A 44-year-old man presents with palpitations. ECG shows a regular narrow-complex tachycardia at 150 bpm with inverted sawtooth-shaped flutter waves best seen in leads II, III and aVF, conducted 2:1 to the ventricles. He is planned for catheter ablation. Which structure forms the critical part of the re-entry circuit?
- A Pulmonary vein ostia
- B Cavotricuspid isthmus ✓
- C Coronary sinus ostium
- D Bundle of Kent
Correct answer: B. Cavotricuspid isthmus
Explanation
Typical atrial flutter is a macro-re-entrant circuit around the tricuspid annulus, with counterclockwise activation producing negative sawtooth waves inferiorly at an atrial rate near 300 bpm. The cavotricuspid isthmus between the tricuspid annulus and inferior vena cava is the zone of slow conduction and the target of linear ablation, which is curative in over 90 percent of cases. Pulmonary vein isolation treats atrial fibrillation, not flutter, and the bundle of Kent belongs to WPW.
Reference: Braunwald's Heart Disease, 12th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.