Internal Cardiac Defibrillator


Internal Cardiac Defibrillator, Automatic Internal Cardiac Defibrillator, Implantable Defibrillator, Implantable Cardioverter-Defibrillator, AICD Electrical Storm

  • Background
  • Device (AICD)
  1. Device discharges current when triggered by life-threatening Arrhythmia
    1. Depending on rhythm, device responds
      1. Over-drive pacing (antitachycardia pacing) OR
      2. Low-energy Synchronized Cardioversion (5 Joules) OR
      3. Low-energy Defibrillation mode (30-45 Joules)
    2. AICDs also have Pacemaker functionality
      1. Base rate of 30-40 beats per minute
  2. Pacemaker-like device with high capacity battery and capacitor
    1. Typical ICDs are 50-120 grams (30-70 ml volume) with 4-9 year battery life
    2. ICD Lead in the right ventricular apex
      1. Defibrillator coils in right ventricle and superior vena cava
    3. Pacing leads
      1. Right atrial lead
      2. Left ventricular pacing lead at the coronary sinus (biventricular ICD or resynchronization devices)
    4. Devices contain an antenna that can transmit events to a home monitoring device
      1. Monitoring device may in turn transmit to a triage clinician
      2. Sends the device discharge and the associated rhythm
  3. Implantation procedure
    1. Device placed in upper left chest below clavicle
    2. Transvenous threading of leads
    3. Defibrillator is tested during implantation by triggering Arrhythmia
    4. Placement in 1-2 hours by electrophysiology, cardiology, or cardiothoracic surgery
    5. Major complications: 1.5%
      1. Hematoma
      2. Displaced lead
      3. Pneumothorax
  • Precautions
  1. Optimal medical therapy is critical
    1. See Congestive Heart Failure
  2. MRI scans have been historically contraindicated
    1. Devices manufactured after 2000 are considered safe (after first 6 weeks)
    2. Avoid MRI with 6 weeks of placement due to device dislodgement
    3. Set AICD to minimal settings (reset after scan)
    4. Risk of lead heating, VT induction
    5. AICD may distort images
    6. EKG monitoring during procedure
    7. Nazarian (2013) Circ Arrhythm Electrophysiol 6(2): 419-28 [PubMed]
  • Indications
  • Primary prevention for Cardiomyopathy (Class I recommendations)
  1. Ischemic Cardiomyopathy
    1. NYHA Class I: Ejection Fraction <30%
    2. NYHA Class II: Ejection Fraction <35%
    3. Inducible VT/VF on EPS with Ejection Fraction <40%
  2. Non-ischemic Dilated Cardiomyopathy
    1. NYHA Class I: Ejection Fraction <35% (consider)
    2. NYHA Class II-III: Ejection Fraction <35%
  • Indications
  • Secondary Prevention (Class I recommendations)
  1. Structural heart disease and history of spontaneous, sustained Ventricular Tachycardia
  2. Cardiac Arrest survivor (after exclusion of completely reversible causes)
    1. Ventricular Fibrillation
    2. Unstable Ventricular Tachycardia
  3. Unexplained Syncope with inducible VT/VF by EPS
  4. Structural abnormalities predisposing to Ventricular Tachycardia (Class IIa recommendation)
    1. Brugada Syndrome with Syncope or Ventricular Tachycardia history
    2. One of more risk factors for Sudden Cardiac Death AND
      1. Hypertrophic Cardiomyopathy or
      2. Arrhythmogenic Right Ventricular Dysplasia (ARVD)
  • Contraindications
  1. Last revascularization procedure within 3 months
  2. Last Myocardial Infarction within 40 days
  3. Life Expectancy <1 year
  4. Arrhythmia otherwise treatable with catheter ablation or other procedure (e.g. WPW)
  • Management
  • Troubleshooting other ICD problems
  1. See Implanted Cardiac Defibrillator Infection
  2. Oversensing
    1. See below
    2. Results in shock delivered based on non-VT stimulus (e.g. muscle Fasciculations, SVT)
  3. Undersensing
    1. Failure to terminate VT/VF
    2. Presents with Palpitations, Dizziness, Syncope
    3. Possible causes
      1. Displaced or Fractured lead
      2. AICD malfunction or dead battery
      3. Change in Defibrillation threshold or delivered shock strength
      4. VT Defibrillation threshold rate is set below the patient's current rate
  4. Altered Defibrillation threshold
    1. Typically set at the time of AICD implantation based on testing
    2. Threshold may be altered by Electrolytes, acid-base, Hypoxemia, CHF, Antiarrhythmics
  • Management
  • Patient has received shock with device
  1. See Cardiac Electrical Storm
  2. Indications for immediate evaluation and monitoring (typically admitted)
    1. More than one shock delivered
    2. Cardiovascular (e.g. Chest Pain) or other systemic symptoms immediately preceded the shock
    3. Syncope
  3. Disposition
    1. Immediate emergency department evaluation for indications as listed above
    2. Routine cardiology clinic follow-up in 24 hours is sufficient if no emergent indications
  4. Evaluation
    1. See Pacemaker for evaluation of devices with Chest XRay, Electrocardiogram and Interrogation
    2. Interrogate device
      1. Identify triggering rhythm (e.g. Ventricular Tachycardia)
      2. Identify rhythms for which shock would be inappropriate triggers
