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 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[1]
- 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

References

Sovari AA et al. Second-Degree Atrioventricular Block Treatment & Management. eMedicine. Apr 28, 2014. http://emedicine.medscape.com/article/161919-treatment#showall.

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[Sovari-1] Sovari AA et al. Second-Degree Atrioventricular Block Treatment & Management. eMedicine. Apr 28, 2014. http://emedicine.medscape.com/article/161919-treatment#showall.