I also have the Adapta...since June of this year...& have had hiccups, headaches, short of breath, no energy, & PVCs like crazy. Never had them like this!! I can feel them ALL the time. They have medicated me to control them but I still feel them.
They didn't set my Heart Rate right after surgery which was bad. That's been fixed, they say.
This is my LIFE they are messing with & I am rather angry about this, to say the least!!
Have the doctors been able to tell you anything about why your heartrate is all over the place and you are having low oxygen and weakness since the pacemaker replacement? My father is experiencing similar symptoms since his pacemaker was replaced in August. The battery in his old one ran low and they replaced it with a Medtronic Adapta. His heart races with any little movement (even just walking a few feet) and he has trouble breathing, whereas with the old pacemaker (even with a low battery) he was fairly active with no problems. They haven't been able to find any cause yet and insist the problem is not the pacemaker because the 'computer' says it is functioning properly.
Sorry you haven't gotten any input from someone with experience. So far I have been spared needing a pacemaker...but I know others who have them and have read about them here...so here's what I think:
1) It appears your new pacemaker needs to be "adjusted"
2) I don't understand the old stable 80 bpm pace maker, didn't your heart rate go up when you were moving about, going up stairs say?
3) Are the new pacemaker variations exhibited when you are not changing your activity level, say all are at a true rest?
4) You symptoms must be diagnosed, but it sounds like you lower limit may be too low.
Talk with your doctor(s) and/or other technical support if there is such a thing. I do recall reading about people having their pacemaker adjusted.