Inappropriate Sinus Tachycardia vs. ???

[SMW65]

Trying to figure this out. Saw an EP yesterday and scheduled a holter on Thursday.

Healthy 45 year old woman, physically active. Did a sprint Tri in october, rhr is 55. On my jogs, I can't run faster than a 12-13 min mile with heart rate continuing to climb to 190. The first 10 minutes I'm fine, then I'm breathless and have to stop every 4 min to catch my breath.
EP says "Inappropriate Sinus Tach" and will rule out Atrial tachycardia? with a holter. When I look at the symptoms of IST, it says regular heart rate over 100, but my rhr sitting around is in the 60's (68 at the dr.s yesterday). As I like to compete and exercise a lot, I don't want to be on BB to slow it down, but running is tough when I have to stop all the time. Is this something that I have to live with? I ran 2 half marathons 10 years ago and don't remember it being this hard, I seemed to be able to control my heart rate better even though it was still on the higher side. Any input would be appreciated!!

[SMW65]

thank you for your feedback. After wearing a heart rate monitor for most of the day yesterday I did notice my heart rate hover around 100-120 while moving through the day. It only settled when I sat down.
It helps alot to hear of someone else that likes being on the beta blockers. All the posts regarding medication are so negative, but I figure most people only post their negative reactions vs. posting their positive experiences.
I did have a treadmill test and the results were normal which makes me think this is IST. My lab levels showed a slight increase of norepinephrine and cortisol so I know the adrenaline is in there.
again, thank you for sharing your experience!

[is_something_wrong]

Not easy this one, I had this condition but in my case, the problem was a combination of mental issues and poor exercise condition.

My resting heart rate was at that time 50-55 (completely relaxed, in bed after sleep) but all the stress made my heart rate climb significantly higher during the day. Even slight exercise like walking was scary (because I got PACs) and heart rate during exercise was at least 50 BPM too high. I remember having a heart rate of 220 just by walking up a hill, but that was along with an almost chronic state of panic.

Beta blockers solved my issue. Strangely enough, it improved my exercise condition a lot, because the anxiety didn't get the heart to race and it filled properly with blood. I started to exercise more and more heavy. Now my heart rate is 150 when walking at 4 mph with 12 degrees incline. If I increase speed to 6 mph with 12 degrees incline my heart rate is 180, which I think is normal.

Listen to your EP and do the Holter test (though a stress test is possibly better to differ between atrial tachycardia and sinus tachycardia). If the atrial tachycardia origin right next to the SA node, it looks similar. Make sure you exercise a lot during the 24h test.