Premature Artial Contractions (PAC's) or PVC's before or after the exercise are dangerous?

I read somewhere that before or after the exercise if palpitations happens they increase a chance of sudden death. Although I didn't find a lot of sources that said this. I have Generalized Anxiety Disorder and minimal mitral valve prolapse ,but sometimes when I don't feel anxious they happen! Even though I avoid any stimulants such as caffeine etc.. I had holter test and echo done and they found PAC I m still worried especially when they say that if you have a valve disease such as MVP PAC's and PVC's are dangerous.