Pacemaker Modes

Pacemaker modes use a 3–5 letter code describing

  1. Chamber paced
  2. Chamber sensed
  3. Response to sensing
  4. (Optional) Rate modulation
  5. (Optional) Multisite pacing
Pacemaker Code
First letter
(chamber paced)
Second letter
(chamber sensed)
Third letter
(chamber response)
A — atrium A — atrium O — no response
V — ventricle V — ventricle I — inhibited
D — atrium and ventricle D — atrium and ventricle T — triggered
O — no pacing O — no sensing D — atrium and ventricle
— atrium triggers ventricle

Core Modes

DDD (Dual paced, dual sensed, dual response)

  • Paces: Atrium + Ventricle
  • Senses: Atrium + Ventricle
  • Response:
    • Triggers ventricular pacing after sensed atrial beat (AV synchrony)
    • Inhibits pacing if intrinsic activity present
  • Use:
    • Most common
    • AV block with intact sinus node
    • Sick sinus + AV conduction disease

Key: Maintains AV synchrony → most “physiologic”

VVI (Ventricle paced, ventricle sensed, inhibited)

  • Paces: Ventricle only
  • Senses: Ventricle
  • Response: Inhibits pacing if intrinsic ventricular beat
  • Use:
    • Atrial fibrillation with slow ventricular response
    • When atrial lead not needed or not possible

No AV synchrony → can cause pacemaker syndrome

AAI (Atrium paced, atrium sensed, inhibited)

  • Paces: Atrium
  • Senses: Atrium
  • Response: Inhibits if intrinsic atrial beat
  • Use:
    • Pure sinus node dysfunction
    • Intact AV conduction

Requires reliable AV conduction

DDI (Dual paced, dual sensed, inhibited only)

  • Paces: Atrium + Ventricle
  • Senses: Atrium + Ventricle
  • Response: Inhibits only (no tracking of atrial beats)
  • Use:
    • Prevents rapid ventricular pacing in atrial tachyarrhythmias

No atrial tracking → safer in AF/flutter

DOO / VOO / AOO (Asynchronous modes)

  • No sensing
  • Fixed-rate pacing regardless of intrinsic rhythm
  • Use:
    • Magnet mode
    • OR / electrocautery situations

Can cause R-on-T if competing rhythm

4th Letter (Rate Modulation “R”)

  • Example: DDDR, VVIR
  • Adjusts pacing rate based on activity (motion, respiration)
  • Use: chronotropic incompetence
PPM Comparison
Mode AV synchrony Tracks atrium Typical use
DDD Yes Yes AV block, most patients
VVI No No AF with slow rate
AAI Yes N/A Sinus node dysfunction
DDI Partial No Atrial arrhythmias
DOO No No Temporary/asynchronous

Trick

  • DDD = Does Everything
  • VVI = Ventricle Only
  • AAI = Atrium Only
  • DDI = Dual but Doesn’t track