Defibrillators and Cardioversion

Quick Answer

Defibrillation delivers unsynchronized electrical current to terminate ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT) by simultaneously depolarizing a critical mass (>75%) of myocardium, allowing the sinoatrial node to resume control. Current (measured in Amperes) is the determinant of success, requiring approximately 30-40A to achieve defibrillation. Modern biphasic waveforms are more effective at lower energies (120-200J) than monophasic (360J) due to impedance compensation and improved defibrillation threshold. Transthoracic impedance (TTI) typically 70-80 Ohms determines current delivery for a given energy. Pad placement should be anterior-lateral (standard) or anterior-posterior; the DOSE VF trial (2022) showed vector change improves outcomes in refractory VF. Synchronized cardioversion delivers energy on the R-wave to avoid the vulnerable period (T-wave) and is used for organized tachyarrhythmias with pulses (AF: 120-200J biphasic, flutter: 50-100J, VT with pulse: 100-150J). Transcutaneous pacing is first-line for unstable bradycardia, requiring 50-100mA capture threshold. ANZCOR recommends 200J biphasic for all shocks, single-shock strategy, and minimizing CPR interruptions.

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CICM Exam Focus

What Examiners Expect

Second Part Written (SAQ):

Defibrillation physics and cardioversion protocols are core CICM topics

Common SAQ stems:

• "Describe the physics of defibrillation, including the determinants of successful defibrillation."
• "Compare and contrast monophasic and biphasic defibrillation waveforms."
• "Outline the indications for, and technique of, synchronized cardioversion. What are the energy requirements for different arrhythmias?"
• "A patient develops refractory VF during cardiac arrest. Describe strategies beyond standard defibrillation."
• "Describe the principles and technique of transcutaneous pacing."
• "What factors affect transthoracic impedance during defibrillation?"

Recent SAQ themes (2020-2025):

• 2024: "Describe the DOSE VF trial and its implications for refractory VF management."
• 2023: "Compare defibrillator pad placements (anterior-lateral vs anterior-posterior). What does the evidence show?"
• 2022: "Outline the ANZCOR recommendations for electrical therapy during cardiac arrest."
• 2021: "Describe the management of a patient with an ICD who presents in VF."
• 2020: "A patient requires urgent cardioversion for atrial flutter. Outline your approach."

Second Part Hot Case:

Typical presentations involving electrical therapy:

• Post-cardiac arrest patient with recurrent VF - device troubleshooting
• Patient with new AF requiring rate vs rhythm control decision
• Unstable bradycardia requiring transcutaneous pacing
• Patient with ICD receiving multiple shocks

Examiners assess:

• Understanding of defibrillation principles
• Safe preparation and delivery of synchronized cardioversion
• Recognition of when to escalate therapy (DSED, vector change)
• Appropriate pacing initiation and capture confirmation
• Integration with resuscitation algorithm

Second Part Viva:

Expected discussion areas:

• Physics of defibrillation (Ohm's law, energy vs current)
• Monophasic vs biphasic waveform mechanisms
• Transthoracic impedance determinants
• Pad placement evidence (Schmidt trial, DOSE VF)
• Energy selection for different arrhythmias
• R-on-T phenomenon and synchronization
• Pacing thresholds and capture verification
• Complications of electrical therapy

Examiner expectations:

• Understand physics underlying successful defibrillation
• Evidence-based approach to energy selection
• Systematic cardioversion technique with safety considerations
• ANZCOR guideline knowledge

Common Mistakes

• Confusing energy (Joules) with current (Amperes) as determinant of success
• Not understanding that impedance affects current delivery
• Forgetting to synchronize during cardioversion of organized rhythms
• Using cardioversion for polymorphic VT (treat as VF - unsynchronized)
• Not confirming mechanical capture during transcutaneous pacing
• Placing pads directly over pacemaker/ICD generator
• Cardioverting AF >48 hours without considering stroke risk
• Starting transcutaneous pacing at excessive current (painful)

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Key Points

Must-Know Facts

1. Defibrillation Principle: Current (Amperes) depolarizes myocardium; requires 30-40A to terminate VF by simultaneously depolarizing >75% of myocardium (critical mass hypothesis) (PMID: 9750152)

2. Ohm's Law: I = V/R; for a given energy, current delivery is inversely proportional to impedance. High impedance = reduced current = reduced success (PMID: 11133372)

3. Biphasic Superiority: Biphasic waveforms achieve equivalent or better success at lower energy (120-200J) vs monophasic (360J); reduced myocardial dysfunction and skin burns (PMID: 12685516)

4. Transthoracic Impedance (TTI): Normal 70-80 Ohms; increased by obesity, COPD, hairy chest, dry pads, poor contact; decreased by gel pads, firm pressure, exhalation phase

5. ANZCOR Energy Recommendations: Biphasic 200J for all shocks (VF/pVT); if device-specific data suggests different energy, use that; escalate to maximum if first shock fails

6. Pad Placement: Anterior-lateral (standard) or anterior-posterior; Schmidt trial (2021) showed anterior-lateral more effective for AF cardioversion (77% vs 70%); DOSE VF (2022) showed vector change improves refractory VF

7. Synchronized Cardioversion: Energy delivered on R-wave to avoid vulnerable period; AF 120-200J, flutter 50-100J, SVT 50-100J, VT with pulse 100-150J (all biphasic)

8. Single Shock Strategy: One shock followed immediately by 2 minutes CPR; rhythm check after CPR cycle; minimizes hands-off time (PMID: 20956256)

9. Transcutaneous Pacing: Capture threshold typically 50-100mA; set rate 60-80 bpm; confirm mechanical capture with femoral pulse or arterial line; sedation required if conscious

10. Refractory VF Strategies: DOSE VF trial showed DSED (30% survival) and vector change (22%) superior to standard shocks (13%) after 3 failed shocks; consider amiodarone, magnesium, correct reversible causes

Memory Aids

Mnemonic SHOCK: Defibrillation success factors

• S: Size of pads (larger = lower impedance)
• H: Hair removal (reduces impedance)
• O: Orientation of pads (optimal vector)
• C: Contact quality (firm pressure, gel)
• K: Keep pauses short (minimize hands-off time)

Mnemonic DICE: Cardioversion preparation

• D: Defibrillator checked and synchronized
• I: IV access and sedation ready
• C: Confirm rhythm and indication
• E: Emergency equipment (airway, drugs) available

"8 cm Rule": Keep pads at least 8 cm from pacemaker/ICD generator

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Definition and Epidemiology

Definition

Defibrillation is the delivery of an unsynchronized electrical shock across the heart to terminate life-threatening ventricular arrhythmias (VF and pVT). The term derives from "de-fibrillate"

• to stop fibrillation.

Cardioversion is the delivery of a synchronized electrical shock timed to the R-wave of the cardiac cycle, used to terminate organized tachyarrhythmias with a pulse.

Electrical pacing uses repetitive low-energy electrical stimuli to depolarize the myocardium at a set rate, treating bradyarrhythmias.

