What is the initial approach to a patient presenting with sinus bradycardia?

Sinus Bradycardia Workup

Begin by documenting the bradycardia on ECG (heart rate <60 bpm, sinus origin) and immediately determine if symptoms are directly attributable to the slow heart rate—if the patient is asymptomatic, no workup or treatment is needed. 1, 2

Initial Clinical Assessment

Establish symptom-bradycardia correlation first:

• Document whether syncope, presyncope, lightheadedness, dyspnea, fatigue, or confusion occurs specifically during bradycardic episodes 1, 2
• Asymptomatic bradycardia (common in athletes, young individuals, during sleep) requires no intervention 1
• Use cardiac monitoring matched to symptom frequency: Holter monitor (24-72 hours) for daily symptoms, event recorder/mobile telemetry for weekly symptoms, or implantable monitor for episodes >30 days apart 2

Comprehensive Medication Review (Priority #1)

This is the most critical step—immediately review all negative chronotropic agents: 1, 2

• Beta-blockers 3, 2
• Non-dihydropyridine calcium channel blockers (diltiazem, verapamil) 3, 2
• Digoxin 3, 2
• Antiarrhythmic drugs (sodium-channel blockers like flecainide, potassium-channel blockers like amiodarone) 3, 2
• Lithium, methyldopa, risperidone, cisplatin, interferon 3

Consider dose reduction or discontinuation if not essential (e.g., switch beta-blocker to ACE inhibitor/ARB for hypertension) 1

Laboratory Evaluation for Reversible Causes

Order these specific tests based on clinical suspicion: 3, 1, 2

Essential labs:

• Thyroid function tests (TSH, free T4) to identify hypothyroidism—a key reversible cause that responds to thyroxine replacement 1, 2
• Electrolytes: potassium (both hypokalemia and hyperkalemia), calcium, magnesium 3, 1, 2
• Arterial blood gas if acidosis suspected 2

Condition-specific testing:

• Lyme titer if endemic area exposure or compatible clinical features (Lyme disease, legionella, psittacosis, typhoid, malaria, leptospirosis, Dengue, viral hemorrhagic fevers, Guillain-Barré) 3, 2
• Troponin/cardiac biomarkers if acute MI suspected (especially inferior MI causing vagal stimulation) 3
• Imaging for elevated intracranial pressure if neurologic symptoms present 2

Additional Reversible Causes to Evaluate

Screen for these clinical scenarios: 3, 2

• Acute myocardial ischemia/infarction (especially inferior wall) 3
• Severe hypothermia (therapeutic post-cardiac arrest cooling or environmental) 3, 2
• Obstructive sleep apnea 3, 2
• Hypoxemia, hypercarbia 3, 2
• Hypovolemic shock 3
• Athletic training/hypervagotonía 3
• Post-cardiac surgery (valve replacement, CABG, maze procedure) 3
• Heart transplant (acute/chronic rejection) 3
• Drug toxicity (toluene, organophosphates, tetrodotoxin, cocaine) 3

When Advanced Testing Is NOT Indicated

Electrophysiology study (EPS) should NOT be performed in asymptomatic patients unless other indications exist 1

• EPS may be considered (Class IIb) only in symptomatic patients with suspected sinus node dysfunction when diagnosis remains uncertain after completing all noninvasive evaluations 1

Critical Pitfall to Avoid

The most important error is failing to identify reversible causes before considering permanent pacing. 1 Complete the aggressive investigation for medications, hypothyroidism, electrolyte abnormalities, infections, and elevated intracranial pressure first. 1 Ensure documented temporal correlation between symptoms and bradycardia before attributing symptoms to heart rate. 1

Acute Management (If Hemodynamically Unstable)

Only treat if symptomatic with hemodynamic compromise: 3

• Atropine 0.5-1 mg IV (may repeat every 3-5 minutes to maximum 3 mg) is reasonable to increase sinus rate 3, 4
• Do NOT use atropine in heart transplant patients without autonomic reinnervation (Class III: Harm) 3
• Consider isoproterenol, dopamine, dobutamine, or epinephrine if low likelihood of coronary ischemia (Class IIb) 3
• Temporary pacing indicated if medications fail 3

In acute MI with sinus bradycardia and severe hypotension: treat with IV atropine first; if accompanied by high-degree AV block without stable escape rhythm, use IV positive chronotropic medication (epinephrine, vasopressin, and/or atropine), then temporary pacing if unresponsive 3

Management Pathway

Address reversible causes first: 2

• Manage underlying condition causing bradycardia 2
• Permanent pacing should only be considered after reversible causes excluded or cannot be adequately managed 2
• In acute settings with hemodynamic compromise, temporary interventions may bridge to definitive diagnosis 2