Antiarrhythmic Comparison: Amiodarone vs Adenosine vs Atropine — When to Use Which

Step 1: Does the patient have a pulse?

• NO PULSE → Is the rhythm VFib or pulseless VTach?

  • YES → Amiodarone 300 mg IV push (first dose)
    • Given during CPR after initial defibrillation attempts fail
    • Second dose: 150 mg IV push if needed
    • Mixed in D5W only — precipitates in normal saline
    • Continue CPR; do NOT pause compressions to push the drug
  • NO (asystole/PEA) → Epinephrine is the drug — none of these three apply
    • Atropine is NO longer recommended for asystole per current ACLS

• HAS A PULSE → Go to Step 2

Step 2: Is the heart rate fast or slow?

• FAST (tachycardia) → Go to Step 3
• SLOW (symptomatic bradycardia, HR typically < 60 with hypotension, altered LOC, or chest pain) → Atropine
  • Dose: 0.5 mg IV every 3-5 minutes
  • Max total dose: 3 mg
  • Mechanism: blocks vagal tone → increases HR
  • If atropine fails → transcutaneous pacing or dopamine/epinephrine drip
  • Do NOT use in heart transplant patients (denervated heart won't respond)

Step 3: Tachycardia — Is the QRS narrow or wide?

• NARROW QRS (< 0.12 sec) → Suspect SVT → Adenosine

  • Try vagal maneuvers first (bearing down, ice to face)
  • First dose: 6 mg rapid IV push → immediate 20 mL NS flush
  • If no conversion in 1-2 minutes: 12 mg rapid IV push → flush
  • May repeat 12 mg × 1 more
  • Must use the IV site closest to the heart (antecubital or above)
  • Half-life is < 10 seconds — sluggish push = wasted drug
  • Warn the patient: brief chest tightness, feeling of "impending doom," transient asystole is expected
  • Contraindicated in 2nd/3rd-degree heart block, WPW with atrial fibrillation

• WIDE QRS (≥ 0.12 sec) + PULSE → Suspect stable VTach → Amiodarone

  • Dose: 150 mg IV over 10 minutes (NOT rapid push when patient has a pulse)
  • Follow with maintenance infusion: 1 mg/min × 6 hr, then 0.5 mg/min × 18 hr
  • Monitor for hypotension during infusion — slow the rate if BP drops
  • Assess thyroid and pulmonary function (long-term toxicity: thyroid, lungs, liver, corneal deposits)
  • If patient becomes unstable or loses pulse at any point → immediate synchronized cardioversion or defibrillation

Critical Discrimination Summary