Your father is in a difficult situation. Severe aortic stenosis in particular tends to progress rapidly once symptoms have started. If he feels his symptoms are unbearable, you could consider getting a second surgical opinion here at the Cleveland Clinic. We do quite a bit of high risk surgery. However, both he and his family would need to realize that the risk of death (or major complications such as stroke or kidney failure)from the surgery in an 88 year old who requires a double valve replacement is not small, probably at least 25%. The recovery period in the hospital would be at least a couple of weeks and the overall recovery period would likely be several months. If he were able to get through the surgery and recovery period OK, his symptoms would likely be much better. Again, I would not recommend surgery unless his shortness of breath is truly limiting the quality of his life. Another option, if the SVT and VT episodes are what is bothering him, would be to visit a cardiac electrophysiologist to see if there is the possibility of eliminating the arrhythmia.
I wish your family and your father the best when it comes to this decision. I know it's hard. I was through this with my father, and I know how difficult it is making such a decision. How does your father feel about having the surgery? My father did not want to have the surgery, and I abided by his wishes.
My cardiologists also are affiliated with Allegheny in Pittsburgh, but when it comes time for surgery I will have it done at Cleveland Clinic.
I'll keep you and your family in my prayers.