Mechanisms of atrial flutter and atrial fibrillation: distinct entities or two sides of a coin?

The fact that patients frequently have both atrial flutter and atrial fibrillation is well established clinically, and suggests a mechanistic interaction. The major such interaction, we suggest, is that atrial fibrillation is usually required for the development of a line of functional block between the venae cavae, which, in turn, is required for the development of classical atrial flutter. A second major interaction, we suggest, is that when a stable atrial flutter of very short cycle length develops, it will cause fibrillatory conduction and, thereby, maintain atrial fibrillation. We do not mean to suggest that the latter mechanism is the only cause of atrial fibrillation, as it certainly is not. However, we do believe it is probably an important mechanism of atrial fibrillation, and perhaps the most common form of atrial fibrillation, at least at its inception. But without a doubt, there is a clear interaction between atrial fibrillation and atrial flutter. They are at least kissing cousins, and commonly may be responsible for causing each other. In that sense, at the very least, they are certainly two sides of a coin.