Defibrillator Modes – Study Notes

1. Overview

• Defibrillator = critical crash cart equipment.

• Modes:

  1. Defibrillation

  2. Synchronized cardioversion

  3. Transcutaneous pacing (TCP)

• Pads preferred over paddles: safer, easier, allow ECG monitoring.

• Pad placement:

  • Anterior-apex: below clavicle + left lateral chest.

  • Anterior-posterior: front of chest + between scapula (preferred).

2. Defibrillation

• Definition: Delivers an unsynchronized electrical shock to completely depolarize the myocardium → allows SA node to restart normal rhythm.

• Indications:

  • Ventricular fibrillation (VF).

  • Pulseless ventricular tachycardia (pVT).

• Not for: Asystole or PEA (pulseless electrical activity).

• Timing: Every minute delay ↓ success by 7–10%.

• Energy settings:

  • Monophasic: 360 J (older, rare).

  • Biphasic (modern):

    • ZOLL: 120 → 150 → 200 J.

    • Philips: 150 J (all shocks).

    • LifePak 15: 200 → 300 → 360 J.

  • Internal paddles: much lower (5–10 J, escalate).

• Steps: Attach pads → select energy → charge → clear patient → shock → resume CPR.

3. Synchronized Cardioversion

• Definition: Shock delivered in sync with the R wave (avoids T wave → prevents VF).

• Indications: Tachyarrhythmias with a pulse when unstable.

  • SVT.

  • Atrial fibrillation.

  • Atrial flutter.

  • Ventricular tachycardia with a pulse.

• Stable patients: try meds first (adenosine, rate/rhythm control).

• Energy settings:

  • Monophasic: 100 → 200 → 360 J.

  • ZOLL: 75 → 120 → 150 J.

  • Philips: 100 → 150–200 J.

  • LifePak 15: 100 → 200 → 300 J.

  • For SVT/flutter: may start as low as 50 J.

• Steps:

  • Sedate if possible.

  • Attach pads → select sync mode → confirm R-wave markers → charge → press & hold shock until delivered.

4. Transcutaneous Pacing (TCP)

• Definition: External pacing by delivering impulses through pads to stimulate ventricular contraction.

• Indications:

  • Symptomatic bradycardia unresponsive to atropine.

  • High-degree AV block (Mobitz II, third-degree).

  • Temporary measure until transvenous or permanent pacemaker.

• Setup:

  • Use anterior-posterior pad placement.

  • Attach ECG leads for monitoring (pads only deliver impulses).

• Steps:

  1. Select pacer mode.

  2. Set rate (usually 60 bpm).

  3. Start at lowest output → gradually increase until capture.

     • Capture = pacing spike followed by wide QRS.

  4. Increase slightly above capture threshold (safety margin).

5. High-Yield Reminders

• Defibrillation = VF/pulseless VT only (unsynchronized).

• Cardioversion = tachyarrhythmia with pulse (synchronized).

• TCP = bradycardia/high-degree block when atropine fails.

• Always clear patient before shocks.

• Resume high-quality chest compressions immediately after defibrillation.