A 58-year-old man presents with palpitations. 12-lead ECG shows a regular narrow-complex tachycardia at 150 bpm. Close inspection reveals sawtooth flutter waves in leads II, III, and aVF, with upright waves in lead V1. The flutter waves are negative in the inferior leads. What is the most likely atrial rate and mechanism?
- A Atrial rate 250/min, automatic focus in the right atrium
- B Atrial rate 200/min, micro-reentry within the AV node
- C Atrial rate 300/min, macro-reentrant circuit (counterclockwise typical flutter) ✓
- D Atrial rate 350/min, multiple wandering atrial foci
Correct answer: C. Atrial rate 300/min, macro-reentrant circuit (counterclockwise typical flutter)
Explanation
Typical counterclockwise atrial flutter has an atrial rate of approximately 300 bpm (range 240-340) producing sawtooth F waves that are negative in leads II, III, aVF and upright in V1. With 2:1 AV conduction, the ventricular rate is about 150 bpm. This is a macro-reentrant circuit around the tricuspid annulus, not an automatic focus or AV nodal reentry.
Reference: Goldberger's Clinical Electrocardiography, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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