A 4-month-old boy is brought to the Emergency Department after a brief episode at home in which he suddenly became pale, appeared to breathe irregularly and went floppy while being held after a feed. His mother estimates that the episode lasted around 30 seconds and resolved spontaneously. He returned fully to his usual baseline shortly afterwards.

During the history, she reports that an almost identical self-resolving episode occurred the previous evening. He has otherwise been feeding normally, with no fever, cough, vomiting or rash. He was born at term, has no known medical problems and appears well on examination in the department, with normal observations and no focal abnormality identified.

After detailed assessment, no alternative diagnosis is apparent.

According to Royal College of Emergency Medicine learning guidance, which of the following represents the minimum investigation set recommended for this presentation?