Updated: 12/7/2021

Bradycardia

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https://upload.medbullets.com/topic/422861/images/sinus_bradycardia.jpg
https://upload.medbullets.com/topic/422861/images/first_degree_av_block.jpg
https://upload.medbullets.com/topic/422861/images/mobitz_i.jpg
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https://upload.medbullets.com/topic/422861/images/mobitz_ii.jpg
https://upload.medbullets.com/topic/422861/images/third_degree_av_block.jpg
  • Snapshot
    • 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)
  • Introduction
    • 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
  • Presentation
    • Symptoms
      • lightheadedness
      • fatigue
      • generalized weakness
      • presyncope or syncope
      • angina
    • Physical exam
      • hypotension
      • bradycardia
  • Studies
    • 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
  • Treatment
    • 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
  • Complications
    • Syncope
    • Cardiac death

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