Sinus bradycardia

Sinus bradycardia is a sinus rhythm with a heart rate < 60/minute. It can be physiological, affecting healthy individuals, or pathological due to sinus node dysfunction (SND). The diagnosis is confirmed by ECG. Patients with unstable bradycardia are managed according to the ACLS unstable bradycardia algorithm. Mild asymptomatic sinus bradycardia usually requires no further workup or treatment. Patients with symptoms or a heart rate < 50/minute are evaluated for SND, with management directed at the underlying cause. Select patients with SND are candidates for placement of a permanent pacemaker.

See also "Management of bradycardia" and "Sinus node dysfunction."

• Physiological sinus bradycardia: : caused by high vagal tone in healthy individuals; (e.g., athletes, healthy young adults, or occurrence during sleep) ^[1]
• Pathological sinus bradycardia: caused by SND
  • Intrinsic conditions affecting the sinoatrial node (SA node), e.g., degeneration, ischemia, infiltration, and fibrosis
    • Acute coronary syndrome and/or chronic coronary disease
    • Cardiomyopathies
  • Extrinsic factors affecting SA node conduction, such as vagal tone, medications, and metabolic abnormalities
    • Vasovagal response
    • Beta blockers, calcium channel blockers, sedative-hypnotic drugs, cholinergic agents
    • Electrolyte abnormalities
    • Hypoxia
    • Hypothermia
    • Hypothyroidism
  • See "Etiology of sinus node dysfunction" and "Reversible causes of sinus node dysfunction" for details.

• Physiological sinus bradycardia: usually asymptomatic
• Pathological sinus bradycardia: often manifests with clinical features of bradycardia

Approach ^[1]

• All patients: Obtain ECG to confirm sinus bradycardia.
• Likely physiological sinus bradycardia: No further workup is required in healthy individuals (e.g., athletes, healthy young adults, or occurrence during sleep) with mild, asymptomatic sinus bradycardia.
• Symptomatic bradycardia or heart rate < 50/minute: Initiate diagnostics for sinus node dysfunction.

Do not delay initial management of bradycardia for detailed diagnostics in patients with clinical features of unstable bradycardia.

ECG ^[2]

• Rate < 60/minute ^[1]
• P wave in all leads, with normal polarity
• Regular P–P intervals

• Sinus node dysfunction
• Atrioventricular block
• See "Overview of bradyarrhythmias."
• See "Causes of bradycardia."

The differential diagnoses listed here are not exhaustive.

Patients with signs of unstable bradycardia ^[1][3][4]

• Begin initial management of bradycardia, e.g., ECG, IV access, and monitoring.
• Follow the unstable bradycardia algorithm, including, as indicated:
  • IV atropine
  • Transcutaneous pacing AND/OR IV infusion of either dopamine or epinephrine
  • Transvenous pacing
• Manage reversible causes of bradycardia.
• Consult cardiology.

Hemodynamically stable patients ^[1]

See "Initial management of sinus node dysfunction" for a general approach and disposition.

• Physiological sinus bradycardia: no treatment needed ^[2]
• Pathological sinus bradycardia ^[5]
  • Asymptomatic patients: observation
  • Symptomatic patients
    • Identify and treat any reversible causes of SND.
    • Irreversible causes: Consider permanent pacemaker placement or PDE inhibitors for patients with severe and/or frequent symptoms.
    • See "Treatment of sinus node dysfunction" for details.