Hi and welcome to MM Almacfarlane.
don't let them take the coil out but perhaps reduce you oestrogen dose. Palapations are a nuisance but are quite common with menopause and nothing not worry about really, so maybe put up with these - a lower dose of patch might stop the bleeding. How long have you had the Mirena? If more than 4 years then this needs changing.
I doubt very much there is anything ominous going on, so don't worry - if they were concerned they would have fast tracked you. It's most likely the higher dose of oestrogen caused the bleeding and only 60% of women are bleed free with the Mirena anyway.
Try to be patient - hopefully teh gynaecologist will reassure you. You do need the HRt to protect you bones and heart and should be on HRt till at least 50. DG x