Atrioventricular block

Last updated: December 1, 2022

Summarytoggle arrow icon

Atrioventricular block (AV block) is characterized by an interrupted or delayed conduction between the atria and the ventricles. There are three degrees of AV block, categorized according to the extent of the delay or interruption. First-degree blocks are identifiable on ECG by a prolonged PR interval. Second-degree AV blocks are further divided into four subtypes: Mobitz type I (also called Wenckebach), Mobitz type II, 2:1 AV block, and high-grade AV block. In Mobitz type I blocks, a progressive prolongation of the PR interval culminates in a nonconducted P wave (“dropped beat”). Mobitz type II blocks generate dropped QRS complexes at regular intervals (e.g., 3:2, 4:3, or 5:4), often leading to bradycardia. A 2:1 AV block has a regular pattern in which every second atrial impulse is not conducted to the ventricles. In second-degree high-grade AV block, two or more consecutive P waves do not generate a ventricular response. A third-degree AV block, also known as complete heart block, involves the total interruption of the electrical impulse between the atria and ventricles. The complete absence of conduction results in a ventricular escape rhythm, whose rate depends on the level at which the escape rhythm is generated. AV blocks may be asymptomatic or cause symptoms of bradycardia. Depending on the heart rate, symptoms can be severe and include heart failure or syncope. Asymptomatic patients with first-degree and Mobitz type I blocks usually only require observation, whereas higher-degree blocks necessitate permanent pacemaker insertion.

Overviewtoggle arrow icon

See “Management approach to patients with AV block” for more information on investigations, monitoring, definitive treatment, and stabilization of unstable bradycardia.

Overview of atrioventricular blocks [1][2][3]
Type of AV block ECG findings Typical management

First-degree AV block

  • Low risk of progression to a higher degree heart block or sudden cardiac arrest
  • Asymptomatic patients require no treatment and can be followed-up as outpatients.
  • Consider an elective pacemaker for select patients.
Second-degree AV block Mobitz type I

2:1 AV block

  • Every second impulse from the atria is not conducted to the ventricles.
  • Regular rhythm
  • Narrow QRS complexes (< 0.12 s)
Mobitz type II

High-grade AV block

  • ≥ 2 consecutive impulses from the atria are not conducted to the ventricles.
  • Typically regular rhythm
  • Wide QRS complexes (> 0.12 s)
Third-degree AV block

Etiologytoggle arrow icon

See also “Causes of bradycardia.”

Etiology of atrioventricular blocks

Examples [2]

Structural heart disease

Pathophysiologytoggle arrow icon

Clinical featurestoggle arrow icon

First-degree AV blocktoggle arrow icon

Second-degree AV blocktoggle arrow icon

Mobitz type I (Wenckebach) [2]

First-degree and Mobitz type I second-degree AV blocks may be seen in healthy individuals, e.g., in athletes with increased vagal tone. Patients are often asymptomatic.

Mobitz type II [2]

  • Description
    • Single or intermittent nonconducted P waves without QRS complexes
    • The PR interval remains constant.
    • The conduction of atrial impulses to the ventricles typically follows a regular pattern, e.g.: [2]
      • 3:2 block: regular AV block with 3 atrial depolarizations but only 2 atrial impulses that reach the ventricles (heart rate = ⅔ SA node rate)
      • 4:3 block: regular AV block with 4 atrial depolarizations but only 3 atrial impulses that reach the ventricles (heart rate = ¾ SA node rate)
    • While 2:1 block follows a regular pattern, it cannot be classified as Mobitz type I or II and is classified separately (see “2:1 AV block”). [2]
  • Risk of progression to complete heart block: high (> 50%), as it is typically due to infranodal block (usually in the His-Purkinje system) [7]

Mobitz type II block can progress to third-degree heart block; therefore, all patients should be admitted for continuous cardiac monitoring and treatment.

