Yes, atrial flutter is definitively a macroreentrant tachycardia.
Atrial flutter is a macro-reentrant arrhythmia characterized by organized reentry circuits that occupy large areas of the atrium, distinguishing it fundamentally from focal mechanisms. 1, 2, 1
Mechanism and Circuit Characteristics
The 2015 ACC/AHA/HRS guidelines explicitly define atrial flutter as a macroreentrant atrial tachycardia (AT), with the reentry circuits occupying large areas of atrial tissue 1, 2. This is in direct contrast to focal atrial tachycardias, which arise from automatic, triggered, or microreentrant mechanisms at localized sites 3.
Types of Reentrant Circuits
Cavotricuspid Isthmus-Dependent (Typical) Flutter:
- The most common form involves a macro-reentrant circuit around the tricuspid annulus
- The circuit propagates through the cavotricuspid isthmus (CTI) between the tricuspid valve and inferior vena cava
- Counterclockwise rotation produces the classic "sawtooth" pattern with negative flutter waves in inferior leads 4, 1, 2
- The 2003 ACC/AHA/ESC guidelines specifically state: "Cavotricuspid isthmus–dependent flutter is caused by a macro–re-entrant right atrial circuit around the tricuspid annulus" 4
Non-Isthmus-Dependent (Atypical) Flutter:
- These are also macroreentrant circuits but do not involve the CTI
- Include perimitral circuits, left atrial roof reentry, and circuits around surgical or ablation scars 1
- All maintain the fundamental macroreentrant mechanism 5
Key Distinguishing Features from Focal Tachycardias
The macroreentrant nature can be confirmed through:
- Entrainment pacing: Post-pacing intervals equal to tachycardia cycle length at circuit sites 5
- Activation mapping: Sequential activation around large anatomical structures rather than centrifugal spread from a point source
- Response to ablation: Termination by creating a line of block across the circuit isthmus 4
Clinical Implications
Understanding flutter as macroreentry is critical because:
- Ablation strategy: Success requires creating bidirectional conduction block across the critical isthmus (>97% success for typical flutter) 6
- Rate characteristics: Typically 250-350 bpm with organized, regular atrial activity 4, 1
- Risk of 1:1 conduction: The organized circuit can conduct rapidly to ventricles, unlike the disorganized activity of atrial fibrillation 7, 8
Common Pitfall
Do not confuse "pseudo-focal" atrial tachycardias with true focal mechanisms. Some macroreentrant circuits can show centrifugal propagation at breakthrough sites when one atrial layer bypasses another, mimicking focal origin on initial mapping. However, entrainment maneuvers reveal the true macroreentrant nature (PPI within 0-21 ms of tachycardia cycle length) 9.
The distinction matters: focal ATs require ablation at the point of origin, while macroreentrant flutter requires isthmus ablation to interrupt the circuit 3.