ICD Emergencies in ICU

Quick Answer

Implantable cardioverter-defibrillator (ICD) emergencies in ICU include inappropriate shocks, ICD storm, device malfunction, lead problems, and deactivation considerations. These situations require understanding of device function, rapid intervention, and multidisciplinary collaboration.

Immediate Management Priorities:

1. ICD Storm (≥3 shocks in 24 hours):

   • Apply magnet over generator to disable tachycardia therapies
   • Correct reversible causes (electrolytes K⁺ 4.0-4.5, Mg²⁺ ≥1.0 mmol/L)
   • Beta-blockade (esmolol or metoprolol) - essential first-line
   • Deep sedation (propofol) to reduce sympathetic drive
   • Amiodarone 300 mg IV bolus then 900 mg/24h infusion
   • Consider stellate ganglion block, catheter ablation, or ECMO if refractory

2. Inappropriate Shocks:

   • Apply magnet to prevent further shocks
   • Urgent device interrogation
   • Reprogram detection criteria and discrimination algorithms
   • Treat underlying arrhythmia (AF rate control, SVT treatment)

3. Magnet Application:

   • Disables tachycardia detection and therapy
   • Does NOT disable pacing function (pacing continues VVI at 65-100 bpm magnet rate)
   • Effects are manufacturer-dependent and programmable
   • Must have external defibrillation available

4. Device Deactivation:

   • Ethical end-of-life consideration, not euthanasia
   • Requires informed consent, family discussion, documented process
   • Performed by device technician or via magnet taping
   • Continue pacing if patient is pacemaker-dependent

Critical Numbers:

• ICD storm: ≥3 shocks in 24 hours requiring intervention
• Normal lead impedance: 200-1200 ohms
• Defibrillation threshold: should be ≤25J with 10J safety margin
• Magnet effect: suspends detection while in place (manufacturer-dependent)

ICU Mortality: ICD storm 20-30% in-hospital mortality; inappropriate shocks associated with 2-fold increased mortality risk (PMID: 22083657)

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CICM Exam Focus

Written Exam (SAQ)

Common SAQ Stems:

• "A 62-year-old patient with an ICD presents to ICU having received 6 shocks in the past 4 hours. Outline your assessment and management approach."
• "Discuss the approach to ICD management in a patient undergoing emergency surgery requiring electrocautery."
• "A patient with advanced heart failure and an ICD is transferred to ICU for palliative care. Discuss the ethical and practical considerations for ICD deactivation."
• "Describe the causes and management of inappropriate ICD shocks."

Expected Depth:

• ICD storm definition, aetiology, and tiered management algorithm
• Magnet application effects (manufacturer-specific differences)
• Inappropriate shock causes (SVT, AF, lead fracture, oversensing)
• Device-procedure interactions (MRI, electrocautery, cardioversion)
• End-of-life deactivation ethics and process
• Lead complications including recalls (Sprint Fidelis, Riata)

Hot Case Presentations

Typical Scenarios:

• Patient receiving recurrent ICD shocks with magnet taped over device
• Post-cardiac surgery patient with ICD and new arrhythmias
• Terminal patient with ICD requiring deactivation discussion
• Patient with lead fracture and inappropriate shock history

Examiner Expectations:

• Structured approach to device assessment
• Knowledge of magnet effects and limitations
• Ability to coordinate with device technician/electrophysiology
• Sensitive communication regarding device deactivation
• Indigenous health considerations for remote patients with devices

Viva Topics

Expected Discussion Areas:

• ICD components, sensing algorithms, therapy zones
• ATP vs shock therapy - when each is used
• Electrical storm pathophysiology and management escalation
• MRI compatibility and safety protocols
• Psychological impact of ICD shocks
• S-ICD vs transvenous ICD considerations

Common Examiner Questions:

1. "What is the difference between magnet application and device deactivation?"
2. "Describe the programming zones of an ICD"
3. "What are the causes of failure to terminate VT/VF?"
4. "How would you manage a patient requiring urgent MRI who has an ICD?"

Common Mistakes

1. Assuming magnet application disables pacing (it does NOT)
2. Not recognising manufacturer-specific magnet responses
3. Delaying magnet application during shock storm
4. Failing to secure external defibrillation before magnet use
5. Not involving electrophysiology/device team early
6. Inappropriate use of Class IC antiarrhythmics in structural heart disease
7. Not addressing psychological impact of multiple shocks
8. Confusing device deactivation with assisted dying

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Key Points (10)

Must-Know Facts

1. ICD Storm Definition: ≥3 separate episodes of VT/VF requiring device therapy within 24 hours; associated with 20-30% in-hospital mortality and 2-5 fold increased long-term mortality risk (PMID: 25193880)

2. Magnet Effect on ICDs: Suspends tachycardia detection and therapy while magnet remains in place; does NOT affect pacing function; effects are manufacturer-dependent and some devices have programmable magnet response (PMID: 17509379)

3. Inappropriate Shocks: Account for 10-20% of all ICD shocks; most common causes are AF/atrial flutter (50%), sinus tachycardia (25%), SVT (15%), and oversensing from lead problems or EMI (10%) (PMID: 16027254)

4. ICD Components: Generator (battery, capacitors, sensing/pacing circuits, microprocessor); leads (sensing, pacing, high-voltage coils); most ICDs also provide bradycardia pacing (VVI, DDD, CRT-D) (PMID: 29574943)

5. Therapy Zones Programming: VT zone (slower VT, ATP first-line), VF zone (faster rates, shock primary), VT-1/VT-2 zones allow tiered therapy; modern programming favours higher rate cutoffs and longer detection to reduce inappropriate therapy (MADIT-RIT: PMID: 23257378)

6. ATP (Antitachycardia Pacing): 8-beat burst pacing at 88% of VT cycle length; terminates 90% of monomorphic VT; painless; first-line therapy in VT zone; may accelerate to VF (1-4% risk) (PMID: 15687846)

7. Lead Fracture Red Flags: Sudden change in impedance (high impedance = conductor fracture; low impedance = insulation breach); inappropriate shocks from noise oversensing; Sprint Fidelis and Riata ST/Optim leads have FDA advisories (PMID: 18441929, 22285053)

8. Beta-Blockers in Electrical Storm: Essential first-line therapy; reduce sympathetic drive and recurrent arrhythmias; IV metoprolol or esmolol; continue/initiate oral beta-blocker unless contraindicated (PMID: 25193889)

9. Stellate Ganglion Block: Left stellate ganglion block (or bilateral) for refractory electrical storm; temporarily reduces sympathetic input to heart; bridge to catheter ablation; performed by anaesthesia/pain medicine (PMID: 28463082)

10. ICD Deactivation Ethics: Ethically permissible withdrawal of treatment (not euthanasia); requires informed consent; should be offered to all patients with life-limiting illness; documented discussion essential; pacing function may be continued (PMID: 25179915, 24819389)

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Red Flags

Immediate Life-Threatening Features

Device-Specific Red Flags

Procedural Red Flags

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ICD Basics and Physiology

ICD Indications

Primary Prevention (no prior cardiac arrest):

• LVEF ≤35% with NYHA Class II-III symptoms despite ≥3 months GDMT (MADIT-II: PMID: 11907286, SCD-HeFT: PMID: 15659722)
• LVEF ≤30% at least 40 days post-MI (MADIT-II)
• Hypertrophic cardiomyopathy with risk factors
• Arrhythmogenic right ventricular cardiomyopathy with risk factors
• Long QT syndrome with syncope despite beta-blockade
• Brugada syndrome with spontaneous Type 1 ECG

Secondary Prevention (prior cardiac arrest or sustained VT):

• Survived VF or haemodynamically unstable VT not due to reversible cause (AVID: PMID: 9382893)
• Sustained VT with structural heart disease
• Syncope with inducible VT at EPS

ICD Components and Function

Generator (Pulse Generator):

• Battery: Lithium-silver vanadium oxide, 6-8 year lifespan
• Capacitors: Store charge for defibrillation (up to 40J delivered)
• Microprocessor: Arrhythmia detection algorithms, programmable
• Sensing circuits: Detect cardiac signals, differentiate VT from SVT
• Memory: Stores electrograms, event logs

