The enzyme is tyramine. I know because I spent about 50 years wondering why my heart rate and blood pressure would increase uncomfortably several hours after eating certain foods, particularly pizza. Eventually I learned that some people react this way to consuming too much of this enzyme. (Some consumption is OK, but on accumulating a 'high' quanitity the tyramine is not properly metabolised and the negative affects kick in.) The most obvious (and demonstrable) culprit for me is aged cheese (hence pizza!), even though I don't take any drugs that would inhibit tyramine metabolism. Search for tyramine rich food (mostly fermented foods, but also overripe bananas) and you can formulate a list of foods to try to avoid to see if it helps....
I only ran across one or two studies saying there was some enzyme in OVER ripe bananas that could affect heart rhythm, but I didn't save the links and can't seem to find them now. I also didn't have any other symptoms listed for banana allergies, or even having too much potassium.
(BTW I've also gone through multiple periods of PVCs, for which I could never discover a trigger, but who knows maybe they are subtly related.)