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CCDS IBHRE EXAM QUESTIONS AND VERIFIED ANSWERS
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CCDS IBHRE EXAM QUESTIONS ANDVERIFIED ANSWERS
Rheobase is the lowest point on a strength-duration curve with an endlessly long
pulse duration.
Chronaxie time - Determine the pulse width at twice the rheobase value. It
approximates the optimal stimulation pulse duration.
Charge (formula): ANSWER Charge= I(current) x T(time)
Furman's formula: Energy (microjoules) = I (current) x V (voltage) x T (pulse
width).
ANSWER Voltage (electromotive force) = I (current/flow of electrons) x R
(resistance to current flow in ohms).
The coupling interval that causes a detectable delay in impulse conduction is
known as the functional refractory period.
The effective refractory period is the longest coupling interval associated with a
block.
Devices that do not interact with pacemakers - ANSWER 1. Microwave oven,
2. CT/Ultrasound 3. X-ray (diagnostic)
Devices that generate temporary or one-beat inhibition: ANSWER 1. EAS 2.
Cellphones: 3. Arc Welding 4. Airport metal detector 5. TENS 6. Electric
appliances, including electric blankets and power tools
Devices that could harm the pacemaker - ANSWER 1. MRI 2. Defibrillator 3.
Cardioversion 4. Cautery/RF ablation 5. Radiation Therapy
Resistance in Series - ANSWER Series means that the start of one resistance is
connected to another.
,Add the resistances: R1 + R2 = total resistance. EX: A LEAD FRACTURE
(fractures increase impedance).
Resistance in Parallel - ANSWER: Parallel indicates that all resistances are
connected to the same place.
(R1xR2)/(R1+R2) equals total resistance.
EXAMPLE: LEAD INSULATION faults (insulation faults reduce impedance).
Are permanent pacemakers based on continuous voltage or current? -
ANSWER: All permanent pacemakers are constant voltage devices.
Some temperature pacemakers are constant voltage, but the majority are
constant current.
LOAD - ANSWER Load is the impedance (or resistance) applied to a circuit.
A system with a SMALL load (low impedance) applied to the circuit is called a
constant current device.
A system with LARGE load is described as 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 more than three seconds is documented.
NOTE: The patient may be asymptomatic with two or three
Slew rate equals the peak slope of an electrogram.
Slew rate = change in voltage/change in time.
Normal slew rate in the atrium - ANSWER >.3 V/s
Normal slew rate in ventricle - ANSWER >.5 V/s
,The steroid utilised in electrodes is dexamethasone sodium phosphate in the
silicone core (a corticosteroid).
Steroid-Eluting Electrodes: ANSWER 1. The acute threshold is quite flat when
compared to non-steroid electrodes.
2. The initial capture threshold is comparable to non-steroid leads.
Pros of Silicone Rubber Lead Insulation: ANSWER 1. Can be readily repaired
2. Flexible
3. Proven performance history.
4. Easy to create.
Cons of Silicone Rubber Lead Insulation: ANSWER 1. High friction
coefficient.
2. Absorbs lipids.
3. More thrombogenic and fibrotic.
4. Cuts easily.
5. Tears readily if suture is tied too tightly.
6. Large diameter.
Polyurethane 80A - Bad Answer
Polyurethane 55D - ANSWER GOOD
Pros of polyurethane lead insulation: ANSWER 1. largely nonthrombogenic and
fibrotic.
2. Thin walls.
3. High tear friction.
4. resists cutting.
5. Low friction coefficient.
Cons of polyurethane lead insulation: ANSWER 1. Cannot be repaired.
2. relatively stiff
3. difficult to make.
Pacemaker Syndrome Causes: ANSWER 1. Loss of audiovisual
synchronisation
2. Sustained retrograde conduction
, 3. When exercise requires rate modulation, a single ventricular rate is used.
About 25% of individuals who are just paced from the ventricle may have some
degree of severity due to pacemaker syndrome.
Pacemaker syndrome diagnosis - ANSWER 1. Observe fluctuations in
peripheral blood pressure.
2. Cannon "A" wave at the neck
3. History alone
Pacemaker Syndrome Management - ANSWER Restore AV Synchrony
In ventricular alone PM, lower the pacing rate to minimise ventricular only
pacing.
Do not increase the pacing rate.
Fallback: ANSWER 1. Decouples atrial and ventricular events at the upper rate
limit.
2. The ventricular inhibited pacing rate eventually decreases to a predetermined
lower or "fallback" rate over a programmed duration.
3. When the fallback rate is met, atrial synchronisation is re-established.
Rate smoothing: ANSWER 1. Large cycle to cycle changes were eliminated by
limiting the paced rate from altering more than a specific percentage (3%, 6%,
12%, etc) from one V-V interval to the next.
2. Eliminates substantial swings in rates during fixed-ratio or pseudo-
Wenckebach blocks.
FOUND IN GDT Devices
sensor upper rate behaviour - ANSWER If the sinus rate is faster than the sensor
indicated rate, P synchronous pacing takes place.
If the sensor indicated rate is faster, AV pacing at the sensor indicated rate takes
place.
Mixed scenario: After a few cycles of sensor-driven AV pacing, a sinus rate
arises that is quicker than the sensor-indicated rate. The sensor-driven atrial
output will be blocked, a PR interval will begin, and ventricular output will
occur at the end of the sensor-AV interval. The ventricular rate will be equal to
the sensor-indicated rate, but the PV interval may be greater than expected.
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