Bradycardia

Bradycardia is defined as heart rate of less than 60 beats per minute. It is a common finding that often does not require treatment in the absence of symptoms.

Differential Diagnosis

• Sinus bradycardia
  –Heart rate <60 bpm with normal-appearing P waves before each QRS wave (narrow complex)
  –Most often due to increased vagal tone or medications (e.g., β-blockers)
  –Normally seen in healthy young adults and well-trained athletes
  –May occur with hypothermia, advanced liver disease, hypothyroidism, sinoatrial node disease, anorexia nervosa, sleep disorders, and increased intracranial pressure
• Medications (e.g., β-blockers)

• Sinus node dysfunction
  –May occur as result of sinus node fibrosis (e.g., aging) or infiltrative diseases (e.g., amyloidosis)
  –SSS: Symptomatic bradycardia with sinus node dysfunction
  –Tachycardia-bradycardia syndrome: SSS manifested by tachyarrhthymias alternating with bradyarrhthymias
• Heart block
  –First-degree AV block: Fixed prolongation of PR interval (PR ≥200 msec); results from slowed conduction through AV node
  –Second-degree AV block, Mobitz I (Wenckebach): Results from delayed conduction through AV node; progressive prolongation of PR interval occurs until a QRS is dropped (typically benign)
  –Second-degree AV block, Mobitz II: Results from disease in the bundle of His; PR is constant, but sporadic P waves are not conducted (may be life threatening because of risk of complete heart block or ventricular asystole)
  –Complete heart block: Atrial impulses are not conducted to the ventricles; thus, atrial activity occurs independent of ventricular activity (AV dissociation, with atrial rate faster than ventricular rate)

• Congenital heart block
• Aortic stenosis
• Myocardial infarction
  –More common with inferior wall MI
• Atrial fibrillation/flutter with high-degree block
• Infections (e.g., Lyme disease)

Workup and Diagnosis

• History and physical exam
  –Associated symptoms may include lightheadedness, palpitations, dyspnea, chest pain, and syncope
  –Medication history
  –Thorough review of symptoms to identify precipitants of increased vagal tone (e.g., nausea, pain, headache)
  –Assess for hemodynamic instability (blood pressure, level of consciousness), jugular venous pressure (cannon A waves are highly suggestive of AV dissociation), and soft S1 (suggests PR prolongation)

• ECG is diagnostic
• Further diagnostic tests may include echocardiogram, electrophysiologic testing, and cardiac catheterization

Treatment

• Airway, breathing, and circulation
• Sinus bradycardia: Treatment is not usually necessary
  –Treat reversible causes (e.g., withdraw medications, thyroid hormone supplementation for hypothyroidism)
  –If symptomatic or hemodynamic instability is present, administer IV atropine or epinephrine
  –Electrical pacing is indicated only in severe cases
• Remove offending medications if possible
• Sinus node dysfunction: Treat reversible causes; often requires pacemaker placement
• Wenckebach: Treatment not usually necessary
• Mobitz II: More serious than Mobitz I, because sudden cardiac death may occur
  –Pacemaker placement is indicated for symptomatic bradycardia, documented asystole >3 seconds, coexistent neuromuscular disease, or concomitant high-grade conduction disease
  –Electrophysiologic testing to determine need for pacemaker
• Complete heart block requires pacemaker

Book Source Details

• Book Title: In a Page: Signs and Symptoms
• Author(s): Scott Kahan, Ellen G. Smith
• Year of Publication: 2004
• Copyright Details: In a Page: Signs and Symptoms, Copyright © 2004 Lippincott Williams & Wilkins.

Other Book Chapters Related to Arrhythmia

Read excerpts from these other book chapters related to Arrhythmia:

Copyright Details: In a Page: Signs and Symptoms, Copyright © 2008 Williams & Wilkins.

More About Causes of Arrhythmia

• Back to symptom: Arrhythmia: Introduction (review 234 causes)
• Next Book Extract About Arrhythmia: Palpitations (In a Page: Signs and Symptoms)
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More About This Book: Title: In a Page: Signs and Symptoms Authors: Scott Kahan, Ellen G. Smith Publisher: Lippincott Williams & Wilkins Copyright: 2004 ISBN: 1-4051-0368-X

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