Other variants

2:1 AV block [2]

High-grade AV block [2][7]

Third-degree AV block (complete heart block)toggle arrow icon

Differential diagnosestoggle arrow icon

Management of AV blockstoggle arrow icon


Management approach to patients with AV block [2]
Low-risk AV block High-risk AV block
Type of AV block
Unstable patients
Stable patients
  • Obtain cardiac imaging on all patients
    • Preferred initial test: TTE
    • Consider advanced cardiac imaging, e.g., MRI, CT, or TEE

Evaluation of underlying causes [2][13]

Management of low-risk AV block [2]

  • Patients on medication that can cause or exacerbate AV conduction
    • Monitor for progression with periodic ECGs.
    • Discontinue if patients have other preexisting conduction abnormalities. [13]

Indications for pacemaker placement [2]

Patients with an irreversible AV block and the following:

  • Infranodal block
  • Neuromuscular disease associated with AV block (known or suspected): refer to a specialist for possible pacemaker.
  • Certain symptomatic patients
    • Assess for correlation of symptoms using an ambulatory Holter monitor.
      • Permanent pacing is indicated if symptoms clearly correlate with AV block.
      • If symptoms do not correlate, continue monitoring as an outpatient

Management of high-risk AV block [2][13]

Acute management checklisttoggle arrow icon

All patients

Hemodynamically unstable patients (see “Unstable bradycardia”)

Hemodynamically stable patients

Referencestoggle arrow icon

  1. Heger JW, Niemann JT, Criley JM. Cardiology. Lippincott Williams & Wilkins ; 2004
  2. Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay. J Am Coll Cardiol. 2019; 74 (7): p.e51-e156.doi: 10.1016/j.jacc.2018.10.044 . | Open in Read by QxMD
  3. Tisdale JE, Chung MK, Campbell KB, et al. Drug-Induced Arrhythmias: A Scientific Statement From the American Heart Association.. Circulation. 2020; 142 (15): p.e214-e233.doi: 10.1161/CIR.0000000000000905 . | Open in Read by QxMD
  4. Olshansky B, Chung MK, Pogwizd SM, Goldschlager N. Arrhythmia Essentials E-Book. Elsevier Health Sciences ; 2016
  5. Aronow WS, Fleg JL, Rich MW. Tresch and Aronow's Cardiovascular Disease in the Elderly. CRC Press ; 2019
  6. Deedwania P, Raviele A. Clinical and Electrophysiologic Management of Syncope, an Issue of Cardiology Clinics. Elsevier Health Sciences ; 2015
  7. Ziad I; Mille J. Clinical Arrhythmology and Electrophysiology: A Companion to Braunwald's Heart Disease. Saunders ; 2008
  8. Cho SW, Kang YJ, Kim TH, et al. Primary Cardiac Lymphoma Presenting With Atrioventricular Block. Korean Circulation Journal. 2010; 40 (2): p.94.doi: 10.4070/kcj.2010.40.2.94 . | Open in Read by QxMD
  9. Sharma S, Drezner JA, Baggish A, et al. International recommendations for electrocardiographic interpretation in athletes. European Heart Journal. 2017; 39 (16): p.1466-1480.doi: 10.1093/eurheartj/ehw631 . | Open in Read by QxMD
  10. Eagle KA, Baliga RR. Practical Cardiology. Lippincott Williams & Wilkins ; 2008
  11. Abdullah A. ECG in Medical Practice. JP Medical Ltd ; 2014
  12. Dietel M, Suttorp N, Zeitz M, et al.. Harrisons Innere Medizin (2 Bände). ABW Wissenschaftsverlagsgesellschaft (2005) ; 2005
  13. Burri H, Dayal N. Acute management of bradycardia in the emergency setting. Cardiovascular Medicine. 2018; 21 (04): p.98-104.doi: 10.4414/cvm.2018.00554 . | Open in Read by QxMD
  14. Marino BS, Fine KS. Blueprints Pediatrics. Lippincott Williams & Wilkins ; 2009
  15. Jameson JL, Fauci AS, Kasper DL, Hauser SL, Longo DL, Loscalzo J. Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2). McGraw-Hill Education / Medical ; 2018
  16. Murphy JG, Lloyd MA. Mayo Clinic Cardiology Concise Textbook and Mayo Clinic Cardiology Board Review Questions & Answers. CRC Press ; 2007
  17. Kusumoto FM, Goldschlager NF. Cardiac Pacing for the Clinician. Springer Science & Business Media ; 2007
  18. Ferri FF. Ferri's Clinical Advisor 2012. Elsevier Health Sciences ; 2011
  19. Wittich, CM. Mayo Clinic Internal Medicine Board Review. Oxford University Press ; 2019
  20. Olshansky B, Chung MK, Pogwizd SM, Goldschlager N. Arrhythmia Essentials. Jones & Bartlett Publishers ; 2011

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