Classification of Electrical Therapy

Epidemiology

Cardiac Arrest Statistics:

• VF/pVT present in 20-25% of in-hospital cardiac arrests (IHCA); ~50% of out-of-hospital (OHCA) when bystander-witnessed (PMID: 29483385)
• Survival decreases 7-10% per minute without defibrillation (PMID: 8093112)
• Each minute delay to first shock decreases survival by ~10% (PMID: 11134932)

Defibrillation Utilization (ANZICS APD data):

• ~2-5% ICU admissions require defibrillation during resuscitation
• ~1-2% require synchronized cardioversion for arrhythmias
• Transcutaneous pacing: ~1% of ICU patients

First Shock Success Rates (PMID: 11133372):

• Biphasic 120-200J: 85-95% for VF
• Monophasic 360J: 70-85% for VF
• First shock success for AF cardioversion: 70-90% (energy dependent)

Indigenous Health Considerations

• Aboriginal and Torres Strait Islander populations have 1.5-2× higher rates of sudden cardiac death, often at younger ages (PMID: 23140545)
• Higher prevalence of structural heart disease (rheumatic, cardiomyopathy)
• Remote/rural locations may delay access to defibrillation
• Importance of community AED programs in remote communities
• Cultural sensitivity when discussing resuscitation preferences with families
• Involve Aboriginal Health Workers and cultural liaison officers

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Applied Basic Sciences

Defibrillation Physics

Ohm's Law and Energy Equations

The fundamental physics of defibrillation is governed by Ohm's law:

I = V / R

Where:

• I = Current (Amperes) - the actual flow of electrons
• V = Voltage (Volts) - electrical potential difference
• R = Resistance/Impedance (Ohms) - opposition to current flow

Energy Equation:

E = V × I × t
E = I² × R × t

Where:

• E = Energy (Joules)
• t = Duration (seconds)

Critical Insight: While defibrillators are set in Joules (energy), it is current (Amperes) that actually terminates VF. Energy is used because it's easier to standardize across different impedances (PMID: 9750152).

Current as the Determinant of Success

Threshold for Successful Defibrillation: Approximately 30-40 Amperes of peak current is required to achieve defibrillation (PMID: 2613524).

Current Density: The key factor is sufficient current density across the myocardium. Defibrillation requires simultaneous depolarization of a "critical mass" (>75%) of ventricular myocardium to terminate multiple re-entrant wavelets (PMID: 8900009).

Relationship with Impedance:

For fixed energy: I ∝ 1/√R

• Higher impedance → lower current → reduced success
• A 200J shock delivers ~40A at 50 Ohms but only ~25A at 100 Ohms

Transthoracic Impedance (TTI)

Definition: The total resistance to current flow from one electrode to the other across the thorax.

Normal Range: 70-80 Ohms (adult)

Components of TTI:

• Skin-electrode interface (40%)
• Chest wall tissues (40%)
• Lungs (15%)
• Heart (5%)

Factors Affecting TTI (PMID: 3343589):

Modern Impedance-Compensating Defibrillators: Automatically measure TTI before shock delivery and adjust voltage/duration to maintain adequate current (PMID: 11581541).

Defibrillation Waveforms

Monophasic Waveforms

Mechanism: Current flows in a single direction from one electrode to the other.

Types:

1. Monophasic Damped Sinusoidal (MDS): Smooth waveform that returns to zero
2. Monophasic Truncated Exponential (MTE): Abrupt cutoff of current

Characteristics:

• High peak voltage required (~2000-5000V)
• Standard energy: 360J
• No impedance compensation
• Higher myocardial stunning
• More skin burns

Historical Standard: First-generation defibrillators; now largely replaced by biphasic.

Biphasic Waveforms

Mechanism: Current flows in one direction for the first phase, then reverses polarity for the second phase.

Types (PMID: 12685516):

1. Biphasic Truncated Exponential (BTE): Most common; fixed waveform
2. Rectilinear Biphasic (RLB): Rising second phase; Zoll devices
3. Pulsed Biphasic: Some newer devices

Phases of Biphasic Shock:

• Phase 1: Depolarizes myocardium, removes positive charge
• Phase 2: "Sweeps away" residual charge, lowers defibrillation threshold

Advantages of Biphasic (PMID: 11133372):

• Lower energy required (120-200J vs 360J)
• Higher first-shock success rate (85-95% vs 70-85%)
• Less myocardial dysfunction post-shock
• Fewer skin burns
• Impedance compensation built-in
• Equivalent or superior efficacy

ANZCOR Recommendation: "Biphasic waveforms are used for defibrillation" [Good Practice Statement]

Waveform Comparison

Cellular Mechanism of Defibrillation

Fibrillation Mechanism: VF results from multiple re-entrant wavelets propagating chaotically through the ventricles, causing ineffective quivering rather than coordinated contraction.

Defibrillation Mechanism (PMID: 8900009):

1. Critical Mass Hypothesis: Shock simultaneously depolarizes >75% of ventricular myocardium
2. Refractory Period Extension: Depolarized cells enter absolute refractory period
3. Re-entry Termination: With most tissue refractory, wavelet propagation stops
4. SA Node Resumption: Sinus node (ideally the fastest pacemaker) resumes control

Upper Limit of Vulnerability: There is also an upper energy limit above which defibrillation fails, likely due to myocardial damage or re-initiation of fibrillation.

Cardiac Electrophysiology Relevant to Cardioversion

Vulnerable Period: The T-wave represents relative refractory period of ventricular repolarization. A shock during this period can trigger VF (R-on-T phenomenon) (PMID: 14568900).

Synchronization Rationale: Delivering shock during the QRS complex (absolute refractory period) prevents R-on-T phenomenon:

• Myocardium already depolarized during QRS
• Cannot be re-excited to cause VF
• Safe window for organized rhythm termination

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Defibrillator Types

Manual Defibrillators

Definition: Devices requiring trained operator interpretation of rhythm and manual initiation of shock.

Features:

• ECG rhythm display
• User-selected energy levels
• Synchronized cardioversion capability
• Transcutaneous pacing function
• Printer/data recording
• Manual charge and shock buttons

ICU Standard Equipment: Lifepak 15/20, Philips HeartStart XL, Zoll X/R Series

Advantages:

• Operator control of timing and energy
• Faster shock delivery (no analysis delay)
• Synchronized cardioversion capability
• Pacing function

Disadvantages:

• Requires trained operator
• Risk of inappropriate shock if rhythm misinterpreted
• Operator error potential

Automated External Defibrillators (AEDs)

Definition: Devices that automatically analyze rhythm and deliver shock with minimal operator input.

Features:

• Automated rhythm analysis (sensitivity 90-95% for VF)
• Voice/visual prompts
• No energy selection required
• Safety interlocks

In-Hospital Use: ANZCOR recommends AEDs "may be reasonable" in hospitals, but warns of potential "adverse impact of interruptions to CPR, especially in non-shockable rhythms" (PMID: 26477429)

Analysis Algorithm: Uses morphology, rate, and amplitude criteria to identify shockable rhythms:

• VF detection sensitivity: 90-95%
• VF detection specificity: 95-99%
• Analysis time: 5-15 seconds

Limitations:

• Analysis delay during CPR pause
• Cannot synchronize (defibrillation only)
• May miss fine VF (amplitude dependent)
• Cannot be overridden easily

Wearable Cardioverter-Defibrillators (WCD)

Device: LifeVest (Zoll)

Indications:

• Bridge to ICD implantation
• Newly diagnosed cardiomyopathy with reduced EF
• Post-MI high-risk period
• Post-ICD explant for infection

VEST Trial (PMID: 30188406):

• 2,302 post-MI patients with EF ≤35%
• WCD vs control
• No significant difference in sudden death at 90 days (1.6% vs 2.4%, p=0.18)
• Trial criticized for crossover and adherence issues

Mechanism: Continuous ECG monitoring; alerts patient before shock; delivers 150J if VF confirmed and patient unresponsive.

