Atrial Flutter — Sawtooth F Waves MCQ — NEET PG Practice Question | NEETPGAI
Atrial Flutter — Sawtooth F Waves
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stethoscope Medicine
A 68-year-old man with hypertension, type 2 diabetes, and prior mitral valve repair presents with 3 days of palpitations and dyspnea. On examination, he is hemodynamically stable with HR 150/min (regular) and BP 128/76 mmHg. A 12-lead ECG shows a narrow-complex regular tachycardia. The structure marked **A** in the diagram—the characteristic sawtooth pattern of continuous, undulating negative flutter waves in the inferior leads (II, III, aVF)—is pathognomonic for which arrhythmia mechanism?
A. Atrioventricular nodal reentrant tachycardia (AVNRT) with dual AV nodal pathways
B. Typical (counterclockwise) cavotricuspid-isthmus-dependent atrial flutter with 2:1 AV conduction
C. Atypical (clockwise) atrial flutter involving the left atrium
D. Atrioventricular reentrant tachycardia (AVRT) mediated by an accessory pathway
Explanation
Why "Typical (counterclockwise) cavotricuspid-isthmus-dependent atrial flutter with 2:1 AV conduction" is right
The sawtooth pattern of continuous, undulating negative flutter waves in the inferior leads (II, III, aVF) is the pathognomonic ECG hallmark of typical (counterclockwise) atrial flutter. This pattern reflects a fixed macro-reentrant circuit around the tricuspid annulus in the right atrium, with the critical isthmus between the inferior vena cava and tricuspid annulus (cavotricuspid isthmus—CTI). The atrial rate is 300/min, and the 2:1 AV conduction results in a ventricular rate of 150/min. This is the most common form of atrial flutter (~90% of cases) and is characteristic of typical right atrial flutter. (Harrison's 21e, Supraventricular Arrhythmias)
Why each distractor is wrong
Atypical (clockwise) atrial flutter involving the left atrium: Atypical flutter circuits (clockwise typical, left atrial, or post-ablation/post-surgical scar-related) do not produce the classic sawtooth pattern in the inferior leads. The flutter wave morphology differs based on the circuit location and direction. The inferior sawtooth pattern is specific to typical counterclockwise right atrial flutter.
Atrioventricular nodal reentrant tachycardia (AVNRT) with dual AV nodal pathways: AVNRT produces a narrow-complex regular tachycardia but does NOT produce visible flutter waves on the surface ECG. The P wave is typically buried within or immediately after the QRS complex or T wave. The absence of a sawtooth pattern and the presence of visible continuous flutter waves exclude AVNRT.
Atrioventricular reentrant tachycardia (AVRT) mediated by an accessory pathway: AVRT also produces a narrow-complex regular tachycardia but lacks the characteristic sawtooth flutter waves. AVRT typically shows a visible P wave in the ST segment or T wave, not the continuous undulating negative flutter waves seen in atrial flutter. The ECG morphology is distinctly different.
High-YieldNEET PG
The sawtooth pattern in inferior leads (II, III, aVF) = typical atrial flutter; positive flutter waves in V1; absent isoelectric baseline; atrial rate 300/min; most common form (90%); cavotricuspid-isthmus-dependent; macro-reentrant mechanism.
Harrison's 21e, Supraventricular Arrhythmias
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