Wow, bummer. I got a pacemaker this year and wasn't really anticipating more overt heart failure off the back of the thing. Don't know how much more I can go this way. I got it as a "back-up/just in case" pacer and since then every interrogation has been about 80% paced. The bivent pacer will have roughly the same life length. Good luck, these new pieces are SO high tech smart.
If I remember correctly, I think it depends on how ofter the pacer is "active." Are you paced 100% of the time? My dad had a pacemaker put in in 1999 and it was replaced with a Bi-V pacemaker/ICD in 2006. It hadn't worn out, but his EF was low and the unit is considered safer for people with a compromised EF. Hope the procedure goes well and you have renewed energy with your new pacer!