New Guidelines for Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia, affecting more than 2.3 million Americans. Prevalence of AF increases with age, with 1.5 percent occurring in patients from 50 to 59, to greater than 23 percent in patients over 75. AF is associated with increased morbidity with a 2.6-4.5 fold risk of stroke.1 This article will discuss the management of atrial fibrillation, with inclusion of the 2011 ACCF/AHA/HRS Focused Update on Dabigatran.2

Pathophysiology

AF can be insidious and unpredictable in onset. Initial presentation may be silent, without the patient’s knowledge or symptoms. The atria fibrillates, with the electrical impulse arising from cells outside of the sinoatrial node, which causes a loss of atrial contraction and ventricular filling. The fibrillating atria can reduce cardiac output by up to 25 percent, due mainly to the reduction in left ventricular volume. This can result in cardiac remodeling, leading to further cardiovascular impairment.

Initial Management

Initial management is dependent upon the length of time the patient has been in AF, which guides future management.3

If the patient is in AF for fewer than 48 hours, chemical or electrical cardioversion can be attempted. Afterward, the patient is less likely to convert spontaneously and anticoagulation should be considered.

If unable to be determined how long the patient has been in AF, the patient is anticoagulated with low-molecular-weight heparin or heparin. A transesophageal echocardiogram (TEE) is done once the patient has been anticoagulated to identify any clots in the left atrium.

Should a clot be detected, the cardioversion (chemical or electrical) will be deferred and anticoagulation maintained for an additional 3-4 weeks. Otherwise, the cardioversion is performed.

Following a successful cardioversion, anticoagulation continues at least 4 weeks.

Afterward, the patient will be assessed for AF recurrence and thromboembolic risk factors. If present, long-term oral anticoagulation begins.

Progression

After the initial presentation, there are three directions the disease can progress.4

Paroxysmal AF is self-terminating and generally lasts fewer than 7 days (often less than 24 hours). Often this patient will flip in and out of AF without provocation or warning.

The greatest danger is the threat of thromboembolism. Correct diagnosis is crucial to ensure patients are appropriately identified and anticoagulated.

Persistent AF, on the other hand, is not self-terminating and lasts more than 7 days or requires chemical or electrical cardioversion.

Attempts to return the patient to normal sinus rhythm can be made until all options are exhausted. These options include cardioversion, antiarrhythmic therapy and ablation.

The final category of AF is permanent. This patient has tried all treatments above, but has returned to AF after each intervention. At this point, it is appropriate to manage the patient to control the heart rate, reduce symptoms that interfere with quality of life and administer anticoagulation.

Management

Management of patients with AF focuses on reducing symptoms and preventing complications to improve the quality of life.

Reducing symptoms requires rate control and additional rhythm control with cardioversion (either electric or chemical), antiarrhythmic medications or ablation. In addition, the prevention of complications is dependent upon antithrombotic therapy.

The rate-control method of patient management can be achieved with oral or IV medications. Oral pharmacological agents utilized most frequently include digitalis, calcium channel blockers (diltiazem or verapamil), beta blockers (metoprolol or propranolol), and amiodarone.4 As the ventricular rate becomes controlled, the patient becomes less symptomatic.

The rhythm-control method concentrates on returning the patient to a normal sinus rhythm. The ventricular rate will also become controlled. Rhythm control can be achieved with pharmaceutical or electrical cardioversion.

Today, the best practice is to start anticoagulation with heparin or low-molecular-weight heparin, perform a TEE and, finally, perform an electrical cardioversion. For an electrical cardioversion, the patient has already been sedated for the TEE, so it is completed at the same time if no thrombus is identified in the left atrium. Often a patient will be cardioverted and monitored for recurring AF.

If the patient returns to AF after a cardioversion, the next step is to add an antiarrhythmic. The American College of Cardiology (ACC) recommends flecainide, dofetilide, propafenone and ibutilide.4 If the patient does not maintain sinus rhythm, another antiarrhythmic can be attempted, including a different primary choice, or amiodarone.

If pharmaceutical and electrical therapy is unsuccessful, catheter or surgical ablation is the final option, besides accepting AF as a permanent rhythm. Catheter ablation is considered when the patient remains symptomatic despite rate and rhythm control. The success of a catheter ablation is dependent upon the skill and experience of the physician, as well as the pathophysiology of the patient, and is increasingly presented as an option.

Surgical ablation is reserved for patients with atrial enlargement. The success of surgical ablation ranges from 75 percent to 95 percent of patients remaining in sinus rhythm for up to 15 years after the maze procedure.3

The Role of Anticoagulation

Approximately 80,000 strokes annually are associated with AF, as these patients have a 5 percent increased risk per year.1 Reasons for increased risk include previous transient ischemic attack (TIA), stroke or systemic embolism, poor left ventricular function, age greater than 75 years, hypertension, coronary artery disease, diabetes or thyrotoxicosis. Some thromboembolic strokes can be prevented with anticoagulation. In fact, it is estimated anticoagulant therapy can prevent 50 percent of strokes caused by AF, or 40,000 strokes per year. Prevention of these strokes can provide a cost savings of $600 million in healthcare costs annually.

The decision to start anticoagulant therapy is recommended by the ACC based upon risk factors.

Patients with no risk factors should be placed on aspirin 81-325 mg daily. Patients with one moderate risk factor (age 75 or older, hypertension, heart failure, left ventricular ejection fraction < 35 percent, or diabetes mellitus) should be placed on aspirin 81-325 mg daily or warfarin to maintain and INR 2.0-3.0 (target 2.5).

Patients with any high risk factor (previous stroke, TIA or embolism, mitral stenosis or prosthetic heart valve (INR >2.5)) or more than one moderate risk factor should be prescribed warfarin to maintain INR 2.0-3.0 (target 2.5).

A new drug just approved by FDA for use in AF is dabigatran etexilate. It is an oral direct thrombin inhibitor anticoagulant converted to the active direct thrombin (factor IIa) inhibitor. This conversion occurs independently of the cytochrome P-450. This means drug/drug and drug/diet interactions are less likely than with warfarin; dietary restrictions are thus unnecessary with dabigatran.

Dabigatran has a predictable anticoagulant effect at dosages of 150 mg twice a day (for patients with creatinine clearance greater than 30 mL/min). In addition, dabigatran has no waiting time for effectiveness, so the patient does not need to remain hospitalized or give home injections for 96 hours to prevent a thromboembolism. Therapeutic dosage is reached within 2 hours. Contraindications include a prosthetic heart valve, advanced liver disease with clotting disorders and severe renal failure (creatinine clearance <15 mL/min). There is no monitoring required.2

Chances are all nurses will care for patients with AF as it is the most common dysrhythmia. Initial identification and management can be challenging depending on how long the patient has been in AF. Also, if the patient is not able to be converted, symptom management is critical and dependent upon ventricular rate control.

The most critical management of the patient in AF is the appropriate management of anticoagulation. With attention to detail and meticulous patient teaching, stroke prevention can be obtained with anticoagulation management.

References for this article can be accessed here.

Cyndi Holt is a cardiovascular clinical nurse specialist at the Gagnon Cardiovascular Institute at Morristown Memorial Hospital, Morristown, NJ.

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