What is atrial flutter?
Atrial flutter is a rhythmic, fast rhythm that occurs in the atria of the heart. This rhythm occurs most often in individuals with organic heart disease (ie: pericarditis, coronary artery disease, and cardiomyopathy). Atrial flutter is a regular, rhythmic tachycardia originating in the atria. The rate in the atria is over 220 beats/minute, and typically about 300 beats/minute. The
morphology on the surface EKG is typically a sawtooth pattern.
The ventricles do not beat as fast as the atria in atrial flutter. The AV node acts as a safety valve in the event of any fast rhythm of the heart, including atrial fibrillation and atrial flutter. The AV node slows down conduction of the electrical activity, and if it receives the next action potential before it is ready, the impulse will be blocked at the AV node level, and never reach the ventricles. In the case of atrial flutter, there is a very particular block pattern at the AV node level. In atrial flutter, the AV node typically will block every other electrical impulse, or three out of four impulses. If every other impulse is blocked, known as 2:1 block, while the atrial rate is 300 beats/minute, the ventricular rate will be 150 beats/minute. If three out of four beats are blocked, known as 4:1 block, while the atrial rate is 300 beats/minute, the ventricular rate will be 75 beats/minute.
In many individuals, the degree of block is variable - sometimes every other beat is transmitted, sometimes two beats are dropped before the third is transmitted, etc. This is known as varying block. For reasons that are not well understood, a stable 3:1 block is not commonly seen in individuals with atrial flutter. A single individual can have varying degrees of block at different times. The varying degree of block is due to a multitude of factors, including catecholamine release and the use of any drugs that inhibit conduction through the AV node, such as beta blockers, digitalis, and calcium channel blockers.
Atrial flutter can sometimes degenerate to atrial fibrillation and sometimes atrial fibrillation will organize back into atrial flutter and at times even one atrium may be in an organized rhythm and the other atrium may be in a disorganized rhythm. Atrial flutter may arise in otherwise healthy people without any evidence of heart disease, or may be secondary to scarring or stretching diseases of the atrium, just like AF. Atrial flutter shares some features with AF in that it causes symptoms similar to those of AF, it can also increase the risk of stroke by blood clot formation in the heart which breaks off and migrates to the brain. An important difference with atrial fibrillation, though, is that many patients with atrial flutter can have their arrhythmia treated by catheter ablation with a very good probability of success. At times, when antiarrhythmic drugs are used for patients with atrial fibrillation, atrial fibrillation may be organized by the antiarrhythmic drug into atrial flutter and catheter ablation can then be successfully performed, a treatment sometimes referred to as hybrid therapy. In this circumstance, the antiarrhythmic drug is continued after the ablation has been performed to prevent recurrences of AF.