My 13-year-old, 6ft, 135 lb son has a resting HR of 115-125bpm, with intermittent increases (unknown cause), accompanied by continuous cold hands with delayed cap refill. He denies CP but c/o pressure with exertion. I ve recorded HR of 180 bpm after running 1 mile, with prolonged recovery period. Sometimes his HR remains elevated for 15min or so. Any suggestions on what to look for?