A 1-month-old cyanotic infant has an ECG showing left axis deviation, dominant R wave in V6, absent right ventricular forces, and normal-sized heart on chest X-ray with reduced pulmonary markings. The MOST likely diagnosis is:

• A Tetralogy of Fallot
• B Ebstein anomaly
• C Transposition of the great arteries
• D Tricuspid atresia with normally related great arteries ✓

Explanation

Tricuspid atresia obligates all systemic venous return through the right atrium into the left atrium, so the left ventricle dominates and the ECG shows left axis deviation with absent right ventricular dominance, a pattern unusual among cyanotic lesions. Tetralogy and transposition show right axis deviation and right ventricular hypertrophy, and Ebstein shows giant right atrial P waves with right bundle branch block, which excludes all three distractors.

Reference: Park's Pediatric Cardiology for Practitioners, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.