Get a home monitor system, google the correct positioning for monitoring bpm, do it daily until the appointment so you have some data to bring with you. Dont call it "White Cost Hypertension". From your post history it sounds like you have just plain old general anxiety. Let them know, and that you expect your heartrate to be high. But also you need to realize, your heart is beating at a level of a moderate cardiac workout while sitting in the office. That's concerning enough for doctors to not just brush it off just because you say you're anxious. Even so, that's a fast heartrate even for being really anxious so it's not something to brush off.