        1. Sinus Tachycardia
        2. Atrial Fibrillation with Rapid Ventricular Rate
      3. Identify triggers not due to Dysrhythmia
        1. Muscle Fasciculations
        2. Electromagnetic interference
    3. Diagnostics
      1. Electrocardiogram
      2. Serum Electrolytes
      3. Chest XRay
        1. Evaluate for lead displacement or lead Fracture
      4. Troponin
        1. Anticipate mild Troponin elevation associated with Defibrillation event
        2. However, Troponins that continue to rise may indicate Acute Coronary Syndrome
  5. Management
    1. See Cardiac Electrical Storm
    2. Unstable Patient with multiple shocks delivered (or Cardiac Arrest)
      1. Rapid assessment per ACLS protocol (assume appropriate shocks)
      2. Evaluate for causes of persistent ventricular Dysrhythmias (See 6H6T)
      3. An appropriately shocking AICD may be left enabled to continue shocking through Resuscitation
        1. External Defibrillation is unlikely to be as effective as an implanted Defibrillator
        2. CPR may be performed despite AICD shocks (voltage is too low to harm rescuers)
      4. If disabling AICD (e.g. malfunctioning)
        1. Avoid applying external Defibrillator pads directly over the AICD pocket (within 10 cm of pocket)
        2. Apply a magnet over the AICD to disable its shock feature (but not its pacing)
      5. Central venous access should be placed on opposite side of the AICD
        1. Anticipate ipsilateral chronic thrombosis of the central veins on the AICD side
    3. Stable patient with multiple shocks delivered (Electrical Storm)
      1. Electrical Storm is defined as >3 episodes of sustained VT, VF or appropriate AICD shocks
        1. Two or more appropriate shocks in a 24 hour period is a high risk of death
      2. Evaluate for CHF, ACS, Electrolyte abnormalities, Hyperthyroidism
      3. Initiate Antiarrhythmics (e.g. Amiodarone) in Consultation with cardiology
      4. Admit patients for further monitoring, management
    4. Stable patient with an appropriate shock delivered
      1. Admit or observe as per indications above
      2. Exclude underlying cause (admit if these are present)
        1. Myocardial Ischemia with secondary Arrhythmia
        2. Decompensated Congestive Heart Failure
        3. Electrolyte disturbance (Hypokalemia, Hypomagnesemia)
      3. Discharge home with cardiology follow-up after underlying causes excluded
    5. Stable patient with an inappropriate shock delivered
      1. Continuous telemetry monitoring
      2. Disable the device and monitor if multiple shocks were delivered
        1. Tape magnet over the device (see below)
        2. Apply transcutaneous pads (at least 10-15 cm from device) in case of lethal Dysrhythmia
  6. References
    1. Jones and Orman in Herbert (2012) EM:Rap 12(5): 4-6
    2. Mattu and Swaminathan (2024) Refractory VF, EM:Rap 5/27/2024
  • Management
  • Turning off device
  1. Monitor on telemetry while device deactivated
  2. Indications
    1. Emergency surgery
      1. Consult with electrophysiology if adequate time
    2. Palliative Care
      1. Device may repeatedly apply shocks at end-of-life (before device can be formally turned off)
    3. Multiple inappropriate shocks
    4. During Central Line Placement (prevent inappropriately triggered shocks)
    5. Transcutaneous Pacing
  3. Older device response to magnet
    1. Device deactivated by applying a large magnet (typically doughnut shaped) over the device
      1. Device will only be disabled as long as magnet is over the device
      2. Consider taping magnet in place
    2. Device reactivated by removing magnet
      1. Device will reactivate within 10 seconds
  4. Newer device response to magnet
    1. Device is deactivated by applying magnet
      1. Device beeps with each QRS for 30 seconds
      2. Device then emits a continuous tone when disabled
      3. Once disabled, the magnet may be removed
    2. Device is reactivated by applying magnet
      1. Device beeps with each QRS with magnet applied to signify reactivation
      2. Magnet may be removed after device reactivated
  • Efficacy
  1. High risk patients (see above) have a significant mortality reduction (30-55%) with AICD placement
    1. Moss (2002) N Engl J Med 346(12): 877-83 [PubMed]
    2. Moss (1996) N Engl J Med 335(26): 1933-40 [PubMed]
  • Complications
  • Acute complications associated with placement
  1. See Cardiac Pacemaker
  2. Thrombosis
    1. Affects axillary, subclavian, innominate, veins and superior vena cava
    2. Chronic thrombosis is common, and typically asymptomatic (occurs in 50% of ICD placements)
    3. Acute thrombosis is less common (<3.5%) presenting with ipsilateral arm swelling
  • References
  1. Mallemat, Swaminathan and Egan in Herbert (2014) EM:Rap 14(10): 5-7
  2. Vanlandingham (2015) Crit Dec Emerg Med 29(10): 2-14
  3. Myerburg (2008) N Engl J Med 359(21): 2245-53 [PubMed]
  4. Stevenson (2006) J Card Fail 12(6): 407-12 [PubMed]
  5. Turakhia (2010) Am Fam Physician 82(11): 1357-66 [PubMed]