CCDS IBHRE
Rheobase - correct answer ✔the lowest point on a strength duration curve at
an infinitely long pulse duration
Chronaxie time - correct answer ✔the pulse width at twice the rheobase
value. It approximates the most efficient stimulation pulse duration
Charge (formula) - correct answer ✔Charge= I(current) x T(time)
Furman's formula - correct answer ✔Energy(microjoules)=
I(current)xV(voltage)xT(pulse width)
Ohms law formula - correct answer ✔Voltage(electromotive force)=
I(current/flow of electrons) x R(resistance to current flow in ohms)
Functional Refractory Period - correct answer ✔the coupling interval which
first results in a measurable degree of delay in impulse conduction
Effective Refractory Period - correct answer ✔the longest coupling interval to
be associated with block
Devices with NO interaction with pacers - correct answer ✔1. microwave
oven, 2. CT scan/Ultrasound 3. X-rays (diagnostic)
Devices that cause transient or 1 beat inhibition - correct answer ✔1. EAS 2.
Cellphones 3. Arc Welding 4. airport metal detector 5. TENS 6. Electric
appliances such as electric blanket & power tools
,Devices that may damage the pacemaker - correct answer ✔1. MRI 2.
Defibrillator 3. Cardioversion 4. Cautery/RF Ablation 5. Radiation Therapy
Resistance in Series - correct answer ✔Series means the beginning of one
resistance is connected to another
Sum the resistances: R1+R2= total resistance. EX: A LEAD FRACTURE
(fractures INCREASE impedance)
Resistance in Parallel - correct answer ✔Parallel means all the resistances
are connected to the same point.
(R1xR2)/(R1+R2)= total resistance
EX: LEAD INSULATION DEFECTS (insulation defects DECREASE
impedance)
Permanent pacemakers are constant voltage or constant current? - correct
answer ✔ALL permanent pacemakers are constant voltage devices.
SOME temp pacemakers are constant voltage, most are constant current.
LOAD - correct answer ✔Load refers to impedance (or resistance) applied to
a circuit.
A system with a SMALL load (low impedance) applied to the circuit is said to
be a constant current device
A system with LARGE load is said to be a constant voltage device
,Guidelines for Permanent Pacing - correct answer ✔1. Patient is
symptomatic
2. The heart rate is less than 40 bpm
3. Asystole of greater than 3 seconds is documented
NOTE: Pt may be asymptomatic with 2 or 3
Slew Rate - correct answer ✔Slew rate = peak slope of an electrogram
slew rate= change in voltage/ change in time
Normal slew rate in atrium - correct answer ✔>.3 V/s
Normal slew rate in ventricle - correct answer ✔>.5V/s
Steroid used in electrodes - correct answer ✔dexamethasone sodium
phosphate in the silicone core(a corticosteriod)
Steroid-Eluting Electrodes - correct answer ✔1. The acute threshold is
relatively flat compared to non-steroid electrodes
2. The initial capture threshold is similar to non-steroid leads
Silicone Rubber lead insulation Pros - correct answer ✔1. Can easily be
repaired
2. Flexible
3. Proven performance history
, 4. Easy to make
Silicone Rubber lead insulation cons - correct answer ✔1. high friction
coefficient
2. Absorbs lipids
3. More thrombogenic and fibrotic
4. Cuts easily
5. Tears easily if suture tied too tightly
6. Large diameter
polyurethane lead insulation cons - correct answer ✔1. cannot be repaired
2. relatively stiff
3. hard to make
Pacemaker Syndrome Causes - correct answer ✔1. Loss of AV synchrony
2. Sustained retrograde conduction
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