Lead System:

ICD Configurations:

Sensing and Detection

Rate Detection:

• Heart rate calculated from R-R intervals
• Programmable rate cutoffs define zones
• Detection requires sustained rate above threshold (e.g., 12 of 16 intervals)

VT vs SVT Discrimination Algorithms:

Programming Zones (Modern Approach - MADIT-RIT):

MADIT-RIT Trial (2012) (PMID: 23257378):

• Higher rate cutoffs (200 bpm) reduced inappropriate therapy by 75%
• No increase in syncope or death
• Changed paradigm toward less aggressive programming

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Therapy Delivery

Antitachycardia Pacing (ATP)

Mechanism:

• Rapid ventricular pacing terminates re-entrant VT
• Pacing captures the excitable gap of the re-entry circuit
• Results in bidirectional collision and circuit extinction

Standard Protocol:

• Burst pacing: 8 beats at 88% of VT cycle length
• If unsuccessful: 8 beats at 84% (second attempt)
• Ramp pacing: Decreasing cycle length with each beat

Efficacy:

• Terminates 90-95% of monomorphic VT (PMID: 15687846)
• Painless - patient often unaware
• Risk of VT acceleration to VF: 1-4%
• ATP during charging allows shock if ATP fails

When ATP is Inappropriate:

• Polymorphic VT (too fast, unstable)
• VF (disorganised rhythm)
• Very fast VT (>250 bpm)
• Haemodynamically unstable VT

Cardioversion and Defibrillation

Cardioversion (Synchronised):

• Lower energy (10-35J)
• Synchronised to R-wave
• For organised rhythms (VT)

Defibrillation:

• Higher energy (typically 25-40J)
• Not synchronised
• For VF and very fast VT

Defibrillation Threshold (DFT):

• Minimum energy required to terminate VF
• Tested at implant (ideally ≤25J with 10J safety margin)
• Factors increasing DFT:
  • Amiodarone (increases by 30-60%)
  • Cardiomegaly
  • Pericardial effusion
  • Metabolic derangement
  • Lead maturation/fibrosis

Shock Waveform:

• Biphasic (modern devices): Lower energy required, more effective
• Tilted waveform optimises energy delivery

Therapy Sequence Example

Typical VT Episode:

1. Arrhythmia onset detected (rate >170 bpm)
2. Detection criteria met (30 of 40 intervals)
3. VT discrimination (SVT unlikely)
4. ATP burst 1 delivered
5. If unsuccessful → ATP burst 2
6. If unsuccessful → Shock 1 (25J)
7. If unsuccessful → Shock 2-6 (up to 40J each)
8. Maximum 6-8 therapies per episode typically programmed

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Inappropriate Shocks

Definition and Epidemiology

Definition: ICD shock delivered for a rhythm other than VT/VF

Incidence:

• 10-20% of patients experience inappropriate shocks
• Account for 20-35% of all shocks delivered
• Risk factors: younger age, history of AF, single-chamber device

Impact:

• Associated with 2-fold increased mortality (PMID: 22083657)
• Psychological trauma, PTSD, depression (PMID: 22393352)
• Battery depletion
• Proarrhythmia (shock-induced VT/VF rare)

Causes of Inappropriate Shocks

Recognition

Clinical Features:

• Shock during activity or stress (sinus tachy)
• Shock with irregular palpitations (AF)
• Shock with arm movement (myopotentials)
• Multiple shocks in quick succession (oversensing)

Device Interrogation Findings:

• Electrograms show supraventricular morphology
• Irregular R-R (AF)
• High-frequency noise (lead fracture)
• Rate below VF zone at shock delivery

Management

Immediate:

1. Magnet application - prevents further shocks
2. Reassurance and sedation if multiple shocks received
3. Treat underlying arrhythmia:
   • AF: Rate control (metoprolol, diltiazem)
   • SVT: Adenosine, beta-blocker
   • Sinus tachycardia: Treat cause (sepsis, hypovolaemia)

Device Reprogramming:

• Increase VT detection rate (e.g., 170 → 200 bpm)
• Extend detection duration (more intervals required)
• Enhance SVT discriminators
• Adjust sensitivity if oversensing
• Enable ATP during charging (shock may be avoided)

Lead Assessment:

• Check impedance trends (sudden increase = fracture)
• Fluoroscopy for lead integrity
• Consider lead revision if abnormal

Prevention Strategies (MADIT-RIT, PREPARE, EMPIRIC trials):

• Higher rate cutoffs
• Longer detection intervals
• ATP before shock for fast VT
• Improved SVT discrimination algorithms

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ICD Storm

Definition

ICD Storm: ≥3 separate VT/VF episodes requiring device therapy (ATP or shock) within 24 hours (HRS 2015: PMID: 25827376)

Electrical Storm: ≥3 separate VT/VF episodes within 24 hours requiring intervention (device therapy or external cardioversion/defibrillation)

Epidemiology

• Occurs in 10-20% of ICD patients over device lifetime
• 4% annual incidence
• More common in secondary prevention indication
• Higher with ischaemic cardiomyopathy
• Associated with 2-5 fold increased mortality (PMID: 25193880)

Causes and Precipitants

Acute Management Algorithm

Phase 1: Immediate (0-15 minutes)

1. Apply magnet over ICD generator

   • Suspends tachycardia therapy
   • Pacing continues
   • Ensure external defibrillator available

2. Haemodynamic stabilisation

   • IV access, monitoring
   • If persistent VT/VF: External defibrillation

3. Beta-blockade (First-line pharmacotherapy)

   • Metoprolol IV 5 mg q5min (max 15 mg) then 50-100 mg PO BD
   • OR Esmolol 500 mcg/kg bolus then 50-200 mcg/kg/min infusion
   • Reduces recurrent VT by 80% (PMID: 25193889)

4. Correct reversible factors

   • K⁺ target 4.0-4.5 mmol/L
   • Mg²⁺ target ≥1.0 mmol/L (give Mg²⁺ 2g IV empirically)

Phase 2: Stabilisation (15-60 minutes)

5. Deep sedation

   • Propofol infusion 1-4 mg/kg/hr
   • Reduces catecholamine surge
   • Consider intubation and ventilation if ongoing storm

6. Amiodarone

   • 150-300 mg IV bolus (diluted, over 10-20 minutes)
   • Then 1 mg/min for 6 hours, 0.5 mg/min for 18 hours
   • Total 1.2-1.5 g in first 24 hours

7. Treat underlying cause

   • ACS: Urgent angiography if suspected
   • Sepsis: Antibiotics, source control
   • Heart failure: Diuresis, inotropes as needed

Phase 3: Refractory Storm (>1 hour)

8. Stellate ganglion block

   • Left-sided block or bilateral
   • Ultrasound or fluoroscopic guidance
   • Reduces sympathetic input to heart
   • Bridge to definitive therapy (PMID: 28463082)

9. Catheter ablation

   • Emergent ablation for refractory VT storm
   • Targets scar-related re-entry circuits
   • Success rate 70-90% for monomorphic VT
   • May require ECMO support (PMID: 22921475)

10. Mechanical circulatory support

    • VA-ECMO for haemodynamic support during storm
    • Allows time for ablation/recovery
    • Impella may unload LV

ICD Storm Flowchart

ICD Storm (≥3 shocks/24h)
           │
           ▼
    ┌──────────────────┐
    │  Apply Magnet    │
    │  (Suspend ICD)   │
    └────────┬─────────┘
             │
             ▼
    ┌──────────────────┐
    │  Ensure External │
    │  Defib Available │
    └────────┬─────────┘
             │
             ▼
    ┌──────────────────┐
    │  IV Beta-blocker │
    │  (Metoprolol or  │
    │   Esmolol)       │
    └────────┬─────────┘
             │
             ▼
    ┌──────────────────┐
    │  Correct K⁺/Mg²⁺ │
    │  K⁺ → 4.0-4.5    │
    │  Mg²⁺ 2g IV      │
    └────────┬─────────┘
             │
             ▼
    ┌──────────────────┐
    │  Deep Sedation   │
    │  (Propofol)      │
    └────────┬─────────┘
             │
             ▼
    ┌──────────────────┐
    │  Amiodarone      │
    │  300 mg IV then  │
    │  infusion        │
    └────────┬─────────┘
             │
     Storm controlled?
        /          \
      Yes           No
       │             │
       ▼             ▼
   ┌────────┐   ┌──────────────────┐
   │ Wean   │   │ Stellate Block   │
   │ sedation│   │ +/- Ablation    │
   │ Reprogram│  │ +/- ECMO        │
   └────────┘   └──────────────────┘

