Atrial Flutter
Atrial flutter is an arrhythmia most often caused by reentry within the atrial myocardium. The “common” form of atrial flutter can be recognized by sawtooth-shaped flutter waves that are most prominent in the inferior leads. In most cases, reentry occurs in the right atrium, with the circulating wavefront traveling around the tricuspid annulus, up the atrial septum and down the right atrial free wall (in a counterclockwise direction when viewed from the cardiac apex). Atrial flutter often occurs in the setting of underlying heart disease but can occur in patients with normal hearts. The atrial rate is generally between 250 and 350 beats per minute. In patients with fairly normal AV node function, atrial flutter can conduct down the AV node with a 2:1 ratio resulting in narrow complex SVT at rates between 125 and 170 beats per minute (most often around 140-150 bpm). Intravenous adenosine or even carotid sinus massage can be used to cause transient AV block that will allow visualization of the underlying flutter waves. The acute treatment of flutter should first include slowing the ventricular response to reduce symptoms. This can be accomplished using beta-blockers or calcium-channel blockers. Digoxin is of little or no use for this purpose. Restoration of normal sinus rhythm can be easily accomplished by electrical cardioversion, although antiarrhythmic drugs can occasionally be used for this purpose. Intravenous ibutilide (a Class III antiarrhythmic drug) is approved for the acute termination of atrial flutter and fibrillation. It is 70% effective for atrial flutter and 50% effective for atrial fibrillation, but ibutilide can cause Torsades de Pointes in 3-8% of patients. Since atrial flutter is due to electrical disease within the atrial myocardium, it commonly recurs and usually requires long-term antiarrhythmic therapy with a Class I or Class III antiarrhythmic agent. Beta blockers and calcium channel blockers do not appreciably affect recurrence rates, although they are used to control the ventricular response to atrial flutter. Recurrence rates on antiarrhythmic therapy approach 80% after cardioversion, because the reentry circuit remains present. In comparison, radiofrequency catheter ablation for common atrial flutter is highly effective in eliminating this arrhythmia, with a long-term success rate of 80% or so. This is accomplished by creating a linear burn between the tricuspid annulus and the inferior vena cava, as the isthmus of tissue between these two structures serves as a critical limb in the common atrial flutter circuit. Less common forms of atrial flutter can also be ablated successfully, and three-dimensional mapping computers have made it far easier to identify the location of these flutter circuits.
The risk of thromboembolic complications (such as stroke) in atrial flutter can be almost as high as that of atrial fibrillation. Therefore, anticoagulation with warfarin is indicated in patients with atrial flutter and risk factors for stroke, especially if they are to undergo ablation or elective cardioversion.