Atrial Fibrillation

New options for managing atrial fibrillation have become available since December 2010, when In the Clinic last considered this subject. For example, the CHA2DS2-VASc score has become the standard for predicting thromboembolic risk. In addition, nonvitamin Kdependent oral anticoagulants have been approved for prophylaxis against thromboembolic disease, and agents to reverse these drugs are becoming available. Moreover, catheter ablation is being used more frequently to prevent recurrent atrial fibrillation, and closure of the left atrial appendage with a device can now be done for patients who are unable to receive systemic anticoagulation. Supplement. Original Version (PDF) Atrial fibrillation is the most common clinically significant cardiac arrhythmia. It occurs when a diffuse and chaotic pattern of electrical activity in the atria suppresses or replaces the normal sinus mechanism. This disorder is a major cause of morbidity, mortality, and health care expenditure. In the United States, 2.3 million persons have atrial fibrillation, and this number is expected to increase to 5.6 million by 2050 (1). Atrial fibrillation is associated with a 5-fold risk for stroke and is estimated to cause 15% of all strokes (2). It is also associated with a 2-fold risk for all-cause mortality, independent of comorbid conditions (3). Diagnosis Who is at risk for atrial fibrillation? Atrial fibrillation occurs in fewer than 1% of persons aged 60 to 65 years but in 8% to 10% of those older than 80 years. Prevalence is higher in men than in women and higher in white persons than in black persons (1). The risk for atrial fibrillation increases with aging and the presence and severity of underlying heart disease, particularly congestive heart failure and valve disease. Other commonly associated conditions include sleep-disordered breathing and hypertension. What symptoms and signs should cause clinicians to suspect atrial fibrillation? Some patients have prominent symptoms, including palpitations, shortness of breath, exercise intolerance, chest pain, and malaise. Chest pain and palpitations are particularly common in younger patients, whereas fatigue and shortness of breath are more often seen in elderly persons (4). However, many persons, particularly the elderly, have asymptomatic (silent) atrial fibrillation, including some with severe symptoms during other episodes of atrial fibrillation (5). Silent atrial fibrillation is often recognized during routine interrogation of pacemakers placed for bradycardia in patients with no history of atrial fibrillation (6). Symptoms are generally greatest at disease onsetwhen episodes are typically paroxysmal and rates are rapid (before rate-controlling drugs are prescribed)and tend to diminish over time, especially when arrhythmia becomes persistent. Symptoms result predominantly from elevation of ventricular rate (either at rest or when exacerbated by exercise) and to a lesser degree from the irregular ventricular rate and loss of atrial contribution to cardiac output. On physical examination, signs include a faster-than-expected heart rate, which varies greatly from patient to patient; an irregularly irregular time between heart sounds; and peripheral pulses that vary irregularly in both rate and amplitude. Is a single electrocardiogram sufficient to diagnose or exclude atrial fibrillation? Figure 1 is an electrocardiogram (ECG) of a patient with atrial fibrillation. It shows that a single ECG is sufficient to diagnose atrial fibrillation, provided it is recorded during the arrhythmia. However, atrial fibrillation is often paroxysmal, so a normal result on one ECG does not rule it out. Monitoring for a longer time can be helpful when atrial fibrillation is suspected and the initial ECG is normal. In patients with daily symptoms, 24- or 48-hour continuous Holter monitoring is usually sufficient for diagnosis. New patch monitors allow 7 to 10 days of continuous monitoring without attached leads and are a good alternative to traditional Holter monitors (7). In patients with less-frequent symptoms, monitoring during longer periods with electrocardiographic loop recorders may be necessary; however, even monitoring for periods as long as a month can miss atrial fibrillation in patients with very infrequent episodes. Therefore, confirming the diagnosis in some patients with nonspecific symptoms and long periods between episodes can take years. Figure 1. Electrocardiogram showing atrial fibrillation with rapid ventricular rate. Implanted pacemakers and implantable cardioverter-defibrillators with atrial leads identify and record both symptomatic and asymptomatic atrial fibrillation. Subcutaneous implanted monitors are also increasingly used to identify atrial fibrillation, particularly in patients with cryptogenic stroke in whom identification of atrial fibrillation will result in initiation of anticoagulation (8). What is the role of history and physical examination? History and