Pharmacotherapy for ICD Storm

PROCAMIO Trial (2017) (PMID: 28405017)

• Procainamide vs amiodarone for stable wide-complex tachycardia
• Procainamide: 67% termination vs amiodarone 38%
• Fewer major adverse events with procainamide
• Consider procainamide for haemodynamically stable VT

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Magnet Application

Magnet Effect on ICDs

General Principle:

• Magnet application suspends tachycardia detection and therapy
• Effect is present only while magnet is held over device
• Pacing function continues unaffected
• Some devices have programmable magnet response

Manufacturer-Specific Responses

Important Variations:

• Some devices emit audible tones when magnet applied
• Response may be programmed off (magnet ineffective)
• Duration of suspension varies (some resume after 30 seconds)
• Device interrogation reveals magnet response programming

When to Apply Magnet

Magnet Application Technique

1. Ensure external defibrillation available (mandatory)
2. Identify generator location (usually left pectoral)
3. Place ring magnet directly over generator centre
4. Secure with tape if ongoing effect needed
5. Monitor ECG continuously
6. Remove magnet when threat resolved

Magnet vs Deactivation

Caveats

• Magnet may be programmed off - interrogation needed to confirm
• Does not disable pacing - bradycardia therapies continue
• External defibrillation must be available
• Not a substitute for formal deactivation in end-of-life

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ICD Deactivation

Ethical Framework

Key Principles (HRS 2015) (PMID: 25827376):

1. Deactivation is withdrawal of treatment - ethically and legally permissible
2. Not euthanasia or assisted dying - patient dies of underlying disease
3. Patient autonomy - competent patient can refuse any treatment
4. Proportionality - burden of therapy may outweigh benefit
5. Documentation - clear record of informed consent

Australian/NZ Context:

• Consistent with ANZICS End-of-Life Guidelines
• Supported by Australian Medical Association position statement
• Does not require court or tribunal approval
• Family involvement encouraged but patient decision paramount

Indications for Deactivation Discussion

Deactivation Process

Step 1: Assess Decision-Making Capacity

• Patient can understand, retain, weigh information
• If incapacitated: Advance directive or substitute decision-maker

Step 2: Informed Discussion

• Explain device function (tachycardia therapy vs pacing)
• Clarify that deactivation prevents shocks, not death
• Discuss that pacing may be continued if providing comfort
• Address concerns about dying process

Step 3: Document Consent

• Written consent preferred but verbal acceptable
• Document discussion, participants, decision
• Specify which therapies to deactivate

Step 4: Technical Deactivation

• Preferred: Device technician programs off tachycardia therapies
• Alternative: Magnet taped over device (temporary measure)
• Pacing decision: Usually continue unless causing discomfort

Step 5: Post-Deactivation Care

• Reassurance about dying process
• Symptom management (dyspnoea, anxiety)
• Psychological support for family

Deactivation Considerations

Psychological Considerations

Patient Concerns:

• Fear of "turning off" life support
• Concern about painful death
• Guilt about "giving up"
• Religious or cultural beliefs

Communication Approach:

• "The device prevents sudden death but does not treat your underlying illness"
• "Turning off the shocks allows natural death to occur when the time comes"
• "You will not feel the device being turned off"
• "We will ensure you are comfortable"

Family Involvement:

• Include in discussions if patient wishes
• Address concerns about witnessing shocks
• Provide bereavement support

Special Populations

Pacemaker-Dependent Patients:

• May have complete heart block
• Turning off pacing may hasten death
• Requires careful discussion of implications
• Some consider this different from withdrawing other treatments

CRT-D Recipients:

• CRT pacing may provide symptom relief
• Consider continuing CRT, deactivating ICD function
• Discuss quality of life vs prolonging dying

Indigenous Health Considerations:

• Cultural beliefs about death and technology
• Family and community decision-making
• Sorry business preparations
• Remote location challenges for technical deactivation
• Consider telehealth consultation with device company

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Failure to Detect or Treat VT/VF

Failure to Detect

Causes:

Management:

• Device interrogation with stored electrograms
• Lower rate cutoff if appropriate
• Shorten detection duration
• Adjust sensitivity
• Lead revision if malposition

Failure to Terminate

Causes:

Management:

• External defibrillation (pads away from generator)
• Increase programmed shock energy
• Change shock polarity/vector
• Address reversible causes (electrolytes, drugs)
• Consider lead repositioning/addition of SVC coil
• DFT testing if stable

DFT Testing

Traditional Approach:

• VF induction with T-wave shock or rapid pacing
• Device shock termination verified
• Minimum energy + 10J safety margin

Modern Approach:

• Many centres no longer routinely test DFT at implant
• SIMPLE trial (PMID: 25594058): No difference in arrhythmic death with vs without DFT testing
• Exceptions: S-ICD (mandatory), revision procedures, high-risk substrate

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Lead Problems

Lead Complications Overview

Lead Fracture

Clinical Presentation:

• Inappropriate shocks (oversensing of noise)
• Failure to pace/sense
• Sudden impedance change

Diagnosis:

• Impedance trends: Sudden increase (>2000 ohms) diagnostic
• Electrograms: High-frequency noise artefact
• Fluoroscopy: May show conductor discontinuity
• Lead integrity alert (Medtronic devices)

Management:

• Disable tachycardia therapy (magnet or reprogramming)
• Lead extraction and replacement
• May add new lead without extraction if infection risk low

Lead Recalls and Advisories

Sprint Fidelis Lead (Medtronic 6930-6949) (PMID: 18441929):

• FDA advisory October 2007
• Fracture rate 2.5-5% at 3-5 years
• Fracture typically at yoke (lead-header junction)
• Causes inappropriate shocks, failure to pace
• Management: Surveillance with Lead Integrity Alert; extraction if malfunction

Riata/Riata ST Lead (St Jude/Abbott) (PMID: 22285053):

• FDA Class I recall December 2011
• Externalized conductors (inside-out insulation failure)
• May cause inappropriate shocks, sensing failure
• Screening: Fluoroscopy for conductor externalisation
• Management: Replace if symptomatic or electrically abnormal

Lead Extraction

Indications (HRS 2017) (PMID: 28342719):

• Device infection (Class I)
• Non-functional lead interfering with device function
• Venous occlusion preventing new lead placement
• Patient preference

Techniques:

• Simple traction (rarely successful for leads >1 year)
• Locking stylet with traction
• Powered sheaths (laser, mechanical rotation)
• Open surgical extraction

Risks:

• Mortality 0.3-0.5% (higher with older leads)
• SVC/RA tear requiring emergent sternotomy
• Cardiac tamponade
• Tricuspid valve damage

Australian Context:

• Limited centres with extraction expertise
• May require interstate transfer
• Cardiothoracic surgery backup essential

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Post-Shock Care

Immediate Assessment

After ICD Discharge:

1. Assess patient condition

   • Conscious vs unconscious
   • Haemodynamically stable vs unstable
   • Preceding symptoms (palpitations, syncope)

2. History of event

   • What was patient doing?
   • Any prodrome?
   • Number of shocks felt
   • Chest pain, dyspnoea

3. 12-lead ECG

   • Current rhythm
   • ST changes (ischaemia)
   • QT interval

4. Device interrogation (URGENT)

   • Confirm appropriate vs inappropriate therapy
   • Review electrograms
   • Check lead parameters
   • Battery status

Device Interrogation Analysis

Key Information:

• Date/time of episodes
• Detected rate and duration
• Electrogram morphology
• SVT discriminator results
• Therapy delivered (ATP, shocks, number)
• Termination success
• Lead impedances (trends)
• Battery voltage

Interpreting Electrograms:

Psychological Support

Psychological Impact of Shocks:

