Cardiac Devices

Question 1

Battery Voltage Over Time
BOL
RRT
EOL

Answer 1

BOL: beginning of life
RRT: recommended replacement time
EOL: end of life (change with 6 months left!)

Question 2

Factors Affecting Current Drain

Answer 2

Pulse amplitude
Pulse width
Pacing rate
Pacing mode
Percent pacing
Lead resistance

Question 3

Lead Integrity

Answer 3

Check via lead impedance
Normal values: 200-1500 ohms (depends on manufacturer, can be 2000 ohms)
Compare current lead impedance with prev follow up: 20% delta

Question 4

High lead vs low lead impedance

Answer 4

High lead impedance: conductor coil fracture

Low lead impedance: insulation fracture

Question 5

Unipolar Pacing

Answer 5

Pro: large pacing artifact on surface ECG
Con: pocket stimulation, will not operate out of pocket

Question 6

Unipolar Sensing

Answer 6

Pro: supposed to have better intrinsic signal strength, better sensing
Con: more susceptible to electromagnetic interference (EMI), myopotential interference, & far-field sensing

Question 7

Bipolar Pacing

Answer 7

Pro: no pocket stimulation
Con: small pacemaker artifact on ECG

Question 8

Bipolar Sensing

Answer 8

Pro: less susceptible to myopotential inhibition, EMI, and far-field sensing
Con: may not detect some PVCs if foci is perpendicular to the + and - poles

Question 9

Implantable Cardiac Monitor (Loop Monitor)

Answer 9

Implanted in pt and records IEGMS
Battery lasts 3 yrs
Helps diagnose underlying arrhythmias that 12 lead or Holter misses
Aids in deciding what type of cardiac device a pt would be best suited for (low vs high voltage vs CRT device)

Question 10

Sensing

Answer 10

Ability of pacemaker to sense intrinsic signal

Depends upon: amplitude, slew rate, frequency

Question 11

Sensitivity

Answer 11

Minimum intracardiac signal that will be sensed by pacemaker to initiate pacemaker response (inhibited or triggered)
The lower the #, the more sensitive

Question 12

V = IR

Answer 12

V = voltage (in volts, v, difference in potential energy between 2 points)
I = current (in milliampere, mA), the rate of transfer/flow of electricity
R = resistance (in ohms, opposition to the flow of electrical current through a material)

Question 13

High Resistance

Answer 13

High Resistance (‘open circuit’)
> 2500 ohms
Chronic lead system
Fracture lead conductor coil
Acute lead system
Loss of contact between the terminal pin of the lead and the pacemaker header set screw

Question 14

Low Resistance

Answer 14

Low Resistance (‘shorted circuit’)
< 250 ohms
Insulation break-down
Insulation cut by suture
Degradation of the insulation
Subclavian Crush Syndrome

Question 15

Capture

One-to-one capture

Answer 15

Capture: the depolarization and resultant contraction of the atria or ventricles in response to a pacemaker stimulus

One-to-one capture occurs when each pacemaker stimulus causes a corresponding depolarization and resultant cardiac contraction

Question 16

Capture Threshold

Answer 16

the minimum amount of electrical energy that consistently produces a cardiac depolarization; can be measured in:
Voltage
Pulse width / duration (in ms)
Milliamperes
Charge (microcoulombs)
Energy (microjoules)

Question 17

Capture Threshold Test

Answer 17

Test: reduce the energy (voltage or pulse width) of the stimulus until it no longer results in depolarization = loses capture
Then, increase until 100% capture is regained
This is the capture threshold
Permanent pacing parameters = threshold + safety margin

Question 18

Strength Duration Curve
Rheobase
Chronaxie Point

Answer 18

A description of the capture threshold at multiple pulse widths (under the curve: non capture)
Rheobase: the lowest voltage threshold at an infinitely wide pulse width
Chronaxie point: the pulse width at twice the rheobase voltage (where you would program the pacemaker – generally would give you the best battery performance)

Question 19

Safety Margin

Answer 19

a ratio of the measured capture threshold to the programmed output
Clinical standard is 2:1
Safety Margin = Programmed Output / Capture Threshold

Question 20

Fusion Beat

Answer 20

the combination of an intrinsic beat and a paced beat
Morphology varies – a fusion beat does not look like a paced or an intrinsic beat
Fusion beats contribute to the contraction of the chamber being paced

Question 21

Pseudofusion Beat

Answer 21

a pacing pulse falls on an intrinsic beat – the pacing pulse is ineffective and the intrinsic complex is not altered

Question 22

Oversensing

Answer 22

the sensing of events other than P or R-waves by the pacemaker circuitry
Oversensing leads to underpacing

Question 23

Oversensing causes & solutions

Answer 23

Causes:
Insulation break
Intermittent lead fracture
Myopotentials 
EMI
Concealed extrasystoles

Solutions:
Program sensitivity to a higher number
Program the refractory period longer

Question 24

Undersensing

Answer 24

failure of the pacemaker circuitry to sense intrinsic P or R-waves
Undersensing may cause the pacemaker to emit inappropriately-timed, asynchronous, or competitive output pulses
Undersensing leads to overpacing

Question 25

Undersensing causes & solutions

Answer 25

Causes:
Inadequate cardiac signal
Dislodged lead
Insulation break

Solutions:
Program sensitivity to a lower number
Reprogram polarity

Question 26

Loss of Capture

Answer 26

the emitted pacemaker stimulus does not cause depolarization and resultant cardiac contraction

Loss of capture occurs when the pacemaker’s programmed energy is less than the stimulation threshold

Question 27

Loss of capture causes & solutions

Answer 27

Loss of Capture Causes:
Dislodged lead
Exit block
Insulation break
Perforation (in heart! Can check with chest X-ray)
Twiddler’s Syndrome (flipping of lead in pocket)

Solutions:
Program voltage higher
Program pulse width higher
Reprogram polarity
Reposition pacing electrode
Replace pacing electrode