Atrial Flutter with 2:1 AV Conduction — Sawtooth Waves
medium
stethoscope Medicine
A 67-year-old man with hypertension, obstructive sleep apnea, and mild COPD presents with 2 days of palpitations and lightheadedness. His heart rate is regular at exactly 150 bpm. A 12-lead ECG is obtained. The structure marked **A** in the diagram shows a characteristic sawtooth pattern that is negative in the inferior leads and positive in V1. What is the most likely diagnosis?
A. Atrioventricular nodal reentrant tachycardia (AVNRT)
B. Atypical (clockwise) atrial flutter with 2:1 AV conduction
C. Typical counterclockwise cavotricuspid isthmus-dependent atrial flutter with 2:1 AV conduction
D. Atrial fibrillation with rapid ventricular response
Explanation
Why Typical counterclockwise cavotricuspid isthmus-dependent atrial flutter with 2:1 AV conduction is right
The sawtooth flutter wave pattern marked A that is negative (downward) in the inferior leads (II, III, aVF) and positive in V1 is pathognomonic for typical counterclockwise cavotricuspid isthmus-dependent atrial flutter. This pattern reflects the macroreentrant circuit traveling up the interatrial septum and down the right atrial free wall. The regular narrow-complex tachycardia at exactly 150 bpm with an atrial rate of ~300 bpm reflects 2:1 AV conduction, which is the classic presentation of typical atrial flutter. This diagnosis is further supported by the patient's risk factors (hypertension, OSA, obesity, COPD) and the ECG findings. Per Braunwald's Heart Disease, the sawtooth flutter wave morphology is the single most pathognomonic ECG feature of typical atrial flutter.
Why each distractor is wrong
Atypical (clockwise) atrial flutter with 2:1 AV conduction: Atypical clockwise flutter produces flutter waves that are positive (upward) in the inferior leads, not negative. The negative inferior flutter waves seen in A specifically indicate counterclockwise (typical) flutter, not clockwise atypical flutter.
Atrial fibrillation with rapid ventricular response: Atrial fibrillation produces irregular, chaotic baseline undulations (fibrillation waves) without the organized, regular sawtooth pattern seen in A. The rhythm would also be irregularly irregular, not regular at exactly 150 bpm. The clear sawtooth morphology excludes AF.
Atrioventricular nodal reentrant tachycardia (AVNRT): AVNRT produces a narrow-complex tachycardia but does not generate the characteristic sawtooth flutter waves seen in A. AVNRT typically shows P waves buried within or immediately after the QRS complex, not the organized atrial flutter waves at 300 bpm. The ECG morphology is distinctly different.
Braunwald's Heart Disease, 12th Edition, Chapter 39: Atrial Fibrillation and Flutter; ACC/AHA/HRS Guideline on the Management of Adult Patients with Supraventricular Tachycardia
Practice similar questions
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.
