TopsDrop pretty much nailed it. Always assess your patient, not just the monitor. Is your patient hemodynamically stable or not? A 1st degree block is pretty insignificant, in my opinion, and all of the docs and cardiologists I have worked with would be pretty ticked if you called them at 0300 just to notify them of that, unless your patient was experiencing symptoms, which is very rare. Many of the cardiac medications (beta blockers, calcium channel blockers, cardiac glycosides) will cause a 1st degree block due to the slowing of AV conduction. Treatment generally isn't warranted unless the block is associated with an MI.
As TopsDrop mentioned, BBBs isn't really within the scope of an RN's practice...but the easiest way to differentiate between them is the "turn signal theory." Imagine a turn signal lever and look at V1. If it's going down (left), it's a LBBB. If it's going up (right), it's a RBBB. Very easy and simple trick.
Now, about the 5-lead monitoring system. That 5h lead (V) lead can be placed in any of the V lead positions (V1-V6):
V1-V2 = septal
V3-V4 = anterior
V5-V6 = lateral
I've seen so many people (whether it be nurses, CNAs, EMTs...) just slap that V lead smack dab in the middle of the chest. That's incorrect. That lead placement is the same as if you were doing a 12-lead EKG. So for example, if you wanted to monitor V6, that electrode would go on the 5th ICS, mid-axillary line.
As for which lead to monitor, there was a practice alert put out by the AACN about the "ST segment fingerprint." This is the pattern of ST segment elevation and/or depression unique to a particular patient based on the anatomic site of coronary occlusion. This can be obtained during a STEMI or PCI. If the fingerprint is not known, AACN recommends monitoring leads III and V3 (inferior, anterior), which corresponds with the LAD and RCA. Here is a link to the practice alert powerpoint: http://www.readinghealth.org/doc/Pag...geID=DOC015798
Most places have lead II as the standard because it is a bipolar lead and supposedly the most useful for detecting cardiac dysrhythmias as it lies close to the cardiac axis (the overall direction of cardiac movement) and allows the best view of P and R waves.
Hope this helps.