unlike POTS (where tachycardia in POTS is triggered by orthostatic stress), IST occurs independent of body position
POTS patients usually have a normal resting supine HR
both predominately affecting young women.
The key 🔑 to making a diagnosis of IST is ambulatory monitoring; IST patients, unlike patients with POTS, demonstrate relative night-time supine tachycardia.
Of course, other common supraventricular tachycardias may need to be excluded, though these generally have a distinct onset and offset of symptoms and are not primarily postural in presentation.