Comment: The most important question in these situations is the location of the block – that is, is this proximal AV block in the AV node, or distal block in the His Purkinje  system.  Distal block implies severe conduction system disease with a higher risk of complete AV block and a fragile or absent escape with life threatening bradycardia.  On the other hand, with proximal block, there is usually a faster escape rhythm, and this rhythm is responsive to autonomic modification and will be faster with vagal withdrawal (eg: atropine) or sympathetic stimulation (exercise). Clues that this is distal block include the presence of distal conduction system disease (bifascicular block), the normal PR interval on the conducted beats, the absence of progressive PR prolongation preceding the block, and the presence of sinus tachycardia all without prolongation of the PP intervals just preceding the block.  All of these features strongly suggest this is block in the His Purkinje system