II. Pathophysiology
- Impaired conduction in Atria, AV Node or His-Purkinje
III. Types: First Degree Atrioventricular Node Block
- Causes
- Normal finding in >1% of healthy adults
- Inferior wall ischemia (right Coronary Artery) if onset in acute presentations
- Increased vagal tone (responds to Atropine)
- Hypothyroidism
- Medications
- Findings
- Regular narrow-complex rhythm at 40-60 beats/minute
- Prolonged PR Interval >0.20 seconds
- Treatment
- None needed
IV. Types: Second Degree Atrioventricular Node Block
- Also known as Sinoatrial Exit Block
- Type I Second Degree Atrioventricular Node Block
- Known as Mobitz I or Wenckeback Block
- Acute condition affecting AV Node
- Causes: Functional, reversible defects
- Inferior Myocardial Ischemia
- Rheumatic Fever
- Digitalis Toxicity
- Increased vagal tone
- Beta Blocker
- Response to Maneuvers
- EKG Findings
- Progressive increase PR Interval until beat/QRS Complex dropped
- Cycle repeats after beat dropped
- Type II Second Degree Atrioventricular Node Block
- Known as Mobitz II Block
- Chronic condition affects infranodal conduction path
- Causes: Structural, non-reversible defects
- Anteroseptal Myocardial Infarction
- Lenegre Disease
- Lev Disease
- Cardiomyopathy
- Response to Maneuvers
- EKG Findings
- Intermittent non-conducted P Waves
- No change in PR Interval (remains constant unlike Mobitz 1)
- Regularly dropped QRS waves at consistent interval is typical
- Patterns: 2 to 1, 3 to 1 or 4 to 1
- However, non-conducted P Wave may also occur without pattern
- Prognosis
- Worse than Mobitz I Block
- May progress to complete Heart Block
- Management
- Urgent cardiology Consultation
- Pacemaker indicated
V. Types: Third Degree Atrioventricular Node Block (Complete AV Nodal Block)
- Findings
- Complete electrical and mechanical AV dissociation
- P and QRS waves are present but unrelated
- Images
- Subtypes
- Congenital Third Degree AV Node Block (narrow complex)
- Acquired Third Degree AV Node Block (wide complex)
- Wide complex escape beat at 30 to 45 bpm (infranodal)
- Hemodynamic instability requires stabilization