A 58-year-old woman presents to the emergency department with acute onset dyspnea, pleuritic chest pain, and tachycardia. She has unilateral left calf swelling and tenderness. An ECG is obtained and shows the pattern marked **B** in the diagram. Which of the following pathophysiological mechanisms BEST explains the ECG findings observed in this patient?
A. Acute hyperkalemia-induced depolarization abnormality affecting ventricular repolarization globally
B. Acute left ventricular hypertrophy from chronic systemic hypertension with secondary right atrial enlargement
C. Acute myocardial infarction of the right coronary artery territory with secondary left ventricular dysfunction
D. Acute pressure overload of the right ventricle from thromboembolic occlusion of pulmonary arteries, causing RV strain and hypoxia from ventilation-perfusion mismatch
Explanation
Why option 1 is correct
The ECG pattern marked B — comprising S1Q3T3, T-wave inversions in V1-V4, sinus tachycardia, and incomplete right bundle branch block — is the classic electrocardiographic manifestation of acute pulmonary embolism with right heart strain. According to the ESC 2019 PE Guidelines and Harrison's, this pattern arises from ACUTE PRESSURE OVERLOAD of the right ventricle. When thromboemboli (typically from lower extremity or pelvic DVT) suddenly occlude pulmonary arteries, pulmonary vascular resistance increases acutely. This causes RV dilation, RV pressure overload, and RV strain. The resulting hypoxia from ventilation-perfusion mismatch and acute RV dysfunction produce the characteristic ECG findings: sinus tachycardia (most common, 40%), S1Q3T3 pattern (classic but only 20% sensitive), and T-wave inversions in V1-V4 (the most specific ECG sign of RV strain in PE). The clinical presentation of acute dyspnea, pleuritic chest pain, unilateral leg swelling, and tachycardia further supports acute PE with RV strain.
Why each distractor is wrong
Option 2 (Acute RCA MI): While acute RCA infarction can produce some ECG changes, it does NOT produce the combination of S1Q3T3 + anterior TWI V1-V4 + sinus tachycardia + iRBBB. RCA MI typically shows ST elevation in inferior leads (II, III, aVF) and right-sided leads (V4R), not the pattern described. The clinical presentation (bilateral leg swelling, acute dyspnea without chest pain typical of MI) is inconsistent with acute coronary syndrome.
Option 3 (Acute hyperkalemia): Hyperkalemia produces peaked (tented) T waves, prolonged PR interval, widened QRS, and loss of P waves — NOT the S1Q3T3 pattern or anterior T-wave inversions. The clinical context (DVT risk, acute dyspnea) does not suggest hyperkalemia.
Option 4 (LV hypertrophy from hypertension): Chronic LV hypertrophy produces LV strain pattern (lateral T-wave inversions, prolonged QTc) and left axis deviation, NOT S1Q3T3 or anterior RV strain pattern. The acute presentation is incompatible with chronic hypertensive disease.
High-YieldNEET PG
T-wave inversion in V1-V4 PLUS lead III is the MOST SPECIFIC ECG sign of PE; S1Q3T3 is classic but only 20% sensitive; sinus tachycardia is the most common ECG finding (~40%); normal ECG does NOT exclude PE (seen in 25% of confirmed cases).
ESC Pulmonary Embolism Guidelines 2019; Harrison 21e Ch. 273
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