• 20-30% develop clinically significant anxiety
• 10-15% develop PTSD symptoms (PMID: 22393352)
• Depression, avoidance behaviour
• Reduced quality of life
• Fear of activity, social withdrawal

Risk Factors for Psychological Morbidity:

• Multiple shocks
• Inappropriate shocks
• Younger age
• Female sex
• Pre-existing anxiety/depression
• Lack of social support

Interventions:

• Psychoeducation about device function
• Cognitive behavioural therapy
• Support groups
• Cardiac rehabilitation
• Consider psychiatric referral for severe symptoms
• Mindfulness-based stress reduction

Ongoing Management

Medical Optimisation:

• Heart failure medications (GDMT)
• Beta-blocker (reduce recurrence)
• Antiarrhythmic (if recurrent VT)
• Electrolyte maintenance

Device Reprogramming:

• Address cause of inappropriate shocks
• Optimise detection and therapy zones
• Enable ATP where appropriate

Follow-Up:

• Device clinic within 1-2 weeks
• Cardiology review
• Address reversible causes
• Psychological screening

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S-ICD Considerations

Subcutaneous ICD Overview

Components:

• Pulse generator: Left lateral chest wall (mid-axillary line, 5th-6th intercostal space)
• Subcutaneous lead: Parasternal position, tunnelled
• No transvenous leads or vascular access

Advantages:

• No vascular access required
• No risk of lead-related endocarditis
• Easier extraction
• Suitable for young patients, congenital heart disease

Disadvantages:

• No bradycardia pacing capability
• No ATP (only shock therapy)
• Larger generator
• Higher shock energy required (80J max)
• Screening ECG required (T-wave oversensing risk)

S-ICD-Specific Issues

Screening:

• Mandatory pre-implant ECG screening
• Assess T-wave to R-wave ratio in multiple vectors
• 7-15% of patients fail screening due to oversensing risk

Inappropriate Shocks:

• Higher rate than transvenous ICD (8-13% vs 6-8%)
• T-wave oversensing most common cause
• Myopotential oversensing (exercise)
• SMART Pass algorithm reduces oversensing

Failure Modes:

• Cannot deliver ATP (shocks only)
• Inappropriate sensing from different vectors
• Generator pocket issues (larger device)
• Lead migration (rare)

Special Considerations:

• No MRI compatibility (older models)
• Longer charge time (up to 14 seconds)
• Higher DFT requirement (65J typically programmed)
• DFT testing mandatory at implant

S-ICD in ICU

Management Differences:

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Device Interactions

MRI and ICDs

Background:

• Historically contraindicated (heating, movement, programming reset)
• Modern MR-conditional devices allow safe scanning
• Requires specific protocol

MR-Conditional Requirements:

• Device and ALL leads must be MR-conditional
• Specific field strength limits (usually 1.5T, some 3T)
• SAR (specific absorption rate) limits
• Whole-body vs partial scan restrictions
• Lead implant duration requirements

Protocol for MR-Conditional Device:

1. Confirm device MR-conditional status
2. Device technician programs MRI mode
3. Continuous monitoring during scan
4. Reinterrogation and reprogramming post-scan
5. Verify lead parameters unchanged

Non-MR-Conditional Device (Emergency Scan):

• Risk-benefit discussion essential
• Radiologist, cardiologist, device specialist input
• Continuous monitoring, resuscitation available
• Limit scan time and SAR
• Immediate post-scan interrogation

Electrocautery

Risks:

• Oversensing of cautery current → inappropriate shock
• Damage to generator circuits
• Reset to backup mode
• Lead tip heating (rare)

Management (PMID: 25827376):

Pacemaker-Dependent Patient:

• Consider programming to asynchronous mode (VOO/DOO)
• Backup transcutaneous pacing available

External Cardioversion/Defibrillation

Risks:

• Device damage
• Lead damage
• Threshold increase
• Circuit reset

Safe Practice:

• Paddle/pads position: ≥8 cm from generator
• Anterior-posterior position preferred
• Avoid current path through device/leads
• Use lowest effective energy
• Interrogate device post-cardioversion

Radiotherapy

Risks (PMID: 28364024):

• Cumulative radiation damage to circuitry
• Random memory errors
• Battery depletion
• Circuit failure

Management:

• Shield generator if possible (5 half-value layers of lead)
• Avoid direct beam on generator
• Weekly device checks during therapy
• Interrogation before and after each session
• Consider device relocation for thoracic tumours

Other Interactions

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Australian and New Zealand Context

Device Services

Major ICD Implanting Centres:

• All tertiary hospitals with cardiac electrophysiology services
• NSW: Royal Prince Alfred, Westmead, St Vincent's, John Hunter
• VIC: Alfred, Royal Melbourne, Monash
• QLD: Prince Charles, Royal Brisbane
• WA: Royal Perth, Fiona Stanley
• SA: Royal Adelaide, Flinders
• NZ: Auckland, Christchurch, Wellington

Remote Monitoring:

• Most ICDs have remote monitoring capability
• Automatic transmission of data to clinic
• Alerts for arrhythmias, lead issues, battery status
• Reduces clinic visits (especially important for remote patients)
• Australian Medicare rebate for remote monitoring

Indigenous Health Considerations

Disparities:

• Higher rates of ischaemic heart disease (2-3 times)
• Higher rates of rheumatic heart disease
• Earlier age of cardiac events
• Lower rates of device implantation
• Geographic barriers to device services

Cultural Considerations:

• Family and community involvement in decisions
• Extended family may be decision-makers
• Sorry business and cultural obligations
• Language barriers (interpreter services essential)
• Distrust of medical system in some communities

Remote Management Challenges:

• Distance from device clinics
• Limited local expertise
• Remote monitoring particularly valuable
• Telemedicine consultations with device company
• RFDS and retrieval services for emergencies
• Training local health workers in magnet application

End-of-Life Considerations

Australian Legal Framework:

• Deactivation is lawful withdrawal of treatment
• Does not constitute euthanasia or assisted dying
• Patient or substitute decision-maker can request
• Medical practitioner should facilitate

Documentation:

• Advance Care Directive may address device therapy
• Enduring Power of Attorney (medical) can make decisions
• Goals of care discussion should include device status
• Document discussions clearly in medical record

State Variations:

• Advance Care Directive legislation differs by state
• Most principles consistent nationally
• Local palliative care teams familiar with processes

Guidelines and Resources

Australian Guidelines:

• CSANZ Guidelines on Device Therapy (aligns with international)
• ANZICS-CORE End-of-Life Guidance
• Therapeutic Guidelines: Cardiovascular

Resources:

• HeartFoundation Australia - patient resources
• Cardiac Society of Australia and New Zealand
• Device manufacturer 24-hour support lines
• State retrieval services (MedSTAR, CareFlight, NETS)

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SAQ Practice Questions

SAQ 1: ICD Storm Management (15 marks)

Stem: A 58-year-old man with ischaemic cardiomyopathy (LVEF 25%) and a dual-chamber ICD is admitted to ICU having received 8 shocks from his device in the past 6 hours. He is anxious but haemodynamically stable with BP 105/65 mmHg and HR 85 bpm on the monitor. Device interrogation confirms all shocks were appropriate for VT at 185 bpm, which terminated with each shock but recurred within minutes.

