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Atrioventricular Blocks, Emergency Medicine

Basics

Description

- Mobitz Type II: - Conduction deficit is usually below the level of the AV node. - PR intervals are constant until single or multiple beats are abruptly dropped. - High likelihood of progression to complete heart block - Worse prognosis if associated with an acute MI - Less common than Type I

- Collagen vascular diseases - Infiltrative diseases: - Sarcoidosis - Amyloidosis - Hemochromatosis

- 1st-degree AV block: - Type I 2nd-degree AV block: - 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 treatment required - Avoid AV nodal blocking agents - Evaluate for associated MI, electrolyte abnormalities, medication excess in the appropriate clinical scenarios

- 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

  • Impaired conduction between the atrium and the ventricle through the AV node or His-Purkinje system
  • 1st-degree AV block:Prolonged conduction through the AV nodeVentricular impulses are not lost.Generally benign, and occurs in 1.6% healthy adults.
  • 2nd-degree AV block:Marked by a failure of some atrial impulses to reach ventriclesMobitz Type I (Wenckebach):Usually secondary to conduction deficit in AV node.Progressive prolongation of the pulse-rate (PR) interval until a nonconducted P-wave and a dropped QRS complex occurGenerally benign, but may be a complication of an inferior wall MIMobitz Type II:Conduction deficit is usually below the level of the AV node.PR intervals are constant until single or multiple beats are abruptly dropped.High likelihood of progression to complete heart blockWorse prognosis if associated with an acute MILess common than Type I
  • 3rd-degree AV block:Also known as complete heart blockAll atrial impulses are unable to reach the ventricular conducting system; a ventricular escape pacemaker then takes over, resulting in AV dissociation.Constant PP and RR intervals with variable PR intervals because PP and RR intervals are independent of each other.More severe symptoms occur when the block is lower in the conducting system.If secondary to toxicologic agents, often resolves upon omission of offending toxinNever a benign condition

Etiology

  • Essentially due to:A structural lesionIncrease in inherent refractory periodMarked shortening of the supraventricular cycle
  • MI:1st-degree block and Type I 2nd-degree AV block may be associated with an inferior wall MI:These blocks are transient.AV conduction usually returns to normal with no increased morbidity or mortality.Type II 2nd-degree AV block may be associated with an anterior wall MI:5% anterior wall MIs are associated with AV blocks.Increased mortality secondary to ventricular arrhythmias and left-heart failure
  • Coronary artery disease:Chronic ischemic injury can lead to fibrosis around the AV node
  • Toxicologic:Digoxinβ-blockersCalcium-channel blockersAmiodaroneProcainamideClass 1C agents: Propafenone, encainide, flecainideClonidine
  • Congenital
  • Valvular heart disease
  • Surgical trauma:S/P coronary artery bypass graft or valvular replacement
  • Increased vagal tone
  • Infectious:SyphilisDiphtheriaChagas diseaseTBToxoplasmosisLyme diseaseMyocarditisEndocarditisRheumatic feverAbscess formation in interventricular septum
  • Collagen vascular diseases
  • Infiltrative diseases:SarcoidosisAmyloidosisHemochromatosis
  • Cardiomyopathy
  • Electrolyte disturbances:
  • Myxedema
  • Hypothermia
  • Occurs in children, but is often asymptomatic
  • Associated mortality is highest in the neonatal period.
  • Associated with:Congenitally acquired maternal antibodiesCongenital heart diseaseInfectious etiologies, such as rheumatic fever or myocarditis
  • Be sure to consider potential toxic ingestions in pediatric patients with new AV block

Diagnosis

Signs and Symptoms

History

  • 1st-degree AV block:
  • Type I 2nd-degree AV block:
  • Type II 2nd-degree AV block and 3rd-degree block:Exercise intolerancePalpitationsChest painPresyncope/syncopeAltered mental statusDyspnea, orthopnea

Physical Exam

  • 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 pulseHypotensionMental status changesSigns of heart failure:RalesCyanosisJugular venous distention

Essential Workup

  • A 12-lead EKG to determine the type of block and identify evidence of infarction
  • 1st-degree AV block:
  • 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.

Diagnosis Tests & Interpretation

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

Lab

  • 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

Imaging

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

Differential Diagnosis

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

Treatment

Pre-Hospital

  • 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 blockContraindicated in 3rd-degree heart block with a widened QRS complex
  • Attempts should be made to prevent increases in vagal tone.

Initial Stabilization/Therapy

  • Transcutaneous pacemaker:Necessary for the unstable patient with signs of hypoperfusion:HypotensionChest painDyspneaMental status changes
  • Atropine:Can be administered in:Complete heart block with a narrow QRSSymptomatic sinus bradycardia

Ed Treatment/Procedures

  • 1st-degree AV block:No treatment requiredAvoid AV nodal blocking agentsEvaluate for associated MI, electrolyte abnormalities, medication excess in the appropriate clinical scenarios
  • Type I 2nd-degree AV block:Usually no treatment neededIf symptomatic, atropine will enhance AV conduction
  • Type II 2nd-degree AV block:Temporary transcutaneous or transvenous pacemakerAtropine is not effective and should be avoided
  • 3rd-degree AV block:1st line of treatment: Emergent pacemakerMay transiently respond to atropine with narrow QRS complexesIf 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)

Medication

  • 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

Disposition

Admission Criteria

Monitored bed:

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

Discharge Criteria

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

Followup Recommendations

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

Pearls and Pitfalls

  • 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 properlyFailure to diagnose AV block appropriatelyFailure to initiate transcutaneous pacing in a timely fashionFailure to consult cardiology for permanent pacemaker in a timely fashion

Additional Reading

  • 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. Braunwalds 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

ICD9

  • 426.10 Atrioventricular block, unspecified
  • 426.11 First degree atrioventricular block
  • 426.13 Other second degree atrioventricular block
  • 426.0 Atrioventricular block, complete
  • 426.12 Mobitz (type) II atrioventricular block
  • 426.1 Atrioventricular block, other and unspecified

ICD10

  • I44.0 Atrioventricular block, first degree
  • I44.1 Atrioventricular block, second degree
  • I44.30 Unspecified atrioventricular block
  • I44.2 Atrioventricular block, complete
  • I44.39 Other atrioventricular block
  • I44.3 Other and unspecified atrioventricular block

SNOMED

  • 233917008 Atrioventricular block (disorder)
  • 270492004 First degree atrioventricular block (disorder)
  • 195042002 second degree atrioventricular block (disorder)
  • 27885002 Complete atrioventricular block (disorder)
  • 195039008 partial atrioventricular block (disorder)
  • 28189009 Mobitz type II atrioventricular block (disorder)
  • 54016002 Mobitz type I incomplete atrioventricular block (disorder)