What is atrial flutter?

What is Atrial Flutter?

Atrial flutter is a macroreentrant supraventricular tachycardia characterized by organized, regular atrial activity at rates of 250-350 bpm, most commonly involving a reentrant circuit around the tricuspid annulus through the cavotricuspid isthmus. 1, 2, 1

Mechanism and Classification

Atrial flutter operates through a macroreentrant mechanism where electrical impulses circulate around large anatomical barriers in the atrium, creating a continuous loop of activation 3, 4. This differs fundamentally from atrial fibrillation, which involves multiple chaotic wavelets, and from focal atrial tachycardias, which arise from a single point source.

Types of Atrial Flutter

Cavotricuspid Isthmus-Dependent (Typical) Flutter:

• Counterclockwise (typical): The circuit travels superiorly along the atrial septum and inferiorly along the right atrial free wall through the cavotricuspid isthmus

  • ECG shows predominantly negative "sawtooth" flutter waves in leads II, III, and aVF
  • Positive deflection in V1 with late transition
  • Atrial rate typically 300 bpm (cycle length 200 ms) 1, 2, 1

• Clockwise (reverse typical): Circuit travels in the opposite direction

  • Positive flutter waves in inferior leads
  • Negative flutter waves in V1
  • Also involves the cavotricuspid isthmus 1, 2

Non-Isthmus-Dependent (Atypical) Flutter:

• Macroreentrant circuits that do not involve the cavotricuspid isthmus
• Include perimitral flutter, left atrial roof circuits, and reentry around surgical scars or ablation lesions
• Often occur in patients with atrial scarring from prior cardiac surgery or catheter ablation 1, 5

Clinical Presentation and ECG Features

The hallmark ECG finding is regular, organized atrial activity without the discrete isoelectric baseline seen between P waves in other atrial tachycardias 1. The ventricular rate depends on AV nodal conduction, typically showing 2:1 conduction resulting in a ventricular rate around 150 bpm in patients with normal AV nodal function 6.

Important caveat: Antiarrhythmic drugs or significant atrial disease can slow the atrial rate below the typical 250-350 bpm range, making diagnosis more challenging 1.

Clinical Context and Associated Conditions

Atrial flutter occurs in similar clinical settings as atrial fibrillation and commonly coexists with it 1. After cavotricuspid isthmus ablation for typical flutter, 22-82% of patients develop atrial fibrillation within 2-5 years of follow-up 1.

Risk factors for subsequent atrial fibrillation include:

• Prior history of atrial fibrillation
• Depressed left ventricular function
• Structural or ischemic heart disease
• Increased left atrial size 1

Atrial flutter may also result as a complication of antiarrhythmic therapy for atrial fibrillation, particularly with flecainide, propafenone, or amiodarone 1.

Thromboembolic Risk

Patients with atrial flutter carry the same thromboembolic risk as those with atrial fibrillation and require identical anticoagulation strategies 1. This is a critical clinical point that should never be overlooked—the organized nature of atrial flutter does not confer protection against stroke.

Pathophysiology

The substrate for typical atrial flutter involves the cavotricuspid isthmus—the region of atrial tissue between the tricuspid valve annulus and the inferior vena cava 3. This isthmus forms a critical zone of slow conduction that is essential for maintaining the reentrant circuit 3. The presence of anatomical barriers (unlike the functional barriers in atrial fibrillation) makes this arrhythmia particularly amenable to catheter ablation 3, 7.