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CCDS IBHRE QUESTIONS AND ANSWERS 2024
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QUESTIONS AND ANSWERS
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CCDS IBHRE QUESTIONS AND ANSWERS 2024 Rheobase the lowest point on a strength duration curve at an infinitely long pulse duration Chronaxie time the pulse width at twice the rheobase value. It approximates the most efficient stimulation pulse duration Charge (formula) Charge= I(current) x T(time) Furman's formula Energy(microjoules)= I(current)xV(voltage)xT(pulse width) Ohms law formula Voltage(electromotive force)= I(current/flow of electrons) x R(resistance to current flow in ohms) Functional Refracto ry Period the coupling interval which first results in a measurable degree of delay in impulse conduction Effective Refractory Period the longest coupling interval to be associated with block Devices with NO interaction with pacers 1. microwave oven, 2. CT scan/Ultrasound 3. X -rays (diagnostic) Devices that cause transient or 1 beat inhibition 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 pacema ker 1. MRI 2. Defibrillator 3. Cardioversion 4. Cautery/RF Ablation 5. Radiation Therapy Resistance in Series 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 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? ALL permanent pacemakers are constant voltage devices. SOME temp pacemakers are constant voltage, most are constant current. LOAD 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 1. Patient is symptomatic 2. The heart rate is less than 40 bpm 3. Asystole of great er than 3 seconds is documented NOTE: Pt may be asymptomatic with 2 or 3 Slew Rate Slew rate = peak slope of an electrogram slew rate= change in voltage/ change in time Normal slew rate in atrium >.3 V/s Normal slew rate in ventricle >.5V/s Steroid used in electrodes dexamethasone sodium phosphate in the silicone core(a corticosteriod) Steroid -Eluting Electrodes 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 1. Can easily be repaired 2. Flexible 3. Proven performance history 4. Easy to make Silicone Rubber lead insulation cons 1. high friction coefficient 2. Absorbs lipids 3. More thrombogenic and fibrotic 4. Cuts easily 5. Te ars easily if suture tied too tightly 6. Large diameter Polyurethane 80A BAD Polyurethane 55D GOOD polyurethane lead insulation pros 1. relatively nonthrombogenic/fibrotic 2. thin walls 3. high tear friction 4. resists cutting 5. low friction coefficient polyurethane lead insulation cons 1. cannot be repaired 2. relatively stiff 3. hard to make Pacemaker Syndrome Causes 1. Loss of AV synchrony 2. Sustained retrograde conduction 3. A single ventricular rate when rate modulation is required for exercise Approx 25% of patients only paced from the ventricle may have some level of severity related to pacemaker syndrome Pacemaker syndrome diagnosis 1. Observe fluctuation in the peripheral blood pressure 2. Cannon "A" wave in the neck 3. History alone Pacemaker s yndrome management Restore AV synchrony in ventricular only PM -->lower the pacing rate to minimize ventricular only pacing DO NOT increase the pacing rate FallbackThe benefits of buying summaries with Stuvia:
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