Pacemakers are really wonderful devices. They closely monitor the heart, and when the heart does not keep up to a certain number of heartbeats, it will send a tiny electrical
charge to make your heart beat for you (pacing). Common reasons pacemakers are used are when a person's heart beats very slowly, or when the heart has lost the ability to regulate its own beat.
When your mother is "pacing" 77% of the time, it means that the pacemaker is making her heart beat 77% of the time. Furthermore, her own heartbeat is coming through about 23% of the time. This is not at all abnormal, and it sounds like her pacemaker is functioning well.
The fact that she has a higher BP and some fluid in her legs has nothing to do with her pacemaker, but it may indicate that she has some CHF. Hopefully, hospice can help with that problem.