The AD8232 is advertised as a single lead solution. What does it mean? Is this
a two, three, or more electrodes solution?
The AD8232 is a single lead solution since it amplifies and filters the
differential signal of two
electrodes (a single pair). A one lead solution requires two (sense) electrodes
as a minimum but a third electrode could also be used as an active (drive)
electrode to reduce the common mode interferences.
In summary, the AD8232 is compulsory as a single lead solution implementable
with two or optionally three electrodes.
Nothing stops you from using several AD8232s to build a multi-lead system for
ECG, EOG or EMG. You would need to be careful and average the RLD (right leg
drive) injected back to the body.