Abnormal ECG

Recently my Doctor requested I have an ECG.
The result was abnormal and caused some alarm and I was told to go straight to hospital, where I stayed for 24 hours. I had various tests which all were OK.
I had been on very high doses of Prednisolone and had reduced to
3mg. I increased my dose to 6mg after returning home as I wondered if the reduction to 3mg was the reason I experienced the heart problem.
On my doctor’s suggestion I increased my Prednisolone to 10mg but my usual symptoms - fatigue, breathlessness, eyes closing and muscle weaknesss - haven't improved. I would be pleased to hear if anyone has experienced similar heart problems.