Hi Maree,
Im glad to hear your Cardiologist has looked into this for you. The EKG changes you had mentioned are not normal and deserve further evaluation. Having said that... Our hearts are as unique as we are and our idiosyncrisies that make us individuals. If it were me, I would be reassured by the doctors words and continue to exercise for now despite any palpitations. I would just pay attention over the years as to whether these palpitations change and cause any chest pain, nausea, shortness of breat, etc. if the palpitations started to cause any new symptoms, I would contact my cardiologist office and schedule a follow up appoinment.
Just my two cents, hope it helps.