Yeah, take the med's they are pretty safe. Safer and less unpleasant than a racing heart. And pretty standard to prescribe them initially from everything I read. Once your thyroid is under control you'd probably go off them.
Also my gut feeling is, being hyperthyroid, you might as well toss the the EKG results in the trash for what they are currently worth.
I'd take the beta blocker your GP gave you. Beta blockers are pretty standard treatment for the racing heart caused by hyper. I have a congenital heart defect that makes me susceptible to tachycardia, and I take a beta blocker...works wonders. Beta blockers have been around a long time, so they have a proven track record and are very safe. The only side effect I noticed was a bit of a "slow" feeling when I first started taking it. That either went away in a week or two or I got used to it. I know how uncomfortable and scary tachycardia can be...take the meds your GP gave you...you'll feel much better while you wait to see the endo, because sometimes it takes a while to get in to see one.
My general practitioner is sending my results to the endocrinologist then I'll know more. He gave me a beta blocker but my family is concerned about taking anything before I see a specialist. So I'm praying I can handle the racing heart till then. I also have anxiety so it makes it worse. I guess I'm just new to this and scared.
Do you have the result and reference ranges of your thyroid blood work? Ranges vary lab to lab, so you have to post results and ranges together.
One of the symptoms of hyper thyroid is racing heart. Once you start anti-thyroid meds, your HR will go back to normal. When do you follow up with your doctor to start meds?
Slight damage to your heart will unlikely be permanent.