A 46-year-old man presents with palpitations. ECG shows a regular narrow-complex tachycardia at 150 bpm with identical sawtooth-shaped atrial activity best seen in leads II, III and aVF. What is the most likely mechanism?
- A Ectopic focus arising near the pulmonary veins
- B Re-entry within the AV node using dual pathways
- C Re-entry circuit around the tricuspid annulus involving the cavotricuspid isthmus ✓
- D Accessory pathway mediated macro-re-entry
Correct answer: C. Re-entry circuit around the tricuspid annulus involving the cavotricuspid isthmus
Explanation
Typical atrial flutter is a macro-re-entrant circuit rotating around the tricuspid annulus, dependent on the cavotricuspid isthmus. The atrial rate is usually about 300 bpm, and with 2:1 conduction the ventricular rate classically settles near 150 bpm. Sawtooth flutter waves in the inferior leads confirm the diagnosis. Pulmonary vein ectopy produces focal atrial fibrillation, not organized flutter.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.