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Updated: Dec 28 2021

Atrioventricular (AV) Heart Block

  • Snapshot
    • A 20-year-old man presents to his primary care physician for an annual exam. He is currently feeling well but has some concerns since he occasionally has palpitations. Medical history is unremarkable and he takes a daily multivitamin. He denies any alcohol or smoking history. Family history is significant for his paternal grandfather expiring from a fatal arrhythmia. He is a college student and part of the school's basketball team, which he continued since he was a student in high school. He says that his caffeine intake has increased in these past few weeks due to upcoming final examinations. He is requesting an electrocardiogram (ECG) to ensure his heart is healthy since this worry is interfering with his school work. An ECG demonstrates a PR interval of 0.25 sec and is otherwise unremarkable. (First-degree heart block)
  • Introduction
    • Clinical definition
      • an impairment of the electrical transmission from the atria to the ventricles
    • Etiology
      • idiopathic (most common)
        • e.g., fibrosis and sclerosis of the conduction system
      • ischemic heart disease (2nd most common)
      • ↑ vagal tone
      • familial causes
      • iatrogenic
        • medications
          • e.g., β-blockers, calcium channel blockers, adenosine, digoxin, and amiodarone
        • cardiac procedures
          • e.g., cardiac surgery and transcatheter aortic valve implantation
    • Differential
      • sick sinus syndrome
        • presents with bradycardia, tachycardia, or alternating bradycardia-tachycardia
  • Atrioventricular (AV) Block
    • AV Blocks
      Electrocardiogram Findings
      First degree AV block
      • ↑ PR interval (> 0.2 secs)
      • 1:1 ratio of P waves and QRS complexes
      • No treatment is required unless other ECG changes (prolonged QRS)
      • Typically seen in young patients with a ↑ vagal tone
      • Well-trained athletes
      Second degree AV block (Mobitz type I)
      • Progressive↑ PR interval until a P wave is not followed by a QRS complex (Wenckebach phenomenon)
        • the sequence then repeats
        • QRS complex is narrow
      • Treatment is unnecessary unless the patient is symptomatic
        • use atropine or a temporary pacemaker in symptomatic cases
      • Patients are typically asymptomatic
      • Can be seen in patients with
        • drug intoxication (e.g., β-blockers and digitalis)
        • ↑ vagal tone
      Second degree AV block (Mobitz type II)
      • Fixed PR intervals with occasional dropped QRS complexes
        • QRS complex is typically wide
      • Atropine and pacing for unstable patients
      • Permanent pacemaker
      • May progress to a third-degree heart block
      Third degree (complete) AV block
      • Atria and ventricles depolarize independently
        • P waves and QRS complexes are not rhythmically synchronized
      • Atropine
      • Pacing
      • Permanent pacemaker unless the cause is reversible (such as medications)
      • Can be a complication of Lyme disease
      • Bifasicular block can progress to complete heart block
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