Defibrillators, Implantable

Basics

Description

  • An implantable cardiac device (ICD) is a small battery-powered electrical impulse generator implanted subcutaneously in patients at risk of cardiac arrest from cardiac arrhythmias
  • ICDs monitor heart rhythms, delivering electrical shocks or pacing to restore normal sinus rhythm
  • Positioning of leads via venous return of the heart:
    • Endocardial (RA and RV)
    • Epicardial (LV via coronary sinus)
  • Midaxillary extravascular positioning via subcutaneous placement:
    • Eliminates exposure to systemic circulation (S-ICD
    • These have demonstrated superior performance, with defibrillation success rates over 98% and fewer procedural complications
  • Extravascular (substernal placement) ICD:
    • Retains benefits of extravascular ICD and provides pause, prevention, and antitachycardia pacing with low-energy defibrillation
  • 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
  • 450,000 individuals experience sudden cardiac death yearly in the US:
    • >100,000 devices implanted in the 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:
    • Occurs in 10–20% of ICD recipients
    • Oversensing
    • Inappropriate classification of rapid supraventricular tachycardia (SVT, afib)
  • Device infection:
    • Occurs in 1–12% of patients
    • Biofilm formation in device-related infections underscores the importance of early device removal in confirmed cases
    • Acute:
      • 1–30 d postimplantation
      • Commonly caused by Staphylococcus aureus
    • Subacute:
      • >30 d postimplantation
      • Typically involve Staphylococcus epidermidis or gram-negative bacteria
    • 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%)
  • Do not aspirate pocket hematoma because of risk of infection
  • Vascular occlusion

Etiology

  • 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, catecholaminergic polymorphic VT, arrhythmogenic RV cardiomyopathy
    • Postcardiac surgery
  • 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 SVT:
      • Atrial fibrillation
      • Sinus tachycardia
      • Atrial flutter
      • Other SVTs
  • Device/site related:
    • Wound infection:
      • Staphylococcus aureus (most aggressive and seen early)
      • S. epidermidis (more indolent and later)
      • Escherichia coli, Pseudomonas species, and Streptococcus species (less common)
    • Pocket hematomas
    • Vascular (venous thrombosis/embolism secondary to impedance of venous flow as a result of the ICD lead[s])
    • Infective endocarditis:
      • Inclusion of ICD infections as a predisposition for developing IE in latest modification of Duke criteria

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