Third degree AV block

Background

Rhythm strip showing third degree AV block. Note that the P waves are not related to the QRS complexes (PP interval and QRS interval both constant), demonstrating that the atria are electrically disconnected from the ventricles.

• Also known as complete heart block
• No conduction through the AV node, causing the atria and ventricles beat completely independently from each other
• The ventricular beat is an escape rhythm anywhere from the AV node to the bundle-branches (normally slow, varying from 35 to 45 beats per minute)

Causes

• Congenital
• Acquired
  • Ischemia
  • Increased vagal tone
  • Hypothyroidism
  • Hyperkalemia
  • 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
• Differentiate from AV dissociation without complete heart block

AVD without CHB, courtesy of public access Amal Mattu EKG videos

Disposition

• Admission for pacemaker placement

See Also

• ECG (Main)