My daughter-in-law has come to visit from London. As she is a Dr specialising in neurology I have been picking her brains. I told her about our recent discussions about cake triggering arrhythmia and about preservatives. She does not think that preservatives would cause us trouble. She is adamant that bought cake contains huge amounts of sugar. A sugar rush produces the release of insulin. This results in energy going to blood and then being transported to muscles. And as the heart is a muscle - bingo - possible arrhythmia.
I apologise for my simplistic interpretation of her conclusions but hopefully you will find it helpful.