Hello and thank you for using HCM.
I carefully read your question and I understand you concern.
I will try to explain you something and give you my opinion.
You should know that the heart maximal rate might go up to a value equal to 220 minus the persons age. You don't mention the age of your son, but you should know this fact.
Excessive heart beats might have different causes to simple emotional, physical
stress, coffee or energy drinks consumption, so it is mandatory to avoid them.
Also there are other pathology's like
anemia,
hyperthyroidism or cardiac anomalys.
So, you say that the cardiac echo is normal, the blood analyze is normal and this are very good thinks. I have to remember and recommend to check even the thyroid hormones.
If I was you treating doctor I will recommend a holter rhythm monitoring for 48 h. You don't mention to have done it. This is the best examination to monitor heart rhythm and to know what kind of rhythm issue is this and if it is necessary to treat it medically.
If it is necessary a medical treatment, throw the holter we can judge which is the best one for his age.
Hope I was helpful. Wish your son good health.
Best regards.