A lot depends upon the specific model of pacemaker and the reason you have one.
Here is information I posted a number of years ago about a model of St. Jude Pacemaker:
New Information on Pacemakers
As you can see, it was tested to 7 atmospheres (about 200 feet) with no problems. It was not tested beyond that. On the other hand, I have seen information from other brands saying that they cannot go below 60 feet, but I suspect that limit was placed without testing.
The reason that you have a pacemaker becomes an issue. For some people, it is just there to keep the heart from going too slowly during basal metabolism. For others, it keeps them alive.
Putting those together, if you have a pacemaker that was tested at 7 atmospheres with no signs of problems and you only need it to keep your heart rate from going too low while you sleep, you probably have nothing to worry about. If you have a model that is limited to 60 feet and is necessary to keep you alive, you might want to reconsider your diving career.
It is interesting that it is being recommended for atrial fibrillation, since to my knowledge it does not really have an effect on that condition. What is its purpose?
In short, the person to talk to is your cardiologist. If he or she does not have expertise in diving, make a reference to
@Dr. Doug Ebersole. He is both a distinguished cardiologist and a technical diving instructor.