From the Guidelines
Both atrial flutter and atrial fibrillation involve reentrant circuits, though they differ in their specific mechanisms. Atrial flutter typically features a single, stable macro-reentrant circuit, most commonly circulating around the tricuspid valve annulus in the right atrium, creating regular atrial rates of 250-350 beats per minute, as described in the 2016 guideline for the management of adult patients with supraventricular tachycardia 1. This organized circuit produces the characteristic "sawtooth" pattern on ECG. In contrast, atrial fibrillation involves multiple, chaotic micro-reentrant circuits throughout both atria, resulting in completely irregular atrial activity at rates of 350-600 beats per minute. This disorganized electrical activity creates the irregular baseline without distinct P waves seen on ECG. The reentrant nature of both arrhythmias explains why they respond to similar treatments that interrupt these circuits, including cardioversion, antiarrhythmic medications, and ablation procedures, as noted in the 2014 guideline for the management of patients with atrial fibrillation 1. However, the more complex and multiple circuits in atrial fibrillation often make it more difficult to treat than the single circuit typically seen in atrial flutter. Some key points to consider include:
- Atrial flutter can occur in clinical settings similar to those associated with AF, and atrial flutter can be triggered by AT or AF, as discussed in the 2016 guideline 1.
- It is common for AF and atrial flutter to coexist in the same patient, with studies showing that after CTI ablation, 22% to 50% of patients have been reported to develop AF after a mean follow-up of 14 to 30 months 1.
- Risk factors for the manifesting AF after atrial flutter ablation include prior AF, depressed left ventricular function, structural heart disease or ischemic heart disease, inducible AF, and increased LA size, as outlined in the 2016 guideline 1. The most recent and highest quality study, the 2016 guideline for the management of adult patients with supraventricular tachycardia 1, provides the most relevant information for understanding the mechanisms and treatment of atrial flutter and atrial fibrillation.
From the Research
Atrial Flutter and Atrial Fibrillation Mechanisms
- Both atrial flutter and atrial fibrillation involve reentrant circuits, as suggested by studies 2, 3.
- Atrial fibrillation is thought to be due to simultaneously circulating multiple-reentrant wave fronts, while atrial flutter is thought to be due to a single reentrant circuit 3.
- The conversion of atrial flutter to atrial fibrillation and vice versa is related to the length of an area of functional block in the right atrial free wall 3.
Relationship Between Atrial Flutter and Atrial Fibrillation
- Atrial fibrillation and atrial flutter share a common reentrant mechanism 2.
- The alternation between atrial flutter and atrial fibrillation is significantly associated with the use of a type 1A antiarrhythmic drug 2.
- Atrial flutter and atrial fibrillation can occur in the same patient, and the treatment of one may not necessarily solve the clinical problem of the other 4.
Treatment and Outcomes
- Cavo-tricuspid isthmus ablation is curative in more than 70% of patients with atrial flutter alone, but is frequently unable to prevent atrial fibrillation in patients with both atrial flutter and atrial fibrillation 4.
- Medical cardioversion of atrial fibrillation and flutter with class IC antiarrhythmic drugs can be effective in young patients with and without congenital heart disease 5.
- Flecainide is more effective than propafenone for medical cardioversion of atrial fibrillation 5.