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IBHRE® > Defibrillation concepts > Flashcards

Defibrillation concepts Flashcards

Facilitates an understanding of how generator delivered defibrillation resolves tachyarrhythmia. Explores concepts from energy delivery to waveform generation. Currently weighted 1% in the CCDS exam.

1
Q

What 3 things determine cardiac response to a shock?

A
  1. Passive and active ion channel properties of cell membranes
  2. Properties of electrical connections between cells
  3. Effects on intra-cellular events such as calcium release
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2
Q

A pacing stimulus affects what phase of the action potential?

A

Phase 4 (Diastole).

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3
Q

A defibrillation stimulus affects what phase of the action potential?

A

Phase 2 (plateau) or Phase 3 (polarization).

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4
Q

The following statement describes what phenomena?

‘Secondary sources of electrical potential in tissue sites remote from stim electrodes’.

A

Virtual electrode.

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5
Q

The following statement describes the _____ period.

‘Portion of cardiac cycle’s relative refractory period where shocks can induce VF’.

A

Vulnerable Period.

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6
Q

Shocks in vulnerable period induce VF if which 2 criteria are satisfied?

A
  1. Energy is at or above VF threshold
  2. Below Upper limit of vulnerability
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7
Q

The following statement best describes what?

‘Weakest shock strength where VF is not induced when shock is delivered during vulnerable period’.

A

Upper limit of vulnerability.

Looks like a rhombus on top of T-wave.

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8
Q

What 3 theories define ‘Critical Point’?

A
  1. Winfree
  2. Efimov
  3. DADs
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9
Q

Define the mother rotor theory of VF.

A

Mother rotor is the central generator of wavefronts, which then split into daughter wavefronts.

Terminate the mother generator = terminate the rhythm.

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10
Q

List two predominant programmable parameters that influence defib success.

A
  1. Voltage
  2. Waveform duration (Time constant of cardiac tissue)
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11
Q

What is the benefit of waveform truncation?

A

Truncating the waveform = Improved success.

When compared to allowing the discharge to decay indefinitely. This has been demonstrated as pro-arrhythmic.

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12
Q

Calculate waveform tilt.

A

1 minus (Trailing edge / Leading edge).

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13
Q

Defib waveform tilt reprogramming is only available in which manufacturer?

A

Abbott.

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14
Q

True / False

Defibrillation Threshold = Leading Edge Voltage.

A

True.

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15
Q

What are most estimates of defibrillation membrane time constant?

A

2.5 - 4.5ms.

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16
Q

What is the range of capacitance in todays ICDs (Farads).

A

105-150 uF.

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17
Q

True / False

Cathodal shocks produce expanding, pro-arrhythmic wavefronts away from the physical cathode toward a virtual anode.

A

True.

RV cathodal shock = post-shock virtual anodal electrodes = expanding pro-arrhythmic wavefronts.

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18
Q

True / False

Both appropriate and inappropriate shocks increase risk of mortality.

A

True.

5 fold risk increase with appropriate therapy

2 fold risk increase with inappropriate therapy

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19
Q

What is the success rate of 1st shock therapy?

A

90%.

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20
Q

Following ATP is shock efficacy increased or decreased?

A

Decreased to below 90%.

Thus program max shock energy following ATP.

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21
Q

DFT is normally in what range (Joules)?

A

5-30J.

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22
Q

List two major contraindications for DFT.

A
  1. Severe Aortic Stenosis
  2. Intra-cavity Thrombus
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23
Q

When is the vulnerable period of the T-wave (as a % from onset)?

A

20-60% from T-wave onset.

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24
Q

What is the DFT safety margin?

A

First therapy = 10J below max output.

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25
Q

Define high DFT.

A

<10J below max output.

Occurs in approximately 5% of patients.

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26
Q

What 5 considerations increase risk of high DFT?

A
  1. Young age
  2. Low EF
  3. HCM
  4. Medication (Amiodarone)
  5. High Body Mass Index
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27
Q

List 7 reversible causes of high DFT.

A
  1. Hypotension
  2. Pneumothorax
  3. Effusion / Oedema
  4. Acidosis
  5. Electrolyte imbalance
  6. Medications
  7. Ischemia
28
Q

Which two drugs reduce DFT?

A
  1. Sotalol
  2. Dofetilide
29
Q

List three programmable ways to reduce a high DFT.

A
  1. Program from RV Anode (Normal) to RV Cathode (maybe pro-arrhythmic)
  2. Vector change (Include SVC coil Waveform)
  3. Change tilt (Abbott)
30
Q

List three invasive ways to reduce a high DFT.

A
  1. Reposition to lead to apical position
  2. Implant Subcutaneous array or CS / Azygous Vein defibrillation leads
  3. Upgrade to high output device
31
Q

List two conditions that should be met before programming alterations to defib waveform.

A
  1. High DFT
  2. High HV impedance
32
Q

At what % of capacitor discharge is a biphasic shock commonly interrupted?

A

65% of capacitor discharge.

33
Q

What does Upper Limit of Vulnerability predict?

A

Defibrillation energy that has a 90% chance of success.

34
Q

The following statement best describes what?

‘Lowest shock energy delivered on vulnerable period which does not induce VF’.

A

Upper limit of Vulnerability.

35
Q

What are two major advantages of ULV testing vs DFT testing?

A
  1. Ability to predict DFT without inducing VF
  2. Reproducibility superior to DFT testing
36
Q

List three major limitations of ULV testing vs DFT.

