My 72 Year Old Husband Had A Pacemaker Implanted 6

My 72 year old husband had a pacemaker implanted 6 months ago (although they were unable to insert a 2nd lead due to previous scarring in one chamber of the heart) and subsequently 3 coronary stents. He is feeling fine although can't get his heart rate up during exercise (swimming). My question is why would his breathing at night be highly irregular ?. Gasping, Exhaling very strongly, almost panting at times. At other times, it is regular & peaceful. It does not wake him, but it is loud enough to wake me.