I'm facing the same dilemma. Have an 11 y/o boy that we just acquired in June. His teeth need cleaned. He has a low heart rate. His blood work was all good. But my vet is concerned about the low heart rate. We're going in next week. He's going to give him some atropine to see if it increases his heart rate enough for him to go under anesthesia.
I'm doubly worried right now, since we just lost our Sage. I don't want to lose another in less than a month's time. That said though, she was 15 and sailed through the anesthesia when she had a mast cell tumor removed, and a dental.
I was concerned about putting her through all that at her age, but it had to be done.
I'm going to see what the vet thinks when we go in next week. If he isn't comfortable putting him under, we'll have to figure out something else.
Good luck.