A
  1. Indirect measurement - less accurate
  2. Doesn’t confirm device’s ability to detect arrhythmia like DFT
  3. Multiple shocks required at different coupling intervals - mortality of many shocks potentially worse than DFT
37
Q

List 4 benefits of S-ICD vs ICD.

A
  1. No vascular injury
  2. No systemic infection
  3. No Fluro required
  4. Less invasive
38
Q

List 2 limitations of S-ICD vs ICD.

A
  1. Lack of ATP
  2. Lack of Brady therapy
39
Q

What are the 3 sensing vectors of S-ICD?

A
  1. Primary = B (suprasternal) to can
  2. Secondary = A( sternal notch) to can
  3. Alternate = Sternal notch to Suprasternal
40
Q

What 3 algorithms work in sync in S-ICD systems?

A
  1. Static morphology - compares to sinus rhythm template
  2. Dynamic morphology - compares polymorphic rhythms by beat to beat comparison
  3. QRS width analysis - compares to sinus rhythm template
41
Q

How many shocks will an S-ICD deliver and at what output?

A

5 x 80J

42
Q

Which two studies investigate S-ICD performance?

A
  1. IDE = Cornerstone for FDA approval
  2. EFFORTLESS = Investigates long term follow-up
43
Q

What is the complication free rate of S-ICD for IDE and EFFORTLESS?

A

IDE = 92%

EFFORTLESS = 94%

44
Q

What is the first shock efficacy rate of S-ICD for IDE and EFFORTLESS?

A

IDE = 94.7%

EFFORTLESS = 99.7%

45
Q

Which RA position reduces likelihood of FFRWS?

A

Lateral Free wall.

46
Q

What is a typical leading edge shock voltage range?

A

750-900V.

47
Q

True / False

Biphasic shocks reduce DFT by 30-40% vs Monophasic shocks.

A

True.

48
Q

Waveform tilt is normally at what percentage?

A

50%.

49
Q

True / False

Voltage stored on the capacitor is equal to initial shock waveform.

A

True.

50
Q

True / False

Current thinking predominantly favours the Mother Rotor theory of VF.

A

False.

This theory has fallen out of favour recently.

51
Q

True / False

Shock waveform truncation is pro-arrhythmic vs. non-truncated delivery.

A

False.

Truncated waveforms are less likely to induce arrhythmia.

52
Q

Shocks are predominantly bi-phasic. What is the primary purpose of the 1st phase?

A

Primary purpose of 1st phase of biphasic shock is to maximise voltage change in the cardiac cell membrane.

53
Q

Shocks are predominantly bi-phasic. What is the primary purpose of the 2nd phase?

A

Primary purpose of 2nd phase is to discharge cardiac membrane potential back to 0V.

Effectively removing charge from the 1st phase.

54
Q

The following statement best describes what?

‘Beneficial effect of phase 2 is maximal when it completely removes the charge delivered by phase 1’.

A

Charge Burping / Charge Balancing.

55
Q

Is charge burping less or more likely to induce arrhythmia?

A

Less.

The point is to absorb initial energy and return membrane to 0mV. Thus charge burping is less arrhythmogenic.

56
Q

True / False

Post shock virtual electrodes launch new wavefronts towards the physical shock anode.

A

True.

57
Q

True / False

Anodal shocks produce expanding, pro-arrhythmic wavefronts away from the physical cathode toward a virtual cathode.

A

False.

RV anodal shock = post-shock virtual cathodal electrodes = collapsing, self extinguishing wavefronts

58
Q

True / False

With regards to shock electrode programming.

‘RV cathode produces expanding, proarrhythmic wavefronts, whereas a RV anode produces collapsing, self-extinguishing wavefronts’.

A

True.

RV Cathode is demonstrably more proarrhythmic.

59
Q

ICD charge delivered is the relationship between _______.

A

Initial voltage vs. final voltage on capacitor.

60
Q

Parallel / Series

How are capacitors charged and discharged?

A

Charged in parallel

Discharged in series

61
Q

How do DR ICD leads help prevent far field ventricular over sensing?

A

Short intra-electrode spacing.

62
Q

Why isn’t ATP a feature on pacemakers, only ICD’s?

A

ATP has potential to accelerate arrhythmias into faster, more chaotic rhythms where defibrillation is the only solution. Pacemakers lack the ability to defbrillate.

63
Q

The following statement best describes which ATP pattern?

‘All pacing intervals within a sequence are the same cycle length’.

A

Burst ATP.

64
Q

The following statement best describes which ATP pattern?

‘Pacing intervals within a sequence feature continuously decremented cycle lengths’.

A

Ramp ATP.

65
Q

The use of advanced SVT differentiation algorythms effectively:

  1. Increases sensitivity / Decreases specificity
  2. Decreases sensitivity / Increases specificity
A

2 - Decreases sensitivity / Increases specificity.

Makes the device less sensitive to all arhythmias but makes it more accurate at observing only the arrhythmias it needs to.

66
Q

What is the normal shock impedance range for an ICD lead?

  1. 10-99 ohm
  2. 150-300 ohm
  3. 500 - 1500 ohm
  4. 1000 - 2000 ohm
A

1 - 10-99 ohm.

67
Q

True / False

The following requires a high output device.

‘Patient has x4 35J shocks fail to terminate VF - shocks are biphasic with alternating polarities’

A

False - safety margin is too low. High output devices max out at ~45J.

Implantation of a subcutaneous array would give the necessary safety margin and should be implanted.

IBHRE® (24 decks)

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