Non-conducted P waves represent either a 2nd or 3rd degree AV block. Mobitz 1 can be ruled out as there is no progressive lengthening of the PR interval before the dropped beats, thus leaving Mobitz 2 and 3rd degree as our only possibilities. It’s tempting to see so many non-conducted P waves and jump intellectually to a 3rd degree block. However, closer inspection reveals that when there are QRS complexes, they have a consistent PR interval. A 3rd degree would not have such as the ventricles are being depolarized independently of electrical activity above the AV node (i.e., P waves). The narrow QRS complexes SUGGEST a second degree block; however, if the ventricular escape rhythm in a 3rd degree block originates high enough in the conduction system a narrow complex QRS complex is possible. The PR interval in this case tells the tale. This is a Mobitz 2.