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. The QRS complexes represent an escape rhythm arising from the ventricle.

• 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

Management

• If symptomatic, standard ACLS guidelines for symptomatic bradycardia to include
  • Atropine 0.5mg IV q3-5min PRN total dose of 3mg
  • Transcutaneous pacing, followed by transvenous pacing
  • Dopamine IV consider for low BP 3mcg/kg/minute titrate up to 20 mcg/kg/minute
  • Dobutamine IV consider for heart failure at 5mcg/kg/minute titrate up to 20mcg/kg/minute if needed for HR and BP augmentation
• Treat underlying etiology
• Avoid AV nodal blocking agents (e.g. β-blockers)

Disposition

• Admission for pacemaker placement

See Also

• ECG (Main)