Questions:

a) Define ICD storm and outline the immediate management priorities for this patient. (6 marks)

b) Describe the pharmacological management of electrical storm, including mechanism of action of key agents. (5 marks)

c) What non-pharmacological interventions may be considered if arrhythmia remains refractory? (4 marks)

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Model Answer:

a) Definition and Immediate Management (6 marks)

ICD Storm Definition:

• ≥3 separate VT/VF episodes requiring device therapy within 24 hours (1 mark)
• This patient meets criteria (8 shocks in 6 hours) (0.5 marks)

Immediate Management Priorities:

1. Apply magnet over ICD generator (1 mark)

   • Suspends tachycardia detection and therapy
   • Prevents further distressing shocks while treating cause
   • Ensure external defibrillator immediately available

2. Correct reversible precipitants (1 mark)

   • Potassium: Target 4.0-4.5 mmol/L
   • Magnesium: Give 2 g IV empirically, target ≥1.0 mmol/L
   • Review and stop proarrhythmic drugs
   • Check troponin to exclude acute ischaemia

3. Beta-blockade - FIRST-LINE pharmacotherapy (1 mark)

   • IV metoprolol 5 mg boluses (max 15 mg)
   • OR esmolol infusion 50-200 mcg/kg/min
   • Essential for reducing sympathetic drive and VT recurrence

4. Supportive care (0.5 marks)

   • Anxiolysis/sedation
   • Continuous ECG monitoring
   • IV access, resuscitation equipment

b) Pharmacological Management (5 marks)

(1 mark each for beta-blocker, amiodarone, and one other agent with dose and mechanism)

c) Non-Pharmacological Interventions (4 marks)

1. Stellate ganglion block (1 mark)

   • Left-sided (or bilateral) stellate ganglion block
   • Performed by anaesthesia/pain medicine with ultrasound guidance
   • Temporarily reduces sympathetic input to heart
   • Bridge to definitive therapy

2. Catheter ablation (1.5 marks)

   • Emergent ablation for refractory VT storm
   • Targets scar-related re-entry circuits (in ischaemic cardiomyopathy)
   • 70-90% acute success for monomorphic VT
   • May require intubation/sedation
   • Consider ECMO support for haemodynamic instability

3. Mechanical circulatory support (1 mark)

   • VA-ECMO for haemodynamic support during storm/ablation
   • Allows time for antiarrhythmic effect and recovery
   • Impella may provide LV unloading

4. Device reprogramming (0.5 marks)

   • Consider ATP optimisation
   • May allow painless VT termination

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SAQ 2: ICD and End-of-Life Care (15 marks)

Stem: A 74-year-old Aboriginal woman with advanced heart failure (NYHA IV, LVEF 15%) and a CRT-D device is transferred from a remote community in the Northern Territory for symptom palliation. She is now bedbound, has been clearly informed her prognosis is weeks, and has expressed a wish to focus on comfort and return home to be with her family for "sorry business." She is concerned about receiving painful shocks from her device.

Questions:

a) Discuss the ethical and legal considerations regarding ICD deactivation in this context. (5 marks)

b) Outline the practical process for device deactivation, including which device functions may be continued. (5 marks)

c) Describe the specific cultural and logistical considerations relevant to this Indigenous patient from a remote community. (5 marks)

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Model Answer:

a) Ethical and Legal Considerations (5 marks)

Ethical Framework:

1. Deactivation is withdrawal of treatment (1 mark)

   • Ethically permissible under principle of patient autonomy
   • Patient has right to refuse any medical treatment
   • Consistent with HRS 2015 Expert Consensus and ANZICS End-of-Life guidelines
   • NOT euthanasia or assisted dying - patient dies of underlying disease

2. Proportionality of treatment (1 mark)

   • Burden of shock therapy (pain, distress) may outweigh benefit
   • Device originally implanted for life-prolongation
   • In palliative setting, goals have changed
   • Shocks may prolong dying process rather than life

3. Informed consent requirements (1 mark)

   • Patient has decision-making capacity (competent)
   • Has been clearly informed of prognosis
   • Understands consequences of deactivation
   • Verbal consent acceptable, written consent preferred
   • Document discussion clearly

4. Legal framework (1 mark)

   • Lawful in all Australian jurisdictions
   • Does not require court or tribunal approval
   • Consistent with Advance Care Directive principles
   • Northern Territory legislation supports patient-directed care

5. Clinical appropriateness (1 mark)

   • Shock therapy may cause suffering without meaningful benefit
   • Multiple shocks at end of life are distressing for patient and family
   • Proactive discussion should be standard care in advanced illness

b) Practical Deactivation Process (5 marks)

Pre-Deactivation Steps:

1. Confirm decision-making capacity (0.5 marks)

   • Patient understands information, retains it, can weigh options
   • Aboriginal Health Worker (AHW) may assist with communication

2. Informed discussion and documentation (1 mark)

   • Explain difference between defibrillator and pacing functions
   • Clarify that deactivation prevents shocks, does not cause death
   • Document discussion, participants, decision in medical record
   • Written or verbal consent

Technical Deactivation Options:

3. Preferred: Device programmer (1 mark)

   • Device technician uses manufacturer programmer
   • Select which therapies to deactivate
   • Can be done in hospital or community if technician available
   • Telehealth support from device company may assist

4. Alternative: Magnet application (1 mark)

   • Ring magnet taped over generator
   • Suspends tachycardia therapy while in place
   • Temporary measure until programming available
   • Suitable for urgent situations or remote settings

Functions to Consider:

5. What to deactivate and what to continue (1.5 marks)

• This patient has CRT-D: CRT pacing may improve comfort by reducing dyspnoea
• Discuss with patient whether any symptoms attributed to pacing

c) Indigenous and Remote Considerations (5 marks)

Cultural Considerations:

1. Family and community involvement (1 mark)

   • Extended family central to Aboriginal decision-making
   • Patient's expressed wish is to be with family for "sorry business"
   • Family meeting with Aboriginal Health Worker (AHW) or Aboriginal Liaison Officer (ALO)
   • Ensure family understands and supports decision

2. Sorry business and dying traditions (1 mark)

   • Patient wishes to return home - priority is facilitating this
   • Traditional practices around death and dying vary by community
   • Cultural obligations may influence timing and location of death
   • Respect patient's cultural preferences

3. Communication (1 mark)

   • Use interpreter if English not first language
   • AHW can assist with culturally appropriate communication
   • Ensure patient truly understands what deactivation means
   • Allow time for family consultation

Logistical Considerations:

4. Remote location challenges (1 mark)

   • Distance from device services (no device technician locally)
   • Options:
     • Programme before discharge
     • Telehealth consultation with device company
     • Train local health workers in magnet application
   • Magnet and tape sent home with patient if not programmed off

5. Ongoing support (1 mark)

   • Liaise with remote community health service
   • Ensure symptom management plan
   • Royal Flying Doctor Service (RFDS) aware if needed
   • Palliative care telehealth support available
   • Bereavement support for family

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Hot Case Scenarios

Hot Case 1: Recurrent ICD Shocks

Setting: Cardiac ICU, Day 1 post-admission

One-Minute Summary:

"This is Mr. K, a 63-year-old man with ischaemic cardiomyopathy, LVEF 20%, who was admitted 4 hours ago after receiving multiple ICD shocks at home. He has a history of anterior MI 3 years ago, subsequent ICD implantation for primary prevention, and one previous appropriate shock 18 months ago.

He was at rest when he experienced palpitations followed by 4 shocks in rapid succession over 15 minutes. Paramedics found him in sinus rhythm but anxious. Since arrival, he has received 2 further shocks despite appearing to be in sinus rhythm on the monitor.

On examination, he is distressed, BP 100/60, HR 75 regular, saturating 95% on 2L. There is a left pectoral ICD generator visible, JVP elevated 4 cm, bibasal crackles, and mild peripheral oedema. I note a magnet has been taped over his device.

My immediate priorities are:

1. Confirm magnet is correctly positioned and working (no further shocks)
2. Urgent device interrogation to determine appropriate vs inappropriate shocks
3. If inappropriate shocks: identify cause (lead issue, AF, oversensing)
4. Correct electrolytes, optimise heart failure management
5. Psychological support for device-related distress

My main concerns are lead fracture causing inappropriate therapy, given he has received shocks while apparently in sinus rhythm, and background heart failure decompensation as a precipitant."

Examiner Questions:

Q: "The device interrogation shows shocks were delivered for signals at 250 bpm, but the electrograms show irregular, low-amplitude signals between R-waves. What is the likely diagnosis and how would you manage it?"

