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    Atrioventricular Blocks – First, Second and Third Degree


    Last Updated Jun 05, 2022
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    By Joe Finkler, Manjot Kahlon


    Atrioventricular (AV) block:

    • Conduction block between the atrium and ventricles at the level of the AV node and/or Bundle of His.
    • First and second-degree AV blocks represent partial impairment of conduction.
    • Third degree AV blocks represent complete impairment of conduction.
    • Top three reversible causes: Drugs, Ischemia, Electrolytes.

    Diagnostic Process

    Clinical manifestations:

    • May be asymptomatic or symptomatic (weakness, dizziness, fatigue, dyspnea, syncope) or manifest as heart failure secondary to bradycardia.
    • First degree AV block have higher probability of developing atrial fibrillation.
    • Mobitz Type II AV block can progress to third degree AV block and asystole.
    • Third degree AV block is a risk factor for asystole and sudden cardiac death.

    ECG characteristics:

    Recommended Treatment

    Criteria for admission:

    • Newly acquired AV block or symptomatic advanced patients should be admitted to the hospital.

    General recommendations:

    • Look for reversible causes of AV block.
    • Top 3 = Drugs (including overdose); ischemia, and hyperkalemia.
    • 4 drugs that typically cause bradycardia in overdose = Calcium channel blockers, Beta blockers, Digoxin and Clonidine.
    • Consider also organophosphate exposure, opioids, and amiodarone.
    • Treatment summary:
      • Markedly symptomatic or hemodynamically unstable patients with second- or third-degree block should be started on drugs/fluids and temporary transcutaneous pacing until a reversible cause is identified or permanent pacemaker is placed.
      • Bradycardia Emergency Clinical Summary

    Block-specific recommendations:

    • Drugs used

    Quality Of Evidence?


    These recommendations are based on the ACLS guidelines, weak observational data and expert opinion. There is a lack of randomized controlled trials for medications to treat AV blocks.


    Related Information


    Reference List

    1. Walls R., Hockerberger R., & Gausche-Hill M. (eds) Rosen’s Emergency Medicine: Concepts and Clinical Practice. 9th ed. Philadelphia, PA: Elsevier; 2018.

    2. Sauer, W.H. (2022). Etiology of atrioventricular block. UptoDate. Retrieved April 2nd, 2022 from https://www.uptodate.com/contents/etiology-of-atrioventricular-block

    3. Sauer, W.H. (2022). Second-degree atrioventricular block: Mobitz type II. UptoDate. Retrieved April 2nd, 2022 from https://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-ii

    4. Sauer, W.H. (2022). Third-degree (complete) atrioventricular block. UptoDate. Retrieved April 2nd, 2022 from https://www.uptodate.com/contents/third-degree-complete-atrioventricular-block

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