Second Degree Type 1 (also known as Mobitz I or Wenckebach) is another type of AV block. It is characterized by progressive prolongation of the PR interval...followed by a blocked ⛔ P wave. What's a blocked P wave? When a P wave doesn't "get through" and there is no resulting QRS complex! Essentially, we see the atria fire, but the signal doesn't make it to the ventricles. This is also called a 'dropped' QRS complex. After the dropped QRS complex, the PR interval resets - and the cycle repeats!