Another possible factor could be the fact that doctors tend to make more mistakes during operations on Fridays compared to start of week.
STEMI centers (this is picked up by EMS and these ambulances are redirected to appropriate centers) have 24/7 cath lab coverage and any major one will have an ER bypass even during afterhours to expedite care.
In fact more and more hospitals (and all the major ones) announce a “Code STEMI” overhead either when the ambulance is dispatched or as soon as the ECG showing ST elevations is discovered in triage/ER to activate the team and reduce door-to-balloon time.
I maintain enough competence to know when it looks like it could be critical so I can call for help, but realistically that's happening anyway as soon as someone gets unstable as I haven't resuscitated someone in years.
I haven't looked at a real patient's ECG in probably 7 years now. If you were the patient, would you even want me to? I'd rather just do the smart and safe thing, call for help.
No subspecialist (or even specialist) can maintain competence in all areas of medicine, it's hard enough keeping up my general radiology skills. It's a good thing none of us practice in silos by definition.