Your 13 year old son had a borderline ekg after fainting what could this mean?

Although I didn't faint, I am am 13 and I had a EKG, the nurses whom checked me said it could be caused by depression or playing sports, these make you heart rate slow, as I was told, and cause you to need a EKG. Again though, it could be either depression or playing sports. Athlete's tend to have a low heart rate, ( It is abnormal for a 13 year to have a lower heart rate than adults, this is why they need a EKG also.)