Third degree AV block

Background

Third degree AV block or complete heart block is a disorder in which there is no conduction through the AV node. This result is escape rhythm anywhere from the AV node to the bundle-branches. Escape rhythm is slow and varies from 35 to 45 beats per minute.

• Atria and ventricles beat independently from each other

Causes

• Congenital
• Acquired
  • Ischemia
  • Drugs
  • Structural heart disease

Clinical Features

• Dizziness
• Syncope
• Hypotension

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

• No atrial impulses are conducted
  • P waves normal and regular P-P intervals unrelated to slower regular R-R intervals
  • QRS narrow if block above bundle of His
  • QRS wide if block below bundle of His
  • PR variable

Management

• Pacemaker placement

Disposition

• Admission

See Also

• ECG (Basics)