Atrial fibrillation (AF or A-fib) is the most common cardiac arrhythmia (heart rhythm disorder). It may cause no symptoms, but it is often associated with palpitations, fainting, chest pain, or congestive heart failure. In some cases, however, AF is caused by idiopathic or benign conditions.
AF may be identified clinically when taking a pulse, and its presence can be confirmed with an electrocardiogram (ECG or EKG) that demonstrates the absence of P waves and an irregular ventricular rate.
In AF, the normal regular electrical impulses generated by the sinoatrial node are overwhelmed by disorganized electrical impulses usually originating in the roots of the pulmonary veins, leading to irregular conduction of ventricles impulses that generate the heartbeat. AF may occur in episodes lasting from minutes to days ("paroxysmal") or may be permanent in nature. A number of medical conditions increase the risk of AF, in particularmitral stenosis (narrowing of the mitral valve of the heart).
The risk of stroke is increased fivefold in individuals with AF.The degree of increased risk may be substantial, depending on the presence of additional risk factors (such as high blood pressure). AF may be treated with medications to either slow the heart rate to a normal range ("rate control") or revert the heart rhythm to normal ("rhythm control"). Synchronized electrical cardioversion can be used to convert AF to a normal heart rhythm. Surgical and catheter-based ablation may be used to prevent recurrence of AF in some individuals. Depending on the risk of stroke and systemic embolism, people with AF may use anticoagulants such as warfarin, which substantially reduces these risks but may increase the risk of major bleeding, mainly in geriatric patients. The prevalence of AF in a population increases with age; 8% of people over 80 have AF. Chronic AF leads to a small increase in the risk of death.
Classification
AF Category | Defining Characteristics |
---|---|
First detected | only one diagnosed episode |
Paroxysmal | recurrent episodes that self-terminate in less than 7 days |
Persistent | recurrent episodes that last more than 7 days |
Permanent | an ongoing long-term episode |
The American College of Cardiology (ACC), American Heart Association (AHA), and the European Society of Cardiology (ESC) recommend in their guidelines the following classification system based on simplicity and clinical relevance.
All patients with AF are initially in the category called first detected AF. These patients may or may not have had previous undetected episodes. If a first detected episode self-terminates in less than 7 days and then another episode begins later on, the case has moved into the category of paroxysmal AF. Although patients in this category have episodes lasting up to 7 days, in most cases of paroxysmal AF the episodes will self-terminate in less than 24 hours. If instead the episode lasts for more than 7 days, it is unlikely to self-terminate, and it is called persistent AF. In this case, the episode may be still terminated by cardioversion. If cardioversion is unsuccessful or not attempted and the episode is ongoing for a long time (e.g., a year or more), the patient's AF is called permanent.
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Episodes that last less than 30 seconds are not considered in this classification system. Also, this system does not apply to cases where the AF is a secondary condition that occurs in the setting of a primary condition that may be the cause of the AF.
Episodes that last less than 30 seconds are not considered in this classification system. Also, this system does not apply to cases where the AF is a secondary condition that occurs in the setting of a primary condition that may be the cause of the AF.
Using this classification system, it is not always clear what an AF case should be called. For example, a case may fit into the paroxysmal AF category some of the time, while other times it may have the characteristics of persistent AF. One may be able to decide which category is more appropriate by determining which one occurs most often in the case under consideration.
In addition to the above four AF categories, which are mainly defined by episode timing and termination, the ACC/AHA/ESC guidelines describe additional AF categories in terms of other characteristics of the patient.
- Lone atrial fibrillation (LAF) – absence of clinical or echocardiographic findings of other cardiovascular disease (including hypertension), related pulmonary disease, or cardiac abnormalities such as enlargement of the left atrium, and age under 60 years
- Nonvalvular AF – absence of rheumatic mitral valve disease, a prosthetic heart valve, or mitral valve repair
- Secondary AF – occurs in the setting of a primary condition that may be the cause of the AF, such as acute myocardial infarction, cardiac surgery, pericarditis, myocarditis, hyperthyroidism,pulmonary embolism, pneumonia, or other acute pulmonary disease
Signs and symptoms
AF is usually accompanied by symptoms related to a rapid heart rate. Rapid and irregular heart rates may be perceived as palpitations or exercise intolerance and occasionally may produceangina (if the rate is faster and puts the heart under strain) and congestive symptoms of shortness of breath or edema. Sometimes the arrhythmia will be identified only with the onset of a stroke or a transient ischemic attack (TIA). It is not uncommon for a patient to first become aware of AF from a routine physical examination or ECG, as it may be asymptomatic in many cases.
As most cases of AF are secondary to other medical problems, the presence of chest pain or angina, symptoms of hyperthyroidism (an overactive thyroid gland) such as weight loss and diarrhea, and symptoms suggestive of lung disease would indicate an underlying cause. A history of stroke or TIA, as well as hypertension (high blood pressure), diabetes, heart failure and rheumatic fever, may indicate whether someone with AF is at a higher risk of complications.A higher risk of embolus can be assessed using the CHADS2 score.
Rapid heart rate
Presentation is similar to other forms of rapid heart rate and in some cases may be asymptomatic. The patient may complain of palpitations or chest discomfort. The rapid uncoordinated heart rate may result in the heart being unable to provide adequate blood flow and oxygen delivery to the rest of the body. Therefore, common symptoms may include shortness of breath, shortness of breath when lying flat, and sudden onset of shortness of breath during the night (paroxysmal nocturnal dyspnea), and may progress to swelling of the lower extremities (peripheral edema). Owing to inadequate blood flow, patients may also complain of light-headedness,may feel like they are about to faint (presyncope), or may actually lose consciousness (syncope).
The patient may be in significant respiratory distress. Because of inadequate oxygen delivery, the patient may appear blue (cyanosis). By definition, the heart rate will be greater than 100 beats per minute. Blood pressure will be variable, and often difficult to measure as the beat-by-beat variability causes problems for most digital (oscillometric) non-invasive blood pressure monitors. It is most worrying if consistently lower than usual (hypotension). Respiratory rate will be increased in the presence of respiratory distress. Pulse oximetry may confirm the presence of hypoxia related to any precipitating factors such as pneumonia. Examination of the jugular veins may reveal elevated pressure (jugular venous distention). Lung exam may reveal crackles, which are suggestive ofpulmonary edema. Heart exam will reveal an irregular but rapid rhythm.