What is the initial treatment for acute sinus bradycardia?

Initial Treatment for Acute Sinus Bradycardia

For symptomatic sinus bradycardia, atropine 0.5-1 mg IV (may be repeated every 3-5 minutes to a maximum dose of 3 mg) is the first-line treatment. 1

Assessment of Symptomatic vs. Asymptomatic Bradycardia

Symptomatic Bradycardia (requires treatment):

• Heart rate typically <50 bpm with:
  • Hypotension (systolic BP <80 mmHg)
  • Signs of hypoperfusion
  • Chest pain/ischemia
  • Shortness of breath
  • Altered mental status
  • Syncope or presyncope
  • Escape ventricular arrhythmias

Asymptomatic Bradycardia (no treatment needed):

• Heart rate <60 bpm without symptoms
• Stable vital signs
• No signs of hypoperfusion

Treatment Algorithm

First-Line Treatment:

1. Atropine 0.5-1 mg IV
   • May repeat every 3-5 minutes
   • Maximum total dose: 3 mg
   • Goal: Achieve minimally effective heart rate (~60 bpm)
   • Avoid doses <0.5 mg (may paradoxically worsen bradycardia) 1

If Inadequate Response to Atropine:

1. Second-Line Treatments 1, 2:

   • Dopamine: 5-20 mcg/kg/min IV infusion

     • Start at 5 mcg/kg/min and increase by 5 mcg/kg/min every 2 minutes
     • Caution: Doses >20 mcg/kg/min may cause vasoconstriction or arrhythmias

   • Epinephrine: 2-10 mcg/min IV or 0.1-0.5 mcg/kg/min IV

     • Titrate to desired effect

   • Isoproterenol: 20-60 mcg IV bolus followed by doses of 10-20 mcg

     • Alternative: Infusion of 1-20 mcg/min based on heart rate response
     • Use only in patients at low likelihood of coronary ischemia

2. Transcutaneous Pacing 1, 2:

   • Indicated when pharmacological therapy fails
   • Apply transcutaneous patches and activate promptly if needed
   • Consider for patients with high risk of progression to complete heart block

Special Considerations

Reversible Causes

Always identify and treat reversible causes of sinus bradycardia 1:

• Medications (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics)
• Acute myocardial ischemia/infarction
• Electrolyte abnormalities (hyperkalemia, hypokalemia, hypoglycemia)
• Hypothyroidism
• Increased vagal tone
• Hypothermia
• Hypoxemia, hypercarbia, acidosis

Medication-Specific Antidotes 1:

• Beta-blocker overdose: Glucagon 3-10 mg IV with infusion of 3-5 mg/h
• Calcium channel blocker overdose: 10% calcium chloride 1-2 g IV every 10-20 min
• Digoxin overdose: Digoxin antibody fragments (dosage based on amount ingested)

Important Cautions

• Heart transplant patients: Atropine should NOT be used (Class III: Harm) as it is ineffective due to cardiac denervation 1
• Infranodal AV block: Atropine is ineffective and should not be used for AV block occurring at an infranodal level (type II second-degree AV block or third-degree AV block with wide QRS) 1
• Asymptomatic bradycardia: No treatment is needed (Class III) 1

Progression to Permanent Pacing

If bradycardia is persistent and symptomatic despite medical therapy, or if reversible causes cannot be identified and treated, consider temporary transvenous pacing as a bridge to permanent pacemaker implantation 1, 2.

Remember that the goal of treatment is to improve symptoms and hemodynamic status while identifying and addressing the underlying cause of the bradycardia.