Implantable Cardioverter-Defibrillators (ICDs)

Components:

• Pulse generator (battery, capacitor, electronics)
• Lead system (sensing, pacing, shocking)
• Programming interface

Functions:

1. Bradycardia pacing: Standard pacemaker function
2. Antitachycardia pacing (ATP): Burst pacing to terminate VT
3. Cardioversion: Synchronized low-energy shocks
4. Defibrillation: High-energy unsynchronized shocks

Typical Programming:

• VT zone: 150-200 bpm → ATP, then shocks
• VF zone: >200 bpm → immediate shock
• Detection intervals: 12-30 beats

ICU Management of ICD Patients:

Magnet Response: Placing magnet over ICD temporarily suspends tachyarrhythmia detection (not pacing); does NOT permanently deactivate device.

MADIT-RIT Trial (PMID: 23126252): High-rate cutoff (>200 bpm) or delayed therapy programming reduced inappropriate shocks and mortality.

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Energy Selection

Defibrillation (VF/pVT)

ANZCOR Guideline 11.4 Recommendations:

Evidence Base (PMID: 11133372):

• Schneider trial: 150J biphasic equivalent to 200-360J monophasic
• First shock success: 96% (biphasic) vs 59% (monophasic escalating)
• Overall conversion: 100% (biphasic) vs 84% (monophasic)

Device-Specific Recommendations:

• Zoll: 120J, 150J, 200J
• Philips: 150J, 150J, 200J
• Physio-Control: 200J, 300J, 360J
• If unknown: Use 200J as default

Paediatric Defibrillation (ANZCOR Guideline 12.2):

• Initial: 4 J/kg
• Subsequent: 4-8 J/kg (maximum 10 J/kg or adult dose)

Synchronized Cardioversion

Energy Selection by Arrhythmia (ANZCOR Guideline 11.9):

Key Principle: Start with recommended energy; if unsuccessful, escalate to maximum and reassess rhythm/sync mode.

Schmidt Trial (PMID: 34283181):

• Anterior-lateral pad placement more effective than anterior-posterior for AF cardioversion
• 77% vs 70% first shock success (p=0.02)
• Implication: Start with anterior-lateral; switch to anterior-posterior if fails

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Pad Placement

Standard Positions

Anterior-Lateral (Sterno-Apical)

Placement:

• Right pad: Right of sternum, below right clavicle
• Left pad: Left mid-axillary line, level with V6 electrode (apex)

Advantages:

• Quick application
• Familiar to most providers
• Effective for most patients

Optimal Apical Pad Position: The apical electrode must be sufficiently lateral - place in mid-axillary line, not too anterior (ANZCOR recommendation).

Anterior-Posterior

Placement:

• Anterior pad: Left precordium, over apex
• Posterior pad: Left infrascapular region, posterior to heart

Advantages:

• Heart "sandwiched" between electrodes
• Theoretically optimal vector through cardiac mass
• Preferred for transcutaneous pacing (lower threshold)

Evidence for Pad Placement:

Schmidt Trial (2021) (PMID: 34283181):

• RCT of 572 patients for elective AF cardioversion
• Anterior-lateral vs anterior-posterior
• Result: Anterior-lateral SUPERIOR for AF cardioversion
• First shock success: 77% vs 70% (p=0.02)

DOSE VF Trial (2022) (NEJM):

• Refractory VF after 3 standard shocks
• Vector change (move from A-L to A-P) improved survival
• VF termination: 80% (vector change) vs 68% (standard)

Clinical Application:

1. Start with anterior-lateral for most situations
2. If cardioversion fails, change vector to anterior-posterior
3. For transcutaneous pacing, anterior-posterior may achieve lower capture threshold

Special Considerations

Pacemaker/ICD Patients

ANZCOR Recommendation: "Place the defibrillator pad/paddle on the chest wall ideally at least 8 cm from the generator position."

Rationale:

• Avoid direct shock through generator (may damage circuitry)
• Avoid elevated lead impedance causing undersensing
• Device should be interrogated post-resuscitation

If Generator in Standard Position (left pectoral):

• Use anterior-posterior placement, OR
• Place right pad well away from generator

Pregnant Patients

• Standard pad placement safe
• Fetal monitoring if viable pregnancy
• Left lateral tilt to avoid aortocaval compression
• Energy selection unchanged

Obese Patients

• Standard pad placement
• May need higher energy due to increased impedance
• Firm pressure important for electrode contact
• Consider anterior-posterior if lateral position ineffective

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Synchronized Cardioversion vs Defibrillation

Key Differences

When to Synchronize

Synchronize (SYNC mode):

• Atrial fibrillation
• Atrial flutter
• Supraventricular tachycardia
• Monomorphic VT with pulse
• Any organized rhythm with pulse

Do NOT Synchronize (Defibrillation mode):

• Ventricular fibrillation
• Pulseless VT
• Polymorphic VT (Torsades)
• Pulseless patient (any rhythm)

Critical Point: Polymorphic VT (including Torsades de Pointes) should be treated with unsynchronized defibrillation because:

• QRS morphology constantly changing
• Synchronization may not identify QRS reliably
• Delay in shock delivery
• Risk of degeneration to VF

Cardioversion Technique

Pre-Procedure Checklist (DICE mnemonic):

1. D - Defibrillator:

   • Check device function
   • SYNC mode activated (confirm sync markers on R-waves)
   • Set appropriate energy
   • Pads applied correctly

2. I - IV access and sedation:

   • Secure IV access
   • Resuscitation drugs available
   • Sedation prepared (propofol 0.5-1 mg/kg, midazolam 0.05-0.1 mg/kg, or ketamine 0.5-1 mg/kg)
   • Consider analgesia (fentanyl 1 mcg/kg)

3. C - Confirm indication:

   • Verify rhythm on 12-lead ECG
   • Assess hemodynamic status
   • Consider anticoagulation status (AF >48h)
   • Evaluate reversible causes

4. E - Emergency equipment:

   • Airway equipment ready
   • Suction available
   • Emergency drugs (atropine, adrenaline, amiodarone)
   • External pacing capability

Procedure Steps:

1. Confirm rhythm and indication
2. Ensure SYNC mode active and markers visible on R-waves
3. Apply pads in anterior-lateral or anterior-posterior position
4. Administer sedation; wait for adequate sedation
5. Charge defibrillator to selected energy
6. Clear area: "I'm clear, you're clear, everybody's clear"
7. Deliver shock (may need to hold button longer - waits for R-wave)
8. Assess rhythm and patient response
9. If unsuccessful, increase energy and repeat
10. If SYNC markers unreliable or patient deteriorates, use unsynchronized shock

Post-Cardioversion Monitoring:

• Continuous ECG monitoring
• Blood pressure monitoring
• Assess level of consciousness
• 12-lead ECG to confirm sinus rhythm
• Watch for arrhythmia recurrence

Anticoagulation Considerations

AF Duration and Stroke Risk (PMID: 32860505):

Post-Cardioversion: Anticoagulation for minimum 4 weeks (risk of stunning and delayed thrombus formation) (PMID: 22922413).

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Transcutaneous and Transvenous Pacing

Transcutaneous Pacing (TCP)

Indications (ANZCOR Guideline 11.9):

• Symptomatic bradycardia unresponsive to atropine
• High-risk of asystole:
  • Recent asystole
  • Mobitz Type II AV block
  • Complete heart block
  • Ventricular standstill >3 seconds
• Bridge to transvenous pacing

Technique:

1. Pad Placement: Anterior-posterior preferred (lower capture threshold) (PMID: 2320445)

   • Anterior: Left precordium
   • Posterior: Left infrascapular region

2. Settings:

   • Mode: Demand (or fixed in certain situations)
   • Rate: 60-80 bpm (typically 70)
   • Current: Start at 0-30 mA

3. Finding Capture:

   • Increase current gradually (5-10 mA increments)
   • Watch for pacing spike followed by wide QRS
   • Typical capture threshold: 50-100 mA (PMID: 6371520)
   • Some patients require up to 200 mA

4. Confirm Mechanical Capture:

   • Check femoral pulse (not carotid - muscle artifact)
   • Arterial line waveform
   • Pulse oximetry plethysmograph
   • Blood pressure improvement

5. Set Safety Margin:

   • Increase 5-10 mA above capture threshold
   • Or 10% above threshold

Failure to Capture (threshold >150-200 mA):

• Check electrode contact
• Change to anterior-posterior position if not already
• Increase output to maximum
• Consider underlying causes (massive MI, electrolyte disturbance)
• Prepare for transvenous pacing

Analgesia/Sedation: TCP at high current is painful; provide sedation if hemodynamically tolerated (ketamine, midazolam, fentanyl).

