This may be a stupid question, but one of my patients HR showed in the low 20, however 1 of the 5 leads was off. Is it a true heart rate or not?
No. Just like it can show a rhythm other than what the heart may actually be in. Sometimes a-fib or other crazy rhythms are shown when leads are too close together too. For accuracy all the leads need to be on and properly placed.
Did you assess your patient? What did they look like? This is why you need to assess your patient and treat, not assess and treat the monitor. I would expect a patient with a HR of 20 to look very sick because they aren't perfusing very well with that rhythm. In regards to the leads, everyone gave good advice here.