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

Initial Workup for Bradycardia

The initial workup for bradycardia should include a 12-lead ECG, comprehensive history focusing on symptoms and medication review, physical examination, and basic laboratory tests to identify underlying causes. 1

Definition and Initial Assessment

Bradycardia is defined as a heart rate less than 60 beats per minute, though clinically significant bradycardia typically presents with a heart rate below 50 beats per minute. The key components of the initial evaluation include:

Immediate Assessment

• Assess airway, breathing, and circulation
• Provide supplementary oxygen if hypoxemic 1
• Establish IV access
• Apply cardiac monitor
• Obtain 12-lead ECG (essential component of initial evaluation) 1
• Measure blood pressure and pulse oximetry

History Elements to Obtain

• Symptom assessment: syncope, near-syncope, dizziness, fatigue, dyspnea, chest pain
• Timing, duration, and triggers of symptoms
• Medication review (focus on beta-blockers, calcium channel blockers, digoxin, amiodarone, ivabradine, clonidine) 2
• Medical history (particularly cardiovascular and thyroid disease)
• Family history of cardiac conduction disorders or sudden cardiac death 2

Physical Examination Focus

• Vital signs (including postural blood pressure changes)
• Cardiovascular examination (heart sounds, murmurs, jugular venous pressure)
• Signs of underlying structural heart disease
• Neurological assessment (if syncope is present)

Laboratory and Diagnostic Testing

Basic Laboratory Tests

• Electrolytes (particularly potassium, magnesium, calcium)
• Renal function tests
• Thyroid function tests
• Complete blood count
• Cardiac biomarkers (if ischemia is suspected)

Diagnostic Tests Based on Initial Findings

1. 12-lead ECG - To identify:

   • Type of bradyarrhythmia (sinus bradycardia, AV block, etc.)
   • Conduction abnormalities (bundle branch blocks, fascicular blocks)
   • Signs of ischemia or prior infarction
   • QT interval abnormalities 1, 2

2. Ambulatory Cardiac Monitoring - If symptoms are intermittent:

   • 24-48 hour Holter monitor for frequent symptoms
   • Event recorder for less frequent symptoms
   • Mobile cardiac telemetry for correlation of symptoms with rhythm 1, 2

3. Advanced Testing (based on initial findings):

   • Echocardiogram (if structural heart disease is suspected)
   • Exercise electrocardiographic testing (for suspected chronotropic incompetence or exercise-related symptoms) 1
   • Electrophysiology study (may be considered in selected patients when noninvasive evaluation is nondiagnostic) 1

Common Pitfalls to Avoid

• Not distinguishing physiologic from pathologic bradycardia: Bradycardia can be normal in athletes or during sleep 3
• Focusing only on heart rate: Correlation between symptoms and bradycardia is essential for determining clinical significance 1
• Overlooking medication effects: Many commonly prescribed medications can cause bradycardia 1, 2
• Missing intermittent bradycardia: Single ECG may miss paroxysmal bradyarrhythmias, requiring extended monitoring 1
• Treating asymptomatic bradycardia unnecessarily: Asymptomatic bradycardia generally does not require intervention 2

Special Considerations

• In patients with syncope, the initial ECG provides a diagnosis in only approximately 5% of cases, but abnormal findings may predict adverse outcomes 1
• For patients with exercise-related symptoms, exercise electrocardiographic testing is reasonable 1
• For patients with suspected chronotropic incompetence, exercise testing can help establish the diagnosis 1
• If 2:1 AV block of unknown level is present, exercise testing may help determine the level of block 1

The workup should be guided by the severity of symptoms, presence of underlying heart disease, and risk factors for conduction system disease. Determining whether bradycardia is the cause of symptoms is crucial for appropriate management decisions.