30th April 2024

A 22-year-old woman presents with recurrent episodes of fainting, especially when standing for long periods or in crowded, hot places.

A 22-year-old woman presents with recurrent episodes of fainting, especially when standing for long periods or in crowded, hot places. Each episode is preceded by lightheadedness, nausea, and blurred vision. She has no history of heart disease or seizures. Her physical examination and routine blood tests are normal.

Which investigation is most likely to confirm the diagnosis?