I am a cardiologist and limited by not seeing the EKG and myself here. So, I will try to answer your question to best of my knowledge.
Cardiologists consider right axis deviation of significance if it is more than +105 degrees. Being obese
at 13 years of age that is childhood obesity
is a malady of our daily life style. If on examination the doctor has been unable to find any cardiac abnormality in him, on basis of EKG he, in all probability normal heart. Let your son be examined by a cardiologist if every thing is normal he would need change in life style which will include playing outdoor games and proper diet. Your doctor may ask for an echocardiography
and Doppler, Lipid profile
, fasting blood sugar these tests will remove worry you justifiably have for your son. Once the tests excludes any illness your son should embark upon healthy life style of balanced diet, exercise and stress
With Best Wishes
Dr Anil Grover