Out-of-hospital defibrillation with automated external defibrillators: postshock analysis should be delayed

Area of Science:

• Cardiology
• Emergency Medicine
• Medical Device Technology

Background:

• American Heart Association guidelines recommend immediate rhythm analysis after automated external defibrillator (AED) shocks.
• Post-shock electrical silence or organized activity can precede recurrence of ventricular fibrillation (VF) or ventricular tachycardia (VT).
• The optimal timing for identifying recurrent VF/VT after defibrillation is not well-established.

Purpose of the Study:

• To investigate the time to recurrence of VF/VT after a defibrillation attempt using an AED.
• To evaluate the effectiveness of current AED protocols in identifying recurrent life-threatening arrhythmias.

Main Methods:

• Screened 222 AED tapes from 96 patients with out-of-hospital cardiac arrest over 18 months.
• Excluded pediatric and traumatic cases from a single emergency medical services system.
• Measured time from defibrillation to recurrent VF/VT by blinded cardiology fellows.

Main Results:

• Only 20% of VF/VT recurrences were identified within 6 seconds.
• 73% of VF/VT recurrences occurred by 60 seconds, and 90% by 90 seconds post-defibrillation.
• Eighty percent of VF/VT recurrences were missed by immediate analysis.

Conclusions:

• Current AED protocols miss a significant percentage of recurrent VF/VT.
• Postponing rhythm analysis to at least 30 seconds after defibrillation is recommended.
• Incorporating 30 seconds of chest compressions before AED analysis could increase VF/VT identification to 52%.