Transvenous Pacing

Indications:

• Failure or inadequacy of transcutaneous pacing
• Need for prolonged pacing
• More reliable capture required
• Pre-operative for high-risk surgery

Access Routes:

• Right internal jugular (preferred - direct route)
• Left subclavian
• Femoral (bedside, no fluoroscopy required)

Technique (Blind Bedside Insertion via Femoral):

1. Insert venous sheath (6-7 French) into femoral vein
2. Advance pacing catheter (balloon-tipped if available)
3. Connect to pacing box (negative to catheter tip)
4. Set initial output: 5 mA, rate 80 bpm
5. Advance slowly, watching for:
   • RV position: negative deflection on lead I, positive on II/III
   • Contact: Injury current (ST elevation) on catheter ECG
6. Confirm capture (pacing spike with QRS, LBBB morphology)
7. Determine threshold (minimum mA for consistent capture)
8. Set output 3× threshold (safety margin)
9. Secure catheter; obtain CXR

Fluoroscopic Guidance: Preferred when available; allows precise positioning in RV apex.

Complications:

• Failure to capture
• Lead displacement
• Perforation (pericardial effusion, tamponade)
• Arrhythmias during insertion
• Venous thrombosis
• Infection

Pacing Threshold and Output

Capture Threshold: Minimum energy required for consistent myocardial depolarization

Transcutaneous Pacing:

• Threshold: 50-100 mA (mean ~65-75 mA)
• Set output: Threshold + 10% or + 5-10 mA

Transvenous Pacing:

• Threshold: 0.5-1.5 mA (much lower due to direct contact)
• Set output: 3× threshold (typically 3-5 mA)

Factors Increasing Threshold:

• Myocardial infarction
• Hyperkalemia
• Acidosis
• Hypoxia
• Antiarrhythmic drugs
• Lead displacement

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ARC/ANZCOR Guidelines Summary

ANZCOR Guideline 11.4 Key Recommendations

Timing:

• Deliver defibrillation as soon as defibrillator available [Good Practice Statement]
• Single shock strategy followed by 2 minutes CPR

Waveform and Energy:

• Biphasic waveforms preferred [Good Practice Statement]
• Biphasic: 200J default for all shocks (device-specific data may suggest alternatives)
• Monophasic: 360J for all shocks
• Escalate to maximum if first shock unsuccessful

Pad Placement:

• Anterior-lateral or anterior-posterior positions
• At least 8 cm from pacemaker/ICD generator
• Self-adhesive pads preferred over paddles

AEDs in Hospital:

• May be reasonable to facilitate early defibrillation
• Be aware of potential adverse impact of CPR interruptions

ANZCOR Guideline 11.9 Key Recommendations

Bradycardia:

• Atropine 500-600 mcg IV (up to 3 mg total)
• If unresponsive: Adrenaline infusion 2-10 mcg/min
• Transcutaneous pacing if pharmacotherapy fails or high-risk features
• Pacing: Demand mode, 70-80 bpm, increase mA until capture

Tachyarrhythmias:

• Unstable with adverse features → Immediate synchronized cardioversion
• Broad complex regular → Amiodarone 300 mg IV, consider cardioversion
• Narrow complex regular → Vagal maneuvers, then adenosine 6 mg, 12 mg, 12 mg
• Atrial fibrillation → Rate control (beta-blocker/CCB), consider anticoagulation

Peri-Arrest:

• Amiodarone 300 mg IV over 10-20 min for refractory arrhythmias
• Followed by 900 mg infusion over 24 hours

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Refractory Ventricular Fibrillation

Definition

Refractory VF: VF that persists after ≥3 standard defibrillation attempts.

DOSE VF Trial (2022)

Study Design:

• Cluster-randomized trial, 6 paramedic services in Ontario, Canada
• 405 patients with OHCA remaining in VF after 3 standard shocks
• Three arms:
  1. Standard defibrillation (continued anterior-lateral)
  2. Vector Change (switch to anterior-posterior)
  3. Double Sequential External Defibrillation (DSED)

DSED Technique:

• Two defibrillators
• One pad set anterior-lateral, second set anterior-posterior
• Rapid sequential shocks (<1 second apart)

Results:

Key Finding: DSED doubled survival to hospital discharge compared to standard shocks (RR 2.21, p=0.009).

Clinical Implications:

1. After 3 failed shocks, change strategy
2. If single defibrillator available: Vector change (move pads to A-P position)
3. If second defibrillator available: Consider DSED
4. Continue optimizing reversible causes (amiodarone, magnesium, ECPR)

Other Strategies for Refractory VF

Pharmacological:

• Amiodarone 300 mg IV (PMID: 11096338)
• Magnesium 2 g IV (if hypomagnesemic or Torsades)
• Correct acidosis, hyperkalemia

Mechanical:

• High-quality CPR with minimal interruptions
• Mechanical CPR (LUCAS, AutoPulse) for prolonged resuscitation
• Consider ECPR (extracorporeal CPR) if available

Interventional:

• Emergency PCI for suspected acute coronary occlusion
• ECPR/ECMO as bridge to definitive therapy

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Complications of Electrical Therapy

Defibrillation/Cardioversion Complications

Immediate:

• Skin burns (more common with monophasic, poor contact)
• Myocardial stunning (transient dysfunction)
• Arrhythmia induction (if poor synchronization)
• Muscle contractions (may dislodge lines/tubes)

Post-Procedure:

• ST-elevation (transient, usually resolves)
• Troponin elevation (minimal with biphasic)
• Pulmonary edema (rare)
• Aspiration (ensure airway protection)
• Thromboembolism (AF cardioversion without anticoagulation)

Post-Defibrillation Myocardial Dysfunction

Mechanism: High-energy shocks cause transient myocardial stunning through:

• Direct membrane damage
• Calcium overload
• Oxidative stress

Clinical Features:

• Transient hypotension post-ROSC
• Reduced ejection fraction
• Typically recovers within 24-48 hours

Biphasic Advantage: Lower energy = less myocardial dysfunction (PMID: 11133372)

Pacing Complications

Transcutaneous:

• Pain/discomfort (requires sedation)
• Skin burns (prolonged use)
• Failure to capture
• Diaphragm/muscle stimulation
• Interference with ECG interpretation

Transvenous:

• Venous access complications (hematoma, pneumothorax, arterial puncture)
• Arrhythmias during insertion
• Lead displacement
• Cardiac perforation/tamponade
• Thrombosis
• Infection/endocarditis

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Indigenous Health Considerations

Aboriginal and Torres Strait Islander Populations

Epidemiology:

• 1.5-2× higher sudden cardiac death rates (PMID: 23140545)
• Higher rates of rheumatic heart disease
• Earlier onset cardiovascular disease
• Higher prevalence of risk factors (diabetes, hypertension, smoking)

Access Barriers:

• Remote communities may lack AED access
• Delayed response times for emergency services
• Distance to tertiary cardiac services

Cultural Considerations:

• Involve Aboriginal Health Workers in resuscitation discussions
• Family/community involvement in decision-making
• Respect for cultural practices around death and dying
• Explain procedures in culturally appropriate way
• Sorry Business may affect family availability

Community Programs:

• AED placement in remote communities
• Community CPR training programs
• Telehealth support for remote resuscitation
• RFDS coordination for cardiac emergencies

Māori Health Considerations

• Similar cardiovascular disparities
• Whānau (family) involvement essential
• Cultural protocols around medical procedures
• Interpreter services when needed
• Respect for tikanga (customs)

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SAQ Practice Questions

SAQ 1: Defibrillation Physics (20 marks)

Stem: A 58-year-old man develops ventricular fibrillation during a STEMI. The resuscitation team delivers a 200 Joule biphasic shock, but VF persists.

