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Flashcards in Sensing Deck (35):
1

Bipolar sensing - where is the anode and cathode

Both anode (+) and cathode (-) are in the heart

2

Unipolar sensing - where is the anode and cathode

Anode (+) is the generator // Cathode (-) is in the heart

3

What should slew rates exceed at implant for P and R waves

P-wave = 0.5vS

R-wave = 0.75vS

4

What two components determine IEGM sensing

Amplitude

Slew rate

5

What range of Hz are sensing amplifiers most sensitive

30-40Hz

6

What are the approx field of view for uni and bipolar sensing circuits in cms

Unipolar = 30-50cm (Tip to can)

Bipolar = 3-5cm (Tip to ring)

7

Which sensing is more susceptible to far field over-sensing

Unipolar

REMEMBER OVERSENSING = UNDERPACING

8

What is a potential problem of over sensing if sensed on atrial channel in DDD

Inappropriate ventricular tracking of noise

9

What is the signal density of Atrial and Ventricular signals

Fourier transformation determines

Atrial = 80-100Hz

Ventricular = 10-30Hz

10

What components determine polarisation effect

Pulse width

High output

Electrode size

11

Amplitude and slew abruptly decline 1wk post implant - when do values return

6-8wks later

12

Unlike pacing, sensing circuits should have low/no resistance TRUE/FALSE

TRUE - Pacing lead design may result in diminished sensing

13

What is the difference between source impedance and input impedance

Source impedance = Voltage drop from origin of IEGM to proximal portion of lead

Input impedance = Impedance of sensing amplifier itself

14

EGM seen by the pacemaker is the ratio between what two impedances

Source impedance vs Input impedance

Large difference = less signal attenuation

15

What factors affect sensing accuracy

Lead integrity
Electrode characteristics and placement
Lead polarity
EMI
Properties of the myocardium

16

A fractured wire with intermittent contact will lead to over sensing or under sensing

Over sensing

17

A fractured wire with no contact will lead to over sensing or under sensing

Under sensing

18

What are acceptable sensing values for P and R waves in pacemakers AND ICDs

P wave >2mV

R-wave >7mV ICD >10mV

19

At max ICD sensitivity where are myopotentials likely to arise from

Diaphragm or pectorals

More likely to occur in integrated bipolar leads

Do noise provocation

20

4 ways to reduce ICD over sensing

Reduce max sensitivity

Decrease LRL or Increase AV delay (Minimise RV pacing)

Prolong detection interval - Transient over sensing will terminate

Implant separate RVOT sensing lead which is further from diaphragm

21

3 ways to stop T-wave over sensing

Reduce max sensitivity

Increase refractory periods

Reduce auto sensitivity aggressiveness

22

Non physiologic sensing intervals could be due to

Loose set screw in header

Lead defect

23

Is it necessary to have both near field and far field sensing channels in ICD systems

Yes

Far field helps to show morphology changes and also can detect atrial signals - thus showing VT vs SVT

24

If ICD sensing can't be sorted with programming, what can be done

Re-intervention should strongly be considered

E.g. Small R-wave // Big T-wave

25

How does the noise algorithm work

Differences between near field (TIP-RING) and far field (Coil-Can) EGM

26

Noise secondary to a conductor failure will be seen on which egm

Near field (Tip-Ring)

A conductor fracture won't interfere with far field EGM

27

Noise algorithm is ineffective against EMI - Why?

Because noise will be seen on both near field and far field channels - thus therapy will be delivered

28

Is ICD sensitivity more of less sensitive following a paced beat

More sensitive - to prevent pacing into VF

29

With ICD sensing are post pacing blanking intervals longer or shorter than post sensing intervals

Post pacing blanking periods are LONGER

30

4 ways to reduce ICD oversensing

Decrease max sensitivity of generator (Not ideal)
Decrease brady rate to minimise pacing
Prolong detection intervals (transient noise will time out)
Implant separate sensing lead in RVOT

31

How to decrease TWOS

Decrease max sensitivity
Prolong refractory periods
Alter auto sensitivity (Start and delayed decay)

32

Which field (near/far) is more likely to detect morphology changes

Far field used for morphology changes (Wavelet)

33

Difference between consecutive and probablistic

Consecutive = one after the other
Probabilistic = certain amount in a certain time period

34

What do VF counters generally accept % wise

75%

35

How long should an ICD take to charge

5-12 seconds