What is the initial workup and management for a patient presenting with bradycardia (abnormally slow heart rate)?

Bradycardia Differential and Initial Workup

The initial workup for bradycardia should include a 12-lead ECG, vital signs assessment, focused history for reversible causes, and laboratory tests (thyroid function, electrolytes, drug levels) based on clinical suspicion, with immediate treatment with atropine 0.5-1 mg IV for symptomatic patients. 1, 2

Definition and Clinical Significance

• Bradycardia is defined as a heart rate <60 beats per minute, though clinically significant bradycardia is generally <50 beats per minute
• Assessment should focus on:
  • Presence of symptoms (syncope, dizziness, chest pain, dyspnea, fatigue)
  • Hemodynamic stability (blood pressure, signs of shock)
  • ECG findings (sinus bradycardia vs. AV blocks)

Differential Diagnosis

Physiologic Causes

• Athletic training/conditioning
• Sleep
• Increased vagal tone
• Normal variant in some individuals

Pathologic Causes

1. Medication-Related

   • Beta-blockers
   • Non-dihydropyridine calcium channel blockers
   • Digoxin (including toxicity)
   • Antiarrhythmic drugs (amiodarone, sotalol)
   • Chemotherapeutic agents (cisplatin, paclitaxel) 2

2. Cardiac Causes

   • Acute myocardial infarction (especially inferior MI)
   • Sinus node dysfunction (sick sinus syndrome)
   • AV nodal disease
   • Heart transplant rejection 1

3. Neurologic Causes

   • Increased intracranial pressure
   • Spinal cord injury
   • Central nervous system abnormalities 2

4. Metabolic/Endocrine

   • Hypothyroidism
   • Hypopituitarism
   • Electrolyte abnormalities (especially hyperkalemia)
   • Hypothermia
   • Hypoglycemia 1, 2

5. Infectious

   • Lyme disease
   • Typhoid fever
   • Viral myocarditis
   • Endocarditis 2

Initial Workup Algorithm

Step 1: Immediate Assessment

• Check vital signs (BP, RR, O2 saturation, temperature)
• Establish IV access
• Apply cardiac monitor
• Obtain 12-lead ECG (Class I, LOE B-NR) 1
• Assess for signs of hemodynamic instability or end-organ hypoperfusion

Step 2: Focused History

• Medication use (especially negative chronotropes)
• Recent illnesses or infections
• Cardiac history
• Syncope or presyncope episodes
• Timing and nature of symptoms

Step 3: Laboratory Testing

• Basic metabolic panel (potassium, sodium, calcium, magnesium)
• Thyroid function tests
• Digoxin level (if applicable)
• Cardiac biomarkers (if suspected ischemia)
• Lyme titer (in endemic areas or with suggestive history)
• Blood pH 1

Step 4: Additional Diagnostic Studies

• For infrequent symptoms (>30 days between episodes), consider long-term ambulatory monitoring with an implantable cardiac monitor if initial evaluation is nondiagnostic (Class IIa, LOE C-LD) 1
• In selected cases, electrophysiology study may be considered if noninvasive evaluation is nondiagnostic (Class IIb, LOE C-LD) 1

Immediate Management for Symptomatic Bradycardia

1. First-line treatment: Atropine 0.5-1 mg IV (may be repeated every 3-5 minutes to a maximum dose of 3 mg) 1, 3

   • Note: In patients with coronary artery disease, limit total dose to 0.03-0.04 mg/kg 3
   • Caution: Atropine should NOT be used in heart transplant patients without evidence of autonomic reinnervation (Class III: Harm) 1

2. If atropine ineffective:

   • Dopamine 5-20 mcg/kg/min IV
   • Epinephrine 2-10 mcg/min IV
   • Isoproterenol 1-20 mcg/min IV (avoid in suspected ischemia) 1

3. For refractory cases: Consider transcutaneous pacing as a bridge to transvenous pacing 4

Special Considerations

Beta-blocker or Calcium Channel Blocker Overdose

• For calcium channel blocker overdose: IV calcium (calcium chloride 1-2 g or calcium gluconate 3-6 g)
• For both: Glucagon 3-10 mg IV with infusion of 3-5 mg/h
• High-dose insulin therapy: IV bolus of 1 unit/kg followed by infusion of 0.5 units/kg/h 1

Digoxin Overdose

• Digoxin antibody fragment (dosage dependent on amount ingested or known digoxin concentration) 1

Post-Heart Transplant

• Aminophylline 6 mg/kg in 100-200 mL IV over 20-30 min
• Theophylline 300 mg IV, followed by oral dose of 5-10 mg/kg/d 1

Common Pitfalls to Avoid

1. Failing to identify and treat reversible causes before considering permanent pacing
2. Using atropine in patients with Mobitz type II or third-degree AV block (may worsen block)
3. Using atropine in heart transplant patients (may cause paradoxical heart block or sinus arrest in 20% of patients) 1
4. Overlooking medication-induced bradycardia as a common and reversible cause
5. Treating asymptomatic bradycardia in patients who don't require intervention

The evidence strongly supports a systematic approach to bradycardia that prioritizes identifying and treating reversible causes while providing appropriate supportive care for symptomatic patients. Research demonstrates that approximately 50% of patients with hemodynamically unstable bradycardia respond to atropine therapy 5, with those presenting with sinus bradycardia more likely to respond than those with AV block 6.