I am not a pediatric cardiologist, but in adults control of blood pressure and heart rate with medications such as beta blockers can prevent the progression of dilatation of aortic aneurysms.
Please have yourself and son checked for connective tissue disorders by a geneticist. There are many symptoms like easy bruises, very flexable, early arthritis, poor eyesight, and many others. Symptoms usually run "true" in a family but sometimes children can have a worse case called a mutation. We do use blood pressure medications to control the growth rate.