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The Use of Warfarin for Atrial Flutter
Jaclyn M. Ripley, PharmD Candidate
Atrial flutter is a cardiac arrhythmia defined as a rapid regular rhythm involving the right atrium. It differs from atrial fibrillation (A-fib) in that “fibrillation” describes the heart beating in a rapid irregular rhythm. However, the consequences to the body and the management of atrial flutter are similar, if not the same1. Atrial flutter alone is an uncommon arrhythmia because it usually turns into atrial fibrillation, or can return to normal sinus rhythm on its own. In many patients, it is common for atrial flutter to alternate with periods of atrial fibrillation. When this occurs, there is also the risk of developing a blood clot, as with atrial fibrillation by itself2.
Symptoms due to atrial flutter typically depend on the ventricular rate, or the “heart rate”. If the heart rate is less than 120 beats per minute, and at a regular rate, there may be no symptoms. However, if the heart rate is greater than 120 beats per minute, a person can experience palpitations. These palpitations can compromise cardiac output, or the amount of blood that the heart puts out during every beat1. If the heart is beating too fast, then it can not contract properly, and an inadequate amount of blood is pumped to the body. Symptoms that can arise from this lack of proper contraction are dizziness and/or fainting1.
Atrial flutter is typically diagnosed by an electrocardiogram (ECG) that shows “flutter waves” or a “saw tooth” pattern. The ECG will show that the atrial rate (the rate at which the atrium is beating) is usually around 250-350 beats per min. The ventricular rate is usually lower than the atrial rate, often 150-220 beats per minute1.
Medical therapy that is used is directed toward slowing the ventricular heart rate, rather than correcting the arrhythmia. Drugs such as digoxin, verapamil, and beta-blockers, such as atenolol or metoprolol, are useful in slowing down the ventricular rate1. Warfarin is also used in the treatment of atrial flutter, although not for the purpose of slowing the ventricular heart rate2.
Warfarin is typically used in atrial flutter to decrease the risk of developing a thrombus, or blood clot, that may cause a stroke. There are few studies published about the use of warfarin in atrial flutter alone; however, because this arrhythmia is so closely related to atrial fibrillation, and can indeed have periods where A-fib is present, it is often grouped with atrial fibrillation in terms of treatment with warfarin. No clinical trials have studied the role of warfarin therapy in patients with atrial flutter alone, but it is known that patients with atrial flutter are at an increased risk of developing atrial fibrillation. Therefore, it is reasonable to treat patients who have atrial flutter using the same antithrombotic therapy as for patients who have atrial fibrillation. The guidelines from the American College of Chest Physicians (ACCP) suggest that patients with atrial flutter should be assessed and treated based on the same risk-based recommendations as for atrial fibrillation2.
Atrial fibrillation is the most common cardiac arrhythmia, and is a strong risk factor for having an ischemic stroke, increasing the risk fourfold to fivefold in all age groups. When stroke occurs in patients with atrial fibrillation, is it usually due to a cardiogenic embolism (a blood clot that originated in the heart)2. When the atrium is not contracting properly, blood can pool in the heart and form a clot. When this blood clot is pumped out to the body, it may become lodged in a vessel, such as in the brain. A blood clot in the brain can cut off the brain’s oxygen supply, and part of it dies. The end result is a stroke, which can leave a person paralyzed or even cause death.
The best way to prevent a cardiogenic embolism is to use anticoagulation therapy with warfarin or aspirin. The drug that is selected for treatment depends upon the risk factors of the patient. Risk factors that put a patient at high risk of having a stroke are:
In patients with a history of any of these risk factors, it is recommended to use warfarin for anticoagulation therapy, with a target INR range of 2.0 to 3.0.
Patients who are 65 to 75 years old and have atrial fibrillation, but none of the above risk factors, are at intermediate risk of having a stroke. Treatment for these patients can be with either warfarin at an INR range of 2.0 to 3.0, or aspirin 325 mg daily.
Patients who have none of the above risk factors and who are younger than 65 years old may be treated with aspirin 325 mg daily.
Although aspirin is mentioned above as an option in treating patients with A-fib, and therefore atrial flutter, it should be known that anticoagulation with warfarin has “far greater efficacy in preventing stroke, and particularly in preventing severe ischemic stroke, in atrial fibrillation.” The option of aspirin is for lower-risk groups only, where the benefit of anticoagulation with warfarin may not outweigh the risk of bleeding and the burden of anticoagulation therapy. However, if protection against stroke is valued more highly than reducing the risk of bleeding, then warfarin may be the optimal choice over aspirin therapy when treating atrial fibrillation or flutter2.
References:
1. Merck Manual of Diagnosis and Therapy, The. Section 16. Cardiovascular Disorders. Chapter 205. Arrhythmias.
2. Singer DE, Albers GW, Dalen JE, et al. Antithrombotic therapy in atrial fibrillation: The seventh ACCP conference on antithrombotic and thrombolytic therapy. Chest 2004;126;429-456.
©2005 Jaclyn M. Ripley
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Last updated June 14, 2007