Well, left atrial enlargement can be related to overweight and tachycardia, among other things, and can signify that the heart is sort of overworked and is trying to compensate.
But none of us on this board is a medical professional. In this case, everything depends on your doctor's familiarity with *you* as a patient. Cardiology is really, really specialized, and if you are worried, good heavens, call your doctor back and tell him/her that you are worried, and ask for an explanation!