CICM SAQ 2016.1 Q2

Question

You are assessing a patient on the first post-operative day following an aortic valve replacement. There are atrial and ventricular epicardial wires in place and the patient is being paced at 90/min in a DDD mode.

  • a) Define sensitivity with respect to cardiac pacing. (20% marks)
  • b) Describe the steps that you would perform to check and set sensitivity. (30% marks)
  • c) In addition to checking sensitivity, what other daily checks would you perform in regards to the temporary pacing system? (20% marks)
  • d) The patient becomes completely pacemaker dependent and the pacemaker suddenly completely fails to pace. List the actions to troubleshoot the pacemaker. (30% marks)

Answer

Answer and interpretation

a) Define sensitivity with respect to cardiac pacing. (20% marks)

The ‘sensitivity (as numerically represented on the pacing generator) is the minimum current that the pacemaker is able to sense. A lower number thus corresponds to a greater sensitivity.

b) Describe the steps that you would perform to check and set sensitivity. (30% marks)

This is only checked when the patient has an intrinsic rhythm which affords some cardiovascular stability.

  • Set the pacemaker rate 10 below patients intrinsic rate
  • Set the output to a very low value e.g., 0.1mA
  • Setting the pacemaker to asynchronous mode by turning the sensitivity to its lowest
    value (highest mV setting) after setting the output current to its lowest value (e.g.
    0.1mA) so as to not capture but trigger the pacing indicator.
  • The sensitivity is then gradually increased (lower mV) until the pacemaker senses the
    patients intrinsic HR and the pacing indicator no longer illuminates but the sensing
    indicator does. This is the sensing threshold.
  • The final setting is usually half this determined value
    OR also acceptable-
  • Gradually decrease sensitivity (with output set to low value and pacemaker set to 10
    below intrinsic rate) and watch for sensing flash on box to disappear. Final setting is usually half this value.

c) In addition to checking sensitivity, what other daily checks would you perform in regards to the temporary pacing system? (20% marks)

  • Underlying heart rate
  • Capture threshold
  • Appropriate pacing mode for the patient
  • Impulse generator- battery
  • (Maximum tracking rate, AV interval, post ventricular atrial refractory period (PVARP)
    should be noted, but do not require daily checks once set)

d) The patient becomes completely pacemaker dependent and the pacemaker suddenly completely fails to pace. List the actions to troubleshoot the pacemaker. (30% marks)

  • Increase output to maximum (20mA)
  • Select VOO (fixed ventricular pacing) to overcome inappropriate over sensing
  • Check all leads/connections/batteries
  • Replace impulse generator if faulty
  • Consider reversing the polarity on the V wires
  • Consider percutaneous lead through skin

Pass rate: 90%
Highest mark: 8.75


Exams LITFL ACEM 700

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Emergency physician MA (Oxon) MBChB (Edin) FACEM FFSEM with a passion for rugby; medical history; medical education; and informatics. Asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | vocortex |

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