Bottom line in my opinion, this is a question for your Dr and you need to be honest with your Dr on what drugs your doing. All he is doing in prescribing the meds based on the results of his tests, and probably do not know the full scope of what you were taking. By him adding another medication to the ix because he may think you have a heart condition may ctually cause you much more harm then good. While I hate to be crass here, but we are not doctors here nor can we give medical advise. Your playing with large amounts of opposite medications and by your Dr now prescribing you a medication that may not be needed as the irregular heart rate was likely cause by your mix of stims and downers, now add into that a medication to treat a medical condition once the drugs are out of your system could wind you up in a hospital with a new problem brought on by not giving your doctor your full run down, in fact on a more serious side and not to scare you but be 100% truthful could kill you if you really don't need this extra med in the first place. I would consult your DR or Pharmacist before taking the medication he prescribed and tell them exactly what you did the night and the day before your appointment. It could literally become a life saver.
Yes some may say that I am out to scare people with my responses too questions like this, but this is after all a harm reduction site, not a rehab, drug clinic, not in anyway a medical clinic. So my personal opinion is to be completely honest with your DR, he may even tell you that regardless it is safe to take the meds, but do you really want to play Russian roulette with your life?
Be safe.