Second degree AV block type I

Background

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

• Usually asymptomatic
• Those who are symptomatic may present with:
  • Lightheadedness/dizziness
  • Presyncope or syncope

Differential Diagnosis

AV blocks

• First degree AV block
• Second degree
  • Second degree AV block type I (Wenkebach)
  • Second degree AV block type II
• Third degree AV block
• AV dissociation without complete heart block

Evaluation

Workup

• ECG

Diagnosis

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

Management

• 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

Disposition

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

See Also

• AV blocks