(a) Explain the physics of defibrillation, including the role of current, voltage, impedance, and energy. (8 marks)

Model Answer:

Ohm's Law Application (2 marks):

• I = V/R (current = voltage / impedance)
• Current (Amperes) is the determinant of successful defibrillation
• Defibrillators are set in Joules but deliver current

Energy Equation (2 marks):

• E = V × I × t or E = I² × R × t
• Energy represents total work done
• For fixed energy, higher impedance = lower current

Current Requirements (2 marks):

• 30-40 Amperes peak current required for defibrillation
• Critical mass hypothesis: >75% myocardium must be simultaneously depolarized
• This terminates re-entrant wavelets of VF

Impedance Factors (2 marks):

• Normal transthoracic impedance: 70-80 Ohms
• Increased by: obesity, hairy chest, dry pads, poor contact, hyperinflated lungs
• Decreased by: conductive gel, firm pressure, successive shocks

(b) Compare monophasic and biphasic waveforms. Why is biphasic preferred? (6 marks)

Model Answer:

Monophasic Waveform (2 marks):

• Current flows in single direction
• Requires high energy (360J)
• No impedance compensation
• Higher peak voltage (2000-5000V)
• More myocardial stunning and skin burns

Biphasic Waveform (2 marks):

• Current flows in one direction then reverses
• Phase 1: Depolarizes myocardium
• Phase 2: "Sweeps" residual charge, lowers defibrillation threshold
• Types: Biphasic Truncated Exponential (BTE), Rectilinear Biphasic (RLB)

Clinical Advantages of Biphasic (2 marks):

• Lower energy effective (120-200J)
• Higher first-shock success: 85-95% vs 70-85%
• Impedance compensation maintains adequate current
• Less myocardial dysfunction
• Fewer skin burns
• Schneider trial (PMID 11133372): 96% vs 59% first shock success

(c) What strategies would you employ if VF persists after three standard shocks? (6 marks)

Model Answer:

Immediate Actions (2 marks):

• Continue high-quality CPR with minimal interruptions
• Administer adrenaline 1 mg IV (if not already given)
• Give amiodarone 300 mg IV bolus

Defibrillation Strategies (DOSE VF Trial) (2 marks):

• Vector change: Move pads from anterior-lateral to anterior-posterior position
  • "Improved VF termination: 80% vs 68%"
• Double Sequential External Defibrillation (DSED): If second defibrillator available
  • Two sets of pads (A-L and A-P), rapid sequential shocks
  • "Survival to discharge: 30.4% vs 13.3% (doubled)"

Address Reversible Causes (2 marks):

• 4Hs: Hypoxia, Hypovolemia, Hypo/Hyperkalemia, Hypothermia
• 4Ts: Tension pneumothorax, Tamponade, Toxins, Thrombosis
• Check glucose, magnesium (give 2g IV if hypomagnesemic)
• Consider ECPR if available for refractory arrest

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SAQ 2: Cardioversion and Pacing (20 marks)

Stem: A 72-year-old woman is admitted to ICU with new-onset atrial fibrillation with rapid ventricular response (HR 156/min, BP 78/52 mmHg). She has chest pain and is becoming drowsy.

(a) Describe your approach to synchronized cardioversion for this patient. Include preparation, energy selection, and technique. (8 marks)

Model Answer:

Preparation (3 marks):

• Confirm indication: Unstable AF with adverse features (hypotension, chest pain, altered consciousness)
• Establish IV access
• Apply monitoring (ECG, SpO2, BP)
• Prepare airway equipment (suction, bag-mask, intubation equipment)
• Draw up sedation (propofol 0.5-1 mg/kg or ketamine 0.5-1 mg/kg)
• Have emergency drugs available (atropine, adrenaline, amiodarone)

Device Preparation (2 marks):

• Select defibrillator with synchronization capability
• Apply self-adhesive pads (anterior-lateral position)
• Activate SYNC mode - confirm sync markers visible on R-waves
• Select energy: 120-200J biphasic for AF (I would select 200J initially)

Technique (3 marks):

• Administer sedation; ensure adequate depth
• Charge defibrillator
• Clear all personnel: "I'm clear, you're clear, everyone's clear"
• Deliver shock (hold button until shock delivered - waits for R-wave)
• Assess rhythm and hemodynamic response
• If unsuccessful: escalate energy, ensure SYNC remains active, consider pad position change

(b) Explain the rationale for synchronization and the risks if synchronization fails. (4 marks)

Model Answer:

Rationale for Synchronization (2 marks):

• Shock delivered during R-wave (absolute refractory period)
• Myocardium already depolarized during QRS
• Cannot be re-excited, therefore safe timing

Vulnerable Period Concept (2 marks):

• T-wave represents relative refractory period (ventricular repolarization)
• Shock during T-wave can cause R-on-T phenomenon
• This induces ventricular fibrillation (VF)
• Therefore, organized rhythms with pulse require synchronization
• Exception: Polymorphic VT (treat as VF - unsynchronized)

(c) The patient converts to sinus rhythm but 6 hours later develops symptomatic bradycardia (HR 34/min) with Mobitz Type II AV block. Describe your approach to transcutaneous pacing. (8 marks)

Model Answer:

Indication Confirmation (2 marks):

• Symptomatic bradycardia with adverse features
• Mobitz Type II = high-risk for progression to complete heart block
• Atropine often ineffective in Mobitz II (infranodal block)
• Transcutaneous pacing indicated as bridge to transvenous

Pad Placement (2 marks):

• Anterior-posterior position preferred (lower capture threshold)
• Anterior pad: Left precordium over apex
• Posterior pad: Left infrascapular region, behind heart

Initial Settings (2 marks):

• Mode: Demand (asynchronous if concern about sensing)
• Rate: 70 bpm (above intrinsic rate)
• Current: Start at 0 mA, increase gradually

Achieving and Confirming Capture (2 marks):

• Increase current in 5-10 mA increments
• Watch for: Pacing spike followed by wide QRS complex
• Typical capture threshold: 50-100 mA
• Confirm mechanical capture: Check femoral pulse (NOT carotid)
• Alternative: Arterial line waveform, pulse oximetry plethysmograph
• Set output 10% above threshold as safety margin
• Provide sedation/analgesia if patient conscious

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Viva Scenarios

Viva 1: Defibrillation Principles

Opening Statement: "You are the ICU registrar called to a cardiac arrest. A 52-year-old man has collapsed in the ward. The nurses have commenced CPR and the cardiac arrest team has arrived. The monitor shows ventricular fibrillation."

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Examiner: "The defibrillator is charging. What are the principles of successful defibrillation?"

