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IBHRE® > Pulse generators > Flashcards

Pulse generators Flashcards

Covers aspects of generator construction from materials and components to battery chemistry and depletion characteristics. Currently weighted 3.5% in the CCDS exam.

1
Q

Typically what material is used for the construction of the pacemaker can/case?

A

Titanium

It’s biologically inert, lightweight and hardwearing

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2
Q

Typically what chemical composition is used in modern day pacemaker batteries?

A

A composition of Lithium Iodine.

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3
Q

What are 4 major benefits of using Lithium Iodine for a pacemaker battery?

A
  1. Long shelf life
  2. Predictable decay for 90% of battery life
  3. Hermetically sealed in device
  4. Capacity between 0.8 and 2.5aH
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4
Q

What is the approximate beginning of service (BOS) voltage of Lithium Iodine based pacemakers?

A

Approximately 2.8V.

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5
Q

Why isn’t Lithium Iodine used for Implantable Cardiac Defibrillator (ICD) batteries?

A

Unable to generate the high voltages required to charge capacitors quickly.

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6
Q

Which chemical composition is used in modern day Implantable Cardiac Defibrillators (ICDs)?

A

Silver Vanadium Oxide.

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7
Q

What is the approximate beginning of service (BOS) voltage of Silver Vanadium Oxide based ICDs?

A

3.2V.

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8
Q

Internal resistance (resistance within the battery itself) remains low in ICD batteries till approximately what % of discharge?

A

80%.

Post 80% internal resistance increases substantially.

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9
Q

Why is it beneficial for ICD batteries to have an extremely low internal resistance?

A

Lower internal resistance = more rapid flow of energy.

Low resistance equates to significantly reduced charge times.

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10
Q

What is the purpose of a Zener Diode?

A

To protect the integrated circuit from high external voltages E.g. External Defibrillation.

The zener diode will shunt excess energy back down the device leads into the myocardium, thus sparing the fragile internal circuitry.

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11
Q

What is the purpose of the capacitors in an ICD?

A

To act as an electrical reservoir that stores charge.

Imagine the capacitor as a bathtub, the battery a tap and water flowing as energy. The Bath/Capacitor fills with Water/Energy until full when it can discharge. The time it takes to run a bath is known as capacitor charge time.

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12
Q

What two materials are capacitors made from?

A

Tantalum or Aluminium.

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13
Q

What is the energy density of the two types of capacitors?

A
  1. Tantalum = 5j/cm3
  2. Aluminium = 3j/cm3
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14
Q

What is the approximate energy density of a device battery?

A

>3000J/cm3.

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15
Q

The following statement best describes which capacitor material?

‘Has a higher energy density but that density means they can’t be charged to as high voltage’.

A

Tantalum.

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16
Q

The following statement best describes which capacitor material?

‘Has a lower energy density but that density means they can be charged to a higher voltage’.

A

Aluminium.

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17
Q

ICDs generally have either all Aluminium or all Tantalum Capacitors - never mixed!

Typically in what quantity would you find each material in an ICD?

A
  1. x2 Aluminium Capacitors
  2. x3 or x 4 Tantalum Capacitors
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18
Q

Which capacitor material requires periodic charges and why?

A

Aluminium.

Dielectric cracks or imperfections in the foil open up. This allows charge to ‘leak’ out. Imagine trying to fill a bathtub (capacitor) with the plug out. The time taken to fill the tub (charge time) is longer. Putting the plug back in (fixing the dielectric cracks) reduces fill time. Fix the cracks by runing a ‘capacitor reform’.

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19
Q

An aluminium capacitor has dielectric cracks, what is the % increase in charge time?

A

20-50% increase in charge time.

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20
Q

ICD charge time delays <50% could be caused by what?

A

Dielectric leakage (aluminium cracks).

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21
Q

ICD charge time delays >50% could be caused by what?

A

Battery voltage reduction ERI/EOS.

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22
Q

True / False

Charging an aluminium capacitor after a long period (>6m) seals any dielectric leaks.

A

True.

Aka Capacitor Reform.

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23
Q

True / False

Tantalum capacitors require regular cap reforms in order to prevent dielectric leakage

A

False.

