I could almost always feel it when I started going into tachycardia. I had a hard time interrupting it during exercise. And if I didn't get a vagal maneuver to work early in the process it was a lot harder to stop it. Once a short circuit got established it would just go galloping on for a while. Maybe you'll have better luck stopping your episodes on the bike than I did. I didn't actually have many episodes while I was exercising though. It was more common for me to have them immediately after stopping exercise. Occasionally, when I would stop at a street crossing for traffic one would start up.

Be sure to maintain your electrolyte balance when riding, especially on long rides. Remember that electrolytes affect heart rhythm.

Also, a wearing a Road ID might be a good idea. Some people actually pass out from these fast rhythms. I never did, but YMMV.