In big-city Canada, patients with heart attack symptoms will usually have an ECG done by paramedics before arriving.
In the US, this has quite survival advantage.
https://heart.bmj.com/content/100/12/944
I don’t know if it’s standard practice to do another upon arrival, but it is redundant and should probably take a back seat to activating other processes that need to happen.
It also helps send them to the most appropriate facility.
If you are having chest pain, call 911. If you mention "chest pain" to them, you hear a beep in the background, and everything else is a machine.
In my locale, the paramedics carry a portable EKG. If they decide to take you for a ride, they have an EKG machine in the ambulance that's networked to the hospital, and a cardiologist is now on your team. When you arrive, you get wheeled into a special room where an entire heart attack team is standing there, waiting for you.
At that point they do another EKG, and as I understand it, their machine has a larger number of electrodes, so they can get more detailed information from it. The patient is never off an EKG at this point, and it's not a discrete step, but is a continuous monitor.
A blood test will confirm the presence of an enzyme that's produced if the heart muscle is stressed. This is a rapid test, the lab is ready and waiting for the sample.
So, the second EKG isn't really consuming time, since other stuff is happening concurrently, and they need the EKG running continuously to make minute by minute decisions. Regardless of what happens, you're on the EKG until you go home.
I don't know if rural or poorer locations have less sophisticated processes.
If you are having chest pain, call 911.