What is the management of heart block?

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Management of Heart Block

Heart block management depends on the type, location, and hemodynamic consequences, with temporary pacing indicated for symptomatic bradycardia unresponsive to medical therapy and permanent pacing for persistent high-grade AV block. 1

Types of Heart Block and Initial Assessment

Heart block refers to delayed or interrupted conduction of electrical impulses between the atria and ventricles. The classification includes:

  • First-degree AV block: PR interval >200 ms
  • Second-degree AV block:
    • Type I (Mobitz I/Wenckebach): Progressive PR prolongation until a beat is dropped
    • Type II (Mobitz II): Sudden dropped beats without PR prolongation
  • Third-degree (Complete) AV block: No conduction between atria and ventricles

Management Algorithm

First-degree AV Block

  • Generally requires no specific treatment 1
  • Monitor for progression to higher-grade block
  • Recent evidence suggests it may not always be benign and could progress to higher-grade block requiring pacemaker implantation in some patients 2

Second-degree AV Block

  • Type I (Mobitz I):

    • If asymptomatic: Observation only
    • If symptomatic or with hypotension: IV atropine 0.5-1 mg 1
    • If associated with inferior MI: Usually transient and responds to atropine 1
    • If fails to respond to atropine: Consider temporary pacing 1

  • Type II (Mobitz II):

    • Indication for temporary pacing regardless of symptoms 1
    • High risk of progression to complete heart block
    • Urgent angiography if associated with acute MI 1

Third-degree (Complete) AV Block

  • Temporary pacing is indicated for:

    • Symptomatic bradycardia 1
    • Hemodynamic instability 1
    • Ventricular rates <40 bpm 1
    • Failure to respond to atropine 1

  • Permanent pacing is indicated for:

    • Persistent advanced AV block after acute phase 1
    • Complete heart block with bilateral bundle branch block 1
    • Symptomatic AV block at any level 1

Specific Scenarios

Heart Block in Acute MI

  • Inferior MI:

    • Heart block often occurs at AV nodal level
    • Usually transient and responds to atropine
    • Initial dose: 0.3-0.5 mg IV, repeated up to total of 1.5-2.0 mg 1
    • Temporary pacing if unresponsive to atropine 1

  • Anterior MI:

    • Heart block often occurs at infra-Hisian level
    • Higher risk of progression to complete heart block
    • Prophylactic temporary pacing may be warranted with new bundle branch block or bifascicular block 1
    • Urgent revascularization indicated 1

Heart Block in Myocarditis

  • Temporary pacing for symptomatic heart block 1
  • Persistent AV blocks may require permanent pacing 1
  • Device selection should consider LV dysfunction and potential for recovery 1

Pharmacological Management

  • Atropine:

    • Mechanism: Competitive antagonism of muscarinic acetylcholine receptors 3
    • Dosage: 0.5-1 mg IV, may repeat to total of 1.5-2 mg 1
    • Indications: Symptomatic sinus bradycardia, Type I second-degree AV block with hypotension 1
    • Contraindications: Infranodal block (Type II second-degree or third-degree with wide QRS) 1
    • Caution: Doses <0.5 mg may paradoxically worsen bradycardia 1

  • Isoproterenol:

    • Consider when temporary pacing not immediately available 1
    • Titrate to heart rates >90 bpm

Pacing Approaches

Temporary Pacing

  • Transcutaneous pacing:

    • Immediate intervention for emergency situations
    • Bridge to transvenous pacing
    • Painful for conscious patients

  • Transvenous pacing:

    • More stable and reliable than transcutaneous
    • Access via internal/external jugular, subclavian, femoral, or brachial veins 1
    • Placement in right ventricular apex

Permanent Pacing

  • Indicated for:
    • Persistent complete heart block 1
    • Persistent advanced AV block at His-Purkinje level 1
    • Symptomatic AV block at any level 1
    • Transient advanced block with bundle branch block 1

Important Considerations and Pitfalls

  • Do not use atropine for infranodal blocks (Type II second-degree or third-degree with wide QRS) as it may worsen the block 1

  • Recognize reversible causes of heart block before permanent pacemaker implantation:

    • Medication effects (beta-blockers, calcium channel blockers, digoxin)
    • Electrolyte abnormalities
    • Acute ischemia
    • Infectious causes (Lyme disease, endocarditis) 4

  • New bundle branch block or bifascicular block in anterior MI indicates extensive infarction and high risk for complete heart block - consider prophylactic temporary pacing 1

  • Monitor patients with first-degree AV block as recent evidence suggests it may not be entirely benign and could progress to higher-grade block 5, 2

  • Urgent angiography with revascularization is indicated for heart block associated with acute MI in patients who have not received reperfusion therapy 1

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

4
Research

Reversible Causes of Atrioventricular Block.

Cardiac electrophysiology clinics, 2021

5
Research

First-degree AV block-an entirely benign finding or a potentially curable cause of cardiac disease?

Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc, 2013

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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