Updated: 12/1/2020


Review Topic
  • A 22-year-old man presents to his primary care physician for an annual examination. He currently has no acute complaints but is worried he has "heart disease" since his father died from a "heart attack." He denies any episodes of lightheadedness or syncopal episodes. He exercises regularly as he is part of his university's basketball team. An electrocardiogram demonstrates sinus rhythm with a PR interval of 250 ms. He is provided reassurance that nothing needs to be done. (First-degree atrioventricular block)
  • Overview
    • electrical activation of the heart usually is initiated by the sinatrial (SA) node
    • bradycardia results from impaired impulse initiation from the SA node or impaired impulse conduction from the SA node to the atria or ventricles
      • leads to a pulse < 60/min
    • common causes of bradycardia include
      • SA node dysfunction
      • atrioventricular (AV) node conduction block
  • Etiology
    • SA and AV node dysfunction
      • sick sinus syndrome (seen in SA node dysfunction)
      • carotid sinus hypersensitivity
      • inferior wall myocardial infarction (seen in SA node dysfunction and sometimes AV node dysfunction)
        • electrocardiogram demonstrate ST-segment elevation in II, III, and aVF
      • senile amyloidosis
      • medications (e.g., beta-blockers)
      • increased intracranial pressure
      • malignancy
      • radiation
      • infectious
  • Symptoms
    • lightheadedness
    • fatigue
    • generalized weakness
    • presyncope or syncope
    • angina
  • Physical exam
    • hypotension
    • bradycardia
  • Electrocardiogram
    • diagnostic study of choice
      • sinus bradycardia 
        • P wave is upright in leads I, II, and aVL, and a negative P wave in lead aVR
      • first-degree AV block 
        • PR interval is > 200 ms
      • second-degree AV block
        • Mobitz type I 
          • progressive PR interval lengthening with a subsequent "dropped" QRS complex
        • Mobitz type II  
          • fixed prolonged PR interval (> 200 ms) with a "dropped" QRS complex
      • third-degree AV block (complete heart block) 
        • no supraventricular pulses are conducted to the ventricles due to an absence of AV node condution
          • the atria and the ventricles independently contract
  • Overview
    • management of bradycardia depends on the patient's hemodynamic stability and type of bradycardia
      • hemodynamically unstable patients are managed with 
        • intravenous atropine 
        • temporary transvenous pacing
          • once hemodynamic stability is achieved, patients are monitored with transcutaneous pacing pads
            • patients are also evaluated for underlying and reversible causes of their bradycardia
    • management of bradycardia depends on the underlying cause
      • e.g., bradycardia secondary to hypothyroidism is managed by treating the hypothyroidism
  • Conservative
    • observation
      • indication
        • asymptomatic first degree AV block
        • asymptomatic Mobitz type I
  • Medical
    • atropine
      • indication
        • hemodynamically unstable bradycardia
      • comments
        • 0.5 mg is given every 3-5 minutes if needed
        • maximum dose is 3 mg
  • Procedural
    • tranvenous pacing
      • indication
        • hemodynamically unstably bradycardia in patients unresponsive to intravenous atropine 
    • permanent pacemaker 
      • indication
        • hemodynamically stable patients with Mobitz type II and third degree AV heart block with no identifiable reversible cause
  • Syncope
  • Cardiac death

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