Atrioventricular Blocks

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Atrioventricular Blocks

• EMS Technology
• Temple College

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Topics for Discussion

• First Degree Heart Block(1 AV Block)
• Second Degree Heart Block (2 AV Block)
• Type I (Wenckebach)
• Type II
• Term Mobitz also used
• Third Degree Heart Block(3 AV Block) (Complete
  Heart Block)

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First Degree AV Block

• Delayed conduction thru AV node
• Results in prolonged PRI
• Impulses allowed thru AV node depolarize the
  ventricles
• A characteristic of an underlying rhythm but not
  a rhythm
• e.g. Sinus rhythm with 1 AV Block

• Characteristics
• Regularity and Rate based on underlying rhythm
• P waves are normal
• P wave may be hidden in preceding T wave
• PQRS is 11
• PRI gt 0.20 seconds
• QRS WNL

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First Degree AV Block

• Causes
• ANS - ? adrenergic or ? parasympathetic
  stimulation
• Ischemia and AMI, particularly RCA occlusion
• Myocarditis - rheumatic fever, Lupus
• Pharmacologic - ß blockers, Ca Channel blockers,
  Digitalis, TCAs

• Patient Care Issues
• May progress to increased AV blockade
• Treatment usually focused on
• Underlying Cause
• ? sympathetic or ? parasympathetic tone

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Second Degree AV Block

• Two Types
• Type I (Wenckebach Phenomenon)
• Type II
• Some impulses but not all are allowed through
  the AV nodal system
• The pattern of AV blockade determines the type of
  2 AV Block

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Second Degree AV Block - Type I

• Impulses proceed thru AV nodal system with
  increasing difficulty
• Conduction delay results in progressively ?PRI
• Blocked impulse results in absent QRS
• Term usually assoc with Sinus rhythms

• Characteristics
• P waves normal
• Atrial rate gt ventricular rate
• R-R irregular
• Grouped beating
• QRS lt 0.12 seconds

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Second Degree AV Block - Type I

• Causes
• Similar to First Degree AV node Block
• May be transient in AMI

• Patient Care Issues
• Less likely to progress to 3 AV Block
• Ventricular Rate is issue of concern
• May require ? ventricular rate
• ? sympathetic or ? parasympathetic tone
• Rarely, external pacing

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Second Degree AV Block - Type II

• Blocked impulse results in absent QRS
• No changes in PRI
• Block is mostly likely distal to AV nodal system
  (bundle of His)

• Characteristics
• P waves normal
• Atrial rate gt ventricular rate
• Ventricular rate often slow
• PRI normal when present
• QRS lt 0.12 seconds
• Regularity depends on degree of conduction

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Second Degree AV Block - Type II

• Causes
• Indicates disease of the His-Purkinje fibers
• Higher likelihood of progression to 3 AV Block
• Likely in anteroseptal MI

• Patient Care Issues
• Susceptible to symptomatic bradycardia
• Worsened by digitalis, procainamide, lidocaine,
  propranolol, phenothiazines, TCAs
• Prepare for transthoracic pacing

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Third Degree AV Block

• No impulses are conducted through the AV nodal
  system
• Ventricular depolarization is dependent on the
  automaticity of other lower pacemaker sites

• Characteristics
• Atrioventricular dissociation
• P wave normal
• Regular rhythm (P-P, R-R) w/o association
• Atrial rate gt ventricular rate
• QRS ltgt 0.12 seconds

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Third Degree AV Block

• Causes
• Likely an AMI
• Drugs that depress AV conduction
• Digitalis is the most likely

• Patient Care Issues
• Prepare for immediate transthoracic pacing
• Likely to be extremely symptomatic