basics letters of cardiac pacemaker

  • pacemakers are often described by letters
  • modern pacemakers have 5 letters
  • in the ICU, basic pacemakers are usually described with 3 letters

Letters

  1. chamber paced (AVDO)
  2. chamber sensed (AVDO)
  3. mode of operation (ITDO)
  4. programmability: rate responsiveness (OPMR)
  5. tachyarrhythmia response: OPSD

Chamber Paced

  • chamber paced could be atrial, ventricular, dual, or none
    • none paced makes the pacemaker an EKG device

Mode of operation

Inhibited

  • if native rhythm is detected, the pacemaker will inhibit itself
    • with A sensing: if p detected, then there is no atrial pacing
    • with V sensing: no V pace if QRS detected
    • D sensing: each chamber independent but could create AV synchrony problem

Triggered

  • this mode works with dual chamber pacing
  • only applies to ventricular leads
  • when P sensed, ventricular lead is triggered to fire after set PR interval
  • native QRS ignored

Demand

  • combined inhibition and triggering
  • if P wave: atrium inhibited
  • if QRS: V lead inhibited
  • if no QRS: V lead fires after PR interval
  • this maintains AV synchrony

Obligatory

  • obligatory: asynchronous. In this mode the pacemaker will just fire regardless of native rhythm
  • can cause afib or VT/VF when native QRS occurs during T wave

Rate responsiveness

  • none in the ICU

Anti tachycardia

  • None
  • Pacing: overdrive, pace faster to break tachycardia cuircuit
  • Shock
  • Dual shock and pace