I had similar issue a couple of years ago with my Class 1 - did a lot of reading of it. I was sent to do ultrasound and they found nothing. What they explained was that (bar misplacement of the electrodes) it is often the case of "athlete's heart" - your heart slightly enlarged due to exercises and the reading of T reflects it. This is actually good but because they go on the safer side they need to investigate further. So apart from additional expenses and time there is nothing to be worried about.