What is the initial workup for a patient presenting with sinus bradycardia?

Initial Workup for Sinus Bradycardia

The initial workup for sinus bradycardia should include a comprehensive evaluation for reversible causes, assessment of hemodynamic stability, and a 12-lead ECG, with further diagnostic testing guided by the clinical presentation and suspected etiology. 1

Definition and Classification

• Sinus bradycardia is defined as a sinus rhythm with heart rate below normal limits:
  • Adults: <60 beats per minute
  • Neonates: <91 beats per minute in the first week, <107 beats per minute in the first month 2
  • Children: age-dependent lower limits

Initial Assessment

Step 1: Evaluate for Hemodynamic Compromise

• Assess for signs and symptoms of hemodynamic instability:
  • Hypotension
  • Altered mental status
  • Chest pain
  • Shortness of breath
  • Dizziness or syncope 1

Step 2: Obtain 12-Lead ECG

• Confirm sinus bradycardia and rule out other conduction disorders
• Look for:
  • Heart rate <60 bpm
  • Normal P wave morphology
  • Fixed PR interval
  • 1:1 AV conduction
  • Associated conduction abnormalities (AV blocks, bundle branch blocks) 2

Step 3: Identify and Evaluate Reversible Causes

• Medications:

  • Beta-blockers
  • Non-dihydropyridine calcium channel blockers
  • Digoxin
  • Antiarrhythmic drugs 1

• Metabolic/Endocrine:

  • Hypothyroidism
  • Hyperkalemia
  • Hypokalemia
  • Hypoglycemia 1
  • Hypothermia
  • Obstructive jaundice 2

• Neurologic:

  • Increased intracranial pressure
  • Central nervous system abnormalities
  • Meningitis 2

• Cardiac:

  • Myocarditis
  • Ischemia
  • Infiltrative diseases (amyloidosis, sarcoidosis)
  • Post-cardiac transplant 1

• Other:

  • Sleep apnea
  • Hypervagotonia
  • Infection (including typhoid fever) 2, 1
  • Maternal antibodies (in neonates) 2

Laboratory and Diagnostic Testing

• Basic laboratory tests:

  • Complete blood count
  • Comprehensive metabolic panel (including electrolytes)
  • Thyroid function tests
  • Cardiac biomarkers if cardiac ischemia suspected 1

• Additional testing based on clinical suspicion:

  • Echocardiogram: Indicated when structural heart disease or myocarditis is suspected 2
  • Ambulatory ECG monitoring: For intermittent symptoms or to assess severity of bradycardia 1
  • Advanced cardiac imaging: Consider MRI, PET, or CT for specific etiologies (sarcoidosis, amyloidosis, congenital heart disease) 2

Management Approach

• Asymptomatic bradycardia (heart rate >40 bpm without signs of hypoperfusion):

  • Generally requires no immediate treatment
  • Focus on identifying and addressing underlying causes 1

• Symptomatic bradycardia:

  • Ensure adequate oxygenation and ventilation
  • Establish IV access
  • Consider pharmacologic therapy:
    • Atropine 0.5-1 mg IV (first-line)
    • Epinephrine 2-10 mcg/min IV infusion
    • Dopamine 5-20 mcg/kg/min IV infusion 1
  • Consider temporary or permanent pacing for persistent symptomatic bradycardia 1

Special Considerations

• Pediatric patients: Age-specific heart rate norms must be considered 2
• Heart transplant patients: Atropine may be ineffective; consider theophylline or aminophylline 1
• Elderly patients: More likely to have degenerative conduction system disease requiring pacing 1

Common Pitfalls to Avoid

1. Failing to recognize physiologic bradycardia in athletes or during sleep
2. Missing medication-induced bradycardia (careful medication review essential)
3. Overlooking hypothyroidism as a reversible cause
4. Unnecessary treatment of asymptomatic bradycardia
5. Delaying treatment in symptomatic patients with hemodynamic compromise 1

The workup should be tailored to the patient's clinical presentation, with prompt intervention for symptomatic cases and a more deliberate diagnostic approach for stable patients.