How should atrioventricular (AV) block be managed in the emergency department?

Management of Atrioventricular Block in the Emergency Department

For symptomatic AV block with hemodynamic compromise, immediately administer atropine 0.5–1 mg IV while simultaneously preparing transcutaneous pacing pads; do not delay pacing to give multiple atropine doses in unstable patients. 1

Immediate Assessment and Stabilization

• Establish continuous cardiac monitoring, IV access, and supplemental oxygen while assessing for signs of hemodynamic instability—including altered mental status, ischemic chest pain, acute heart failure, hypotension (systolic BP <80–90 mmHg), syncope, or shock 1, 2

• Obtain a 12-lead ECG immediately to confirm the degree of AV block, determine QRS morphology (narrow vs. wide), and evaluate for acute myocardial infarction 1

• Identify the anatomic level of block: narrow-QRS escape rhythms suggest AV-nodal level block (more stable), while wide-QRS escape rhythms indicate infranodal (His-Purkinje) block that may progress rapidly and unpredictably 1

Systematic Evaluation for Reversible Causes

Before proceeding to definitive pacing, rule out reversible etiologies 1, 3:

• Acute myocardial infarction (especially inferior MI with vagally-mediated block)
• Drug toxicity: β-blockers, calcium-channel blockers, digoxin, amiodarone
• Electrolyte disturbances: hyperkalemia, hypomagnesemia
• Infectious causes: Lyme carditis, myocarditis, infectious endocarditis
• Infiltrative diseases: sarcoidosis, amyloidosis
• Thyroid disorders: hypothyroidism or hyperthyroidism

Pharmacologic Management Algorithm

First-Line: Atropine (for AV-Nodal Block)

• Administer atropine 0.5–1 mg IV bolus immediately for symptomatic bradycardia, repeating every 3–5 minutes up to a maximum total dose of 3 mg 4, 1, 2

• Critical warning: Doses <0.5 mg may paradoxically worsen bradycardia via central vagal stimulation and must be avoided 4, 1, 2

• Atropine is effective for: sinus bradycardia, first-degree AV block, and Mobitz I (Wenckebach) second-degree AV block occurring at the AV node level 4, 1

• Atropine is INEFFECTIVE and contraindicated for: Mobitz II second-degree AV block, third-degree AV block with wide QRS complex (infranodal block), and anterior MI with new bundle branch block 4, 1

Second-Line: Chronotropic Infusions (When Atropine Fails)

• Dopamine: Start at 5–10 mcg/kg/min IV infusion, titrate every 2–5 minutes to hemodynamic response, maximum 20 mcg/kg/min 1, 2, 5

• Epinephrine: Initiate at 2–10 mcg/min IV infusion; preferred when severe hypotension requires combined chronotropic and inotropic support 1, 2, 5

• Isoproterenol: Consider 1–20 mcg/min IV infusion for pure chronotropic effect without vasoconstriction, particularly useful when coronary ischemia is unlikely 1

Third-Line: Transcutaneous Pacing

• Apply transcutaneous pacing immediately for hemodynamically unstable patients who do not respond to atropine—this is a Class IIa recommendation 4, 1, 2

• Transcutaneous pacing serves as a bridge to transvenous pacing and is particularly advantageous in patients receiving thrombolytics, as it avoids vascular access complications 4, 1

• Do not postpone transcutaneous pacing to administer additional atropine doses in unstable patients 1

Specific AV Block Management by Type

Mobitz Type II Second-Degree AV Block

• Class II indication for transcutaneous standby pacing with patches applied and system ready for immediate activation 4

• High-risk patients likely to require pacing should receive a temporary transvenous pacemaker due to the significant pain associated with transcutaneous pacing 4

• Atropine is ineffective and should not delay pacing 4, 6

Third-Degree (Complete) AV Block

• Symptomatic third-degree AV block at any level is a Class I indication for temporary pacing 4, 1

• For narrow-QRS escape rhythm (AV-nodal level): trial atropine first, but prepare for pacing if no response 1

• For wide-QRS escape rhythm (infranodal): bypass atropine and proceed directly to transcutaneous pacing while preparing for transvenous access 1, 7

• Escape rates <40 bpm or documented asystole ≥3 seconds mandate urgent pacing regardless of symptoms 1, 8

Transvenous Pacing Indications

Prepare for transvenous pacing access (internal jugular, subclavian, or femoral vein) for 4:

• Class Ia indications:

  • New or indeterminate RBBB with LAFB or LPFB
  • RBBB with first-degree AV block
  • New or indeterminate LBBB
  • Mobitz II second-degree AV block
  • Recurrent sinus pauses >3 seconds unresponsive to atropine

• For anticipated prolonged temporary pacing, an externalized permanent active-fixation lead is preferred over standard passive-fixation temporary leads 1

Post-Myocardial Infarction Considerations

• Inferior MI-associated AV block is often vagally mediated or due to transient AV-nodal ischemia and may respond to atropine or aminophylline 4, 1

• Anterior MI with new bundle branch block suggests infranodal pathology; atropine is contraindicated and pacing is required 1

• A mandatory observation period is required before deciding on permanent pacing because the block may be transient 1

• Permanent pacing is warranted if Mobitz II, high-grade AV block, or infranodal third-degree AV block persists after the observation period 4, 1

Critical Pitfalls to Avoid

• Do not use atropine for infranodal (wide-QRS) blocks—it wastes critical time and is ineffective 4, 1

• Do not delay transcutaneous pacing in hemodynamically unstable patients while giving multiple atropine doses 1, 2

• Do not exceed atropine 3 mg total dose; higher doses may cause central anticholinergic syndrome (confusion, agitation, hallucinations) 2

• Do not assume third-degree AV block is benign based on age alone—definitive evaluation and treatment are required regardless of patient age 1

• In acute coronary ischemia or MI, increasing heart rate with any chronotropic agent (atropine, dopamine, epinephrine) may worsen ischemia or enlarge infarct size—titrate to minimally effective heart rate (~60 bpm) 4, 1

• In heart transplant patients without autonomic reinnervation, atropine may cause paradoxical high-degree AV block; use epinephrine instead 1, 2

Disposition and Definitive Management

• Patients requiring transcutaneous pacing or chronotropic infusions must be admitted to an intensive care unit with continuous cardiac monitoring 2

• Arrange urgent cardiology consultation for transvenous pacing if transcutaneous pacing is ineffective or prolonged support is needed 1, 7

• Permanent pacemaker implantation is the definitive treatment for third-degree AV block after reversible causes have been excluded and is a Class I indication for symptomatic bradycardia, escape rate <40 bpm, or documented asystole ≥3 seconds 1, 8