Pulse generators

Question 1

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

Answer 1

Titanium

It’s biologically inert, lightweight and hardwearing

Question 2

Typically what two elements are used in modern day pacemaker batteries?

Answer 2

Lithium and Iodine. Together forming Lithium Iodide.

Question 3

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

Answer 3

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

Question 4

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

Answer 4

Approximately 2.8V.

Question 5

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

Answer 5

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

Question 6

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

Answer 6

Silver Vanadium Oxide.

Question 7

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

Answer 7

3.2V.

Question 8

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

Answer 8

80%.

Post 80% internal resistance increases substantially.

Question 9

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

Answer 9

Lower internal resistance = more rapid flow of energy.

Low resistance equates to significantly reduced charge times.

Question 10

What is the purpose of a Zener Diode?

Answer 10

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.

Question 11

What is the purpose of the capacitors in an ICD?

Answer 11

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.

Question 12

What two materials are capacitors made from?

Answer 12

Tantalum or Aluminium.

Question 13

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

Answer 13

1. Tantalum = 5j/cm3
2. Aluminium = 3j/cm3

Question 14

What is the approximate energy density of a device battery?

Answer 14

>3000J/cm3.

Question 15

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’.

Answer 15

Tantalum.

Question 16

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’.

Answer 16

Aluminium.

Question 17

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

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

Answer 17

1. x2 Aluminium Capacitors
2. x3 or x 4 Tantalum Capacitors

Question 18

Which capacitor material requires periodic charges and why?

Answer 18

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’.

Question 19

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

Answer 19

20-50% increase in charge time.

Question 20

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

Answer 20

Dielectric leakage (aluminium cracks).

Question 21

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

Answer 21

Battery voltage reduction ERI/EOS.

Question 22

True / False

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

Answer 22

True.

Aka Capacitor Reform.

Question 23

True / False

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

Answer 23

False.

Tantalum doesn’t require cap reform - only aluminium.

Question 24

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

Answer 24

Typically once every 6 months.

Question 25

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

Answer 25

0.5 to 1% of battery capacity.

Question 26

# True / False Therapeutic or Aborted shocks also reform the capacitor like a dedicated cap reform.

Answer 26

False. ## Footnote *The charge must be held and maintained within the capacitors for several minutes.*

Question 27

From a circuitry perspective are capacitors **Anodes** or **Cathodes**?

Answer 27

Capacitors are **Anodes** (Positive Electrode). ## Footnote *Current flows from Positive (Capacitor) to Negative (Lead).*

Question 28

What is the approximate Farad of an ICD capacitor?

Answer 28

90 - 150 Microfarads.

Question 29

# Parallell or Series How are capacitors charged and dissipated?

Answer 29

Charged in **Parallell**. Dissipated in **Series**.

Question 30

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

Answer 30

\<1.5V.

Question 31

'Capacitance is directly proportional to ____ of each conductor'.

Answer 31

The **Surface Area** of each conductor.

Question 32

'Capacitance is inversely proportional to _____ separating each conductor'.

Answer 32

The **Distance** separating each conductor.

Question 33

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

Answer 33

The capacitor size.

Question 34

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

Answer 34

80J. ## Footnote *Battery drain is always approximately double shock value.*

Question 35

# Open or Closed The following statement best describes which type of loop sensor? 'Does not respond to specific physiologic function'.

Answer 35

Open loop sensor.

Question 36

# Open / Closed The following statement best describes which type of loop sensor? 'Responds to specific physiologic function'.

Answer 36

Closed loop sensor.

Question 37

Give two examples of open loop sensors.

Answer 37

1. Piezoelectric 2. Accelerometer

Question 38

Give two examples of partial open loop sensors.

Answer 38

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

Question 39

Give two examples of closed loop sensors.

Answer 39

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

Question 40

# Open / Closed The following statement best describes which type of loop sensor? 'Measure effect and then modify their output accordingly'.

Answer 40

Closed Loop Sensors. ## Footnote *The ability to modify their output in response to a measured effect is known as rate modulation.*

Question 41

List 4 major negatives associated with Open Loop Sensors.

Answer 41

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

Question 42

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

Answer 42

Thoracic Impedance.

Question 43

# True / False Thoracic impedance increases with inspiration.

Answer 43

True. ## Footnote *Air is a poor conductor*

Question 44

# True / False Thoracic impedance decreases with expiration.

Answer 44

True. ## Footnote *Less air = less resistance to electrical flow.*

Question 45

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

Answer 45

Right Ventricular Impedance. ## Footnote *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.*

Question 46

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

Answer 46

1. Output 2. Sensing 3. Pacemaker Codes

Question 47

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

Answer 47

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

Question 48

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

Answer 48

Patients with blended sensors had significantly worse physical function.

Question 49

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

Answer 49

10,000 Ohm.

Question 50

# True / False Housekeeping current drains device battery by approximately 3% per year.

Answer 50

False. ## Footnote \<1% with respect to Lithium-Iodine batteries.

Question 51

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

Answer 51

The Hybrid. ## Footnote *So called due to the fact it contains a mixture of different components.*

Question 52

Where is the 'Feed-through' located?

Answer 52

In the clear epoxy connector block. ## Footnote *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.*

Question 53

# True / False A reed switch will flip in the presence of strong ionising radiation.

Answer 53

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

Question 54

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

Answer 54

1. BOL = 100 2. ERI = 90 3. EOL = 85

Question 55

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

Answer 55

1. BOL = 85 2. ERI = 65

Question 56

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

Answer 56

1. BOL = 100 2. EOL = 85

Question 57

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

Answer 57

Yes.

Question 58

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

Answer 58

The Rectifier.

Question 59

Quiescent current is also known as what?

Answer 59

Housekeeping current.

Question 60

# Lithium / Iodine With respect to lithium iodine batteries, what ions does the anode produce?

Answer 60

Anode produces **Lithium** Ions. ## Footnote *Cathode produces Iodine Ions.*

Question 61

# Lithium or Iodine With respect to lithium iodine batteries, what ions does the cathode produce?

Answer 61

Cathode produces **Iodine** Ions. ## Footnote *Anode produces Lithium Ions.*

Question 62

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?

Answer 62

Increases internal resistance. ## Footnote *Lithium iodide acts as a barrier which resists Ion flow.*

Question 63

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

Answer 63

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

Question 64

Life expectancy of battery = Capacity / \_\_\_\_.

Answer 64

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

Question 65

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

Answer 65

Indifferent plate. ## Footnote *Bipolar systems use the Lead Tip and Lead Ring electrodes.*

Question 66

What type of crystal is described below? 'Generates a voltage when subject to mechanical stress'.

Answer 66

Piezoelectric. ## Footnote *Used in rate response pacemakers.*

Question 67

Define differences between an activity sensor vs accelerometer sensor.

Answer 67

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.

Question 68

Which is more specific - Activity sensor or Accelerometer?

Answer 68

Accelerometer is more specific.

Question 69

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

Answer 69

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.

Question 70

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

Answer 70

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

Question 71

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

Answer 71

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

Question 72

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

Answer 72

Pro - Fast responding. Con - Low specificity.

Question 73

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

Answer 73

Pro - High specificity. Con - Slow responding.

Question 74

# True / False 'In Lithium Iodine batteries, Lithium forms the Anode and Iodine forms the Cathode'.

Answer 74

True.

Question 75

Which of the following impact device longevity? 1. % pacing 2. Lead impedance 3. Output voltage 4. Output pulse width 5. All of the above

Answer 75

5 - All of the above.