A: "This pattern suggests oversensing, most likely from:

1. Lead fracture causing noise artefact - the high-frequency, irregular, low-amplitude signals between R-waves are characteristic
2. This should be confirmed by checking lead impedance trends - a sudden increase to >2000 ohms would support conductor fracture

Immediate management:

• Confirm magnet remains in place (therapy suspended)
• Check impedance: if elevated, this confirms fracture
• Check fluoroscopy to visualise lead integrity
• Ensure external defibrillation available

Definitive management:

• Patient will require lead revision - either:
  • New lead implantation (with or without fractured lead extraction)
  • Lead extraction if causing issues or infection risk

Specific lead concerns:

• I would check the model - Sprint Fidelis leads (Medtronic 6930-6949) have a known fracture risk and FDA advisory
• Riata leads (St Jude/Abbott) may have conductor externalisation

Until lead is replaced, he remains without ICD protection, so I would ensure he remains monitored in a high-acuity environment and optimise medical therapy for his heart failure and arrhythmia risk (beta-blockers, electrolytes)."

Q: "His potassium is 3.2 mmol/L. Does this change your management?"

A: "Yes, hypokalaemia is important for several reasons:

1. Arrhythmia risk: K⁺ 3.2 mmol/L increases his risk of ventricular arrhythmias - both VT/VF and Torsades de Pointes
2. Drug interaction: He is likely on diuretics for heart failure which cause potassium loss
3. Must correct before any intervention

Target: K⁺ 4.0-4.5 mmol/L in this cardiac patient

Replacement strategy:

• IV KCl: 40 mmol in 500 mL over 4 hours (max 20 mmol/hour peripherally, 40 mmol/hour centrally)
• Magnesium: Give Mg²⁺ 10-20 mmol IV as hypokalaemia often coexists with hypomagnesaemia and is refractory without Mg correction
• Review diuretic dosing and consider potassium-sparing agent

Additional considerations:

• Recheck K⁺ every 2-4 hours until stable
• This does not change my diagnosis of lead fracture (inappropriate shocks for oversensing), but does add another layer of risk that must be addressed"

Q: "Walk me through how you would communicate with his family about what has happened and the plan."

A: "I would arrange to speak with Mr. K and his family together (with his consent), in a quiet private space.

Structure of communication:

1. What happened: 'Mr. K's heart device - the defibrillator - has been giving him electric shocks. These shocks are meant to protect him from dangerous heart rhythms, but our testing shows the device has been shocking him by mistake. The wire that connects the device to his heart appears to be damaged, and this is causing false signals that the device interprets as a dangerous rhythm.'

2. What we're doing now: 'We've placed a magnet over the device which temporarily turns off the shock function, so he won't receive any more shocks for now. We're also correcting his potassium level which was low, and this will help protect his heart.'

3. The plan: 'Mr. K will need a procedure to fix the wire - either a new wire will be put in, or the damaged wire replaced. This will be done by the heart rhythm specialists. Until then, he'll need to stay in the ICU where we can monitor him closely.'

4. Addressing distress: 'I understand this has been very distressing. Many patients find receiving shocks from their device frightening and upsetting. This is completely normal. We have support available including psychological counselling if that would be helpful.'

5. Check understanding: 'What questions do you have? Is there anything I can explain more clearly?'

I would document this discussion and ensure the information is also provided to the treating electrophysiology team."

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Hot Case 2: ICD and End-of-Life

Setting: General ICU, Day 3 of admission for comfort-focused care

One-Minute Summary:

"This is Mrs. T, a 72-year-old woman with end-stage heart failure, NYHA IV, LVEF 12%, who has been admitted for comfort-focused care following multiple ICU admissions in the past 6 months with no reversible cause identified. She has a CRT-D device implanted 4 years ago and received a shock 2 days ago during a VT episode.

She is currently comfortable on a low-dose morphine infusion for dyspnoea. Following family meeting and palliative care input, she has clearly stated she does not want resuscitation or further life-prolonging treatments, and wishes to focus on comfort.

On examination, she is alert, rested, BP 95/55, HR 70 paced rhythm, SpO₂ 92% on 2L. She has biventricular pacing visible on the monitor, JVP to earlobes, anasarca.

My immediate priorities are:

1. Address her concern about further shocks from her device
2. Discuss ICD deactivation as part of goals of care
3. Ensure family understanding and support
4. Coordinate with device technician for deactivation
5. Continue symptom management

The key issue is that her ICD may deliver distressing shocks that would be inconsistent with her stated comfort-focused goals."

Examiner Questions:

Q: "How would you approach the discussion about ICD deactivation with Mrs. T?"

A: "I would approach this discussion sensitively, recognising that device deactivation can be emotionally complex.

Before the conversation:

• Confirm her decision-making capacity
• Identify if she wants family present
• Review her understanding of her prognosis
• Ensure adequate time in a private setting

Key elements of discussion:

1. Explore her understanding and concerns: 'I understand you're worried about getting more shocks from your device. Can you tell me more about what's concerning you?'

2. Explain the device functions: 'Your device has two main jobs. First, it helps your heart pump more efficiently - that's the pacemaker part. Second, it can give a shock if your heart goes into a dangerous rhythm - that's the defibrillator part. We can turn these functions on or off separately.'

3. Link to goals of care: 'You've told us you want to focus on being comfortable and not having further aggressive treatments. The shock function of your device is designed to save your life if you have a dangerous heart rhythm. But in your situation, if that rhythm were to happen, a shock might bring you back only to face more suffering, which isn't consistent with your wishes for comfort.'

4. Present the option: 'We can turn off the shock function so you won't receive any more electric shocks. The pacemaker part that helps your heart pump can stay on if it's helping you feel better. This is your choice, and whatever you decide, we will support you.'

5. Address common concerns: 'Turning off the shocks does not cause death - it simply means if a dangerous rhythm occurs, we let nature take its course. This is not the same as asking to die; it's about preventing suffering at the end of life.'

6. Confirm understanding: 'Can you tell me in your own words what we've discussed? Do you have any questions?'

7. Document: I would document the discussion, her decision, those present, and ensure this is communicated to all team members."

Q: "She agrees to deactivation. How would you proceed practically?"

A: "Practical steps for deactivation:

1. Document informed consent:

• Written consent if possible, verbal consent acceptable
• Record discussion, decision, those present
• Update goals of care documentation

2. Coordinate with device service:

• Contact device clinic or on-call technician
• Request attendance to program off ICD therapies
• This may take several hours to organise

3. Temporary measure if technician not immediately available:

• Tape ring magnet over generator
• This suspends tachycardia therapy
• Inform patient and family this is temporary until programming

4. Programming decision:

• Deactivate: VT/VF detection, shock therapy, ATP
• CONTINUE: Bradycardia pacing (prevents symptomatic bradycardia)
• Consider: CRT pacing may provide symptom benefit (discuss with patient)
• In her case with LVEF 12%, CRT likely providing some haemodynamic support

5. Post-deactivation:

• Confirm programming complete
• Provide written confirmation to patient/family
• Document in medical record
• Inform all treating teams (nursing, palliative care)
• Ensure symptom management plan in place

6. Psychological support:

• Acknowledge this is a significant decision
• Reassure about dying process
• Offer chaplaincy or social work if desired"

Q: "Her adult son is distressed and asks whether turning off the device means we're 'killing her.' How would you respond?"

A: "I would acknowledge his distress and address his concern directly.

Response:

'I understand this is very difficult, and it's completely natural to have these concerns. Let me reassure you about what this means.

Turning off the shock function of the device is not killing your mother. Your mother has an illness - heart failure - that cannot be cured, and she is reaching the end of her life from that illness. The device was there to stop sudden death from heart rhythms, but it cannot treat or cure her underlying disease.

If we leave the shocks on and a dangerous rhythm happens, the device might shock her heart back to beating. But she would still have the same advanced heart failure, and she might wake up only to face more suffering - or the shocks might happen over and over at the end of life, which would be distressing for her and for you.

By turning off the shocks, we're allowing your mother to die peacefully from her heart disease, without electric shocks at the end. This is what she has told us she wants - to be comfortable.

This is very different from euthanasia or assisted dying. We're not doing anything to cause her death. We're simply not using a treatment that would only prolong suffering.

The pacemaker part of her device will keep working, so her heart will continue to beat as long as it can. When she dies, it will be from her heart failure, not from turning off the device.

Many families find this decision difficult. Would it help if I arranged for you to speak with our palliative care team or chaplaincy? They have experience supporting families through these decisions.'

I would document this conversation and offer ongoing support to the family."

