Not on HRT but have the palpitations, ecg fine so put down to menopause- it’s not nice at all. I have tried box breathing, I do this for a few minutes and it really helps calm me down, also grounding techniques are really good, they basically distract you out of the panic that comes (for me anyway) with the palpitations- if you Google both things there is good info about both. Hope it gets better for you - hug! X