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NBG Code

Paced Sensed Mode Modulation Multi-site
0-none 0-none 0-none 0 -none
A-Atrium A-Atrium T-triggered R-rate modulated A-Atrium
V-Ventricle V-Ventricle I-inhibited
D-dual D-dual D-dual


Modes of Pacing

Description Indication Limitation
AOO asynchronous atrial Bradycardia w/ intact AV, poor atrial sensing vulnerable Phase → AF
VOO asynchronous ventricular Bradycardia w/ conduction problems and poor ventricular sensing vulnerable Phase → VF
AAI demand atrial Bradycardia w/ intact AV not possible in Atrial Tachycardia
VVI demand ventricular Bradycardia w/ conduction problems / SSS / AF / Overdrive no atrial seqeuential mode
DOO asynchronous AV sequential Bradycardia, which benefits w/ sequential vulnerable Phase → AF or VF
DVI ventricular inhibited, AV sequential Desire for dual chamber pacing with poor atrial sensing risk of AF
DDI dual sensing, AV sequential all possible
DDD AV universal all possible, except atrial tachyarrhythmia not in atrial tachycardia


Specific indications:

  • AVRT: Consider overdrive pacing in AAI
  • AF: VVI
  • Overdrive pacing: when JET rate controlled, pacing 10% faster in AAI or DDD to regain atrial kick with AV conduction
  • Pace termination of reentry tachycardia (either atrial or AVRT): pace AAI 10-20% faster than atrial rate for short burst. If rapid reinitiation after successful capture, try gradually slowing pacing rate after reversion (risk of atrial fibrillation)
  • Atrial ECG: bipolar – attach atrial wire to right arm and left arm lead (atrial ECG prominent in I),;unipolar – attach atrial wire to V1 and V2 (atria ECG prominent in V1 and V2)

Problems & troubleshooting:

  • Daily pacemaker check: underlying rhythm, sensing and capture threshold (set threshold twice as measured)
  • Failure to pace: causes and treatment: threshold (increase output), ischaemia, electrolyte-disturbance (correct), post DC, lead malfunction, medication (flecainide, sotalol, propafenone, lignocaine, procainamide), cross-talk inhibition (reduce sensitivity, reduce output), oversensing (increase sensitivity), can also try to reverse polarity, or addition of skin lead
  • Failure to capture: threshold (increase output), ischaemia, electrolyte disturbance (correct), post DC, medication (flecainide, sotalol, propafenone, lignocaine, procainamide) – can also try to reverse polarity
  • Failure to sense: causes and treatment – sensing threshold (decrease sensing threshold)
  • Pacemaker-mediated tachycardia: change mode to DDI, adjust post ventricular atrial refractory period
  • Failure to track in DDD mode: adjust PVARP, AV interval and upper track rate

Checking and testing the pacemaker:

Patient non-pacing dependent

  • Start setup: atrial & ventricular leads connected to pacemaker (PM) cables, cables unplugged from PM, PM off
  • Turn PM on: default settings appear (DDD, rate 80, atrial (A) output 10 mA, ventricular (V) output 10 mA, A sensing threshold 0.5 mV, V sensing threshold 2 mV


Testing the sensing thresholds:

  • Set rate at least 20% below patient’s rate
  • Turn A and V outputs to 0.1 mA
  • Turn A and V sensing to ‘asynchronous’
  • Slowly increase V sensing by decreasing the number on scale, and observe the V red light
  • Record measured V sensing threshold (?? red light blinking)
  • Set V sensing to default 2 mV
  • Slowly increase A sensing by decreasing number on scale, and observe the A red light
  • Record measured A sensing threshold (?? red light blinking)
  • Set A sensing threshold to default 0.5 mV


Testing the output thresholds:

  • Set rate at least 20% above patient’s rate
  • Slowly increase A output by increasing the number on the scale, and observe ECG for distinct rate change
  • Record measured A capturing threshold
  • Turn A output threshold back to 0.1 mA
  • Slowly increase V output by increasing the number on the scale, and observe ECG for distinct rate and QRS shape change
  • Record measured V capturing threshold
  • Turn V output threshold back to 0.1 mA
  • Turn rate back down to at least 20% below patient’s rate


Final PM setting in backup mode:

  • Check V sensing on 2 mV and V light blinking red
  • Check A sensing on 0.5 mV and A light blinking red
  • Set pacing rate at acceptable backup rate below patient’s own rate
  • Turn A output up to 2x measured A output threshold
  • Turn V output up to 2x measured V output threshold


[1] Anaesthesia. 2007 Apr;62(4):364-73: Reade: Temporary epicardial pacing after cardiac surgery: a practical review. Part 2: Selection of epicardial pacing modes and troubleshooting

[2] Pediatr Crit Care Med 2010 Vol. 11, No. 1: Skippen et al: Pacemaker therapy of postoperative arrhythmias after pediatric cardiac surgery

 All Marc’s PICU cardiology FOAM can be found on PICU Doctor and can be downloaded as a handy app for free on iPhone or AndroidA list of contributors can be seen here.



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