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Source: Sanoski CA, Bauman JL. The Arrhythmias. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. http://accesspharmacy.com/content.aspx?aid=7972803. Accessed June 30, 2012.

  • Bradycardias

  • Abnormally slow heart rate (<60 beats/min in adults).

  • Sinus bradycardia
  • Sick sinus syndrome
  • Atrioventricular (AV) block
  • Vasovagal syndrome

  • Usually results from impaired sinoatrial (SA) node function or conduction abnormalities between SA node and atrium, or within AV node or intraventricular conduction pathways.
  • Sinus bradycardia can be due to heart disease, medications, or normal causes (e.g., in trained athletes).
  • Sick sinus syndrome caused by malfunction of SA node from organic heart disease or normal aging process.
  • AV block caused by slowed or blocked conduction of electrical impulses in AV conduction system.
  • β-Blockers, digoxin, or nondihydropyridine calcium antagonists may cause AV block, primarily in AV nodal area.
  • Vasovagal syncope thought to be neurally mediated process involving stimulation of cardiac mechanoreceptors (Bezold-Jarisch reflex).

  • Frequency of sinus bradycardia unknown.
  • Frequency of sick sinus syndrome in patients with heart disease estimated to be 3 in 5000.

  • Advancing age
  • Hypothyroidism
  • Drugs (e.g., central α2 agonists, cholinesterase inhibitors, calcium channel blockers, digoxin, lithium, β-blockers)
  • Heart disease (e.g., myocardial infarction)
  • Electrolyte imbalances
  • Sleep apnea
  • Head injury
  • Hypothermia
  • Hypoglycemia
  • Toxin exposure

Signs and Symptoms

  • Many bradycardias asymptomatic (e.g., in trained athletes).
  • Symptoms associated with hypotension (e.g., dizziness, syncope, fatigue, confusion).
  • Vasovagal syndrome may cause syncope.
  • If LV dysfunction exists, patients may experience worsening heart failure (HF) symptoms.
  • Signs: Pulse <60 beats/min in adults.

Laboratory Tests

  • Performed if underlying causes suspected (e.g., hypothyroidism, electrolyte imbalances).

Diagnostic Procedures

  • Electrocardiogram (ECG) findings categorize AV block into first-, second-, or third-degree block.
  • Holter monitoring may be used to document the relationship of bradycardia with symptoms.
  • Electrophysiologic studies may be performed for accurate localization of AV block.

  • Identify and correct underlying causes.
  • Resolve symptoms.
  • Prevent recurrences.
  • Avoid complications from surgical procedures and medications.

  • Asymptomatic sinus bradyarrhythmias do not usually require intervention.

  • Discontinue exacerbating medications, if feasible.
  • Permanent ventricular pacemaker is long-term treatment of choice for most patients with significant symptoms.

  • Vasovagal syncope
    • Oral β-blockers (e.g., metoprolol)
    • Other drugs (with or without β-blockers)
      • Fludrocortisone
      • Anticholinergics (scopolamine patches, disopyramide)
      • α-Adrenergic agonists (midodrine)
      • Adenosine analogues (theophylline, dipyridamole)
      • Selective serotonin reuptake inhibitors (sertraline, paroxetine)
  • Atrioventricular block
    • Give atropine (0.5 mg IV every 3–5 minutes, up to 3 mg total dose) for patients with Mobitz II or third-degree AV block who develop signs/symptoms of poor perfusion (e.g., altered mental status, chest pain, hypotension, shock).
    • Epinephrine (2–10 mcg/min) or dopamine (2–10 mcg/kg/min) IV infusion if atropine fails.

  • Assess heart rate, blood pressure, and resolution of symptoms.
  • Observe for side effects if medications are used.

  • Prognosis favorable when appropriate ...

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