Pacing System Components Flashcards
Resistor
Resists the flow of electrical charge (measured in Ohms).
Capacitor
Stores and releases electrical charge (measured in Farad).
Transistor
Electrical switch within a circuit. One pulse generator has billions of individual transistors.
Diode
Allows electrical current to flow in an exclusively unidirectional manner.
Protects PG circuitry from high external voltages.
Rectifier
Converts biphasic signal to a signal with only positive components. Used for sensing.
Complementary Metal Oxide Semiconductor (CMOS)
Elements of microscopic electrical circuitry and creates the channel for the PG being most susceptible to radiation.
Transformer
Converts the input of electrical flow to an output electrical flow of higher voltage and lower current.
What kind of core do high voltage conductor leads typically have?
Silver or platinum due to low resistance
Anode (definition and location)
Positive polarity and signals flow AWAY. Anode is located at ring/can.
Cathode (definition and location)
Negative polarity and signals flow TOWARD. Cathode is located at lead tip in the tissue.
What are the pros to unipolar pacing leads?
- Smaller diameter lead, using a single set screw
- Reliable and more durable
What are the pros to bipolar pacing leads?
- Less chance of extracardiac stimulation at the PG.
- Less chance of myopotential or far-field oversensing.
- Can act as unipolar if so programmed.
What are the materials that compose lead electrodes?
- Platinum with 10% Iridium
- Elgiloy- an alloy of several metals
- Silver and stainless steel
- Activated carbon
What are the two primary forms of lead insulation?
Silicone and polyurethane
What are the advantages of silicone?
Inert, durable, and reliable
What are the advantages of polyurethane?
Smaller lead diameter, easy maneuverability, high tear strength
Coulomb (C)
the fundamental unit of battery capacity
Ampere-hours (A-hr)
A way to express battery capacity. Represents the charge carried by a current of one ampere flowing for one hour.
1 ampere-hour = 3600 coulumbs
What is the purpose of the capacitor in an ICD?
allow the device to deliver a therapeutic, high-voltage, high-energy shock to the myocardium over a few milliseconds. This is something the battery itself could NOT do.
What are pacemaker batteries made of?
Lithium iodine
What are ICD batteries made of?
Lithium silver oxide
Why is lithium silver oxide used in ICDs over lithium iodine?
Supports higher current drains for capacitor charging to deliver ATP and ICD shocks.
What is the approximate voltage at the beginning of life of a lithium iodine (pacemaker) battery?
2.8 V
Resistance (Ohms)
the opposition of flow of electrical current in a conductor. Relates ONLY to electrical components.
Impedance (R)
The total resistance to the flow of current through a conductor including both body tissue and electrical components
Ohms Law
V = IR
V = voltage
I = current
R = resistance (impedance)
Automaticity
The capacity for spontaneous initiation of rhythm beating
Excitability
having a resting membrane potential that is able to undergo rapid, transient reversal in polarity upon activation
In a pacing system, current is determined by ____?
number of electrons that move through a circuit at any given time
In a pacing system, impedance is a function of what?
The conductor (wire), electrode (tip), and myocardium (tissue)
Polarization impedance
accumulation of charges of opposite polarity in the myocardium at the electrode-tissue interface.
Other than a lead fracture, what is another reason that impedance may be high?
the lead is not appropriately seated in the pacemaker header (usually an acute problem).
What factors create impedance within the pacing system?
Lead resistance, tissue impedance, polarization resistance
Current drain (microamperes)
Average amount of current drawn from a battery by the external load
How much current drain do pacemakers usually produce?
10-30 micramperes