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Viva Scenarios

Viva 1: ICD Storm Pathophysiology and Management

Examiner: "A patient with an ICD is brought to your ICU receiving recurrent shocks. Define ICD storm and describe your initial approach."

Candidate: "ICD storm is defined as three or more separate episodes of VT or VF requiring device therapy - either antitachycardia pacing or shocks - within a 24-hour period.

My initial approach follows a systematic framework:

Immediate priorities:

First, I would apply a magnet over the ICD generator. This suspends tachycardia detection and therapy while the magnet remains in place, preventing further distressing shocks while I assess and treat the patient.

Second, I must ensure external defibrillation capability is immediately available, as the patient is now unprotected from VT/VF.

Third, I would assess haemodynamic stability. If the patient is in VT with haemodynamic compromise, I would proceed to external cardioversion.

Critical early interventions:

Beta-blockade is the first-line pharmacological therapy. I would give IV metoprolol 5 mg boluses up to 15 mg, or start an esmolol infusion. Beta-blockers reduce sympathetic drive and are essential for preventing VT recurrence.

Simultaneously, I would correct electrolytes - targeting potassium 4.0-4.5 mmol/L and giving magnesium 2 grams IV empirically regardless of the serum level.

Deep sedation with propofol reduces catecholamine surge and has indirect anti-arrhythmic effects."

Examiner: "The patient continues to have VT despite beta-blockade. What are your next steps?"

Candidate: "For refractory VT despite beta-blockade, I would escalate therapy:

Second-line pharmacotherapy:

Amiodarone is my next agent. I would give a 150-300 mg IV bolus diluted and infused over 10-20 minutes, followed by an infusion at 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours.

Important caveats with amiodarone:

• It increases the defibrillation threshold by 30-60%
• The device may need reprogramming to deliver higher energy
• It has a long half-life and many drug interactions

Alternative agents include lignocaine (1-1.5 mg/kg bolus then 1-4 mg/min infusion) or procainamide. The PROCAMIO trial showed procainamide may be superior to amiodarone for haemodynamically stable VT.

Non-pharmacological escalation:

If the storm continues despite pharmacotherapy, I would consider:

1. Stellate ganglion block - typically left-sided or bilateral, performed by anaesthesia with ultrasound guidance. This temporarily reduces sympathetic input to the heart and can be a bridge to definitive therapy.

2. Emergent catheter ablation - for refractory monomorphic VT, ablation targets the scar-related re-entry circuit. In ischaemic cardiomyopathy, success rates are 70-90%. The patient may require intubation, deep sedation, or even ECMO support during the procedure.

3. Mechanical circulatory support - VA-ECMO provides haemodynamic support and allows time for other interventions."

Examiner: "What are the causes of electrical storm?"

Candidate: "Electrical storm usually has an identifiable precipitant. I categorise causes as:

Cardiac:

• Acute coronary syndrome - ischaemia is the most common cause
• Heart failure decompensation with neurohormonal activation
• Myocarditis

Metabolic:

• Electrolyte disturbances - hypokalaemia and hypomagnesaemia are critical
• Thyroid dysfunction

Drug-related:

• Proarrhythmic drugs - Class IC antiarrhythmics in structural heart disease, QT-prolonging agents
• Digoxin toxicity causes characteristic bidirectional VT
• Catecholamine excess - endogenous or exogenous

Device-related:

• Lead issues affecting sensing or therapy delivery
• Inappropriate programming

Systemic:

• Infection and sepsis causing catecholamine surge
• Fever - particularly important in channelopathies like Brugada syndrome

I would systematically investigate each of these while initiating treatment."

Examiner: "You mentioned amiodarone increases defibrillation threshold. Explain this concept."

Candidate: "The defibrillation threshold, or DFT, is the minimum shock energy required to successfully terminate ventricular fibrillation.

Normal physiology: Defibrillation works by simultaneously depolarising a critical mass of myocardium, terminating the multiple re-entrant wavelets that maintain VF. The energy required depends on the size of the heart, lead position, and myocardial conductivity.

DFT testing: Historically, DFT was tested at implant by inducing VF and confirming termination with the device shock. A 10J safety margin below maximum device output was considered adequate. The SIMPLE trial showed routine DFT testing may not be necessary, but it remains important in certain situations.

Factors increasing DFT:

• Amiodarone: Increases DFT by 30-60% through effects on sodium and potassium channels that stabilise membranes
• Cardiomegaly: Larger hearts require more energy
• Pericardial effusion: Shunts current away from myocardium
• Metabolic derangement: Acidosis, hypoxia, electrolyte abnormalities
• Lead position: Suboptimal shocking vector
• Antiarrhythmic drugs: Most increase DFT

Clinical implications: A patient on amiodarone may have a shock that would normally terminate VF fail to do so. This is why:

• DFT should be tested if amiodarone is initiated in an ICD patient
• Maximum device output should be programmed
• Shock polarity may need adjustment
• In some cases, an additional SVC coil or subcutaneous array is needed"

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Viva 2: Magnet Application and Device Interactions

Examiner: "You are called to theatre where an ICD patient is about to undergo emergency surgery. Describe your approach to perioperative ICD management."

Candidate: "Perioperative ICD management requires systematic assessment of the device, the procedure, and a plan for preventing inappropriate shocks or device damage.

Pre-operative assessment:

1. Device identification:

• Manufacturer and model (from card or interrogation)
• Type: ICD, CRT-D, S-ICD
• Indication: Primary vs secondary prevention
• Current programming and last check date

2. Patient factors:

• Pacemaker dependence (complete heart block, no escape rhythm)
• Recent arrhythmias
• Lead issues or advisories

3. Procedure factors:

• Electrocautery anticipated?
• Distance of surgical field from device?
• Duration of surgery?

Electrocautery management:

The main risk is electromagnetic interference causing:

• Oversensing interpreted as VT/VF → inappropriate shock
• Inhibition of pacing in pacemaker-dependent patient
• Rarely, direct circuit damage

Recommendations:

For surgery more than 15 cm from the generator:

• May proceed without magnet
• Use bipolar cautery if possible
• Short bursts, not sustained application
• Monitor continuously

For surgery within 15 cm of generator (including thoracic and upper abdominal):

• Apply magnet to suspend tachycardia therapy
• For pacemaker-dependent patients: consider reprogramming to asynchronous mode (VOO/DOO)
• Have external defibrillator and transcutaneous pacing available

Cautery technique:

• Bipolar preferred over monopolar
• If monopolar: grounding pad away from device, current path away from leads
• Short bursts, wait 3-5 seconds between applications"

Examiner: "You apply a magnet. What effect does this have, and are there any situations where it might not work?"

Candidate: "Magnet application to an ICD has specific effects that differ from a pacemaker.

Effects of magnet on ICD:

1. Suspends tachycardia detection - the device stops looking for VT/VF
2. Suspends tachycardia therapy - no ATP or shocks will be delivered
3. Effects only last while magnet is in place - removing the magnet restores normal function
4. Pacing continues - the bradycardia pacing function is NOT affected

This contrasts with a pacemaker, where the magnet typically causes asynchronous pacing at a fixed rate.

Manufacturer variations:

Different manufacturers have slightly different responses, and some allow programmable magnet response. For example:

• Some devices beep when the magnet is applied
• The Boston Scientific devices traditionally emit audible tones
• Some devices can have magnet response programmed 'off'

Situations where magnet may not work:

1. Magnet response programmed off - device interrogation would show this
2. Incorrect positioning - magnet must be directly over the generator; S-ICD location differs (left lateral chest)
3. Very old devices - may have different responses
4. Magnet too weak - commercial ring magnets should be used

Verifying magnet effect:

• Most devices have a marker or tone indicating magnet detection
• ECG should show pacing continues (if pacing)
• Device interrogation post-procedure confirms function"

Examiner: "The patient needs an urgent MRI brain for stroke evaluation. What considerations apply?"

Candidate: "MRI in a patient with an ICD requires careful consideration of device compatibility, risk-benefit, and protocol adherence.

