Atrial flutter (AFL) is a tachyarrhythmia arising in the atrium, characterized by rapid, regular atrial depolarization (commonly 250-350 beats per minute [bpm]). Atrioventricular conduction usually occurs in a 2:1 ratio, resulting in a ventricular rate one-half of the atrial rate. AFL may exist as an individual rhythm in a patient or may vacillate with other supraventricular tachycardias (most commonly with atrial fibrillation).

The exact incidence of AFL in the general population is unknown, but incidence increases with age. The condition is more prevalent in men than in women by a ratio of up to 2:1.

Most cases of AFL are associated with an underlying condition, many of which are also associated with atrial fibrillation, though the latter is more common. Cases of AFL without an identifiable predisposing factor ("lone atrial flutter") are far less common.

Common causes and predisposing conditions include:

• Atrial enlargement, from various causes
• Chronic ventricular failure
• Mitral or tricuspid valve regurgitation or stenosis
• Post-cardiac surgery
• Congenital heart disease
• Pre-excitation syndromes like Wolff-Parkinson-White syndrome (WPW)
• Toxins (eg, alcohol)
• Metabolic conditions (eg, thyrotoxicosis)
• Chronic pulmonary disease and pulmonary embolism
• Pericarditis
• Obesity
• Obstructive sleep apnea

A classification of AFL was defined by Wells et al in 1979, distinguishing two types:

1. Type I (typical, common, or counterclockwise isthmus-dependent) – Characterized by a circuit from the high right atrium, down the lateral wall, crossing the isthmus between the orifice of inferior vena cava and the annulus of the tricuspid valve. Slow conduction through the isthmus causes an excitable gap that allows the flutter wave to repeatedly depolarize the atrium, propagating the arrhythmia. Less often, the isthmus-dependent pathway rotates in the opposite direction, which results in "atypical" or "clockwise" type I flutter.
2. Type II – Not fully characterized and broadly defined as an atrial tachycardia with the characteristic continuous, undulating pattern on ECG that does not fit the typical clockwise or counterclockwise flutter pattern. It is less frequent and usually has a higher atrial rate (greater than 350 bpm).

Patients may be asymptomatic, with the rhythm being discovered on a routine physical examination or ECG. In other cases, mild symptoms such as fatigue, dyspnea, chest discomfort, palpitations, or sensation of an irregular heartbeat may be present. Patients may also present with symptoms and signs of cardiac decompensation and poor end-organ perfusion such as dyspnea, dizziness, syncope, and chest pain. They can also have symptoms of thromboembolic complications of AFL such as focal neurological deficits suggestive of a transient ischemic attack (TIA) or stroke, or pleuritic chest pain and dyspnea from pulmonary embolism (PE).