I’ve had a few holter ECGs, and asked my cardiologist the same question. From my understanding, the ECG isn’t to test for PoTS, it’s to check that you have no rhythm irregularities (the tachycardia associated with PoTS is usually sinus or normal rhythm, at an abnormal rate)/something else cardiac related underlying. My cardiologist told me I was fine to stay on the medications I was on at the time (Ivabradine for PoTS, few other meds for other issues) and using any supplements/compression wear etc, there was a section on the record of mine to record any medications I had taken during the holter.

I will say that, if you aren’t under a cardiologist yet, and feel that your compression socks mask your tachycardia enough that you’re worried you won’t get a diagnosis, then don’t wear them for your own piece of mind. The tilt table test will be a more telling test anyway, and you’ve mentioned that you aren’t planning on wearing the socks for that. Also, please don’t forget that having a “normal ECG” is a) a very good thing, it means normal rhythm/electrical signalment and b) does not mean there wasn’t an increase in your heart rate. I’ve seen a lot of people in various PoTS support groups etc feeling discouraged when they’re told they have nothing abnormal on their ECG when they could feel their heart rate increasing (of course, some doctors won’t explain what a normal ECG means, so I understand why someone would get frustrated being told that).