I used to have something like this as a kid. Episodes were much shorter, maybe 30 seconds to 1-2 minutes (but they felt like they lasted forever). Usually occurred when either working hard and easing (sprinting up hill then sitting up) or being sedate and suddenly doing something (sitting at kitchen table then sprinting up stairs).

My HR would be 240 bpm, give or take. I never, ever see that kind of HR. I don't break 200, I did see 189 or something way back when, but 240 is totally insane. For those that don't know what it feels like, put your car in neutral and push the gas pedal to the floor. THe engine will be screaming and nothing is happening. The episodes feel like you haven't breathed fully in a minute or two but your heart rate is crazy high (not just "I'm working" high, it's crazy high).

Ultimately, with me, I have something wrong with my EKG reading. Apparently it makes me look like I'm having a heart attack. This wrong beat thing reverses itself at 112-114 bpm, and when I was doing the nuclear stress tests, at that HR I had the sensation like it was about to have an episode (even though I hadn't for many years). It happened going up as well as going down HR-wise. I carry a reduced copy of my EKG in case I get knocked unconscious so they don't try and fix my heart.

There are two Juniors in the area that had severe versions of this (I guess it's SVT). They both had surgery or something, I don't know, something official, burn a nerve or something? I don't know what it was. They both race.