What is the initial approach to a patient presenting with bradycardia (abnormally slow heart rate)?

Initial Approach to Bradycardia

The initial approach to a patient with bradycardia should focus on assessing the clinical significance of the slow heart rate, identifying underlying causes, and providing immediate treatment if the patient is symptomatic or unstable. 1, 2

Definition and Initial Assessment

• Bradycardia is defined as a heart rate <60 beats per minute, though clinically significant bradycardia is generally <50 beats per minute 1
• Immediately assess:
  • Signs of increased work of breathing and oxygen saturation
  • Vital signs including blood pressure
  • Signs of poor perfusion (altered mental status, ischemic chest discomfort, acute heart failure, hypotension, shock)
  • 12-lead ECG (when available, but don't delay therapy) 1

Systematic Evaluation Algorithm

1. Airway, Breathing, Circulation:

   • Maintain patent airway
   • Provide supplementary oxygen if hypoxemic
   • Establish IV access
   • Apply cardiac monitor 1

2. Determine if bradycardia is causing symptoms:

   • Syncope, dizziness, confusion
   • Chest pain/angina
   • Dyspnea or heart failure
   • Hypotension or shock 2

3. Identify the type of bradycardia on ECG:

   • Sinus bradycardia
   • AV blocks (first, second, or third-degree)
   • Sinus node dysfunction
   • Junctional bradycardia 1, 2

4. Search for reversible causes:

   • Medications: Beta-blockers, calcium channel blockers, digoxin, antiarrhythmics 2
   • Increased vagal tone: Vasovagal response, carotid sinus hypersensitivity 2
   • Metabolic/Endocrine: Hypothyroidism, electrolyte abnormalities (especially hyperkalemia), hypothermia 2
   • Cardiac: Acute myocardial infarction, myocarditis 1, 2
   • Neurologic: Increased intracranial pressure, CNS abnormalities 2
   • Infectious: Lyme disease, endocarditis, myocarditis 2
   • Consider BRASH syndrome: Bradycardia, Renal failure, AV nodal blockers, Shock, and Hyperkalemia 3

Management of Bradycardia

For Asymptomatic Patients:

• Monitor and observe if bradycardia is physiologic or well-tolerated
• Address underlying reversible causes
• Consider expert consultation 1

For Symptomatic/Unstable Patients:

1. First-line treatment: Atropine 0.5 mg IV, may repeat to a total dose of 3 mg 1, 2, 4

   • Atropine works by blocking vagal effects on the AV node and sinoatrial node
   • Onset of action is within 1-2 minutes after IV administration 4

2. If atropine ineffective:

   • Consider IV infusion of β-adrenergic agonists (dopamine or epinephrine) 2
   • Initiate transcutaneous pacing for persistent symptomatic bradycardia 1, 2

3. For refractory cases:

   • Prepare for transvenous temporary pacing 2
   • Consider expert consultation 1

Special Considerations

• Patients with coronary artery disease: Limit total atropine dose to 0.03-0.04 mg/kg to prevent excessive tachycardia 4
• Mobitz type II second-degree AV block or third-degree AV block: These may be less responsive to atropine and more likely to require pacing 1
• Patients on multiple AV nodal blockers: Be vigilant for BRASH syndrome, especially with renal dysfunction and hyperkalemia 3

Indications for Long-term Monitoring

• For patients with infrequent symptoms (>30 days between episodes), consider long-term ambulatory monitoring with an implantable cardiac monitor if initial evaluation is nondiagnostic 1

Indications for Permanent Pacing

• Persistent symptomatic bradycardia
• Second-degree Mobitz type II AV block
• Third-degree AV block not due to reversible causes
• Tachy-brady syndrome
• Chronotropic incompetence 2

Pitfalls to Avoid

• Treating asymptomatic bradycardia unnecessarily
• Missing underlying causes such as medication effects or electrolyte abnormalities
• Delaying treatment in unstable patients while waiting for diagnostic tests
• Overlooking high-risk features that may indicate need for pacing despite minimal current symptoms 1, 2

Remember that approximately 20% of patients with compromising bradycardia may require temporary emergency pacing for initial stabilization, and about 50% may eventually need permanent pacemaker implantation 5.