What is the immediate treatment for a patient with a shockable rhythm, such as ventricular fibrillation or pulseless ventricular tachycardia?

Immediate Treatment for Shockable Rhythm (VF/pVT)

For patients with ventricular fibrillation or pulseless ventricular tachycardia, immediately perform high-quality CPR and defibrillate as soon as the defibrillator is available—this combination of early defibrillation with concurrent high-quality CPR is critical to survival. 1

Initial Management Algorithm

Step 1: Immediate Defibrillation

• Deliver the first shock immediately upon rhythm confirmation without delay 1
• Use 200 J for biphasic defibrillators (or 360 J for monophasic) 1
• If witnessed arrest with defibrillator immediately available on-site, start CPR and use the defibrillator as soon as possible 1
• Defibrillation should occur within 3 minutes of arrest onset 1

Step 2: Resume CPR Immediately After Shock

• Immediately resume chest compressions after shock delivery without pausing to check rhythm or pulse 1, 2
• Continue high-quality CPR for 2 minutes (5 cycles) 1
• Minimize all interruptions in chest compressions—pauses are associated with decreased probability of successful defibrillation 1
• Chest compressions should be performed for at least 51-76% of total CPR time 1

Step 3: Rhythm Check and Second Shock

• After 2 minutes of CPR, briefly pause to check rhythm 1
• If VF/pVT persists, deliver second shock at 200-300 J 1
• Immediately resume CPR after the shock 1, 2

Step 4: Third Shock and Medication Administration

• After another 2 minutes of CPR, check rhythm again 1
• If VF/pVT persists, deliver third shock at 360 J (or maximum energy) 1
• Immediately resume CPR and administer epinephrine 1 mg IV/IO after the third shock 1, 2
• Continue epinephrine 1 mg IV/IO every 3-5 minutes throughout resuscitation 1, 2

Step 5: Antiarrhythmic Therapy for Shock-Refractory VF/pVT

• If VF/pVT persists after 3 shocks, administer either amiodarone 300 mg IV/IO OR lidocaine 1-1.5 mg/kg IV/IO 1, 2, 3
• Amiodarone is given as 300 mg bolus, with a second dose of 150 mg if VF/pVT recurs 1, 3
• Lidocaine is an acceptable alternative if amiodarone is unavailable 1, 2
• Continue CPR for 2 minutes, then reassess rhythm and deliver fourth shock if indicated 1

Critical Timing Considerations

CPR Before Defibrillation: When Is It Appropriate?

• For witnessed arrest with immediate defibrillator availability: shock immediately without preceding CPR 1, 2
• For unwitnessed arrest or EMS response time >5 minutes: 1.5-3 minutes of CPR before first shock may improve outcomes, though evidence is mixed 1, 4
• Current guidelines prioritize immediate defibrillation over routine CPR-first strategies 1, 2

Minimizing Peri-Shock Pauses

• Charge the defibrillator during chest compressions 5
• Limit pre-shock pause to <5 seconds for rhythm analysis and safety check 1, 5
• Resume compressions immediately post-shock without pulse check 1, 2
• Shorter pre- and peri-shock pauses are associated with higher survival rates 5

Important Medication Caveats

Epinephrine Limitations

• Epinephrine increases ROSC and short-term survival but has NOT been shown to improve long-term survival with favorable neurological outcomes 1, 2
• The benefit is primarily through alpha-adrenergic vasoconstriction improving coronary perfusion pressure 1, 2
• Never delay CPR or defibrillation to establish vascular access for medications 1, 2

Antiarrhythmic Drug Limitations

• Neither amiodarone nor lidocaine improve long-term survival or neurological outcomes 1, 2
• Their role is to facilitate successful defibrillation and reduce recurrent arrhythmias 1
• Establishing IV/IO access should not compromise CPR quality or defibrillation timing 1, 2

Medications to Avoid

• High-dose epinephrine (>1 mg) provides no benefit 1, 2
• Vasopressin offers no advantage over epinephrine 1, 2
• Do not use vasopressin in place of or in addition to epinephrine 1

Common Pitfalls to Avoid

• Never perform prolonged pulse checks or rhythm analysis between shocks—this interrupts critical chest compressions 1, 5
• Never delay defibrillation to administer medications first—early defibrillation is the definitive treatment 1, 2
• Never use synchronized cardioversion for pulseless VT—treat as VF with unsynchronized shocks at full energy 1, 6
• Never assume one shock will terminate VF—be prepared for multiple shocks and continued CPR 1
• Never stop CPR for more than 10 seconds except for shock delivery 1, 5

Vascular Access Considerations

• IV access is preferred, but IO access is equally acceptable if IV unsuccessful 2
• Establish access during CPR without interrupting compressions 1, 2
• If endotracheal tube is in place but no vascular access, epinephrine can be given via ET at 0.1 mg/kg (10x the IV dose), though this is not preferred 1