Defibrillators, Implantable

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  • An implantable cardiac device (ICD) is a small battery-powered electrical impulse generator implanted SC in patients at risk of cardiac arrest from cardiac arrhythmias.
  • Lead(s) are positioned via venous return to heart and are endocardial (RA and RV) or epicardial (LV via coronary sinus).
  • The device is able to detect and convert ventricular and atrial arrhythmias to sinus rhythm with electric shocks delivered between the ICD can and coil(s) in the RV (single coil) and the SVC/RA juncture (dual coil).
  • Similar method of implantation as a pacemaker
  • Newly released devices (S-ICD) no longer have endocardial leads reducing the risk of blood infection.
  • 450,000 individuals experience sudden cardiac death yearly in US:
    • >100,000 devices implanted in US each year
    • ICDs have been shown to reduce mortality more effectively than antiarrhythmic drug therapy in patients with left ventricular dysfunction:
      • Absolute risk reduction of mortality of 7% in the 1st 2 yr
      • Benefit over antiarrhythmic drug therapy is limited to patients with ejection fractions of <35%
    • Effective in reducing mortality in hypertrophic cardiomyopathy
    • Both ischemic and nonischemic dilated cardiomyopathy patients show survival benefit with ICD
  • Immediate postimplant complications:
    • Pneumothorax
    • Vascular perforation
    • Acute lead dislodgement
  • Appropriate shocks:
    • 5% a year for primary prevention
    • 20% a year for secondary prevention
  • Electrical storm:
    • ≥2 appropriate shocks delivered within a 24-hr period
  • Inappropriate shocks:
    • 10–20% of ICD recipients
    • Oversensing
    • Inappropriate classification of rapid supraventricular tachycardia
  • Device infection:
    • 1–12% of patients
    • Acute 1–30 days—think staph
    • Subacute >30 days—think Staphylococcus epidermidis or gram negatives
    • 31–66% mortality if the device is left in place
    • Infection may involve the skin, the generator, the defibrillation pocket, or the leads.
    • Coagulase-negative staphylococci (42%)
    • Methicillin-sensitive staphylococci (25%)
    • MRSA (4%)
    • Gram-negative bacilli (9%)
  • Pocket hematoma do not aspirate
  • Vascular occlusion


  • Electrical storm: (≥2 appropriate shocks delivered within a 24-hr period)
    • Unknown
    • Decompensated heart failure
    • Acute ischemia
    • Metabolic disturbances
    • Drug proarrhythmia
    • Thyrotoxicosis
    • Fever with dilated cardiomyopathy
    • Genetic channelopathies, Brugada syndrome, Long QT, catacholaminergic polymorphic VT, arrhythmogenic RV cardiomyopathy
    • Postcardiac surgery
    • ICD induced from left ventricular or T-wave pacing
  • Inappropriate shocks:
    • Oversensing:
      • QRS, T-wave, P-wave, myopotential, electromagnetic interference (EMI)
      • Frequent nonsustained ventricular dysrhythmias
      • Lead fracture
      • Loose setscrew
      • Chatter between leads
      • Header (device circuitry) problem
    • Inappropriate classification of rapid supraventricular tachycardia:
      • Atrial fibrillation
      • Sinus tachycardia
      • Atrial flutter
      • Other supraventricular tachycardias (SVT)
  • Device/site-related:
    • Wound infection:
      • Staphylococcus aureus (most aggressive and seen early)
      • S. epidermidis (more indolent and later)
      • Escherichia coli, Pseudomonas species, and Streptococcal species (less common)
    • Pocket hematomas
    • Vascular (venous thrombosis/embolism secondary to impedance of venous flow as a result of the ICD lead[s])

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