As far as placement is concerned, try not to put the red and green leads over bones such has the clavicle, acromion or coracoid processes. Likewise for the black and white patches being over the iliac crest or rib cage. Signals are degraded when the patches are over bone. With trauma, I've even put the limb leads on the pt's back.
As for the V lead, it SHOULD be able to be placed anywhere the precordial leads would go in a 12 lead EKG and it's prudent to consider placing it where it'll do the most good. For example, if a pt is admitted with an MI showing an infarct on leads V4 and V5 on the 12 lead, I'd probably put the V monitoring lead on V3 or V6 just to watch for any extension of the infarct. Placing it adjacent to where there's a problem helps you watch for any changes.
If the pt is hemodynamically stable, then V1 is usually where I put it.
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