Hello - I haven't been on the site for a while because caretaking for my husband has been very busy and challenging. I would like some feedback on Keytruda side effects if there's anyone here who can share.

My husband was diagnosed almost four years ago with a "Cancer of Unknown Primary" that they have now opted to call Lung Cancer. The cancer is behaving much like lung and the main tumor first appeared in his lung and lymph node central in his chest. Multiple biopsies were inconclusive as to type so we've had to proceed with 'possible lung'. The cancer remained stable for three years and then spread to his hip and spine and grew around his bronchi, cutting off his ability to breath easily (he also has COPD). We used marijuana up to this June and it was holding things at bay or they simply weren't growing. In June we did five rounds of radiation to the center of his chest (it worked with few side effects). We followed with chemo and immunotherapy (Keytruda). The chemo was pretty brutal for him with multiple expected and some unexpected side effects (nausea, diarrhea, fatigue, etc). The uncommon side effects were blood in the urine and fainting. When we switched to maintenance therapy with Alimpta and Keytruda my husband actually got sicker, with more side effects. We have stopped treatment until March when we'll repeat a PET scan. We've had to stop because our last PET showed the cancer has now spread to his adrenal glands, a new tumor has appeared in his lung and an additional lymph node is now showing cancer. So, all in all, it worked for about 3 months and then stopped working and he's been quite ill for the past 11 weeks.
Here is my question - My husband has developed a heart problem which is being tested with a 30 day heart monitor. Oddly, I was the one who questioned his heart function (not supportive care, not oncology, etc). He had a pulse of 180 for two days and now has either Afib or Tachycardia or??? He had no serious heart problems previously. My research shows that Immunotherapy (specifically Keytruda) can put some people at risk for serious heart disease. I'm wondering how to broach the subject with oncology, as they are acting like it's no big deal.
After all we've been through with the doctors being unable to diagnose or treat the cancer and now putting him on a cancer treatment that isn't working and really had no upside and now we are fighting a heart problem...........what to do? Has anyone else experienced heart issues on immunotherapy and does anyone know a good resource to see if the heart condition might improve once the immuno has left his system or if this is now another permenant problem

After weeks of my reaching out to doctors about his not feeling well, it was me who called and got cardiology involved and it only took 12 hours for the cardiologist to realize my husband had a serious heart issue. I'm lost all faith in doctors but since I'm not one (only play one on TV), I need them and I'm not sure how to proceed.
Sorry this is so long. I appreciate anyone who gets to the end of it (ha ha) and has any advice or information that might help me navigate this latest debacle.

Hugs to all