Sorry to get personal, but do you smoke? I had friends with a cat that had heart problems and they were both chain smokers. It was a terrible thing, but the cat died the day after I was visiting them and I saw the difference in breathing in the poor creature when we were home alone during the day (me and the cat) and later in the evening when my friends came home and lit up. Due to living in a high crime area in their city in the UK, they never open the windows, so it was pretty smoky in there. I am asthmatic myself and always take meds and use my inhaler when I visit them. Anwya, he was gasping for air, and they never figured out that it was their cigarettes! I felt really bad the next day when they called me at home to tell me he had died.
No, I am ashamed to say that I didn't say anything. It was already too late when I was there. The cat was doomed.
So if you smoke, please try and do it away from your pet, if you don't, don't start!
Good luck with the treatment. I intend to follow this thread and see what treatment your vet comes up with. Please keep us posted.