What Causes Chest Tightness While Having Pacemaker?

my dad is 72. had a pacemaker installed 12.6 years back. recently he is suffering from severe chest tightness. angiogram done 7 months back, no obstructions observed. the pacemaker company is stating that the battery life is still 5-6 months to go, so they won t replace it. The Doc found TMT report ok. My Query: What test needs to be done further more? is the pain accountable to low battery of PM?