High grade AV block is a type of 2nd degree heart block with a conduction ratio of 3:1, 4:1 or higher. Although AV dissociation is evident in the ECG, Unlike 3rd degree heart block, there is still some relationship between the P waves and the QRS complexes, Indicating the heart block is not “complete”. High-grade AV block may result from either Mobitz I or Mobitz II AV block. In response to extremely slow ventricular rate, junctional escape beats are generated to maintain contraction of the ventricles.