Candidate: "Successful defibrillation depends on delivering adequate current through the myocardium. Current, measured in Amperes, is the determinant of success - not energy per se. Approximately 30-40 Amperes is required to depolarize a critical mass of myocardium - typically greater than 75% - which terminates the multiple re-entrant wavelets causing VF and allows the SA node to resume control.

The relationship follows Ohm's law: I = V/R. For a given energy setting, higher transthoracic impedance results in lower current delivery and reduced success rates."

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Examiner: "What factors affect transthoracic impedance?"

Candidate: "Normal transthoracic impedance is 70-80 Ohms. Several factors increase impedance:

• Poor electrode-skin contact
• Dry electrodes without conductive gel
• Hairy chest
• Obesity
• Hyperinflated lungs (COPD, positive pressure ventilation)
• Small electrode size

Factors that decrease impedance include:

• Gel or self-adhesive pads
• Firm pressure
• Adequate electrode size (8-12 cm diameter)
• Successive shocks (impedance falls approximately 8% with each shock)

Modern biphasic defibrillators compensate for impedance by adjusting voltage and duration to maintain adequate current."

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Examiner: "Compare monophasic and biphasic waveforms."

Candidate: "Monophasic waveforms deliver current in a single direction. They require high energy - typically 360 Joules - and high peak voltages of 2000-5000 Volts. They have no impedance compensation and are associated with more myocardial stunning and skin burns. First shock success rates are approximately 70-85%.

Biphasic waveforms deliver current in one direction then reverse polarity. The first phase depolarizes the myocardium while the second phase effectively 'sweeps away' residual charge, lowering the defibrillation threshold.

The evidence strongly supports biphasic waveforms. The Schneider trial showed that 150 Joule biphasic shocks achieved 96% first-shock success compared to 59% with monophasic escalating doses. Biphasic waveforms are now standard of care, and ANZCOR recommends biphasic for all defibrillation."

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Examiner: "The patient remains in VF after three shocks at 200 Joules. What would you do?"

Candidate: "This is refractory VF. My approach includes:

First, ensure we're providing high-quality CPR with minimal interruptions. I would administer adrenaline 1 mg IV and amiodarone 300 mg IV bolus.

For the defibrillation strategy, the DOSE VF trial from 2022 provides important evidence. After three failed standard shocks, changing strategy improves outcomes:

Vector change - moving the pads from anterior-lateral to anterior-posterior position - improved VF termination from 68% to 80% and survival to discharge from 13% to 22%.

If a second defibrillator is available, Double Sequential External Defibrillation - two sets of pads in different vectors with rapid sequential shocks - improved survival to discharge from 13% to 30%.

I would also systematically address reversible causes: check potassium, glucose, magnesium, consider coronary occlusion, ensure no tension pneumothorax or tamponade. In a centre with capability, ECPR should be considered for refractory arrest."

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Examiner: "The patient has an ICD in situ. How does this change your management?"

Candidate: "Several considerations apply for ICD patients:

For pad placement, I would position pads at least 8 cm from the ICD generator to avoid damaging the device or causing sensing abnormalities. If the generator is in the standard left pectoral position, I would use anterior-posterior placement or ensure the right pad is well away from the generator.

External defibrillation should proceed as normal - the ICD will not interfere with external shocks. However, the ICD may also be attempting to treat the arrhythmia, so I would briefly observe for ICD therapy delivery.

Post-resuscitation, the ICD should be interrogated by electrophysiology to check device function, review stored events, and ensure programming is appropriate.

If the patient is having an ICD storm with multiple appropriate shocks, I would treat with sedation, optimize beta-blockade, administer amiodarone, and arrange urgent cardiology review. If inappropriate shocks are occurring, a magnet placed over the device will temporarily suspend tachyarrhythmia detection."

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Viva 2: Cardioversion and Pacing

Opening Statement: "You are called to the Emergency Department to review a 68-year-old woman who has presented with palpitations and lightheadedness. She has a history of hypertension. Her heart rate is 158/min and irregular, blood pressure 92/58 mmHg. The ECG shows atrial fibrillation with rapid ventricular response."

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Examiner: "How would you approach the management of this patient?"

Candidate: "This patient has new-onset atrial fibrillation with rapid ventricular response and adverse hemodynamic features - specifically hypotension and symptoms of low cardiac output. This is an unstable tachyarrhythmia requiring urgent intervention.

My initial approach would be:

Assessment: ABC approach, confirm the rhythm on 12-lead ECG, establish IV access, apply monitoring.

Given her instability, synchronized electrical cardioversion is indicated. While preparing for cardioversion, I would:

• Apply self-adhesive defibrillation pads
• Prepare sedation - propofol or midazolam with fentanyl
• Ensure airway equipment is immediately available
• Have emergency drugs ready

I would then perform synchronized cardioversion with 200 Joules biphasic as my initial energy."

---

Examiner: "Why is synchronization important?"

Candidate: "Synchronization times the shock delivery to the R-wave of the QRS complex, which represents ventricular depolarization when the myocardium is in its absolute refractory period.

This avoids delivering energy during the vulnerable period - the T-wave - which represents ventricular repolarization. During this relative refractory period, a shock can trigger the R-on-T phenomenon, inducing ventricular fibrillation.

For organized tachyarrhythmias with a pulse - AF, flutter, SVT, monomorphic VT - synchronization is essential. The exception is polymorphic VT, including Torsades de Pointes, where the QRS morphology changes constantly, making synchronization unreliable, and we treat as VF with unsynchronized defibrillation."

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Examiner: "What pad position would you use?"

Candidate: "For cardioversion of atrial fibrillation, I would use the anterior-lateral position as my first choice.

The Schmidt trial from 2021 compared anterior-lateral versus anterior-posterior pad placement specifically for AF cardioversion. Anterior-lateral was actually more effective, with 77% first-shock success compared to 70% for anterior-posterior.

However, if the initial cardioversion fails, I would change the vector to anterior-posterior as a rescue strategy - this is supported by the DOSE VF data showing vector change improves outcomes in refractory arrhythmias.

For transcutaneous pacing, I would prefer anterior-posterior placement, as evidence suggests this achieves lower capture thresholds."

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Examiner: "The patient converts to sinus rhythm but later develops complete heart block with a ventricular rate of 32/min. She is symptomatic with near-syncope. How would you manage this?"

Candidate: "This is a critical bradyarrhythmia requiring immediate intervention. Complete heart block carries a high risk of asystole and cardiac arrest.

I would initiate transcutaneous pacing as the first-line intervention:

Pad placement: Anterior-posterior, which typically achieves lower capture thresholds.

Settings: Demand mode, rate 70 bpm, start current at 0 mA.

Technique: Gradually increase current in 5-10 mA increments while observing the monitor. I'm looking for a pacing spike followed by a wide QRS complex indicating electrical capture.

Confirmation of mechanical capture: This is essential - I would check for a femoral pulse, not carotid, as skeletal muscle contractions in the neck can mimic a pulse. Alternatively, I would use the arterial line waveform or pulse oximetry plethysmograph.

Once capture is achieved - typically at 50-100 mA - I would set the output 10% above threshold as a safety margin.

If the patient is conscious, transcutaneous pacing is painful at high currents, so I would administer sedation with propofol or midazolam plus fentanyl if hemodynamically tolerable.

This is a bridge to definitive therapy - I would arrange urgent transvenous pacing."

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Examiner: "How do you perform transvenous pacing insertion?"

Candidate: "For urgent bedside insertion without fluoroscopy, the femoral approach is preferred as it's technically straightforward and doesn't risk pneumothorax.

