Brief Answer:
Very rare, but it can happen.

Detailed Answer:
Hi dear,
Thanks for choosing HealthcareMagic for your query,
I am Dr Rishu Saxena, Cardiologist and will be answering your query.

As per your question chances of battery leakage in a pacemaker are very rare. However, infection in leads of pacemaker or inflammation in pacemaker pocket(space where pacemaker is implanted) can lead to severe tenderness in breast and surrounding area.

Only way to rule out the possibility is investigations-

-X ray chest AP(not PA) and Lateral view, to rule out pus or any fluid leakage from battery in pocket.

(However If pacemaker is MRI compatible, best would be to go for an MRI)-Gold standard test.
Pocket re-exploration can also be done by your interventionist to see if pacemaker and leads are normal or infected.

Blood routine and microscopy along with culture and sensitivity should be done, to rule out if any bacteria is causing inflammation.As a bacterial infection of pacemaker site increases the risk of infective endocarditis.

Though not asked yet, local infection of the site can also cause pain and tenderness, some times earliest symptom of Gynecomastia is increased breast tenderness in male. In adults hormonal changes can also be responsible for Mastitis.

Advice-

If all cutures and investigations are normal, you should go for physical examination by General surgeon.

Though rare yet leakage in battery of pacemaker is possible, and should be ruled out at earliest to prevent complications like Endocarditis.

Tab Ultracet(Tramadol/Acetaminophen) can be taken SOS for pain, don't take any NSAIDs.

In case you need any other information, I would be happy to help.

Thanks.

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