Sorry to see you are experiencing this. Must be very worrying.

When you say 'racing', what exactly is the rate, and is it steady or does it rise and fall, say with exertion, standing, or when you worry about it?

A pacemaker, depending on the type and for what purpose, should not allow your heart to race if it is of the type that can help to slow the heart. A pacemaker is meant to do what its name suggests....to pace the natural heart rhythm for the current demand or need. Some of them need to be set with a pacing process, and then they are to be monitored. If your HR exceeds 110 BPM or so, say 120-130, that is abnormal and you should seek help at the local ER. Certainly don't let a high rate go unchecked for more than 24 hours because that high a rate suggests that your ventricles are contracting that quickly.