Battery and lead technology Flashcards
Battery
How do you calculate expected battery duration?
Battery life expectancy = Capacity/ drain
The capacity of the battery is in ampere.hour (Ah)
Drain is in ampere (A) = 1 Ampere = 1000000 Microampere
e.g. capacitance = 2 ampere.hour (2Ah)
Drain 25 microampere = 0.000025 ampere
Life expectancy = 2Ah/0.000025A = 80000 hours = about 9 years
What factors contribute to higher battery life expectancy?
Battery life expectancy increases if the current drain is reduced by: using less/ smaller voltage amplitude and shorter pulse width duration pulses
How does the lithium-iodine battery work?
The anode of the lithium-iodine battery produces lithium ions and the cathode produces iodine ions. These ions are moving to the other pole of the battery and recombine into lithium iodine. However the lithium-iodine is not a good electrical conductor and becomes a barrier for the further movement of ions and thus an internal battery resistance is built up. At the BOL the electrolyte barrier is minimal with low internal resistance. At EOL the cathode ions are almost depleted and the internal resistance is very high. As the internal battery resistance increases the voltage decreases.
What does an impedance < 250 ohms and >1000 ohms suggest?
<250 ohms - insulation defect
>1000 ohms - lead fracture
resistance comprises lead resistance and tissue resistance
What is a low and high current density electrode and why is it important?
A high impedance electrode (high current density) is an electrode with insulated centre, therefore a smaller geometrical area. This allows the stimulation current to be concentrated in a small area of the myocardium.
A low impedance electrode (low current density) does not concentrate the current into a small area of the myocardium, more spread, thus less efficient, with increased current drain from the battery which reduces battery longevity.
Why do we use porous electrodes?
A porous layer on the electrode increases contact with the electrolyte and reduces the polarization phenomenom. Low polarization voltage and afterpontential allow good sensing.
What factors can contribute to absence of pacemaker stimuli?
- Normal PMK function due to intrinsic rate higher than pacemaker rate
- Hysteresis with normal pacemaker function
- Pseudomalfunction: overlooking tiny stimuli artefact on ECG
- Normal pulse genrator with poor anodal contact:
a. air preventing contact of the generator with the pocket in unipolar configuration - Lead problems: fracture, loose connection or set screw problem
- Abnormal pulse generator: total battery depletion, component failure, sticky reed switch (magnet application produces no effect)
- Extreme electromagnetic interference
- Oversensing of signals originating from outside or inside pulse generator
- Filter settings of ECG recording masking pacing stimuli
- Saturation of ECG amplifier
List possible causes of undersensing.
Normal situations: VPC with small EGM; Beats falling in blanking or refractory periods
Abnormal situations:
1. poor lead position with low amplitude EGM
2. lead dislodgment: low amplitude EGM
3. hyperkalemia, severe metabolic distrubance, antiarrhythmic drugs
4. transient undersensing after DC CV/ defibrillation
5. chronic fibrosis/ scarring around the electrode
6. signal attenuation with passage of time
7. development of new BBB
8. MI near the electrode
9. jammed magnetic reed switch (rare)
10. interference with reversion to the noise-reversion asynchronous rate
11. attenuation of adequate cardiac signal upon entry in pacing system (rare in modern pacemakers)
What are the battery basic components?
Anode, cathode and electrolyte.
Anode - lithium (+) - provides electrodes
Cathode - iodine (-) - receives electrodes
Electrolyte separates anode from cathode
List possible causes for out of range lead impedance.
Too high:
1. Testing clips/ cables not properly connected to lead pin or programmer
2. Cardiac perforation by lead tip
3. “Wedging” of left ventricular lead tip into a small caliber vessel
4. Pneumothorax
5. Lead connector pin incompletely inserted into header
Too low:
1. Testing cable clips touching each other or metal surgical instruments
2. Overfixation leading to tissue damage or lead tip dislodgement from the myocardium
3. Pulmonary edema (unipolar pacing and defibrillation)
4. Transposition of connector pins of RV and SVC shock coils (dual-coil DF-1 leads only)
How does the impedance behave after the leads are embedded into the myocardium?
Usually there is a slight increase in impedance by ~50 ohms for RA and ~200 ohms for RV when effectively embedded compared to slight decrease in impedance when there is lead tip dislodegement, even after chronic placement.
Why does the tip of the electrode need a small geometric surface area?
The cathode electrodes usually have a small GSA which reduced energy consumption and allows lower pacing thresholds. Multipolar LV leads can have up to four cathodes for multiple pacing vector configurations. This is why the bipolar impedance between a pair of electrodes on LV lead is usually higher (also because LV lead is deeply wedged into a small caliber CS branch) than for a bipolar lead deployed in the RV.
The ring electrode has a larger GSA than the tip electrode.
Why is spacing between tip and shock coil important in ICD leads?
For ICD leads, electrode location has a significant impact on sensing and DF threshold. If spacing too short might cause failure to detect small R waves (VF), if too long might cause high DF threshold.
