Temporary epicardial pacing after cardiac surgery Flashcards
Qualities of epicardial pacing wire
- Steel wire
- Insulated with polytetrafluoroethylene
- Bipolar or unipolar
Reasons epicardial pacing may be required after cardiac surgery
- Hypothermia
- Myocardial oedema
- Electrolyte abnormalities
- Surgical handling
- Scar tissue formation
- Suturing near the AV node or bundle of His
Types of pacing modes and pros/ cons
Fixed/ Asynchronous
Pros
- Continues to pace at a set rate regardless of electrical interference eg. diathermy
Cons
- May pace over patient’s intrinsic rhythm causing R-on-T
Demand/ Synchronous
Pros
- Can be used with patient’s native rate and augment if necessary
Cons
- May interpret electrical interference as native rhythm and inappropriately inhibit pacing box
Epicardial Pacing Nomenculture
3 letters:
1st= Chambers paced A- atria, V- ventricles, D- both or dual
2nd= Chambers sensed, as above
3rd= Response of box to sensing I- inhibition of pacing T- triggering of pacing D- both O- asynchronous
Pacing mode AAI
Indications and Contraindications
AAI= atria paced and sensed, if sensed inhibition of pacing
Indications
- Sinus bradycardia with poor cardiac output
- Prevention of post-op AF
Contraindications
- AV blocks or risk of developing AV blocks
- Poor sensing in atrial leads
Pacing mode VVI
Indications and Contraindications
VVI= ventricles paced and sensed, if sensed inhibition of pacing
Indications
- Patients at risk of developing or with AV block
- Ventricular standstill
- No atrial wires in-situ
Contraindications
- Patients who have improved cardiac output when normal physiological depolarisation occurs
- Poor sensing in ventricular wires
Pacing mode DDD
Indications and Contraindications
DDD= both atria and ventricles are paced and sensed, either atria or ventricle or both may be inhibited or paced in response to sensing e.g. atrial depolarisation occurs but ventricle doesn’t depolarise in a set time, pacemaker will depolarise ventricle
Indications
- AV blocks
- Asystole
- Sinus bradycardia at risk of developing AV block
Contraindications
- Poor sensing from atrial or ventricular wires
- Pacemaker-mediated tachycardia eg. atrial flutter causing rapid depolarisation of ventricles
Pacing mode DDI
Indications and Contraindications
DDI= Both atria and ventricle are sensed and paced, either may be inhibited in response to sensing
Indications
- Patients who have improved CO if physiological depolarisation occurs
- Recurrent paroxysmal AF or flutter
- Previous episode of pacemaker-mediated tachycardia in DDD mode
Contraindications
- Poorly sensed ventricle or atrial leads
Pacing mode VOO
Indications and Contraindications
VOO= Ventricle is paced this is asynchronous there is no sensing
Indications
- Emergency use
- Weaning from bypass when diathermy is being used
Contraindications
- Not constantly monitored for the risk of R-on-T
Pacing mode DOO
Indications and Contraindications
DOO= Atria and ventricle paced with a set AV delay, no sensing, asynchronous
Indications
- Emergency use
- Weaning from bypass when diathermy is being used
Contraindications
- Not constantly monitored for the risk of R-on-T
Prerequisites for a safe pacemaker check
- Normothermic
- Normal K
- ECG and IABP are being continually monitored
Pacemaker sensor threshold check
Sensitivity is the minimum current the pacemaker can sense, the lower the current the greater the sensitivity.
Start in AAI
- Set rate and sensitivity to a point where only the patient’s intrinsic rhythm is present
- The box should now only be sensing the patient’s intrinsic rhythm
- Slowly turn the sensitivity value up until the pacemaker is no longer able to sense atrial activity and starts to pace
- The is the atrial sensing threshold
- Do not set below 1mV
Set the pacing box to VVI
- Set rate and sensitivity to a point where only the patient’s intrinsic rhythm is present
- As above
- Do not set below 2mV
Pacemaker capture threshold check
The minimum pacemaker output required to generate an action potential in the myocardium.
Start in AAI
- Ensure the pacing rate is above the patient’s own intrinsic rate by at least 10bpm
- Turn down the threshold until pacing is dropped
- Turn up again until pacing occurs and the rate is the expected. This is capture threshold.
- Add a safety margin of 5V
Set to VVI
- As above
Pacemaker undersensing and oversensing
Undesensing means the pacemaker isn’t sensing the heart’s own native rhythm, risk of AF and R-on-T
Oversensing means the pacemaker misinterprets other electrical signals as native rhythm or shivering, inappropriately inhibiting the pacemaker.
