Etiology of Sinus Bradycardia

Intrinsic and Extrinsic Causes

Sinus bradycardia results from either intrinsic cardiac dysfunction or extrinsic reversible causes including medications, metabolic derangements, increased vagal tone, infections, and environmental factors, and identifying and treating reversible causes is the critical first step before considering permanent interventions, according to the American College of Cardiology 1
Beta-blockers, calcium channel blockers, and digoxin are the most common medication culprits and should be discontinued or dose-reduced when causing symptomatic bradycardia, as recommended by the American Heart Association 1

Drugs transmitted transplacentally or through breast milk can cause bradycardia in neonates, as reported by the European Society of Cardiology 2, 3
Hypothyroidism is a key reversible metabolic cause, often presenting with characteristic ECG changes, and requires thyroxine replacement, according to the European Society of Cardiology 2, 3, 1
Electrolyte abnormalities, including severe hypokalemia, hyperkalemia, and systemic acidosis, must be corrected, as recommended by the American College of Cardiology 1, 4

Increased intracranial pressure from any cause triggers reflex bradycardia through vagal stimulation, as reported by the European Society of Cardiology 2, 3, 1
Myocarditis can cause bradycardia through direct inflammation of the conduction system, according to the European Society of Cardiology 2

Gastrointestinal distress and acute abdominal pain trigger vagal reflexes causing transient bradycardia, as recommended by the American College of Gastroenterology 4, 5
Increased vagal tone during feeding, sleep, defecation causes physiologic bradycardia in neonates, as reported by the European Society of Cardiology 2, 3
Hypothermia causes dose-dependent bradycardia and must be actively rewarmed, according to the American College of Emergency Physicians 2, 3, 1

The most important clinical error is failing to identify reversible causes before considering permanent pacing, and aggressive investigation for medications, hypothyroidism, electrolyte abnormalities, infections, and increased intracranial pressure must be completed first, as recommended by the American College of Cardiology 1