My mother is wheelchair bound and lives 70 miles away from the cardiologist. Is there some way to get transportation for her?

I agree to avoid the trip if possible, but if not there should be some kind of patient transfer services available, even in a rural area. The services aren't cheap though, I paid around $300 for a wheelchair van to take mom to an appointment around 10 years ago... stretcher service will be much more.

My mom did see her cardiologist once a year although her pacemaker was checked by a separate doctors office. He specialized in pacemakers. Hers was not one that could be checked over the phone. She lived three hours away.
However the manufacturer, for example, Boston Scientific, had reps that could come to a facility to check it.
If the primary reason you are going is for a pacemaker check try this. Get the information on her pacemaker (if you don’t already have it) and call them to see if you can arrange for an on-site check.
Otherwise, I think I would check with the NH dr to see what she recommends for health care going forward. 

Isn't she on a remote monitoring system?

My mother lived in a NH and NEVER saw the cardiologist after her pacemaker was inserted.

What does the doctor say are the consequences of her not being seen?