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Flashcards in Fibrillation concepts Deck (48):
1

What 3 things determine cardiac response to a shock

Passive and active ion channel properties of cell membranes

Properties of electrical connections between cells

Effects on intra-cellular events such as calcium release

2

At what phase of the action potential does pacing effect

Phase 4 (Diastole)

3

As what phase of the action potential does defibrillation effect

Phase 2 (plateau)

OR

Phase 3 (polarization)

4

What is a virtual electrode

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

5

What is the vulnerable period

portion of relative refractory period during cardiac cycle where shocks can induce VF

6

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

At or above VF threshold

BUT BELOW Upper limit of vulnerability

7

What is the upper limit of vulnerability

Weakest shock strength where VF is not induced when sock is delivered during vulnerable period

Looks like a rhombus on top of T-wave

8

What 3 theories define 'Critical Point'

Winfree

Efimov

DADs

9

Define Mother rotor theory of VF

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

Terminate the mother, terminate the rhythm

THIS HAS FALLEN OUT OF FAVOUR RECENTLY

10

What two parameters influence defib success

Voltage

Waveform duration

(Time constant of cardiac tissue)

11

What is the benefit of truncation

Truncating the waveform = Improved success vs. allowing the discharge to decay indefinitely

12

Calculate tilt

1 minus (Trailing edge / Leading edge)

13

Defib waveform reprogramming is only available in which manufacturer

St Jude

14

What are the two principle assumptions of defib waveform model

1: Goal of 1st phase of biphasic shock is to maximise voltage change in cardiac cell membrane

2: Goal of 2nd phase is to discharge membrane potential back to 0 - effectively removing charge of 1st phase

15

What is defib waveform model also know as

Charge balancing

Charge burping

The point is to absorb initial energy and avoid pro-arrhythmia

16

DFT = leading edge voltage TRUE/FALSE

TRUE

17

What is stored energy equivalent to

Capacitance and the square of voltage

18

What are most estimates of defibrillation membrane time constant?

2.5 - 5ms

19

What is the range of capacitance in todays ICDs (FARADS)

105-150 uF

20

Explain the virtual electrode hypothesis of defib

RV cathode shock produces expanding pro-arrhythmic wavefronts

RV anode shock produces collapsing, self extinguishing wavefronts

21

Appropriate and inappropriate shocks increase risk of mortality TRUE/FALSE

TRUE

5 fold higher in appropriate

2 fold higher in inappropriate

22

What is the success rate of 1st shock therapy

90%

23

What happens to the success rate of shock therapy AFTER ATP

Reduces below 90%

Thus program max energy for shock following ATP

24

DFT is normally in what range

5-30J

25

Contraindications for DFT

Severe Aortic Stenosis // Intra-cavity Thrombus

26

When is the vulnerable period of the T-wave (from onset)

20-60% from its onset

27

What is the DFT safety margin

First therapy = 10J below max output

28

Define high DFT

<10J below max output // Occurs in 5% of patients

29

What 5 states increase risk of high DFT

Young age
Low EF
HCM
Meds - Amiodarone
Large BMI

30

What are some reversible causes of high DFT

Hypotension
Pneumothorax
Effusion // Oedema
Acidosis
Electrolyte imbalance
Medications
Ischemia

31

Which drugs reduce DFTs

Sotalol // Dofetilide

32

Non invasive ways to reduce high DFT

RV Anode (Normal) to RV Cathode

Vector change - Include SVC coil

Waveform - Change tilt

33

Invasive ways to reduce high DFT

Reposition to apical position

Subcutaneous array // CS or Azygous Vein leads

Upgrade to high output device

34

What two conditions should be met before programming alterations to defib waveform

High DFT

AND

High HV impedance

35

At what point of discharge is a biphasic shock interrupted

65% of capacitor discharge

36

What does ULV predict

Defib energy which has a 90% chance of success

37

Define ULF

Upper limit of Vulnerability = lowest shock energy delivered on vulnerable period which DOES NOT induce VF

38

What are two major advantages of ULV testing vs DFT testing

Ability to predict DFT without inducing VF

Reproducibility superior to DFT testing

39

Limitations of ULV testing

Indirect measure and doesn't confirm device ability to detect arrhythmia like DFT does

Multiple shocks required at different coupling intervals - mortality of many shocks worse than DFT

40

Benefits of S-ICD vs ICD

No vascular injury
No systemic infection
No Fluro required
Less invasive

41

Limitations of S-ICD

Lack of ATP or Brady support

42

What are the 3 sensing vectors of S-ICD

Primary = B (suprasternal) to Can

Secondary = A( sternal notch) to can

Alternate = Sternal notch to Suprasternal

43

What 3 algorithms work in sync in S-ICD systems

Static morphology - compares to sinus rhythm template

Dynamic morphology - compares polymorphic rhythms by beat to beat comparison

QRS width analysis - compares to sinus rhythm template

44

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

5 x 80J

45

Which two studies investigate S-ICD performance

IDE = Cornerstone for FDA approval

EFFORTLESS = investigates long term follow-up

46

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

IDE = 92%

EFFORTLESS = 94%

47

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

IDE = 94.7%

EFFORTLESS = 99.7%

48

Which RA positive gives less FFRWS

Lateral Free wall