This was an AVB example provided by my training captain in a class that he taught.
Most people will call this a 3:1 2nd degree type 2, or Mobitz 2.
Lets have a look:
First measure your PP interval, and make sure they "march out"
Okay, seems like the PP is pretty consistent. There are 3 p-waves for every R -wave; this favors third degree AV block. Now lets check the RR-interval.
As expected the RR-interval is consistent. This is also highly favorable of third degree AVB, but isn't conclusive. We have to prove complete atrioventricular(AV) disassociation. We do this by measuring our PR-intervals.
If you measure the first PR-interval against the last PR-interval you will see that they do not match. This leads to a couple conclusions.
Either this is a 3rd degree AVB and the atrial rate just happened to be almost exactly 3 times as much as the ventricular rate. If this is true, further monitoring will show the AV disassociation clearer, since the PR-interval is varying.
Or, this is a high grade transient AVB. Meaning this is the end of a Mobitz 2, as it becomes a 3rd degree AVB. I call these Mobitz 3s.
I personally think this is a simple 3rd degree AVB and coincidence confused the masses. If all else fails, and the pattern continues, call it a 3:1 AVB.
ps. If you don't have a fancy set of calipers, a piece of paper works fine. Just draw lines on the pice of paper to measure out your intervals and see if they match.