Tantalum doesn’t require cap reform - only aluminium.

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24
Q

What is the recommended interval to perform a Cap Reform in modern ICDs?

A

Typically once every 6 months.

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25
Q

What is the approximate % of total battery used in order to perform a Cap reform?

A

0.5 to 1% of battery capacity.

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26
Q

True / False

Therapeutic or Aborted shocks also reform the capacitor like a dedicated cap reform.

A

False.

The charge must be held and maintained within the capacitors for several minutes.

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27
Q

From a circuitry perspective are capacitors Anodes or Cathodes?

A

Capacitors are Anodes (Positive Electrode).

Current flows from Positive (Capacitor) to Negative (Lead).

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28
Q

What is the approximate Farad of an ICD capacitor?

A

90 - 150 Microfarads.

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29
Q

Parallell or Series

How are capacitors charged and dissipated?

A

Charged in Parallell.

Dissipated in Series.

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30
Q

A shock might not be initiated if the ICD battery voltage falls below what voltage?

A

<1.5V.

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31
Q

‘Capacitance is directly proportional to ____ of each conductor’.

A

The Surface Area of each conductor.

32
Q

‘Capacitance is inversely proportional to _____ separating each conductor’.

A

The Distance separating each conductor.

33
Q

Besides battery, what is a major determinant of ICD size?

A

The capacitor size.

34
Q

A 40J shock drains the battery by how many joules?

A

80J.

Battery drain is always approximately double shock value.

35
Q

Open or Closed

The following statement best describes which type of loop sensor?

‘Does not respond to specific physiologic function’.

A

Open loop sensor.

36
Q

Open / Closed

The following statement best describes which type of loop sensor?

‘Responds to specific physiologic function’.

A

Closed loop sensor.

37
Q

Give two examples of open loop sensors.

A
  1. Piezoelectric
  2. Accelerometer
38
Q

Give two examples of partial open loop sensors.

A
  1. Temperature
  2. Respiration Rate (These are rarely seen in modern devices)
39
Q

Give two examples of closed loop sensors.

A
  1. CLS (Closed Loop Stimulation) - Biotronik
  2. Minute Ventilation sensor - Boston Scientific
40
Q

Open / Closed

The following statement best describes which type of loop sensor?

‘Measure effect and then modify their output accordingly’.

A

Closed Loop Sensors.

The ability to modify their output in response to a measured effect is known as rate modulation.

41
Q

List 4 major negatives associated with Open Loop Sensors.

A
  1. No direct relationship between levels of activity and metabolic demand
  2. Susceptible to environmental noise
  3. Susceptible to rate increases due to physical pressure on device (sleep on front)
  4. Struggles to respond to cycling and other stationary exercise
42
Q

Minute Ventilation sensors rely on what measurement as a surrogate for metabolic demand?

A

Thoracic Impedance.

43
Q

True / False

Thoracic impedance increases with inspiration.

A

True.

Air is a poor conductor

44
Q

True / False

Thoracic impedance decreases with expiration.

A

True.

Less air = less resistance to electrical flow.

45
Q

Closed Loop Stimulation relies on what measurement as a surrogate for metabolic demand?

A

Right Ventricular Impedance.

The myocardium at the point of lead fixation squashes the lead tip with each contraction. Inotropy reflects metabolic demand, thus stronger contractions = greater impedance changes = faster pacing rate.

46
Q

List 3 actions device Read Only Memory (ROM) is responsible for.

A
  1. Output
  2. Sensing
  3. Pacemaker Codes
47
Q

List 3 actions device Random Access Memory (RAM) is responsible for.

A
  1. Pacing rate
  2. Sensor outputs
  3. Diagnostic storage (Histograms / Trends etc)
48
Q

With respect to blended sensors, what was a major finding of the MOST study?

A

Patients with blended sensors had significantly worse physical function.

49
Q

What is the approximate resistance of an EOL Lithium-Iodine battery?

A

10,000 Ohm.

50
Q

True / False

Housekeeping current drains device battery by approximately 3% per year.

A

False.

<1% with respect to Lithium-Iodine batteries.

