Hi My Dad Had A Cardiac Quintuple Bypass In March

Hi my dad had a cardiac quintuple bypass in march of this year. For the pass month he has been having consistent hiccups that would last hours, disappear and come back later that day or the next day. He had an endoscopy 3 weeks ago; they found h pylori and mild acid reflux. He took the MEDS for h pylori and is on meds for the acid reflux. What would cause these consistent hiccups ? These are the meds he is currently taking:
Potassium Cl 10m eq
Metropolol tartinate 100 mg
Prevastatin 20 mg
Aspirin 81mg
Amlodipine besylate 10mg was 5mg
Hydroclorothiazide 25mg
Benazapril 40mg
Pantoprazole 40 mg