It could also be as simple as his heart remodelling itself which can take several months. This is not uncommon after the heart has been adapting to work harder for years. I know someone who had an aortic valve replaced and during exercise and after exercise, it went nuts because it was so used to working so hard. After about 6 months his heart was back to normal and he was able to stop the BP medication.
Sorry, but there's really no way to know what's going on without letting the doctor evaluate all the possibilities. It could be something as simple as getting your husband's medications properly adjusted. There could be an issue with his activity level changing, as he recovers from the surgery, and maybe he needs different meds or different dosing. I know next to nothing about pacemakers, so I'm going to let others speak to that. If the blood pressure problem persists, your husband may need to have an echocardiogram to check on the functioning of the aortic valve, just to make sure it isn't leaking. Hopefully, his hypertension has nothing to do with the newly replaced valve, and certainly there are numerous other possibilities to rule out and interventions that can be tried. Good luck.