What is the difference between atrial tachycardia and atrial flutter?

Distinguishing Atrial Tachycardia from Atrial Flutter

The fundamental difference is mechanistic: atrial flutter is specifically a macroreentrant atrial tachycardia involving large reentry circuits with fixed or functional barriers, while atrial tachycardia encompasses both focal mechanisms (arising from a circumscribed area with centrifugal spread) and macroreentrant circuits—meaning atrial flutter is actually a subset of atrial tachycardia. 1

Key Mechanistic Distinctions

Atrial Tachycardia

• Originates from a circumscribed focal area with centrifugal spread to both atria 1
• Mechanisms include:
  • Enhanced automaticity 1
  • Triggered activity 1
  • Microreentry (very small reentry circuits) 1
• Characterized by an electrically silent period during the cycle, reflected as an isoelectric baseline between atrial deflections on ECG 1
• Typical cycle length usually ≥250 ms but can be as short as 200 ms 1

Atrial Flutter

• Macroreentrant mechanism involving large reentry circuits with fixed and/or functional barriers 1
• Can be entrained during atrial pacing, a key diagnostic feature 1
• Well-characterized subtypes include:
  • Typical atrial flutter (cavotricuspid isthmus-dependent) 1, 2
  • Reverse typical atrial flutter 1
  • Lesion-related macroreentrant tachycardia 1
  • Left atrial macroreentrant tachycardia 1

Traditional ECG Criteria Are Obsolete

The old ECG-based classification that distinguished these arrhythmias by rate cutoff (240-250 bpm) and presence/absence of isoelectric baseline is no longer valid. 1

• Neither rate nor lack of isoelectric baseline are specific for any particular tachycardia mechanism 1
• The European Society of Cardiology and North American Society of Pacing and Electrophysiology jointly declared this ECG classification obsolete 1
• Modern classification must be based on electrophysiological mechanisms rather than surface ECG patterns 1

Diagnostic Approach

Electrophysiological Mapping

• Focal atrial tachycardia shows:

  • Centrifugal activation from a discrete focus 1
  • Unipolar recordings with negative (QS) patterns at the origin 1
  • Significant portions of cycle length without recorded activity even with comprehensive atrial mapping 1

• Atrial flutter demonstrates:

  • Continuous atrial activation throughout the cycle 3
  • Entrainment with concealed fusion when pacing within the circuit 1
  • Large macroreentrant circuit identifiable by activation mapping 3

Advanced Mapping Technologies

• Non-contact mapping systems reconstruct >3000 simultaneous electrograms for enhanced spatial resolution 1, 4
• Electro-anatomical contact mapping provides precise localization in electromagnetically coded space 1
• Transient entrainment mapping is critical for diagnosing reentrant mechanisms as complement to activation mapping 1, 4

Clinical Implications

Management Differences

• Focal atrial tachycardia ablation targets the discrete focus of origin with high success rates 3, 5
• Typical atrial flutter ablation creates bidirectional conduction block across the cavotricuspid isthmus with the highest success rates among atrial arrhythmias 3, 2, 5
• Atypical flutter ablation requires identification of the critical isthmus within the macroreentrant circuit 6

Common Pitfalls

• Complex intra-atrial conduction disturbances in focal atrial tachycardia can extend activation over most of the cycle length, mimicking macroreentry 1
• Small reentry circuits may resemble focal atrial tachycardia when limited endocardial recordings are obtained 1
• Atypical atrial flutter is merely a descriptive ECG term; the mechanism must be elucidated through mapping and entrainment studies 1