I think it's best to assume that a general e-mail reader wouldn't know that the acronym AVM stands for the medical term "arteriovenous malformation" (I personally don't know what that ailment is all about). For this reason, it's highly advisable to state the medical term--or most such technical terms anyway--in full first, followed by its established acronym enclosed in parenthesis, then preferably defined or described succinctly. Even if your readers already know what the acronym means, I don't think they will find you officious and turn-offish by doing that. They will be appreciative instead of your leaving no room for misinterpretation or confusion.