Was Diagnosed With Multiple Blood Clots In Lung. Is SVT The Cause?

I am 86 years old. Iwas diagnosed in July,2011, via a Cat/Scan, with multiple blood clots in my left lung and a gigantic clot in my right lung. I have been on Warfarin since that time. I have had no re-occurence since returning home from the hospital. I was sent there after a 911 call when I felt like I was about ready to pass out. I have resumed my normal life, including exercise, etc. I was diagnosed seven years ago with SVT by my cardiologist and put on Metoprolol which I have continued to take all this time. I suspect my SVT was probably the cause of the clots even though it is not supposed to be the same danger as AFib and thus wasn t on blood thinners. My cardiologist tells me I will probably be on Warfarin the rest of my life. My Question. What is my prognosis from here on in and do you think the clots may have been evaporated by now. My doctor says the risk/reward ratio of another cat/scan to see if they are gone is not appropriate. In the meantime, as I said before, I have resumed my normal life and feel pretty good for an 86 year old. Your thoughts would be much appreciated.