A 45-year-old man presents with acute dyspnea and pleuritic chest pain. ECG shows sinus tachycardia at 120 bpm, S wave in lead I, Q wave in lead III, and inverted T wave in lead III. What is the most likely diagnosis?
- A Acute inferior STEMI
- B Right ventricular hypertrophy
- C Acute pulmonary embolism ✓
- D Left posterior fascicular block
Correct answer: C. Acute pulmonary embolism
Explanation
S1Q3T3 pattern (S wave in lead I, Q wave in lead III, T inversion in lead III) is a classic but insensitive ECG finding in acute pulmonary embolism, reflecting acute right heart strain. While inferior STEMI also shows changes in lead III, it typically shows ST elevation rather than Q waves and T inversion in the same lead, and would not show the S1 pattern.
Reference: Braunwald's Heart Disease, 12th ed.
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Written and medically reviewed by the StethoPrep medical team.