I appreciate you are concerned. Eight years is a long time for an ECG to change BUT the changes may or may not be real, and if real may or may not be important. I am afraid further conjecture will not help you.
If the CAA have told you you can get the tests done elsewhere there is nothing to stop you seeking out a cardiologist without further delay.
And it is highly likely that once this is sorted you will not need to go through all this again