My Daughter was diagnosed with SVT at 4 years of age. Since then she has had only a few episodes that I know of and she is now 9. When she was 7 she had an extreme episode where her heart rate was 170 bpm 1 hour after running the mile at school. She saw a pediatric cardiologist and they also found a small hole between the upper chambers. Last weekend two nights in a row she woke up saying her heart hurts her heart rate was 130 bpm for an extended period of time. Her heart rate never went below 100 bpm till Tuesday and in the AM it was 69 bpm. She has an appointment on August 4 with a pediatric cardiologist, but my question is will this just continue to get worse the older and more involved she gets in her sports?
As per your description what I find is that she has an Atrial Septal Defect - ASD(size not mentioned). Its seen that ASD patient have increased chances of having arrhythmias like SVT. But SVT are harmless phenomenon and if persists for long periods require some prophylactic medications. I don't think there is anything to worry about future right now except giving some beta blocker medication to her.