A 52-year-old man experiences pulseless electrical activity (PEA) cardiac arrest in the ICU. According to the Hs and Ts mnemonic, which of the following is a reversible cause of PEA but NOT of VF/VT?

• A Tension pneumothorax
• B Hypomagnesaemia (electrolyte disorder)
• C Hyperkalaemia
• D Hypovolaemia ✓

Explanation

The Hs and Ts are reversible causes of PEA and asystole. While many Hs and Ts can cause both PEA and VF, severe hypovolaemia specifically causes PEA or asystole (by reducing preload to near zero, the heart generates electrical activity without mechanical output) and is not a primary cause of VF/VT, which arise from ischaemia, electrolyte abnormalities, and drug effects. Hyperkalaemia, tension pneumothorax, and cardiac tamponade can produce PEA. Hypomagnesaemia most classically causes torsades de pointes (polymorphic VT). The question tests knowledge that PEA is specifically associated with inadequate mechanical filling/output, making hypovolaemia the most exclusive PEA cause.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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