“…And then I would throw down and do v4R to check for right sided involvement.”
EMS providers love cautionary tales. Remember how we used to put a cervical collar on everyone and strap them to a backboard because “what if they have a c-spine injury?” Lead V4r is becoming the new cervical collar. It might be somewhat useful in a limited set of patients but it is often done out of fear of missing a right sided infarct or for reasons like “because so and so said to do it on all patients.” And just like c-collars v4r is probably not needed most of the time we use it. V4r is an example of the streetlight effect.
The streetlight effect is observational bias of looking for answers where it is easiest to look for answers. The name is derived from an old joke:
Late at night, a police officer finds a drunk [sic] man crawling around on his hands and knees under a streetlight. The drunk man tells the officer he’s looking for his wallet. When the officer asks if he’s sure this is where he dropped the wallet, the man replies that he thinks he more likely dropped it across the street. Then why are you looking over here? The befuddled officer asks. Because the light’s better here, explains the drunk man. 
When to do v4r:
- Is there an inferior wall STEMI and you are considering giving nitro? Is the inferior wall STEMI patient significantly bradycardic or tachycardic? Then don’t worry about v4R since you are not going to give nitro anyway. Is the inferior wall STEMI patient hypotensive? Then forget v4r because nitro is not indicated, you need to worry about fluids and perhaps something like an inotrope. If there is an inferior wall MI and the blood pressure is acceptable for nitrates then take a look at v4r.
- Are there ECG changes that suggest something might be going on and you should check out the right side? I’m talking nonspecific or non-diagnostic changes like ST segment depression or elevation, T wave inversions, etc.
- Did the patient get hit in the right side of the chest and you are looking for signs of a right ventricular cardiac contusion? It seems that at least one study has been done on this and the results of looking at v4r to see if there was a right sided cardiac contusion were not diagnostically helpful. 
- You have a patient with dextrocardia.
That is it. No one else is really going to benefit from a right sided ECG. The pneumonia patient at the nursing home who has a normal 12 lead doesn’t need you to throw down and put more stickers on her chest. Focus on what matters, focus on what will change your treatments and the outcomes for your patients.