You won't die from palpitations. Palpitations are simply an awareness of ones own heart beating. They are generally always a benign variation of normal and do not generally represent pathology. If blood work, echo and an 24 ECG haven't detected any abnormalities then there is nothing to worry about. The beta blocker
may help reduce them.
is a problem then your GP can refer you for CBT. The problem with palpitations is the more you worry about them, the worse they are and it can be a catch 22 situation. Things like stress
and caffeine do make them worse.
Some evidence suggests that taking magnesium
(with either supplements or increasing it in the diet), helps palpitations- you could give it a try, just be careful not to over do it though.
I can tell by the tone of your question that you are anxious, this is what is causing your palpitations and/or is making them worse. You have to accept this and realise that until you calm down and accept they are nothing to worry about, nothing is going to improve. You have had tests which have failed to reveal any pathology.