Technique:

1. Insert a 6 or 7 French venous sheath into the femoral vein using sterile Seldinger technique
2. Connect the pacing catheter to the pacing box - negative lead to catheter tip
3. Set initial output to 5 mA and rate to 80 bpm
4. Advance the catheter slowly, watching the ECG for position indicators
5. Look for negative QRS in lead I and positive in II/III suggesting RV position
6. Contact with endocardium shows injury current - ST elevation on catheter ECG
7. Confirm capture - pacing spike with wide QRS, LBBB morphology
8. Determine threshold by reducing output until capture is lost
9. Set final output at 3 times threshold
10. Secure catheter and obtain chest X-ray to confirm position

Complications to monitor for include lead displacement, perforation with tamponade, arrhythmias during insertion, and infection."

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ZCOR? A: 200J default for all shocks (or device-specific recommendation)

13. Q: What energy is used for monophasic defibrillation? A: 360J for all shocks

14. Q: What is the standard energy for cardioversion of atrial fibrillation (biphasic)? A: 120-200J

15. Q: What energy is used for cardioversion of atrial flutter (biphasic)? A: 50-100J (often converts at low energy)

16. Q: Define refractory VF A: VF that persists after ≥3 standard defibrillation attempts

17. Q: What is Double Sequential External Defibrillation (DSED)? A: Rapid sequential shocks from two defibrillators with pads in different vectors (A-L and A-P)

18. Q: What is an AED? A: Automated External Defibrillator - device that analyzes rhythm and delivers shock with minimal operator input

19. Q: What is an ICD? A: Implantable Cardioverter-Defibrillator - implanted device providing pacing, ATP, and defibrillation

20. Q: What is antitachycardia pacing (ATP)? A: Rapid burst pacing from an ICD to terminate VT without delivering a shock

Clinical Reasoning (15 cards)

21. Q: List 4 factors that increase transthoracic impedance A: Poor electrode contact, hairy chest, obesity, COPD/hyperinflated lungs, dry electrodes

22. Q: Why is biphasic defibrillation preferred over monophasic? A: Higher first-shock success (85-95% vs 70-85%), lower energy required, less myocardial stunning, impedance compensation

23. Q: What are the two standard pad positions for defibrillation? A: Anterior-lateral (sterno-apical) and anterior-posterior

24. Q: According to the Schmidt trial, which pad position is more effective for AF cardioversion? A: Anterior-lateral (77% vs 70% first-shock success)

25. Q: When should you NOT synchronize cardioversion? A: VF, pulseless VT, polymorphic VT (Torsades), any pulseless rhythm

26. Q: How far should defibrillation pads be placed from a pacemaker/ICD generator? A: At least 8 cm

27. Q: What are the adverse features indicating unstable bradycardia requiring pacing? A: SBP <90 mmHg, HR <40/min, ventricular arrhythmias, heart failure

28. Q: What are high-risk features for asystole in bradycardia (ANZCOR)? A: Recent asystole, Mobitz II AV block, complete heart block, ventricular standstill >3 sec

29. Q: What pacing rate should be set for transcutaneous pacing? A: 60-80 bpm (typically 70)

30. Q: Why check femoral rather than carotid pulse during transcutaneous pacing? A: Electrical stimulus causes skeletal muscle contractions in the neck that can mimic a pulse

31. Q: What are the main strategies for refractory VF per DOSE VF trial? A: Vector change (move pads A-L to A-P), DSED if second defibrillator available

32. Q: What should you do if transcutaneous pacing fails to capture at maximum output? A: Check electrode contact, change to anterior-posterior position, address underlying causes, prepare for transvenous pacing

33. Q: How long should AF be present before considering anticoagulation prior to cardioversion? A: AF ≥48 hours requires 3 weeks anticoagulation or TOE to exclude thrombus before elective cardioversion

34. Q: What does placing a magnet over an ICD do? A: Temporarily suspends tachyarrhythmia detection (ICD will not deliver shock therapy); does NOT affect pacing

35. Q: What is ICD storm and how is it managed? A: ≥3 ICD shocks in 24 hours; manage with sedation, beta-blockers, amiodarone, address underlying cause, consider ablation

Guidelines/Evidence (15 cards)

36. Q: What is the ANZCOR single-shock strategy? A: Deliver one shock then immediately resume 2 minutes CPR before rhythm reassessment

37. Q: What was the key finding of the Schneider biphasic trial (PMID 11133372)? A: 150J biphasic achieved 96% first-shock success vs 59% with monophasic escalating doses

38. Q: What was the survival to discharge in DOSE VF trial for DSED vs standard? A: DSED 30.4% vs standard 13.3% (doubled survival)

39. Q: What was the survival benefit of vector change in DOSE VF trial? A: Vector change 21.7% vs standard 13.3% survival to discharge

40. Q: What does ANZCOR recommend for AED use in hospitals? A: May be reasonable to facilitate early defibrillation, but be aware of adverse impact from CPR interruptions

41. Q: According to ANZCOR, what is first-line drug for unstable bradycardia? A: Atropine 500-600 mcg IV, repeated up to 3 mg total

42. Q: What is second-line pharmacotherapy for bradycardia per ANZCOR? A: Adrenaline infusion 2-10 mcg/min

43. Q: What was the MADIT-RIT trial finding regarding ICD programming? A: High-rate cutoff (>200 bpm) or delayed therapy programming reduced inappropriate shocks and mortality

44. Q: What is the VEST trial finding for wearable defibrillators? A: No significant difference in sudden death at 90 days (1.6% vs 2.4%, p=0.18) in post-MI patients with EF ≤35%

45. Q: What is the critical mass hypothesis of defibrillation? A: >75% of ventricular myocardium must be simultaneously depolarized to terminate VF (PMID 8900009)

46. Q: What does ANZCOR recommend for refractory arrhythmias peri-arrest? A: Amiodarone 300 mg IV over 10-20 min, followed by 900 mg infusion over 24 hours

47. Q: According to ANZCOR, what pad position should be used? A: Anterior-lateral OR anterior-posterior; apical electrode must be sufficiently lateral

48. Q: What is the evidence for transcutaneous pacing pad position? A: Anterior-posterior position generally requires lower current (mA) to achieve capture (PMID 2320445)

49. Q: When can cardioversion proceed without prior anticoagulation in AF? A: AF <48 hours duration, OR hemodynamically unstable (immediate cardioversion regardless)

50. Q: What is the OPTIC trial finding for ICD shock reduction? A: Amiodarone + beta-blocker most effective at reducing ICD shocks compared to sotalol or beta-blocker alone (PMID 16418466)

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References

Primary Guidelines

1. ANZCOR Guideline 11.4 – Electrical Therapy for Adult Advanced Life Support. Australian and New Zealand Committee on Resuscitation. 2024. https://anzcor.org/

2. ANZCOR Guideline 11.9 – Managing Acute Dysrhythmias. Australian and New Zealand Committee on Resuscitation. 2024.

3. ANZCOR Guideline 7 – Automated External Defibrillation in Basic Life Support. 2024.

4. Panchal AR, et al. Part 3: Adult Basic and Advanced Life Support: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2020;142(16_suppl_2):S366-S468. PMID: 33081529

5. Soar J, et al. European Resuscitation Council Guidelines 2021: Adult advanced life support. Resuscitation. 2021;161:115-151. PMID: 33773825

Landmark Trials

6. Cheskes S, et al. Defibrillation Strategies for Refractory Ventricular Fibrillation. N Engl J Med. 2022;387(21):1947-1956. [DOSE VF Trial]

7. Schmidt AS, et al. Anterior-Lateral Versus Anterior-Posterior Electrode Position for Cardioverting Atrial Fibrillation. Circulation. 2021;144(25):1995-2003. PMID: 34283181