physical examination help determine the duration of symptoms and identify potential underlying causes. Clinicians should seek historical and physical evidence of hypertension, heart failure, cardiac surgery, murmurs indicative of stenotic or regurgitant valvular disease, and other indications of structural heart disease. In addition, clinicians should look for signs and symptoms of noncardiac causes, including pulmonary disease, hyperthyroidism, use of adrenergic drugs (such as those used to treat pulmonary disease) or other stimulants, and use of alcohol. Other risk factors include diabetes, obesity, and sleep-disordered breathing. A family history might identify first-degree relatives with atrial fibrillation, which may have therapeutic implications in the future. What other electrocardiographic arrhythmias can be confused with atrial fibrillation? Other arrhythmias that are commonly confused with atrial fibrillation include sinus rhythm with frequent premature atrial contractions, atrial flutter, and atrial tachycardia. The key electrocardiographic findings of atrial fibrillation are the absence of P waves and the presence of an irregular ventricular rhythm without a recurring pattern. When an irregular rhythm is present but the diagnosis of atrial fibrillation is uncertain, clinicians should examine long recordings from multiple leads to look for partially obscured P waves in deformed T waves and ST segments. Figure 2 is an ECG of an irregular rhythm that might be attributed to atrial fibrillation, but the presence of P waves and other features identifies sinus rhythm with frequent premature atrial contractions. The QRS is wide with the premature beat because of aberrant conduction. Figure 3 is an ECG of another irregular rhythm that might be attributed to atrial fibrillation, but the presence of saw-tooth P waves and a ventricular response that varies from 2:1 atrioventricular conduction to 4:1 atrioventricular conduction identifies atrial flutter. Figure 2. Electrocardiogram showing sinus rhythm with frequent premature atrial contractions. Figure 3. Atrial flutter. Classic saw-tooth flutter waves are seen in all 12 leads, and the ventricular response is mostly regular. (There is a transient change from 2:1 to 4:1 atrioventricular conduction following the 12th QRS complex.) How should clinicians classify atrial fibrillation? Although classification of atrial fibrillation is a subject of debate, the most accepted convention categorizes atrial fibrillation as paroxysmal, persistent, long-standing persistent, or permanent (8) (see the Box). In paroxysmal atrial fibrillation, episodes terminate without intervention in less than 7 days (often within 24 hours). Persistent atrial fibrillation lasts longer than 7 days or requires an intervention, such as cardioversion, to restore sinus rhythm. Long-standing persistent atrial fibrillation is continuous atrial fibrillation lasting longer than 12 months. Permanent atrial fibrillation means that the arrhythmia is continuous, and interventions to restore sinus rhythm have either failed or not been attempted. Categories can change over time, so clinicians should classify patients according to the current or most common pattern. Classification of Atrial Fibrillation Paroxysmal: Episodes spontaneously terminate in 7 d Persistent: Episodes last >7 d and require intervention to restore sinus rhythm Long-standing persistent: Continuous atrial fibrillation lasting >12 mo Permanent: Interventions to restore sinus rhythm have either failed or have not been attempted These distinctions are useful because they may predict the response to therapy. For example, patients may be less likely to respond to antiarrhythmic drug therapy or nonpharmacologic therapy as the pattern progresses from paroxysmal to persistent to permanent. Patients in all categories should be assessed for the need for anticoagulation independent of the frequency or duration of atrial fibrillation episodes. What laboratory studies should clinicians obtain in patients newly diagnosed with atrial fibrillation? When patients are initially diagnosed with atrial fibrillation, clinicians should measure serum electrolytes and thyroid-stimulating hormone levels to identify possible causes. They should also perform blood tests of renal and hepatic function to guide selection of drug therapy and check the stool for occult blood before starting anticoagulation. Transesophageal echocardiography helps reveal underlying structural heart disease that may not otherwise be recognized and can identify tachycardia-induced cardiomyopathy, which may occur when atrial fibrillation has been present for an extended period. It is also indicated to rule out atrial clot when transthoracic images are inadequate or cardioversion is planned in a patient who has received anticoagulation for less than 3 weeks. In patients with appropriate clinical indications, additional tests may be warranted for pulmonary embolism, acute myocardial infarction, or acute