You can say that you had gynecomastia. It's basically true.
My dentist doesn't know I'm trans, and I don't see that it matters. But to a regular physician, especially in an emergency situation, I might very well out myself because what if I'm more badly injured than I thought? What if he wants to rule something out that I didn't even think of?
I saw a sleep specialist about eighteen months ago and outed myself because I thought he should know. I was female on my record, but nobody seems to look for that little tiny "F"; they go by what the patient looks like. So I told him.
Still, I'm not sure what I would have done in your shoes. And now that I think about it, I could have a heart attack while I'm getting a tooth filled or something. Who knows.
Is your trachea okay?