CCDS IBHRE CORE REVIEW SHEET 2026
PACEMAKER AND ICD FUNCTIONING AND
PROGRAMMING PRINCIPLES
◉ Chronaxie time
Answer: the pulse width at twice the rheobase value. It
approximates the most efficient stimulation pulse duration
◉ Charge (formula)
Answer: Charge= I(current) x T(time)
◉ Furman's formula
Answer: Energy(microjoules)= I(current)xV(voltage)xT(pulse
width)
◉ Ohms law formula
Answer: Voltage(electromotive force)= I(current/flow of electrons)
x R(resistance to current flow in ohms)
◉ Functional Refractory Period
,Answer: the coupling interval which first results in a measurable
degree of delay in impulse conduction
◉ Effective Refractory Period
Answer: the longest coupling interval to be associated with block
◉ Devices with NO interaction with pacers
Answer: 1. microwave oven, 2. CT scan/Ultrasound 3. X-rays
(diagnostic)
◉ Devices that cause transient or 1 beat inhibition
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
Answer: 1. MRI 2. Defibrillator 3. Cardioversion 4. Cautery/RF
Ablation 5. Radiation Therapy
◉ Resistance in Series
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
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?
Answer: ALL permanent pacemakers are constant voltage devices.
SOME temp pacemakers are constant voltage, most are constant
current.
◉ LOAD
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
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
Answer: Slew rate = peak slope of an electrogram
slew rate= change in voltage/ change in time
◉ Normal slew rate in atrium
Answer: >.3 V/s
◉ Normal slew rate in ventricle
Answer: >.5V/s
PACEMAKER AND ICD FUNCTIONING AND
PROGRAMMING PRINCIPLES
◉ Chronaxie time
Answer: the pulse width at twice the rheobase value. It
approximates the most efficient stimulation pulse duration
◉ Charge (formula)
Answer: Charge= I(current) x T(time)
◉ Furman's formula
Answer: Energy(microjoules)= I(current)xV(voltage)xT(pulse
width)
◉ Ohms law formula
Answer: Voltage(electromotive force)= I(current/flow of electrons)
x R(resistance to current flow in ohms)
◉ Functional Refractory Period
,Answer: the coupling interval which first results in a measurable
degree of delay in impulse conduction
◉ Effective Refractory Period
Answer: the longest coupling interval to be associated with block
◉ Devices with NO interaction with pacers
Answer: 1. microwave oven, 2. CT scan/Ultrasound 3. X-rays
(diagnostic)
◉ Devices that cause transient or 1 beat inhibition
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
Answer: 1. MRI 2. Defibrillator 3. Cardioversion 4. Cautery/RF
Ablation 5. Radiation Therapy
◉ Resistance in Series
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
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?
Answer: ALL permanent pacemakers are constant voltage devices.
SOME temp pacemakers are constant voltage, most are constant
current.
◉ LOAD
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
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
Answer: Slew rate = peak slope of an electrogram
slew rate= change in voltage/ change in time
◉ Normal slew rate in atrium
Answer: >.3 V/s
◉ Normal slew rate in ventricle
Answer: >.5V/s
