Differences Between Atrial Flutter and Atrial Fibrillation
The main difference between atrial flutter and atrial fibrillation is that atrial flutter is characterized by organized, regular atrial activity with a saw-tooth pattern on ECG, while atrial fibrillation shows uncoordinated atrial activity with irregular fibrillatory waves replacing P waves.
Electrocardiographic Characteristics
Atrial Fibrillation (AF)
- Characterized by uncoordinated atrial activation with deterioration of atrial mechanical function 1
- ECG shows replacement of consistent P waves by rapid oscillations or fibrillatory waves that vary in size, shape, and timing 1, 2
- Ventricular response is typically irregular when AV conduction is intact 1, 2
- Regular RR intervals are possible in the presence of AV block or interference by ventricular or junctional tachycardia 1
Atrial Flutter (AFL)
- More organized than AF, with regular atrial activation 1, 2
- ECG shows characteristic saw-tooth pattern of flutter (f) waves, particularly visible in leads II, III, aVF, and V1 1, 2
- Atrial rate typically ranges from 240 to 320 beats per minute 1, 2
- Often presents with 2:1 AV block, resulting in a regular ventricular rate of 120-160 beats per minute 1, 2
Electrophysiological Mechanisms
- AF results from multiple reentrant wavelets or rapid focal firing, causing chaotic electrical activity 2
- AFL typically involves a single macro-reentrant circuit, most commonly around the tricuspid annulus 2, 3
- AFL can be classified as typical (involving the cavotricuspid isthmus) or atypical 2, 3
Clinical Relationships and Transitions
- AF and AFL may occur in isolation or in association with each other 1
- AF frequently precedes the onset of AFL in almost all instances 4
- AFL can degenerate into AF, and AF can initiate AFL 1
- The ECG pattern can alternate between AFL and AF, reflecting changing atrial activation 1
- 80% of patients who undergo radiofrequency catheter ablation of typical AFL will develop AF within 5 years 2
Thromboembolic Risk Differences
- Patients with AFL have a lower risk of ischemic stroke compared to those with AF 5, 6
- Annual incidence of ischemic stroke in patients with AFL is approximately 1.38% compared to 2.02% in patients with AF 6
- Echocardiographic studies show that spontaneous echocardiographic contrast and thrombus are less prevalent in AFL than in AF 5
- Patients with AFL have better left atrial appendage function and lower coagulation marker levels than patients with AF 5
Treatment Considerations
- Class III antiarrhythmic drugs (e.g., sotalol, amiodarone, ibutilide) are more effective for converting AFL, while Class IA and IC drugs are more efficacious for converting AF 7
- AFL has a higher success rate with catheter ablation compared to AF, with typical AFL being amenable to cavotricuspid isthmus ablation 5
- Despite different pathophysiologies, current guidelines provide identical indications for anticoagulation therapy in both arrhythmias 5
Common Pitfalls in Diagnosis
- AF may be misdiagnosed as AFL when atrial activity is prominent on the ECG in more than one lead 1, 2
- Extremely rapid ventricular rates (over 200 bpm) in either arrhythmia suggest the presence of an accessory pathway 1, 2
- The presence of regular RR intervals does not rule out AF if there is AV block or concurrent junctional tachycardia 1