Chapter 09. Defibrillation

Defibrillation is a critical intervention in Advanced Life Support (ALS) for patients in cardiac arrest due to ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT). It is a key component of the Chain of Survival, aiming to restore normal cardiac rhythm and improve survival outcomes.

Key Topics Covered in Chapter 9

1. Probability of Successful Defibrillation
   • The success of defibrillation depends on the time elapsed since the onset of VF/pVT.
   • Every minute without defibrillation reduces survival by 7–10% if no CPR is performed.
   • Immediate CPR can slow this decline, reducing mortality by 3–4% per minute.
2. Mechanism of Defibrillation
   • Defibrillation involves the passage of an electrical current through the heart to depolarise a critical mass of myocardium.
   • This allows the natural pacemaker (sinoatrial node) to regain control.
   • Key components of a defibrillator:
     • Power source (battery or mains supply)
     • Capacitor (stores and releases electrical energy)
     • Electrodes (pads or paddles placed on the patient’s chest)
3. Factors Affecting Defibrillation Success
   • Transthoracic Impedance (TTI): Electrical resistance of the chest, influenced by:
     • Electrode placement
     • Chest hair (should be shaved if impeding pad adhesion)
     • Skin condition (avoid placing pads over wet or damaged skin)
   • Pre-shock Pause: Delays between stopping CPR and delivering the shock must be minimised (<5 seconds).
   • Continuous Chest Compressions: Interruptions should be minimised, as even short pauses reduce the likelihood of ROSC (Return of Spontaneous Circulation).
4. Shock Energies
   • Biphasic defibrillators are preferred due to lower energy requirements and higher success rates.
   • Energy levels:
     • Initial shock: 150 J (or follow manufacturer’s recommendation)
     • Subsequent shocks: Same or higher energy, up to 360 J for refractory VF/pVT.
5. Safety Considerations
   • Ensure no one is touching the patient during shock delivery.
   • Remove oxygen delivery devices if they could cause sparking.
   • Use correct pad placement:
     • Standard: One pad right of sternum below the clavicle; second pad in the mid-axillary line at V6 level.
     • Alternative: Anteroposterior (front and back) or bi-axillary placements.
6. Use of Automated External Defibrillators (AEDs)
   • AEDs are recommended in environments where trained personnel are unavailable.
   • They provide automated rhythm analysis and voice prompts.
   • In hospitals, AEDs may be useful in unmonitored areas where immediate manual defibrillation is not available.
7. Manual Defibrillation Process
   • Confirm cardiac arrest.
   • Perform CPR while preparing the defibrillator.
   • Charge the defibrillator while continuing chest compressions.
   • Stop CPR for a brief rhythm check (<5 sec).
   • Deliver a shock if VF/pVT is confirmed.
   • Resume CPR immediately after shock delivery.
8. Defibrillation in Children
   • >8 years old: Use standard adult settings.
   • 1–8 years old: Use paediatric pads with energy attenuation.
   • <1 year old: Use AED only if no alternative is available.
9. Synchronised Cardioversion
   • Used for atrial fibrillation (AF), supraventricular tachycardia (SVT), or haemodynamically unstable ventricular tachycardia (VT).
   • Requires synchronisation with the R wave to avoid inducing VF.
10. Implanted Electronic Devices (IEDs)

• Includes pacemakers and implantable cardioverter-defibrillators (ICDs).
• Avoid placing defibrillation pads directly over these devices.

1. Internal Defibrillation

• Used in cardiac surgery or invasive procedures.
• Lower energy (10–20 J biphasic; max 50 J monophasic).