The primary concern of tall peaked T waves is a higher level of potassium in the blood. It also can occur with poor blood supply, particularly if there are changes in the ST segment. It would be appropriate to have a blood test to check the potassium level.
It can be due to poor blood supply, but an old heart attack would usually cause a Q wave.
Poor blood supply is caused by cholesterol plaques that deposit in the artery causing a narrowing that obstructs the flow of blood.
Although an elevated level of cholesterol increases the risk for narrowings, it is possible to get cholesterol narrowing with a normal level of cholesterol. It would require further testing to look for narrowings, as well as a blood test to look for an elevated potassium.
No, it would at least require a stress test, which can be include an exercise echocardiogram, but a resting echocardiogram would not be sufficient.