8. Schneider T, et al. Multicenter, randomized, controlled trial of 150-J biphasic shocks compared with 200- to 360-J monophasic shocks in the resuscitation of out-of-hospital cardiac arrest victims. Circulation. 2000;102(15):1780-1787. PMID: 11133372

9. Kudenchuk PJ, et al. Amiodarone for resuscitation after out-of-hospital cardiac arrest due to ventricular fibrillation. N Engl J Med. 1999;341(12):871-878. PMID: 11096338

10. Olgin JE, et al. Wearable Cardioverter-Defibrillator after Myocardial Infarction. N Engl J Med. 2018;379(13):1205-1215. PMID: 30188406 [VEST Trial]

11. Moss AJ, et al. Reduction in inappropriate therapy and mortality through ICD programming. N Engl J Med. 2012;367(24):2275-2283. PMID: 23126252 [MADIT-RIT Trial]

12. Connolly SJ, et al. Comparison of beta-blockers, amiodarone plus beta-blockers, or sotalol for prevention of shocks from implantable cardioverter defibrillators. JAMA. 2006;295(2):165-171. PMID: 16418466 [OPTIC Trial]

Defibrillation Physics

13. Kerber RE, et al. Energy, current, and success in defibrillation and cardioversion: clinical studies using an automated impedance-based method of energy adjustment. Circulation. 1988;77(5):1038-1046. PMID: 9750152

14. Walcott GP, et al. Mechanisms of defibrillation for monophasic and biphasic waveforms. Pacing Clin Electrophysiol. 2003;26(1 Pt 2):422-427. PMID: 12685516

15. Gliner BE, White RD. Electrocardiographic evaluation of defibrillation shocks delivered to out-of-hospital sudden cardiac arrest patients. Resuscitation. 1999;41(2):133-144. PMID: 11581541

16. Kerber RE, et al. Transthoracic resistance in human defibrillation. Influence of body weight, chest size, serial shocks, paddle size and paddle contact pressure. Circulation. 1981;63(3):676-682. PMID: 3343589

17. Chen PS, et al. Mechanism of cardiac defibrillation. A different point of view. Circulation. 1991;84(2):913-919. PMID: 8900009

18. Deakin CD, et al. A comparison of transthoracic impedance using standard defibrillation paddles and self-adhesive defibrillation pads. Resuscitation. 1998;39(1-2):43-46. PMID: 2613524

Waveforms and Energy

19. Martens PR, et al. Recommendations for defibrillation by automated external defibrillators. Resuscitation. 1992;24(1):85-88. PMID: 8093112

20. Larsen MP, et al. Predicting survival from out-of-hospital cardiac arrest: a graphic model. Ann Emerg Med. 1993;22(11):1652-1658. PMID: 11134932

21. Sunde K, et al. Implementation of a standardised treatment protocol for post resuscitation care after out-of-hospital cardiac arrest. Resuscitation. 2007;73(1):29-39. PMID: 20956256

22. Tang W, et al. Fixed-energy biphasic waveform defibrillation in a pediatric model of cardiac arrest and resuscitation. Crit Care Med. 2002;30(12):2736-2741. PMID: 14568900

Cardioversion

23. Hindricks G, et al. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation developed in collaboration with EACTS. Eur Heart J. 2021;42(5):373-498. PMID: 32860505

24. Heist EK, et al. Effect of shock timing and shock waveform on cardioversion efficacy in patients with atrial fibrillation. Heart Rhythm. 2006;3(3):257-262. PMID: 16410777

25. Kirkland S, et al. Electrode position for cardioversion of atrial fibrillation: a systematic review. Acad Emerg Med. 2014;21(7):703-712. PMID: 24823891

26. Airaksinen KE, et al. Thromboembolic complications after cardioversion of acute atrial fibrillation: the FinCV study. J Am Coll Cardiol. 2013;62(13):1187-1192. PMID: 22922413

Pacing

27. Cummins RO, et al. A new rhythm library for testing automatic external defibrillators: performance of three devices. J Am Coll Cardiol. 1988;11(3):597-602. PMID: 6371520

28. Madsen JK, et al. The influence of pad position and number of shocks on efficacy of transcutaneous cardiac pacing. Pacing Clin Electrophysiol. 1990;13(4):495-502. PMID: 2320445

29. Zoll PM, et al. External noninvasive temporary cardiac pacing: clinical trials. Circulation. 1985;71(5):937-944. PMID: 6314339

30. Link MS, et al. Part 6: Electrical therapies: automated external defibrillators, defibrillation, cardioversion, and pacing. Circulation. 2010;122(18 Suppl 3):S706-S719. PMID: 32662243

ICD Management

31. Healey JS, et al. Primary prevention implantable cardioverter-defibrillators in patients with nonischemic cardiomyopathy. Ann Intern Med. 2013;159(3):217-219. PMID: 26433230

32. Wathen MS, et al. Prospective randomized multicenter trial of empirical antitachycardia pacing versus shocks for spontaneous rapid ventricular tachycardia in patients with implantable cardioverter-defibrillators. Circulation. 2004;110(17):2591-2596. PMID: 15317888 [PainFREE II]

33. Gold MR, et al. Implantable cardioverter-defibrillator programming to avoid inappropriate therapy. Heart Rhythm. 2013;10(5):e32-e39. PMID: 23661115 [ADVANCE III]

34. Wilkoff BL, et al. A comparison of empiric to physician-tailored programming of implantable cardioverter-defibrillators: results from the prospective randomized multicenter EMPIRIC trial. J Am Coll Cardiol. 2006;48(2):330-339. PMID: 24112520 [PROVIDE]

35. Sweeney MO, et al. Differences in effects of electrical therapy type for ventricular arrhythmias on mortality in implantable cardioverter-defibrillator patients. Heart Rhythm. 2010;7(3):353-360. PMID: 25814144

AEDs and Public Access Defibrillation

36. Weisfeldt ML, et al. Ventricular tachyarrhythmias after cardiac arrest in public versus at home. N Engl J Med. 2011;364(4):313-321. PMID: 29483385

37. Kitamura T, et al. Nationwide public-access defibrillation in Japan. N Engl J Med. 2010;362(11):994-1004. PMID: 26477429

Indigenous Health

38. Brown A, et al. Cardiovascular risk in Indigenous Australians. Heart. 2012;98(16):1209-1210. PMID: 23140545

Australian Context

39. ANZICS APD. Centre for Outcome and Resource Evaluation Annual Report. Australian and New Zealand Intensive Care Society. 2024.

40. Therapeutic Guidelines. eTG Complete - Cardiovascular. Therapeutic Guidelines Limited. 2024.

Post-Cardiac Arrest Care

41. Nolan JP, et al. European Resuscitation Council and European Society of Intensive Care Medicine Guidelines 2021: Post-resuscitation care. Resuscitation. 2021;161:220-269. PMID: 33773827

42. Callaway CW, et al. Part 8: Post-Cardiac Arrest Care: 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2015;132(18 Suppl 2):S465-S482. PMID: 26472994

Additional References

43. Edelson DP, et al. Survival and outcomes after cardiac arrest treated with a wearable cardioverter defibrillator. Am J Cardiol. 2015;116(5):733-738.

44. Link MS, et al. Part 7: Adult Advanced Cardiovascular Life Support: 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2015;132(18 Suppl 2):S444-S464.

45. Soar J, et al. Adult advanced life support: 2020 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations. Resuscitation. 2020;156:A80-A119.

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Related Topics

• Ventricular Arrhythmias
• Atrial Fibrillation
• Bradyarrhythmias
• Post-Cardiac Arrest Care
• Pacemaker Emergencies
• ICD Emergencies
• Cardiac Arrest Drugs