Mobitz I (wenckebach) = PR interval progressively longer until a QRS complex is dropped, then the cycle starts over (long, longer, longest, dropped - then you've got a wenchebach). P-P and R-R are irregular.
Mobitz II = intermittent non-conducted P waves... So, I BELIEVE that P-P is regular, while the R-R is irregular. Bad.
Third degree = P-P regular, R-R regular, but the PR interval changes - no association between the P wave and the QRS complex. Really bad.
A first degree block has a PR interval >0.20. Pretty much benign but in rare cases will progress to a higher block.
Long, longer, drop.....you have a Wenckebach (Mobitz I). The PR interval gets longer and longer and then you have a missed beat.
If your P's don't always go through, then you have a Mobitz II. Here, the PR interval stays the same, then you will see a P wave without a QRS.
If your P's and Q's don't agree, you've got yourself a Third Degree. Also known as AV-dissocation. The P waves and QRS complexes are doing their own thing - think of the P's and QRS complexes as "no longer being married to each other."
Bundle branch blocks have a widened QRS complex, but you really need to do a 12-lead to confirm if it is a left or right BBB.