It's not easy to generalise when talking about ECG electrode positioning (number of leads, and all the rest). We need to be a bit more specific.
For a start, consider monitoring
versus diagnostic examinations (
eg, with an electrocardiograph).
Some folk get confused between ECG leads as per Dr.Einthoven, and ECG leads as in physical colour-coded leads! Whilst obviously related, as we know these are not actually the same things!
But (as has already been mentioned) all ECG equipment uses a
differential amplifier.
