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Cardiac Devices

Marcus Threadcraft

Types of Cardiac Implantable Electronic Devices (CIED)

  • For Controlling Arrhythmias: Implantable Pulse Generators
  • Pacemakers: Anti-bradycardia pacing
  • ICDs: Anti-tachycardia pacing and defibrillation
  • Biventricular Pacemakers: CRT for ventricular dyssynchrony (LBBB & Heart Failure)
  • Loop Recorders: implantable devices for monitoring arrhythmias (most often Afib)
  • LVADs: augment cardiac output for end-stage heart failure (not covered here)


  • Provide anti-bradycardia pacing by stimulating myocardium
  • Peripheral permanent pacemakers (PPMs)
  • SubQ generator, transvenous leads
    • Single chamber RV lead
    • Dual chamber RV and RA leads
    • BiV: RV, RA, and LV (coronary sinus) leads
  • Leadless pacemaker
    • Implanted generator in RV


  • Symptomatic Bradycardia
  • Heart Block: 2nd Degree Type II w/ sx or 3rd Degree
  • Sick Sinus Syndrome
  • Carotid Sinus Syndrome
  • After catheter ablation of AV node for AF
  • CRT

Implantable Cardioverter/Defibrillators (ICDs)

  • Pacing lead + defibrillation coil
  • Detect and treat VT/VF v
    • Anti-tachycardia pacing (ATP)- attempts to entrain and terminate VT
    • Defibrillation If ATP unsuccessful


  • Primary prevention
    • HFrEF
      • EF \<35% and NYHA II-III or EF \<30% and NYHA I
      • Must be >90d from revasc, >40d from MI, and on GDMT
    • Arrhythmogenic syndromes
      • Arrhythmogenic RV cardiomyopathy, Brugada syndrome, HCM and cardiac sarcoid with specific risk factors
  • Secondary prevention
    • Hx VF arrest or VT
    • Inducible VT on EP study with history of syncope

Cardiac Resynchronization Therapy (CRT)

  • BiV pacer that coordinates LV/RV contraction through synchronized activation of each ventricle following atrial contraction.
  • -P: CRT pacing only
  • -D: ICD function


  • Class I: LBBB and QRS≥150 with EF\<35%, NYHA II- IV, on GDMT, NSR
  • Class IIa: EF\<35%, NYHA II- IV, on GDMT, NSR AND
    • LBBB & QRS 120-149, non-LBBB & QRS≥150, or EF\<35% and expected to require >40% ventricular pacing

Interpreting Pacemaker Codes

1st Letter 2nd Letter 3rd Letter 4th Letter
A: atrial, V: ventricular, D: dual, O: none, I: inhibition, R: rate-adaptive Chamber Paced Chamber Sensed Response to Sensed Beat Program Features

Examples of Common Pacing Modes

  • VVI: Single RV lead that delivers a beat if no beat sensed. Often used with chronic AF with bradycardia
  • DDDR: Senses and paces both the atria and ventricle. If beat not sensed within a predefined interval, beat delivered. R indicates rate responsivity (changes rate based on changes in patient activity)
  • Magnet: Paces at a fixed rate without respect to native electrical activity (AOO,VOO,DOO). Deactivates ICD shock. Often used in surgery or at end of life to avoid ICD shocks

Additional Configurations

  • Epicardial Leads- pacemaker/defibrillator leads attached to outside of the heart (requires OR) vs traditional transvenous lead placement, which are inserted in the Cath Lab
    • Epicardial Leads generally placed in smaller children or during cardiac surgery with expected need for pacing/defibrillation
  • Abandoned leads
    • Absolute contraindication to MRI (ungrounded, produces heat and thermal Injury In setting of magnetic field)

Placement Complications

  • Acute: pocket hematoma, pneumothorax, myocardial perforation, cardiac tamponade, infection, lead displacement or disconnection
  • Long-term: secondary device infection, lead fracture (lead lifetime 10-15 years), insulation failure


Last update: 2022-05-29 04:05:22