Hey there. My experience with intracardiac atrial ECGs are purely with using epicardial wires, so if you are using them in another sense this response may not be helpful.
We use 'atriagrams' (I don't think this is the technical term but what we use ubiquitously on our unit) usually to differentiate atrial flutter/fib , junctional, or NSR. Using the now amplified atrial signal, you can more clearly see atrial activity, if any, and how that correlated with the patients intrinsic ventricular response. I have attached an image which shows how it amplifies the atrial activity in atrial fibrillation and you can see the larger disorganized fib waves and differentiate it from a irregular flutter. Although this was easily seen as flutter in the top rhythm, this technique is useful when the f waves are not as present in the standard ECG.
As for the technique, these atriagrams use the principle of Einthoven's triangle to replace the right arm lead with an atrial epicardial wire. Lead one makes up the electrical activity going from the right arm to the left arm so by replacing the right arm lead (White) with the atrial wire you are kinda 'zooming in' on the atrial activity. You can 'zoom in' further by also replacing the left arm (black) lead with the second atrial wire however I find that this is usually excessive.
So the down and dirty, put your monitor in lead I, touch the metal of one of the epicardial wires to the metal of the white ECG lead, review the monitor and assess for the presence of now amplified atrial activity. If still unsure, you may additionally attach the second atrial lead to the black ECG lead.
I will try to find more examples from my own clinical practice and update the post. *EDIT* I have found more examples and can send them to you if you would like.