In a 45-year-old man with a history of atrioventricular nodal re‑entrant tachycardia presenting with a regular narrow‑complex tachycardia at 150–170 bpm, could the rhythm be atypical atrial flutter?

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Last updated: November 5, 2026 • View editorial policy

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Could it be atypical flutter?

Yes, atypical atrial flutter is possible but less likely than AVNRT recurrence in this clinical scenario—however, the regular narrow-complex tachycardia at 150-170 bpm with a known AVNRT history strongly favors AVNRT over atypical flutter.

Differential Diagnosis Framework

In a 45-year-old with documented AVNRT presenting with regular narrow-complex tachycardia at 150-170 bpm, you must distinguish between:

Most Likely: AVNRT Recurrence

  • AVNRT characteristically presents as regular narrow-complex tachycardia with abrupt onset/termination 1
  • The rate of 150-170 bpm is typical for AVNRT
  • Prior documented AVNRT makes recurrence the leading diagnosis
  • Research confirms AVNRT can mimic atrial flutter on surface ECG, particularly when P waves are buried in or immediately following the QRS complex 2

Less Likely: Atypical Atrial Flutter

Atypical flutter (non-cavotricuspid isthmus-dependent) involves macroreentrant circuits around the mitral valve annulus or atrial scar tissue 1. Key distinguishing features:

  • Atypical flutter typically shows discrete flutter waves, though morphology varies based on circuit location 1
  • Positive P waves in V1 and across all precordial leads (absent precordial transition) favor left atrial atypical flutter over typical right atrial flutter 3
  • Atrial rates usually faster (often 2:1 conduction producing ventricular rate ~150 bpm)
  • More common post-ablation for atrial fibrillation, not typically associated with AVNRT patients 3

Critical ECG Analysis Points

Look for these specific features to differentiate:

Favoring AVNRT:

  • P waves buried within or immediately after QRS (short RP tachycardia)
  • Pseudo R' waves in V1 or pseudo S waves in inferior leads (retrograde P waves)
  • Abrupt onset/termination if captured
  • Response to vagal maneuvers or adenosine with sudden termination

Favoring Atypical Flutter:

  • More P waves than QRS complexes (2:1 or variable block) 3
  • Positive P waves across all precordial leads suggests left atrial origin 3
  • Sawtooth pattern (though less organized than typical flutter)
  • Gradual slowing with adenosine rather than termination

Important Clinical Associations

There is a well-documented association between AVNRT and inducible atrial flutter (88% of AVNRT patients have inducible flutter during EP studies) 4, 5. This occurs because:

  • Both arrhythmias involve perinodal atrial tissue
  • AVNRT patients often have shorter atrial refractory periods 4
  • However, clinical atypical flutter remains uncommon in AVNRT patients without prior ablation or structural heart disease

Management Implications

The distinction matters because:

  • Atypical flutter is frequently resistant to rate-controlling medications and often requires urgent cardiology/EP consultation 3
  • AVNRT typically responds to vagal maneuvers, adenosine, or AV nodal blockers
  • Atypical flutter may indicate underlying structural disease or prior ablation complications

Diagnostic Approach

  1. Obtain 12-lead ECG during tachycardia focusing on P wave morphology and relationship to QRS
  2. Attempt vagal maneuvers or adenosine (6-12 mg IV push):
    • Sudden termination → AVNRT
    • Transient AV block revealing flutter waves → atrial flutter
  3. If refractory to standard measures or diagnostic uncertainty persists, proceed to EP study for definitive diagnosis 2

Common Pitfall

AVNRT can masquerade as atrial flutter on surface ECG, particularly atypical AVNRT variants where P waves may appear more separated from the QRS 2. When cycle length remains constant despite QRS morphology changes (narrow to wide with aberrancy), this confirms a single SVT mechanism rather than alternating rhythms 6.

Given this patient's established AVNRT history and the typical rate range, recurrent AVNRT is the primary diagnosis until proven otherwise, though atypical flutter remains in the differential and requires ECG confirmation.

References

3
Research

Diagnosing Atypical Flutter in the Post-atrial Fibrillation Ablation Patient: A Case Report.

Clinical practice and cases in emergency medicine, 2023

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