Cite this article as:
Anders, M. Pacing, Don't Forget the Bubbles, 2013. Available at:

NBG Code

0-none0-none0-none0 -none
A-AtriumA-AtriumT-triggeredR-rate modulatedA-Atrium


Modes of Pacing

AOOasynchronous atrialBradycardia w/ intact AV, poor atrial sensingvulnerable Phase → AF
VOOasynchronous ventricularBradycardia w/ conduction problems and poor ventricular sensingvulnerable Phase → VF
AAIdemand atrialBradycardia w/ intact AVnot possible in Atrial Tachycardia
VVIdemand ventricularBradycardia w/ conduction problems / SSS / AF / Overdriveno atrial seqeuential mode
DOOasynchronous AV sequentialBradycardia, which benefits w/ sequentialvulnerable Phase → AF or VF
DVIventricular inhibited, AV sequentialDesire for dual chamber pacing with poor atrial sensingrisk of AF
DDIdual sensing, AV sequentialall possible
DDDAV universalall possible, except atrial tachyarrhythmianot 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

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About Marc Anders

AvatarMarc Anders is a paediatric intensivist.

Author: Marc Anders Marc Anders is a paediatric intensivist.

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