In pulmonary embolism, the EKG pattern S1Q3T3 may appear with or without which conduction abnormality?

• A. Right bundle branch block
• B. Left axis deviation
• C. Atrioventricular block
• D. Normal conduction

Answer: (B)

S1Q3T3 reflects acute right ventricular strain from a pulmonary embolism, a pattern produced by the heart’s sudden load after a PE. It isn’t tied to a single QRS axis or to a fixed conduction abnormality. While right axis deviation is common in PE due to RV overload, the frontal-plane QRS axis can be normal or even leftward in some patients depending on individual heart position and other cardiac conditions. Therefore the S1Q3T3 pattern may be seen with or without left axis deviation. This is why left axis deviation is the conduction pattern listed as the one that may or may not accompany the pattern in PE. In practice, remember that this EKG clue is supportive but not definitive, and diagnosis relies on clinical suspicion plus imaging.