Cardiac Devices Flashcards
Battery Voltage Over Time
BOL
RRT
EOL
BOL: beginning of life
RRT: recommended replacement time
EOL: end of life (change with 6 months left!)
Factors Affecting Current Drain
Pulse amplitude Pulse width Pacing rate Pacing mode Percent pacing Lead resistance
Lead Integrity
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
High lead vs low lead impedance
High lead impedance: conductor coil fracture
Low lead impedance: insulation fracture
Unipolar Pacing
Pro: large pacing artifact on surface ECG
Con: pocket stimulation, will not operate out of pocket
Unipolar Sensing
Pro: supposed to have better intrinsic signal strength, better sensing
Con: more susceptible to electromagnetic interference (EMI), myopotential interference, & far-field sensing
Bipolar Pacing
Pro: no pocket stimulation
Con: small pacemaker artifact on ECG
Bipolar Sensing
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
Implantable Cardiac Monitor (Loop Monitor)
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)
Sensing
Ability of pacemaker to sense intrinsic signal
Depends upon: amplitude, slew rate, frequency
Sensitivity
Minimum intracardiac signal that will be sensed by pacemaker to initiate pacemaker response (inhibited or triggered)
The lower the #, the more sensitive
V = IR
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)
High Resistance
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
Low Resistance
Low Resistance (‘shorted circuit’) < 250 ohms Insulation break-down Insulation cut by suture Degradation of the insulation Subclavian Crush Syndrome
Capture
One-to-one capture
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
Capture Threshold
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)
Capture Threshold Test
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
Strength Duration Curve
Rheobase
Chronaxie Point
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)
Safety Margin
a ratio of the measured capture threshold to the programmed output
Clinical standard is 2:1
Safety Margin = Programmed Output / Capture Threshold
Fusion Beat
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
Pseudofusion Beat
a pacing pulse falls on an intrinsic beat – the pacing pulse is ineffective and the intrinsic complex is not altered
Oversensing
the sensing of events other than P or R-waves by the pacemaker circuitry
Oversensing leads to underpacing
Oversensing causes & solutions
Causes: Insulation break Intermittent lead fracture Myopotentials EMI Concealed extrasystoles
Solutions:
Program sensitivity to a higher number
Program the refractory period longer
Undersensing
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
Undersensing causes & solutions
Causes:
Inadequate cardiac signal
Dislodged lead
Insulation break
Solutions:
Program sensitivity to a lower number
Reprogram polarity
Loss of Capture
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
Loss of capture causes & solutions
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
