What is the difference between atrial fibrillation and atrial flutter?

Differences Between Atrial Fibrillation and Atrial Flutter

Atrial fibrillation and atrial flutter are distinct supraventricular tachyarrhythmias with different electrocardiographic patterns, electrophysiological mechanisms, and clinical implications, though both can lead to similar complications including thromboembolism.

Electrocardiographic Characteristics

Atrial Fibrillation (AF)

• Characterized by uncoordinated atrial activation with consequent deterioration of atrial mechanical function 1
• ECG shows replacement of consistent P waves by rapid oscillations or fibrillatory waves that vary in amplitude, shape, and timing 1
• Ventricular response is typically irregular when AV conduction is intact 1
• Fibrillatory waves have no discernible pattern and lack an isoelectric baseline 1

Atrial Flutter (AFL)

• More organized arrhythmia than AF with regular atrial activation 1
• ECG shows characteristic saw-tooth pattern of flutter (f) waves, particularly visible in leads II, III, aVF, and V1 1
• No isoelectric baseline between flutter wave deflections 1
• Atrial rate typically ranges from 240 to 320 beats per minute 1
• Often presents with 2:1 AV block, resulting in a regular ventricular rate of 120-160 beats per minute (most characteristically around 150 beats per minute) 1
• Flutter waves are typically inverted in ECG leads II, III, and aVF and upright in lead V1 1

Electrophysiological Mechanisms

Atrial Fibrillation

• Results from multiple reentrant wavelets or rapid focal firing, causing chaotic electrical activity 1
• Characterized by uncoordinated atrial activation 1
• Associated with structural and electrical remodeling of the atria over time 1

Atrial Flutter

• Typically involves a single macro-reentrant circuit, most commonly around the tricuspid annulus (typical flutter) 1
• More organized electrical activity than AF 1
• Can be classified as typical (cavotricuspid isthmus-dependent) or atypical (non-cavotricuspid isthmus-dependent) 1

Clinical Relationships and Transitions

• AF and AFL may occur in isolation or in association with each other 1
• Atrial flutter may arise during treatment with antiarrhythmic agents prescribed to prevent recurrent AF 1
• AF may degenerate into atrial flutter, and atrial flutter may convert to AF 1
• ECG pattern may fluctuate between atrial flutter and AF, reflecting changing activation of the atria 1
• 80% of patients who undergo radiofrequency catheter ablation of typical atrial flutter will develop AF within 5 years 1

Treatment Implications

• Both arrhythmias require consideration of rate control, rhythm control, and anticoagulation 2
• Atrial flutter is generally more responsive to class III antiarrhythmic drugs than AF 3
• AF is more responsive to class IA and IC antiarrhythmic drugs 3
• Catheter ablation has higher success rates for typical atrial flutter (>90%) compared to AF 4
• Current guidelines provide identical indications for anticoagulation therapy in both arrhythmias 5

Thromboembolic Risk

• Both arrhythmias are associated with risk of thromboembolism 5
• Some evidence suggests thromboembolic risk may be lower in isolated atrial flutter compared to AF 5
• Echocardiographic studies show spontaneous echo contrast and thrombus are less prevalent in patients with AFL than in those with AF 5
• Patients with AFL generally have better left atrial appendage function and lower coagulation marker levels than patients with AF 5

Common Pitfalls and Caveats

• AF may be misdiagnosed as atrial flutter when atrial activity is prominent on the ECG in more than one lead 1
• Regular RR intervals in AF are possible in the presence of AV block or interference due to ventricular or junctional tachycardia 1
• In patients with implanted pacemakers, diagnosis of AF may require temporary inhibition of the pacemaker to expose atrial fibrillatory activity 1
• Extremely rapid ventricular rates (over 200 beats/min) in either arrhythmia suggest the presence of an accessory pathway 1