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
- chamber paced (AVDO)
- chamber sensed (AVDO)
- mode of operation (ITDO)
- programmability: rate responsiveness (OPMR). This is for people with sinus node dysfunction who need elevated HR when running
- tachyarrhythmia response: OPSD. Don’t really use.
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
Anti tachycardia
- None
- Pacing: overdrive, pace faster to break tachycardia cuircuit
- Shock
- Dual shock and pace
- 1st letter: chamber pased, atrial, ventricular, dual
- 2nd letter: sensing, atrial, ventricular, dual
- 3rd letter: inhibition
- I: inhibit atrial on ventricular pacing
- D: lead in A, V. Sensing in A or V. Can pace in A or V. Can inihibit. Can trigger ventricular pacing based on atrium. AV nodal ablation
- Pacing:
- atrium: p waves
- RV: LBBB
- LV: RBBB
- AV: physiologic QRS
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