I have heard of a similar case like yours. The length becomes longer with age. It was finally diagnosed as some problem with the nerves linking to the heart that triggered the palpitation. He was cured after a minor surgery at heart centre..... The longest it lasts was actually about 15mins where the BP machine could not get any reading. I had already checked with 2 heart specialists in Bangkok and both told me they could not find out the cause, did all sorts of tests including EKG and also scan. ....