Rosen & Barkin's 5-Minute Emergency Medicine Consult (88 page)

DIAGNOSIS

• 1st-degree AV block:
  
  • Asymptomatic
    
• Type I 2nd-degree AV block:
  
  • Pulse irregularities
    
• Type II 2nd-degree AV block and 3rd-degree block:
  
  • Exercise intolerance
    
  • Palpitations
    
  • Chest pain
    
  • Presyncope/syncope
    
  • Altered mental status
    
  • Dyspnea, orthopnea
    

• 1st-degree AV block:
  
  • No discrete physical exam findings
    
• Type I 2nd-degree AV block:
  
  • Regularly irregular pulse
    
• Type II 2nd-degree AV block and 3rd-degree block:
  
  • Irregular pulse
    
  • Hypotension
    
  • Mental status changes
    
  • Signs of heart failure:
    
    • Rales
      
    • Cyanosis
      
    • Jugular venous distention
      

• A 12-lead EKG to determine the type of block and identify evidence of infarction
  
• 1st-degree AV block:
  
  • PR interval >0.20 sec
    
• 2nd-degree AV block:
  
  • Type I: Progressive prolongation of PR interval until there is a nonconducted P-wave and a dropped QRS complex; occurs in repeated cycles; QRS is usually narrow.
    
  • Type II: PR interval remains constant; atrial impulses are not conducted intermittently, giving the appearance of an occasionally dropped ventricular beat; QRS may be prolonged depending on the level of the lesion.
    
• 3rd-degree AV block:
  
  • P-waves occur at consistent intervals.
    
  • QRS complexes occur independently from P-waves but also at consistent intervals.
    
  • QRS complexes are usually narrow unless there is an infranodal conduction disturbance or a ventricular escape rhythm.
    

Additional studies aid in confirming the etiology of the identified AV block.

• Electrolytes
  
• Calcium, magnesium
  
• Cardiac enzymes:
  
  • Especially for Type II 2nd-degree and 3rd-degree blocks
    
• Digoxin level, if patient has been exposed to this medication
  

• CXR:
  
  • May identify cardiomyopathy or CHF
    
• ECG:
  
  • May identify regional wall motion abnormalities or valvular dysfunction
    

• Accelerated junctional rhythm
  
• Idioventricular rhythm
  
• Sinus bradycardia
  
• SA block
  

TREATMENT

• Transcutaneous pacing for unstable Type II 2nd- or 3rd-degree block
  
• Atropine:
  
  • Avoid with Type II 2nd-degree block because it may precipitate complete heart block
    
  • Contraindicated in 3rd-degree heart block with a widened QRS complex
    
• Attempts should be made to prevent increases in vagal tone.
  

• Transcutaneous pacemaker:
  
  • Necessary for the unstable patient with signs of hypoperfusion:
    
    • Hypotension
      
    • Chest pain
      
    • Dyspnea
      
    • Mental status changes
      
• Atropine:
  
  • Can be administered in:
    
    • Complete heart block with a narrow QRS
      
    • Symptomatic sinus bradycardia
      

• 1st-degree AV block:
  
  • No treatment required
    
  • Avoid AV nodal blocking agents
    
  • Evaluate for associated MI, electrolyte abnormalities, medication excess in the appropriate clinical scenarios
    
• Type I 2nd-degree AV block:
  
  • Usually no treatment needed
    
  • If symptomatic, atropine will enhance AV conduction
    
• Type II 2nd-degree AV block:
  
  • Temporary transcutaneous or transvenous pacemaker
    
  • Atropine is not effective and should be avoided
    
• 3rd-degree AV block:
  
  • 1st line of treatment: Emergent pacemaker
    
  • May transiently respond to atropine with narrow QRS complexes
    
  • If block is identified to be toxin-mediated, specific treatments include:
    
    • Digoxin-specific antibodies (digoxin overdose)
      
    • Glucagon and calcium (β-blocker or calcium-channel blocker overdose)
      

• Atropine: 0.5–1.0 mg (peds: 0.01–0.03 mg/kg) IV q5min as necessary
  
• Digoxin-specific antibodies: 10 vials (380 mg) is an appropriate loading dose if digoxin toxicity is strongly suspected:
  
  • Serum level × weight (kg) = number of vials to be administered
    
• Glucagon: 5–10 mg (peds: 50 μg/kg) IV over 5 min
  
• Calcium chloride: 250–500 mg (peds: 20 mg/kg) IV
  

FOLLOW-UP

Monitored bed:

• Type II 2nd-degree block
  
• 3rd-degree block
  

Asymptomatic 1st-degree and Type I 2nd-degree blocks: Ensure follow-up for further outpatient workup.

Asymptomatic 1st-degree and Type I 2nd-degree blocks can follow-up with a cardiologist on a routine outpatient basis.

• Obtaining an EKG rapidly in symptomatic patients is paramount.
  
• Once a high-degree AV block has been diagnosed, initiate transcutaneous pacing immediately.
  
• Obtain a complete history from all available resources; it may help you identify an offending toxin rapidly.
  
• Common pitfalls:
  
  • Failure to interpret EKG properly
    
  • Failure to diagnose AV block appropriately
    
  • Failure to initiate transcutaneous pacing in a timely fashion
    
  • Failure to consult cardiology for permanent pacemaker in a timely fashion
    

• Harrigan RA, Chan TC, Moonblatt S, et al. Temporary transvenous pacemaker placement in the emergency department.
  J Emerg Med
  . 2007;32(1):105–111.
  
• Olgin JE, Zipes DP. Specific arrhythmias: Diagnosis and treatment. In: Libby P, ed.
  Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine.
  8th ed. Philadelphia, PA: Saunders Elsevier; 2008:913–923.
  
• Ufberg JW, Clark JS. Bradydysrhythmias and atrioventricular conduction blocks.
  Emerg Med Clin North Am
  . 2006;24(1):1–9.
  
• Yealy DM, Delbridge TR. Dysrhythmias. In: Marx JA, et al., eds.
  Rosen’s Emergency Medicine: Concepts and Clinical Practice
  . 7th ed. St. Louis, MO: CV Mosby; 2010:93–100.
  

See Also (Topic, Algorithm, Electronic Media Element)

• Bradyarrhythmias
  
• Cardiac Pacemakers
  

CODES

• 426.10 Atrioventricular block, unspecified
  
• 426.11 First degree atrioventricular block
  
• 426.13 Other second degree atrioventricular block
  

BASICS