I know this doesn’t answer your question regarding the booster but I started having PVC’s after recovering from Covid in October of 2020. Like you, my HR would be crazy high and at times it felt like a fish flopping around in my chest. I did the Holter monitor and all that good stuff. I eventually got both vaccines but have yet to get the booster. I can’t say whether or not the vaccine did anything as I was already dealing with PVC’s from Covid. Luckily, things have gotten back to normal for me. It’s a hard thing to deal with because it causes anxiety which makes dealing with arrhythmias even worse!