What is the workup for sinus bradycardia?

Workup for Sinus Bradycardia

The workup for sinus bradycardia must begin with aggressive identification and treatment of reversible causes—particularly medications, hypothyroidism, and metabolic derangements—before considering any invasive testing or permanent interventions. 1

Initial Diagnostic Approach

1. Establish the Diagnosis and Symptom Correlation

• Document bradycardia on ECG with heart rate <60 bpm (clinically significant typically <50 bpm) and confirm sinus origin 2
• Determine if symptoms are directly attributable to bradycardia: syncope, presyncope, lightheadedness, dyspnea, fatigue, or confusion from cerebral hypoperfusion 1
• Asymptomatic bradycardia requires no workup or treatment unless other indications exist, as it is common in athletes, young individuals, and during sleep 2, 3

2. Comprehensive Medication Review

• Immediately review all negative chronotropic medications: beta-blockers, calcium channel blockers, digoxin, sodium-channel blockers, and potassium-channel blocking antiarrhythmics 1, 4
• Consider dose reduction or discontinuation if the medication is not essential (e.g., beta-blocker used solely for hypertension can be switched to ACE inhibitor or ARB) 1
• In neonates, investigate transplacental or breast milk drug transmission 1, 4

3. Laboratory Evaluation for Reversible Causes

• Thyroid function tests (TSH, free T4): Hypothyroidism is a key reversible cause that responds well to thyroxine replacement 1, 4
  • Look for characteristic "mosque sign" ECG pattern (dome-shaped symmetric T wave without ST segment) in hypothyroidism 1
• Electrolytes (potassium, calcium, magnesium): Severe hypokalemia, hyperkalemia, or systemic acidosis can cause bradycardia 1, 4
• Consider additional labs based on clinical context: glucose, renal function, liver function 4

4. Identify Other Reversible Physiological Causes

• Increased intracranial pressure: Evaluate for CNS pathology, meningitis, or mass lesions if neurologic symptoms present 1, 4
• Acute myocardial infarction: Obtain troponins and serial ECGs if chest pain or ischemic symptoms 1, 4
• Obstructive sleep apnea: Screen with history of obesity, daytime tiredness, witnessed apneas—consider polysomnography before pacemaker implantation 1, 5
• Hypothermia: Check core temperature and actively rewarm if present 1, 4
• Infection/sepsis: Myocarditis can cause bradycardia with T wave changes and conduction abnormalities 1, 4
• Increased vagal tone: Consider if bradycardia occurs during feeding, sleep, defecation, or with gastrointestinal distress 1, 6

5. Ambulatory ECG Monitoring (If Symptoms Are Intermittent)

• 24-48 hour Holter monitor or extended event monitor to capture correlation between symptoms and bradycardia episodes 1, 7
• Document minimum heart rate, sinus pauses >3 seconds, chronotropic incompetence with activity 1
• Vagally-mediated bradycardia during sleep (with concomitant P-P prolongation) may be benign and not require treatment 1

6. Echocardiography

• Perform echocardiogram when clinically indicated: suspected myocarditis, heart failure symptoms, or structural heart disease 1
• Not routinely required for isolated asymptomatic sinus bradycardia 1

Advanced Testing (Rarely Indicated)

Electrophysiology Study (EPS)

• EPS should NOT be performed in asymptomatic patients unless other indications for electrophysiological testing exist 1
• EPS may be considered (Class IIb) in symptomatic patients with suspected sinus node dysfunction when diagnosis remains uncertain after all noninvasive evaluations 1, 2
• EPS may be considered (Class IIb) if patient is already undergoing EPS for another indication (e.g., ventricular arrhythmia evaluation) 1
• Measures include sinus node recovery time (SNRT) and sinoatrial conduction time (SACT), but both have limited sensitivity and specificity 1
• Abnormal EPS findings alone should NOT justify pacemaker implantation without clinical correlation 1

Critical Clinical Pitfalls to Avoid

• The most important error is failing to identify reversible causes before considering permanent pacing—aggressive investigation for medications, hypothyroidism, electrolyte abnormalities, infections, and increased intracranial pressure must be completed first 4
• Do not implant a pacemaker in patients with obstructive sleep apnea until nCPAP therapy has been attempted, as bradycardia often resolves with treatment 5
• Do not pursue extensive workup for asymptomatic bradycardia discovered incidentally, especially in young patients or athletes 2, 7
• Ensure documented temporal correlation between symptoms and bradycardia before attributing symptoms to heart rate 1, 3