The horse chestnut works as a kind of herbal Midodrine. It constricts the blood vessels which helps the blood get up to the heart and head easier. For some people, just increasing blood volume with the salt and fluids achieves this and I think that's why the doctor didn't prescribe midodrine right away. He wanted to see if my daughter's POTS would be corrected just by increasing the blood volume and then forcing down the heart rate with the Ivabradine. I could see the fluids and salt weren't enough after about a week, so added the horse chestnut in. I've only tried the specific brand and type mentioned above because it's the aescin in the horse chestnut you need and that product has a particularly high percentage of this. It's also time release, which is good. I was surprised at how well it worked, to be honest. Each person is so different, though. You could have a totally different reaction. Butcher's Broom is another, even more commonly used, herb for vasoconstriction. It didn't work as well and gave my daughter a strange kind of headache the two times she tried it. The licorice was the first thing we tried where we could see a noticeable difference. Way before the POTS diagnosis. If you can get your hands on some pure powdered root it's potentially a good thing to try in conjunction with the fluids as it helps in multiple ways. Just keep an eye on your blood pressure while taking. I'd also take in the morning rather than evening.
I'm in the UK and I think Ivabradine was approved here some time before it was approved in the US. Not sure about Canada. Doctors aren't all necessary aware of it.
I hate sitting in the doctor's office and trying to cram my explanation of the 75 different things going wrong with my daughter, most of which the GP has no clue about, into a 10 minute appointment. My strategy now is to write a letter (they won't accept emails here) very clearly outlining the one specific thing I want help with at the time. I include research evidence and exactly why I want what I want and just get the doc to call me when he's digested what I've written. This has worked so much better than sitting in an appointment getting overly emotional.
Similar experience with GP refusing to do HR test. I told the GP I'd been measuring her heart rate and it looks like she has POTS. He was willing to just accept what I was telling him and not bother to do his own HR readings. I basically forced him to do readings because I wanted some external measurement verifying there was something wrong here. I mean, I'm not the doctor! I'm using a phone app to do measurements! After a year of going to doctors for the ME/CFS where every symptom is just something you're telling them, I was not going to allow the doc not to do his own measurements on this. Then, of course, you keep your fingers crossed this won't be the ONE day you don't have the tachycardia! Things got quite heated in that appointment, but I managed to get him to do the measurements. Thankfully (you know what I mean) her heart rate went way above the 40 increase required.
Your doctor does sound really unsupportive and awful. I will say that you might find in the long run not seeing a cardiologist and having to wait for the specialist may be the best thing. GP wanted to send daughter to paediatric cardio first, before we got to see specialist. I was worried about this because I've read so many stories here and elsewhere of cardios who don't know about POTS and basically find nothing wrong. And then you're one step further back because your records now show a cardiologist has said you're fine. After being on a waiting list to see the cardio for ages, I eventually rang up the specialist myself and found that they would be happy to see my daughter with a referral straight from the GP, so I --surprise surprise--wrote a detailed letter and got GP to agree to the referral. Daughter was diagnosed with POTS right away and got the Ivabradine.
