hi,
thanks for the brief history of your son.
since you mentioned that you have met a cardiologist and also the echo was done and all is Fine, I am sure he won't have much issue.
137/77 is sometimes a normal blood pressure as the demands of the body and it's needs. you should only get worried if the 77 becomes 100-110 or else the 137 is normal as per my thinking.
enlargement of the heart is the bodys mechanism to cope up. remember the proverb - " Demand and supply ".
so when body needs the body modifies it as per the need. by regular exercises and appropriate specific activities he will be more healthier.
never worry with BP as 137/77 until you find any signs or symptoms complained. sometimes BP machine may show a big fluctuation without any signs and symptoms. And without having any signs and symptoms at 137/77 can never help a doctor to come to a proper diagnosis.
due to the physical activity the body is having a BP of 137/77 which is I believe you should not worry.
myself working out for more than 3-4 hours a day and without any sings and symptoms my BP will be 140//99 for which my body's demand and supply is high but I have no symptoms as well.
so.to consider only the
high BP one shouldn't get painic until one finds any signs and symptoms.
with the grace.of God I wish you a speedy recovery