MRI hazards with cardiac devices:

1. Magnetic field effects:

• Force on ferromagnetic components
• Torque causing lead displacement
• Reed switch activation (magnet mode)

2. Radiofrequency effects:

• Tissue heating at lead tip
• Potential for myocardial burns

3. Gradient effects:

• Induced currents
• Inappropriate sensing

4. Device effects:

• Parameter reset
• Battery depletion
• Permanent damage

MR-Conditional devices:

Modern ICD systems may be 'MR-conditional' - meaning they can safely undergo MRI under specific conditions. Requirements typically include:

• All components (generator AND leads) must be MR-conditional
• Specific field strength (usually 1.5T, some 3T)
• SAR limits
• Lead implant duration requirements (usually >6 weeks)
• Whole-body vs scan region restrictions

For an MR-conditional device:

1. Confirm all components are MR-conditional
2. Device technician programs 'MRI mode'
3. Continuous monitoring during scan
4. Minimum scan time necessary
5. Post-scan interrogation and reprogramming

In this emergency stroke scenario, I would:

1. Confirm the clinical necessity - is MRI essential vs CT?
2. If MRI essential: risk-benefit discussion with patient/family, cardiology, radiology
3. If proceeding: continuous monitoring, resuscitation available, limit SAR and scan time
4. Immediate post-scan device interrogation

The decision requires balancing the risk of missed stroke diagnosis against device complications. In many cases, CT is sufficient for acute stroke management."

Examiner: "What about external cardioversion in an ICD patient?"

Candidate: "External cardioversion in an ICD patient requires precautions to protect the device and ensure safety.

Potential complications:

• Direct damage to device circuitry from current
• Lead damage
• Increase in pacing or defibrillation threshold
• Device reset to backup programming
• False VT/VF detection from cardioversion artefact

Safe practice:

1. Pad/paddle position:

• Keep paddles/pads at least 8 cm from the generator
• Anterior-posterior position is preferred over anterior-lateral
• Avoid current pathway directly through the device

2. Energy selection:

• Use the lowest effective energy
• Biphasic waveform

3. Pre-cardioversion:

• Consider having the device interrogated and therapy suspended
• Or apply magnet to prevent post-shock false detection

4. Post-cardioversion:

• Mandatory device interrogation
• Check sensing thresholds, pacing thresholds, impedances
• Check programmed parameters haven't reset
• Verify tachycardia therapy settings

In an emergency where there is no time for device technician involvement, I would proceed with cardioversion using the precautions above, as the immediate life threat takes priority. Device interrogation would follow as soon as possible."

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ZCOR guideline addresses cardiac arrest with devices? A: ANZCOR Guideline 11.10

38. Q: What is the evidence for stellate ganglion block in electrical storm? A: Case series and observational data show effectiveness as bridge to ablation; no RCTs; HRS/EHRA recommend for refractory cases

39. Q: What year was Sprint Fidelis FDA advisory issued? A: October 2007

40. Q: What is the mortality association with inappropriate ICD shocks? A: 2-fold increased mortality (Russo 2012, PMID: 22083657)

41. Q: What guideline supports continuation of CRT pacing at end of life? A: HRS 2015 Expert Consensus - CRT provides symptom relief and continuation is appropriate if not prolonging suffering

42. Q: What percentage of ICD patients experience electrical storm over device lifetime? A: 10-20%

43. Q: What is the annual incidence of electrical storm in ICD patients? A: Approximately 4%

44. Q: What trial evaluated ECMO for refractory VT/VF during ablation? A: Multiple observational studies support ECMO use; no RCTs; enables haemodynamic support during ablation procedures

45. Q: What is the reported in-hospital mortality of ICD storm? A: 20-30%

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Interactive Learning Elements

Device Interrogation Interpretation Exercise

Scenario: A 65-year-old man presents after receiving 4 ICD shocks. Device interrogation is performed.

Interrogation Data:

Lead Parameters:

• RV Sensing: 8.2 mV (baseline 10.5 mV)
• RV Pacing Threshold: 0.75 V @ 0.4 ms
• RV Impedance: 580 ohms (baseline 520 ohms)
• Shock Impedance: 52 ohms (baseline 48 ohms)

Electrogram Review:

• Regular, monomorphic ventricular rhythm at 240-250 bpm
• QRS morphology consistent with baseline conducted rhythm
• AV dissociation present (atrial rate 75 bpm)

Questions:

1. Were these appropriate or inappropriate shocks?
2. What is the diagnosis?
3. What are your immediate management priorities?
4. Are the lead parameters concerning?

Answers:

1. Appropriate shocks - electrograms show VT (monomorphic, regular, AV dissociation)
2. Electrical storm with recurrent monomorphic VT (4 episodes in <10 minutes meets ≥3/24h criterion)
3. Immediate priorities:
   • Apply magnet to prevent further shocks
   • IV beta-blockade (metoprolol or esmolol)
   • Correct K⁺ to 4.0-4.5 mmol/L, Mg²⁺ 2g IV
   • Deep sedation
   • Amiodarone loading
   • Investigate precipitant (troponin, ECG for ischaemia)
4. Lead parameters are stable - no significant change suggesting lead problem; small impedance variation is normal

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Emergency Algorithm: ICD Storm

┌─────────────────────────────────────────────────────────────────┐
│                     ICD STORM ALGORITHM                         │
│                  (≥3 shocks in 24 hours)                        │
└─────────────────────────────────────────────────────────────────┘
                              │
                              ▼
┌─────────────────────────────────────────────────────────────────┐
│ STEP 1: IMMEDIATE (0-5 minutes)                                 │
│ • Apply MAGNET over ICD generator                               │
│ • Ensure external defibrillator available                       │
│ • Assess haemodynamic status                                    │
│ • If VT with compromise: external cardioversion                 │
└─────────────────────────────────────────────────────────────────┘
                              │
                              ▼
┌─────────────────────────────────────────────────────────────────┐
│ STEP 2: FIRST-LINE THERAPY (5-15 minutes)                       │
│ • IV BETA-BLOCKER (essential)                                   │
│   - Metoprolol 5 mg IV q5min (max 15 mg)                        │
│   - OR Esmolol 500 mcg/kg bolus, 50-200 mcg/kg/min              │
│ • Correct electrolytes                                          │
│   - K⁺ target 4.0-4.5 mmol/L                                    │
│   - Mg²⁺ 2 g IV empirically                                     │
│ • Investigate precipitant (troponin, ECG, K⁺, Mg²⁺, drugs)      │
└─────────────────────────────────────────────────────────────────┘
                              │
                              ▼
┌─────────────────────────────────────────────────────────────────┐
│ STEP 3: SECOND-LINE (15-60 minutes)                             │
│ • AMIODARONE 150-300 mg IV, then 1 mg/min infusion              │
│ • Deep sedation (propofol 1-4 mg/kg/hr)                         │
│ • Consider intubation if ongoing storm                          │
│ • Treat underlying cause (ACS → cath lab, sepsis → antibiotics) │
└─────────────────────────────────────────────────────────────────┘
                              │
              Storm controlled?
                    /    \
                  Yes     No
                   │       │
                   ▼       ▼
┌─────────────────┐ ┌────────────────────────────────────────────┐
│ • Wean sedation │ │ STEP 4: REFRACTORY (>1 hour)               │
│ • Device        │ │ • STELLATE GANGLION BLOCK                  │
│   interrogation │ │ • Emergent CATHETER ABLATION               │
│ • Reprogram     │ │ • Consider VA-ECMO support                 │
│ • Electrolytes  │ │ • Procainamide/lignocaine alternative      │
│ • EP follow-up  │ │ • Overdrive ventricular pacing             │
└─────────────────┘ └────────────────────────────────────────────┘

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Key Evidence Summary

Landmark ICD Trials

ICD Storm Evidence

Lead Advisory Evidence

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Related Topics

Prerequisites

• Cardiac Electrophysiology
• Ventricular Arrhythmias in ICU
• Cardiac Arrhythmias Overview

Related Conditions

• Electrical Storm Management
• Bradyarrhythmias and Heart Block
• Post-Cardiac Arrest Care
• Cardiogenic Shock

Related Procedures

• Temporary Pacing
• Cardioversion and Defibrillation
• Catheter Ablation

End-of-Life

• End-of-Life Care in ICU
• Withdrawal of Treatment
• Goals of Care Discussions

---

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