Atrial fibrillation (AF) with a rapid ventricular response: The ECG shows an irregular heart rhythm with no discernible P waves. Rapid atrial fibrillation (AF) may be hard to differentiate from a narrow supraventricular tachycardia (SVT) without close examination of an ECG. The two conditions can result in similar symptoms of heart palpitations and shortness of breath. Patients with rapid AF are not uncommonly given adenosine to treat presumed SVT, as in this case. Although this treatment is typically unsuccessful, the underlying atrial rhythm may be accurately determined when the heart rate briefly slows.

The conversion from a normal sinus rhythm to AF may be due to a number of conditions, including hyperthyroidism, anemia, infection, ischemic heart disease, valvular disease, drug intoxication, or use of stimulants. Increased stress and over consumption of coffee are likely to have been the instigating factors in this patient.

AF is a common arrhythmia characterized by chaotic atrial depolarizations without effective atrial contractions. This rhythm is often seen with increasing age, with a male predominance. This arrhythmia can result in decreased cardiac output and the formation of atrial thrombi. Many patients with AF are asymptomatic, and most have recurrent episodes without knowledge of them.

The American College of Cardiology established a classification system for AF that is based on its duration and etiology. The categories are paroxysmal AF, persistent AF, permanent AF, and lone AF. In paroxysmal AF, the episodes last less than 1 week. If they recur, the condition is considered recurrent paroxysmal AF. In persistent AF, the episodes last longer than 1 week. In permanent AF, the episode lasts longer than 1 year without any attempts for conversion or with attempts that fail. Finally, in lone AF, no underlying structural cardiac or pulmonary disease is found. Patients with lone AF have a low risk of mortality and thromboembolism and may have paroxysmal, persistent, or permanent AF.

The workup for AF involves careful history taking and physical examination, laboratory studies (including a CBC, serum electrolyte tests, toxicology screening, and thyroid function tests), ECG, chest radiography, and echocardiography.

The patient’s history should include the time of onset, the frequency of episodes, any associated symptoms, and any history of treatment for AF. Laboratory studies may be useful in determining possible etiologies of AF. The WBC count may help in finding an underlying infection, and the hemoglobin concentration may demonstrate anemia. Electrolyte levels, such as magnesium and potassium levels, may be abnormal, and an elevated creatinine value may indicate a renal insufficiency. Certain illicit drugs can cause a rapid heart rate; therefore, a toxicology screening may be useful when indicated. Hyperthyroidism can predispose patients to AF. For this reason, an evaluation of thyroid function with measurement of the patient’s thyroid-stimulating hormone (TSH) level is warranted.

AF can be diagnosed when the ECG shows an irregular rhythm with the absence of P waves. In addition, examine the patient for any signs of left ventricular hypertrophy, bundle branch blocks, and atrioventricular (AV) nodal blocks, as well as for evidence of cardiac ischemia or previous myocardial infarction. Chest radiographs may be useful in evaluating the cardiac silhouette for cardiomegaly and the lung fields and vasculature for evidence of airspace disease or pulmonary edema. A transthoracic echocardiogram can be obtained to identify the size and motion of the atria, ventricles, and cardiac valves, and it can reveal pericardial disease. Transesophageal echocardiography is more sensitive than transthoracic echocardiography for diagnosing left atrial thrombus or left atrial appendage thrombus.

Rate control is important in patients who present with rapid AF of more than 72 hours’ duration, and beta blockers (metoprolol or atenolol) or calcium channel blockers (verapamil or diltiazem) are recommended in patients who do not have an accessory pathway. Digoxin and amiodarone are the drugs of choice for controlling rapid AF in patients with left ventricular failure and no accessory pathway; however, digoxin should be loaded over 24 hours. Therefore, it is unlikely to have a notable effect in the acute setting. If unable to achieve rate control with pharmacologic therapy, catheter-directed AV nodal ablation by a cardiologist may be considered. Anticoagulation treatment is also recommended for most patients with persistent AF, and it is typically achieved with warfarin (dosed to maintain an international normalized ratio [INR] of 2.0-3.0). In patients considered to be at low risk for thromboembolism or in patients who have a contraindication to the use of warfarin, aspirin can be given instead.

Conversion to a sinus rhythm may be achieved with pharmacologic agents or with synchronized external electrical cardioversion. Conversion should be done only when the risk of thromboembolism is limited, as in patients with an onset of symptoms more than 72 hours before presentation, in those who received anticoagulation for 3 weeks, or in those in whom transesophageal echocardiographic results rule out a left atrial thrombus.

After successful cardioversion, anticoagulation therapy should continue for at least 1 month to decrease the risk of thromboembolism, which may occur from the formation of a mural thrombus. After cardioversion is done and the patient’s AF reverts to a sinus rhythm, use of daily outpatient antiarrhythmic drugs is not typically recommended, as these drugs have associated risks; therefore, they should be taken only when patients have persistent or frequently recurring symptoms.

Antiarrhythmic drugs that can be used to convert AF to a normal sinus rhythm include ibutilide, flecainide, procainamide, and amiodarone. Each has different risks, success rates, and indications based on the duration of AF. As a group, antiarrhythmic drugs can convert 30-60% of cases of AF to a normal sinus rhythm. Electrical cardioversion has a higher success rate, converting 75-95% of AFs to normal sinus rhythms. Electrical cardioversion may be done in a nonemergency setting after 3 weeks of anticoagulation treatment to decrease the risk of thromboembolism, or it may be required on an emergency basis in a hemodynamically unstable patient. In this situation, AF often has an acute onset, and the benefits of cardioversion outweigh the risks of thromboembolism.

The role of cardioversion to manage AF in the emergency department is an emerging one. Patients who are at low risk, who are clinically stable, and who present to the emergency department with new-onset AF can be treated with chemical or electrical cardioversion and safely discharged, home with close follow-up, by a primary physician or cardiologist.


Images courtesy of ECG Wave-Maven: Self-Assessment Program for Students and Clinicians.


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