Atrial flutter

Atrial flutter (AFL) is a common abnormal heart rhythm that starts in the atrial chambers of the heart. Atrial flutter is characterized by a sudden-onset (usually) regular abnormal heart rhythm on an electrocardiogram (ECG) in which the heart rate is fast. Symptoms may include a feeling of the heart beating too fast, too hard, or skipping beats, chest discomfort, difficulty breathing, a feeling as if one's stomach has dropped, a feeling of being light-headed, or loss of consciousness.

Although this abnormal heart rhythm typically occurs in individuals with cardiovascular disease (e.g., high blood pressure, coronary artery disease, and cardiomyopathy) and diabetes mellitus, it may occur spontaneously in people with otherwise normal hearts. It is typically not a stable rhythm and often degenerates into atrial fibrillation (AF). Medications used to restore a normal heart rhythm (antiarrhythmics) such as ibutilide effectively control atrial flutter about 80% of the time when they are started but atrial flutter recurs at a high rate (70–90% of the time) despite continued use. Atrial flutter can be treated more definitively with a technique known as catheter ablation. This involves the insertion of a catheter through a vein in the groin which is followed up to the heart and is used to identify and interrupt the electrical circuit causing the atrial flutter (by creating a small burn and scar).

Atrial flutter was first identified as an independent medical condition in 1920 by the British physician Sir Thomas Lewis (1881–1945) and colleagues. AFL is the second most common pathologic supraventricular tachycardia but occurs at a rate less than one-tenth of the most common supraventricular tachycardia (atrial fibrillation). The overall incidence of AFL has been estimated at 88 cases per 100,000 person-years. The incidence of AFL is significantly lower (~5 cases/100,000 person-years) in those younger than age 50 and is far more common (587 cases/100,000 person-years) in those over 80 years of age.

Atrial flutter is usually well-tolerated initially (a high heart rate is, for most people just a normal response to exercise); however, people with other underlying heart diseases (such as coronary artery disease) or poor exercise tolerance may rapidly develop symptoms, such as shortness of breath, chest pain, lightheadedness or dizziness, nausea and, in some patients, nervousness and feelings of impending doom.

Rapid heart rates may produce significant symptoms in patients with pre-existing heart disease and can lead to inadequate blood flow to the heart muscle and even a heart attack.

Sudden cardiac death

Sudden death is not directly associated with atrial flutter. However, in individuals with a pre-existing accessory conduction pathway, such as the bundle of Kent in Wolff-Parkinson-White syndrome, the accessory pathway may conduct activity from the atria to the ventricles at a rate that the AV node would usually block. Bypassing the AV node, the atrial rate of 300 beats/minute leads to a ventricular rate of 300 beats/minute (1:1 conduction). Even if the ventricles are able to sustain a cardiac output at such a high rate, 1:1 flutter with time may degenerate into ventricular fibrillation, causing hemodynamic collapse and death.

Pathophysiology

Atrial flutter is caused by a re-entrant rhythm. This usually occurs along the cavo-tricuspid isthmus of the right atrium though atrial flutter can originate in the left atrium as well. Typically initiated by a premature electrical impulse arising in the atria, atrial flutter is propagated due to differences in refractory periods of atrial tissue. This creates electrical activity that moves in a localized self-perpetuating loop, which usually lasts about 200 milliseconds for the complete circuit. For each cycle around the loop, an electric impulse results and propagates through the atria.

The impact and symptoms of atrial flutter depend on the heart rate of the affected person. Heart rate is a measure of ventricular rather than atrial activity. Impulses from the atria are conducted to the ventricles through the atrio-ventricular node (AV node). In a person with atrial flutter, a 12-lead electrocardiogram (ECG) will demonstrate the atrial chambers of the heart contracting at a rate of 280–300 beats per minute whereas the ventricular chambers of the heart typically beat at a rate of 140–150 beats per minute.

Diagnosis

Typical atrial flutter is recognized on an electrocardiogram by the presence of characteristic "flutter waves" at a regular rate of 250 to 350 beats per minute. Flutter waves may not be evident on an ECG in atypical forms of atrial flutter. Individual flutter waves may be symmetrical, resembling p-waves, or maybe asymmetrical with a "sawtooth" shape, rising gradually and falling abruptly or vice versa. If atrial flutter is suspected clinically but is not clearly evident on ECG, acquiring a Lewis lead ECG may be helpful in revealing flutter waves.

Classification

There are two types of atrial flutter, the common type I and rarer type II. Most individuals with atrial flutter will manifest only one of these. Rarely someone may manifest both types; however, they can manifest only one type at a time.

Type I

thumb|300px|right|Type I atrial flutter, counterclockwise rotation with 3:1 and 4:1 [[AV node|AV nodal block.]]

thumb|300px|Atrial flutter with a two to one block. Note the P waves hiding in the T waves in leads V1 and V2

Type I atrial flutter, also known as common atrial flutter or typical atrial flutter, has an atrial rate of 240 to 340 beats/minute. However, this rate may be slowed by antiarrhythmic agents.

The reentrant loop circles the right atrium, passing through the cavo-tricuspid isthmus – a body of fibrous tissue in the lower atrium between the inferior vena cava, and the tricuspid valve. Atypical atrial flutter rarely occurs in people who have not undergone previous heart surgery or previous catheter ablation procedures. Left atrial flutter is considered atypical and is common after incomplete left atrial ablation procedures. Atypical atrial flutter originating from the right atrium and heart's septum have also been described.

Management

In general, atrial flutter should be managed in the same way as atrial fibrillation. Because both rhythms can lead to the formation of a blood clot in the atrium, individuals with atrial flutter usually require some form of anticoagulation or antiplatelet agent. Both rhythms can be associated with dangerously fast heart rates and thus require medication to control the heart rate (such as beta blockers or calcium channel blockers) and/or rhythm control with class III antiarrhythmics (such as ibutilide or dofetilide). However, atrial flutter is more resistant to correction with such medications than atrial fibrillation.

Ablation

Due to the reentrant nature of atrial flutter, it is often possible to ablate the circuit that causes atrial flutter with radiofrequency catheter ablation or pulsed field ablation. Catheter ablation was considered to be a first-line treatment method for many people with typical atrial flutter due to its high rate of success (>90%) and low incidence of complications,

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