I was recently diagnoised with IST and it happens when I stand up every time. I was put on Ivabradine and it have help so much I rarly get over 130 beats now even walking fast and if I do it returns to a lower HR prety quick.
My BP also drops a lot when I stand up and this has gotten a lot better on Ivabradine as well.
Sorry i answered to the shorter post above. Most definately anxiety can effect your heart rate like crazy...i understand the 300 range been there done that converted also by the hospital lived to tell no big deal moving on. You may be seriously taking this to another level w. all of this worry but i would seriously talk to your heart doc about the ablation because like i posted before that is a great procedure for SVT. Sounds like you are all over the place and with electrical current in our heart it is not surprising when it starts misfiring. Again i had the ablation for SVT a couple of years ago and have never had another episode since and i was definately progressive like yourself starting out in the 80's and over a 90 day period ended up in the mid 300's....that was when you say oh oh i gotta thing i gotta go and do something about it. I am sure your doc told you that the biggest risk factor is tossing a clot so hopefully they have you on a blood thinner or at the very least aspirin each day. There is nothing at all saying here and we cannot say that you have a dangerous arrythmia that is the docs call...only you and the doc know your body but when you get sick enough of having the issues like all of us you'll get proactive and do something about it....we're here for you Kasper just reach out okay?
How are your thyroid levels? My first suspicion here was hyperthyeroidism or other metabolic problems.
Sorry to hear about your extremely high SVT (AVNRT?). I hope they found the cause and schedule you for ablation if needed.
To your IST issues: Possibly, but as your blood pressure is low, it's very possible your body just have to work a little harder when you stand up, to properly increase your blood pressure. Another issue is, when your are anxious, your heart will fire significantly faster upon exertion, and the "gap" between sitting, standing and exercising increases further. It's normal - I get this too whenever I get obsessed with my heart rate.
Try one test: Forget about your heart rate for 1 week. Method of thinking: "Well, I can possibly miss a dangerous arrhythmia. But if I manage to go through with this test, I will feel better the rest of my life".
By the way, how did you feel when your HR was 300? How did adenosine work? Abruptly terminating arrhythmia? I ask because I'm a bit curious about this subject (see my post:)