What's going on with Maddie

We found out Maddie is having a little heart trouble recently.  Oct. 15th I took her in for her 7 year check up and everything was fine until the Dr took her heart rate and it was 124.  This is after sitting around in a waiting room and in a Dr office for awhile and it was that high.  The Dr took it a couple more times and it was still that fast.  The Dr. knew we would be seeing her specialist for her ADHD in 10 days and she wanted him to take her pulse then.  So we did and after she had been sitting pretty still for 30 or so min it was 130.  The Dr suggested that we get an EKG and a blood draw for a thyroid test.  The thyroid came back normal and we had to wait for the EKG until this past Monday.  So we went to the pediatric cardiologist and they did an ultra sound.  The good new is her heart function is normal, the bad news, her heart rate was 144.  They did a test where she lays down for 2 min and takes her pulse it was 125, then she sits for 2 min and it was 134 then she stands for 2 min and it was 145.  SO, then it was over to the hospital to get a Holter monitor put on her which is a portable monitor that has 5 electrodes all over her chest and it monitors for 24 hours.  We turned that in Tues. afternoon and hopefully we'll have something back from that by the end of the week.  I think the next thing is that we will take her off her ADHD meds and I think monitor her again.  I think we are just looking at all the options of why her little heart is beating so fast. The thing that concerns me is that she had heart issues when she was born that once she had a blessing they were no longer a problem.  SO for now we are in a holding pattern until we get the info from the monitor.  I will update as I get information.