Pacing

NBG Code

I	II	III	IV	V
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

 

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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)

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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

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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

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References:

[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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