What is the first medication to administer in a code for bradycardia (slow heart rate)?

First Medication for Bradycardia in a Code Situation

Atropine is the first-line medication to administer in a code situation for symptomatic bradycardia, at a dose of 0.5-1 mg IV every 3-5 minutes, with a maximum total dose of 3 mg. 1, 2

Initial Assessment and Treatment Algorithm

1. Confirm symptomatic bradycardia:

   • Heart rate < 50 beats per minute with symptoms
   • Symptoms include: hypotension, altered mental status, chest pain, dyspnea, or signs of shock

2. First-line medication:

   • Atropine 0.5-1 mg IV 2, 1, 3
   • May repeat every 3-5 minutes
   • Maximum total dose: 3 mg
   • Monitor response after each dose

3. If inadequate response to atropine:

   • Initiate transcutaneous pacing (TCP) OR
   • Begin IV infusion of β-adrenergic agonists:
     • Dopamine: 5-20 mcg/kg/min IV
     • Epinephrine: 2-10 mcg/min IV
     • Isoproterenol: 2-10 mcg/min IV 2, 1

Mechanism of Action

Atropine is an antimuscarinic agent that competitively blocks the effects of acetylcholine at muscarinic receptors. In the heart, it blocks vagal stimulation, which increases sinoatrial node automaticity and enhances atrioventricular conduction 3. This leads to an increase in heart rate and improved cardiac output in bradycardic patients.

Special Considerations

• Heart transplant patients: Atropine should NOT be used as it may be ineffective due to cardiac denervation. Consider aminophylline or theophylline instead 2, 1

• Type of bradycardia: Atropine is most effective for sinus bradycardia and AV nodal blocks, particularly those caused by increased vagal tone 4

• Caution in infranodal blocks: Patients with AV blocks at the His-Purkinje level may paradoxically worsen with atropine administration 5

• Pediatric dosing: For pediatric patients, atropine dosing is 0.02 mg/kg (minimum single dose: 0.1 mg, maximum single dose: 0.5 mg for a child, 1.0 mg for an adolescent) 2

Potential Pitfalls

1. Low-dose paradoxical effect: Very low doses of atropine (<0.5 mg) may paradoxically worsen bradycardia due to central vagotonic effects before peripheral vagolytic effects occur 6

2. Infranodal blocks: In patients with infranodal AV blocks, atropine may worsen the bradycardia or even cause asystole 5

3. Medication-induced bradycardia: In cases of beta-blocker or calcium channel blocker overdose, specific antidotes should be considered:

   • Beta-blocker overdose: Glucagon 3-10 mg IV
   • Calcium channel blocker overdose: 10% calcium chloride 1-2 g IV 2

4. Refractory cases: For bradycardia resistant to atropine, consider aminophylline as an alternative before pacemaker placement, particularly in spinal cord injuries 7

Remember to continuously monitor the patient's response to treatment and be prepared to escalate therapy if the patient remains symptomatic despite atropine administration.