51
Q

What is the name of the small circuit board that computer elements are attached to?

A

The Hybrid.

So called due to the fact it contains a mixture of different components.

52
Q

Where is the ‘Feed-through’ located?

A

In the clear epoxy connector block.

It describes the wires that travel through the epoxy into the titanium can, thus allowing for sensing input and stimulation output through a hermetically sealed device.

53
Q

True / False

A reed switch will flip in the presence of strong ionising radiation.

A

False.

Reed switches detect strong Magnetic Fields emitted by magnets such as those found in a programmer header or MRI machine.

54
Q

What is the magnet rate for Boston devices at each stage of life?

A
  1. BOL = 100
  2. ERI = 90
  3. EOL = 85
55
Q

What is the magnet rate for Medtronic devices at each stage of life?

A
  1. BOL = 85
  2. ERI = 65
56
Q

What is the magnet rate for Abbott devices at each stage of life?

A
  1. BOL = 100
  2. EOL = 85
57
Q

Is the magnet rate the same for Boston and Abbott devices at BOL and EOL?

A

Yes.

58
Q

Which component takes negative and positive signals and turns them into one signal?

A

The Rectifier.

59
Q

Quiescent current is also known as what?

A

Housekeeping current.

60
Q

Lithium / Iodine

With respect to lithium iodine batteries, what ions does the anode produce?

A

Anode produces Lithium Ions.

Cathode produces Iodine Ions.

61
Q

Lithium or Iodine

With respect to lithium iodine batteries, what ions does the cathode produce?

A

Cathode produces Iodine Ions.

Anode produces Lithium Ions.

62
Q

Lithium iodide is a discharge product from the movement and recombination of Lithium and Iodine ions. What does the build up of this product do to the internal resistance of the battery?

A

Increases internal resistance.

Lithium iodide acts as a barrier which resists Ion flow.

63
Q

Is internal battery resistance low or high at BOL (Beginning of life)?

A

Low.

The presence of discharge product lithium iodide is minimal, thus the barrier or resistance to flow is minimal. This builds over time.

64
Q

Life expectancy of battery = Capacity / ____.

A

Life expectancy (Years) = Capacity (Ampere Hrs) / Drain (Micro Amperes).

65
Q

A unipolar sensing configuration is achieved by the Lead Tip and the _______ plate of the generator.

A

Indifferent plate.

Bipolar systems use the Lead Tip and Lead Ring electrodes.

66
Q

What type of crystal is described below?

‘Generates a voltage when subject to mechanical stress’.

A

Piezoelectric.

Used in rate response pacemakers.

67
Q

Define differences between an activity sensor vs accelerometer sensor.

A
  1. Activity sensor has the piezoelectric crystal glued to inside of can. This detects pressure on the can.
  2. Accelerometer sensor has mass attached to a suspended piezoelectric crystal that deforms the crystal in response to movement.
68
Q

Which is more specific - Activity sensor or Accelerometer?

A

Accelerometer is more specific.

69
Q

List one way an activity sensor can be fooled by a false positive.

A

Patient lies down face first on the generator (going to sleep on front), which puts pressure on the can and gives rise to an increase in HR.

70
Q

List one way an accelerometer can be fooled by a false positive.

A

Tapping on the can with fingers can elicit an increase in heart rate.

71
Q

List one way a minute ventilation sensor can be fooled by a false positive.

A

Movement of the arm = change in thoracic impedance, which elicits an increase in HR.

72
Q

List 1 pro and 1 con with respect to non physiologic sensors (Accelerometer, Piezo etc).

A

Pro - Fast responding.

Con - Low specificity.

73
Q

List 1 pro and 1 con with respect to physiologic sensors (QT, MV etc).

A

Pro - High specificity.

Con - Slow responding.

74
Q

True / False

‘In Lithium Iodine batteries, Lithium forms the Anode and Iodine forms the Cathode’.

A

True.

75
Q

Which of the following impact device longevity?

  1. % pacing
  2. Lead impedance
  3. Output voltage
  4. Output pulse width
  5. All of the above
A

5 - All of the above.

IBHRE® (24 decks)

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