The other day I had another couplet event, this time it felt like a subtle "beep-beep" and the rate was astonishingly fast. I estimated the rate to be well over 200 bpm, probably over 250 bpm. Should I be concerned? I once read (can't remember where) that the rate of a non-sustained tachycardia is directly tied to its prognostic significance. The faster the non-sustained tach, the more ominous. Is this true?