6th March 2024

A 34-year-old patient presents to ED with symptoms of palpitations without haemodynamic instability.

A 34-year-old patient presents to ED with symptoms of palpitations without haemodynamic instability. He is found to be in fast AF which does not appear to be settling with fluids and beta blockers (2.5mg bisoprolol, 5mg metoprolol). The ED doctor asks the cardiology registrar for advice. On review, the patient gives a specific history of the onset of palpitations, having come on this morning, around 4 hours prior. An echocardiogram is performed in ED and no abnormalities are noted. The patient is given a 50 mg tablet orally, commonly referred to as a ‘pill in the pocket’ and reverts to sinus rhythm. Given the likely drug used, what phase of the cardiac action potential does it act on?

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