What did you son's doctor say about the ECG results?
Today most ECG printouts come with a computer generated 'explanation'.These mean absolutely nothing without a real live cardiologist to interpret the printouts.
ECGs are incredibly complex. Variations in various places mean multiple things. Cardiologists spend years in training to learn to read these things and often need to do so within the context of a patient's history and symptoms.
A nine-year-old really needs a pediatric cardiologist to take a look at the ECG if there are questions or concerns. I would not feel comfortable with an adult cardiologist.
In fact my own nine-year-old went to her pediatric cardiologist for follow-up just last Monday. Interpretations can be very different in a child than an adult. For example, in my daughter's case, an ECG last year for a fainting episode indicated that she might have a condition that was from a genetic thing for a child but from uncontrolled hypertension for an adult.
Even though the ECG indicated the condition MIGHT be present, we needed to do an echocardiogram to determine if this was accurate or a meaningless variation. Turns out that for us, it was a meaningless variation probably due to the fact that she is very skinny and her chest wall is thin because of this, the ECG can indicate problems that are not truly there. Another explanation for the aberrant ECG is that the leads were placed wrong especially on the side. There is very little wiggle room to get good and accurate results especially on a child.
The bottom line: the ECG printout indicated that my daughter had a very serious, life-threatening, genetic condition. The truth is that she does not and the good news is that she does not even need anymore follow-ups!! 
THANK YOU GOD FOR PEDIATRIC CARDIOLOGISTS WHO ARE TRAINED IN THEIR PROFESSIONS BETTER THAN A COMPUTER! 
If you have questions or concerns about you son's results, do not hesitate to ask his doctors. You deserve a clear thorough explanation! I pray that you get good results!