Did your doctor say it was the vaccine that caused this? You could have had AFib for months without knowing it.
First, this is a huge correlation vs. causation thing.
Second, a protein antibody causing AFib (a condition that is pretty common by the way) is like a million times less likely than your habits when it comes to age, smoking, alcohol, weight, diet, exercise, stress levels, caffeine intake, family history, etc. etc. etc. Any decent cardiologist will be able to at least narrow down potential causes.
Third, as an FYI, they've been doing studies on vaccines causing AFib for years and years. This is because AFib is pretty common so naturally throughout the past 20 years or so when people get a vaccine then AFib they think it's the vaccine that caused it. Anthrax, Flu, Hep B, Polio, etc. have all had very specific studies done to see if that vaccine caused AFib in people who got vaccinated. The stats overwhelmingly have said no.
Sucks you have AFib. Take the blood thinners, cut back on the caffeine, quit smoking if you do, etc.