My mom was in the same type of situation as your dad. She had a 90 percent blockage in her main artery and was told she could have a heart attack at any time. My sister and I did alot of research to see what options, other than heart surgery was available. Because of the position of the blockage the only option for my mom was bypass surgery. We asked the surgeon about other methods, including chelation, but that was not an option for her. I'm not suggesting that it is not an option for your dad, but you need to discuss this with his surgeon. Find out where the blockage is, as we did with our mom. It was very scary for us but it's been four months since the surgery and she is doing great!
Talk to the surgeon, doctor, specialist to find out what is best for your dad. Let us know how it works out for your dad.