Hey Philip,
I was implanted about 7 weeks ago with a Medtronic Versa, supposedly the Versa and the Adapta are the better ones out there for athletes. I wish I could tell you that I have no problems with it but the truth is I'm experiencing all sorts things when I ride, I have to have patience with my doctor as we go through all the settings and try different things. Right now I have the Rate Response and Accelerometer turned on, I think this is actually causing me some problems, I think the Rate Response senses when I am riding and increase the heart rate more than what is necessary so my heart rate with very little effort is high. My upper sensing rate is set to 150 and when I get close to that rate (which is very easy with this Rate Response and Accelerometer) I start to experience some flutters, I don't know if it's atrial flutter/fib/tachy but it pretty much stops me in my tracks.
I have spoken to some runners/marathoners that have the Versa and the Adapta and they are very happy with it, a lot of them are excellent runners turning in sub 3 hour marathons.
I wish I could help more. BTW, what is the reason you have your PM and how has it affected your cycling?