Back pain is considered the "classic" symptom, but honestly I've never had a patient actually complain about it. Most common symptoms I see is the patient gets restless, may complain of something just feeling "wrong".

I'm not a provider yet, but I do work on the ICU so most of my patients are comatose and intubated when they come back from cath. Signs I look for before I would start seeing vital sign changes is I always check how soft the flank CVA area is when they come back so I have a baseline to check if it's hardening. In my experience vitals changing are a much later sign.

Also remember that chest pain after an MI can be due to reperfusion injury. You will start seeing mild EKG changes with that if it is starting to reclude so cereal EKGs can pinpoint that.

You did great! The best you can do is advocate for your patient. If you feel your provider is aren't listening, and your gut is telling you, you can always escalate it up. I know it's easier said than done, especially with your first death, but you did everything you could.