Second degree AV block type I


Types of second degree AV block
  • Also known as a Mobitz I or Wenkebach AV block
  • Disturbance of atrial impulse conducting through the AV node
  • Considered more benign than Mobitz II as it is not associated with histological changes

Clinical Features

Differential Diagnosis

AV blocks




Type I A-V block (5:4) with acute inferior infarction
  • ECG with:
    • Progressive prolongation of PR interval on consecutive beats
    • Dropped QRS beat not conducted to ventricle after maximal PR prolongation
    • After dropped QRS complex, PR interval resets and again begins the cycle of progressive prolongation


  • Generally benign condition that does not require management after ruling out MI, drug toxicity, electrolyte imbalance and other unusual causes
  • Symptomatic patients can be treated with atropine or isoproterenol to transiently improve conduction or with transcutaneous or transvenous pacing if there is associated hypotension[1]


  • Generally outpatient
  • 2:1 block[2]
    • May be unable to determine if Type I or Type II
    • If so, assume type II and admit with cardiology consult

See Also

External Links


  1. Jones, W., and Napier, L. Atrioventricular block second-degree. Statpearls. Jan 2019
  2. Sovari AA et al. Second-Degree Atrioventricular Block Treatment & Management. eMedicine. Apr 28, 2014.