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

Initial Workup for New Onset Bradycardia

The initial workup for new onset bradycardia should include assessment of vital signs, 12-lead ECG, oxygen administration if hypoxemic, cardiac monitoring, IV access, and identification of potentially reversible causes while simultaneously evaluating for signs of hemodynamic instability. 1

Definition and Clinical Assessment

Bradycardia is defined as a heart rate <60 beats per minute, but clinically significant bradycardia typically presents with a heart rate <50 beats per minute 1. The workup should focus on determining:

1. Whether the bradycardia is appropriate or inappropriate for the clinical condition
2. If the bradycardia is causing symptoms or hemodynamic compromise
3. The underlying mechanism (sinus node dysfunction vs. AV block)
4. Potential reversible causes

Initial Evaluation Algorithm

Step 1: Immediate Assessment

• Assess airway, breathing, and circulation
• Check vital signs including blood pressure and oxygen saturation
• Evaluate for signs of hemodynamic instability:
  • Altered mental status
  • Ischemic chest discomfort
  • Acute heart failure
  • Hypotension
  • Signs of shock 1

Step 2: Establish Monitoring and Access

• Apply cardiac monitor to identify rhythm
• Establish IV access
• Administer oxygen if hypoxemic (hypoxemia is a common cause of bradycardia) 1
• Obtain 12-lead ECG to better define the rhythm and identify potential causes 1

Step 3: Determine Bradycardia Type

• Sinus Node Dysfunction (SND): Sinus bradycardia, ectopic atrial rhythm, junctional rhythm, sinus pauses, or chronotropic incompetence 1
• AV Block: First-degree (PR >0.20 sec), second-degree (Mobitz type I or II), or third-degree (complete) 1

Step 4: Identify Potential Causes

• Medications (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics)
• Electrolyte disturbances (hyperkalemia)
• Increased vagal tone
• Acute myocardial infarction (especially inferior MI)
• Hypothyroidism
• Sleep apnea
• Increased intracranial pressure
• Hypothermia
• Infectious causes (Lyme disease, endocarditis)
• Congenital heart disease
• Infiltrative diseases (amyloidosis, sarcoidosis)
• Neuromuscular disorders 1

Diagnostic Testing

1. 12-lead ECG: Essential component of initial evaluation to:

   • Confirm rhythm and rate
   • Assess nature and extent of conduction disturbance
   • Document other abnormalities suggesting structural heart or systemic disease 1

2. Laboratory Studies:

   • Complete blood count
   • Electrolytes, BUN, creatinine
   • Cardiac biomarkers
   • Thyroid function tests

3. Additional Testing (based on clinical suspicion):

   • Ambulatory ECG monitoring for intermittent symptoms
   • Echocardiogram to assess structural heart disease
   • Exercise testing to evaluate chronotropic incompetence
   • Implantable cardiac monitor for infrequent symptoms 1

4. Electrophysiology Study (EPS): May be considered in selected patients when noninvasive evaluation is nondiagnostic 1

   • Helps assess sinus node function
   • Evaluates AV conduction
   • Identifies anatomic location of conduction disorders

Important Considerations

• Asymptomatic vs. Symptomatic: Not all bradycardias require treatment. Asymptomatic patients with minimal bradycardia may not need intervention 1

• Mobitz Type II AV Block: This type of block is usually below the AV node within the His-Purkinje system and is often symptomatic with potential to progress to complete heart block 1

• Atropine Cautions:

  • May be ineffective in type II second-degree or third-degree AV block with new wide-QRS complex
  • Use cautiously in acute coronary ischemia as increased heart rate may worsen ischemia
  • Ineffective in cardiac transplant patients 1, 2
  • Doses <0.5 mg may paradoxically worsen bradycardia 1

• Temporary Pacing: Consider early for patients with hemodynamically significant bradycardia unresponsive to medical therapy or when bradycardia is likely to progress to complete heart block 1

By following this systematic approach to the evaluation of new onset bradycardia, clinicians can efficiently identify the cause and determine appropriate management strategies to improve patient outcomes.