pacing concepts Flashcards
Voltage is…
the force that causes electrons to move through a circuit
voltage is often referred to as the
amplitude
current is measured in
Milliamps
is current programmable?
no
impedance is
the opposition to current flow from the electrode to the myocardium
current is
the actual continuing volume of flow of electricity
ohms law is
current x resistance (V=IxR)
if impedance remains constant and the voltage decreases….
the current decreases
if the voltage is constant and the impedance decreases….
the current increases
1.5v as output divided by 397 ohms for resistance equals
0.00378 A or 3.78 milliAmps
Which of these are true of current in a pacing system?
-Determined by the amount of electrons that move through the circuit
-Represented by the letter “i”
-Measured in mA
typical impedance range
200-1000 ohms
low resistance in impedance can be caused by….
Leaks in the hose (insulation leak)- which results in low resistance, high current drain, and early battery depletion
high resistance can be caused by…
a lead conductor break or
if a fracture is not complete, what can happen?
you can see both high and low impedance values
another result of an insulation break
oversensing- the EGM can often pick up abnormal electrical signals
What would you expect to happen with a lead fracture?
Current would decrease while impedance would increase
What would you expect to happen if there’s an insulation break?
Impedance drop, increased current, potential loss of capture
two stages of the lead maturation process
inflammation and fibrosis
lead maturation may eventually…
raise capture threshold
do steroid eluting leads have an effect on threshold?
no
pulse width
duration of the current flow
safety margin
2x amplitude or 3x pulse width threshold
acceptable sensing values
A >/=1 mV, V= >/= 3 mV
how do pacemakers sense?
electrical activity of myocardial cells between the cathode and the anode
