Yes it was probably a result of reducing your dose
A 'racing' heart rate is something I get when my oestrogen level is low - the first time I had it, it was also accompanied by feeling faint/dizzy. Once any cardiac related issue was ruled out my HRT dose was increased. Recently I had a return of the high heart rate despite being on high dose patch but it looks like it was due to poor absorption.
Maybe stick with your 2 pumps