II. Pathophysiology

  1. Impaired conduction in Atria, AV Node or His-Purkinje

III. Types: First Degree Atrioventricular Node Block

  1. Causes
    1. Normal finding in >1% of healthy adults
    2. Inferior wall ischemia (right Coronary Artery) if onset in acute presentations
    3. Increased vagal tone (responds to Atropine)
    4. Hypothyroidism
    5. Medications
      1. Digitalis affect
      2. Non-Dihydropyridine Calcium Channel Blocker
      3. Beta Blocker
  2. Findings
    1. Regular narrow-complex rhythm at 40-60 beats/minute
    2. Prolonged PR Interval >0.20 seconds
  3. Treatment
    1. None needed

IV. Types: Second Degree Atrioventricular Node Block

  1. Also known as Sinoatrial Exit Block
  2. Type I Second Degree Atrioventricular Node Block
    1. Known as Mobitz I or Wenckeback Block
    2. Acute condition affecting AV Node
    3. Causes: Functional, reversible defects
      1. Inferior Myocardial Ischemia
      2. Rheumatic Fever
      3. Digitalis Toxicity
      4. Increased vagal tone
      5. Beta Blocker
    4. Response to Maneuvers
      1. Bradycardia improves in response to Atropine and Exercise
      2. Worsens with carotid massage
    5. EKG Findings
      1. Progressive increase PR Interval until beat/QRS Complex dropped
      2. Cycle repeats after beat dropped
  3. Type II Second Degree Atrioventricular Node Block
    1. Known as Mobitz II Block
    2. Chronic condition affects infranodal conduction path
    3. Causes: Structural, non-reversible defects
      1. Anteroseptal Myocardial Infarction
      2. Lenegre Disease
      3. Lev Disease
      4. Cardiomyopathy
    4. Response to Maneuvers
      1. Mobitz II AV Block is an infranodal disorder, that does not respond to Atropine
      2. Atropine may worsen degree of Mobitz 2 block (e.g. from 2:1 to 4:1)
      3. Mobitz II AV Block also worsens in response to Exercise
    5. EKG Findings
      1. Intermittent non-conducted P Waves
      2. No change in PR Interval (remains constant unlike Mobitz 1)
      3. Regularly dropped QRS waves at consistent interval is typical
        1. Patterns: 2 to 1, 3 to 1 or 4 to 1
        2. However, non-conducted P Wave may also occur without pattern
    6. Prognosis
      1. Worse than Mobitz I Block
      2. May progress to complete Heart Block
    7. Management
      1. Urgent cardiology Consultation
      2. Pacemaker indicated

V. Types: Third Degree Atrioventricular Node Block (Complete AV Nodal Block)

  1. Findings
    1. Complete electrical and mechanical AV dissociation
    2. P and QRS waves are present but unrelated
  2. Images
    1. cv_ekg_avBlock3.jpg
  3. Subtypes
    1. Congenital Third Degree AV Node Block (narrow complex)
      1. Narrow complex escape rhythm at 45 to 60 bpm (vagal or above the AV Node)
      2. Associated with limited Exercise tolerance
    2. Acquired Third Degree AV Node Block (wide complex)
      1. Wide complex escape beat at 30 to 45 bpm (infranodal)
      2. Hemodynamic instability requires stabilization
        1. Transcutaneous Pacing

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