heart rhythm. Paddles then are placed over the chest and the upper back. Patients are sedated (anesthetized) intravenously with medication, which is followed by a strong electric shock through the paddles. The shock converts the atrial fibrillation to a normal rhythm. After cardioversion, patients are observed for several hours or overnight to make sure that their normal heart rhythm is stable.
Effectiveness of electrical cardioversion
Electrical cardioversion is more effective than medications alone in terminating atrial fibrillation and restoring a normal rhythm. Electrical cardioversion successfully restores a normal rhythm in over 95% of patients.
Limitations of electrical cardioversion
While electrical cardioversion is effective in converting AFib to a normal heart rhythm, the normal rhythm may not continue for long. Approximately 75% of patients successfully treated with electrical cardioversion experience a recurrence of atrial fibrillation within 12 to 24 months. Older patients with enlarged atria and ventricles who have had atrial fibrillation for a long time are especially prone to recurrences. Thus, most patients who undergo successful cardioversion are placed on oral medications to prevent recurrences of arrhythmia.
Risks and candidates for electrical cardioversion
What are the risks of electrical cardioversion?
The risks of electrical cardioversion include stroke, burns to the skin, and in rare instances, death. However, these complications are very uncommon.
Who are candidates for electrical cardioversion?
Doctors usually recommend that all patients with chronic sustained AF undergo at least one attempt at cardioversion. Cardioversion usually is attempted with medications first. If medications fail, electrical cardioversion can be considered. Sometimes a doctor may choose to use electrical cardioversion first if AFib is of short duration (onset within 48 hours) and the transesophageal echocardiography shows no blood clots in the atria.
Electrical cardioversion is performed urgently (on an emergency basis) on patients with severe and potentially life-threatening symptoms caused by AFib. For example, some patients with rapid AFib can develop chest pain, shortness of breath, and dizziness or fainting. Chest pains in these individuals are due to an insufficient supply of blood to the heart muscles. Shortness of breath indicates ineffective pumping of blood by the ventricles. Fainting or dizziness usually is due to dangerously low blood pressure.
What is rate control therapy?
Recent studies have shown that an acceptable alternative to cardioversion (chemical or electrical) is rate-control therapy. In this therapy, the doctor will leave the individuals in AFib provided their rate of ventricular contractions is under good control, the output of blood from the heart is adequate, and their blood is adequately thinned by warfarin to prevent strokes. The rate in these patients can be controlled using medications such as beta-blockers, calcium channel blockers, digoxin, or AV node ablation with pacemaker implantation. Rate-control therapy is used to simplify therapy and avoid the side effects of anti-arrhythmic medications (medications used to treat and prevent atrial fibrillation).
Over long periods of observation, individuals treated with rate-control therapy had similar survival and quality of life as compared to those who undergo repeated electrical or chemical cardioversions.
Suitable candidates for rate-control therapy include:
- Patients who have had atrial fibrillation for more than one year
- Patients with significant disease of the heart valves
- Patients with enlarged hearts as a result of heart failure or cardiomyopathy (heart muscle weakness)
- Patients with significant or intolerable side effects with medications for atrial fibrillation
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