CCDS IBHRE Exam Test With Complete Solution

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 Refractory 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 pacemaker - 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 greater 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. Tears 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 syndrome management - Restore AV synchrony in ventricular only PM --lower the pacing rate to minimize ventricular only pacing DO NOT increase the pacing rate Fallback - 1. Decouples atrial & ventricular events at the upper rate limit 2. The ventricular inhibited pacing rate then gradually decrements to a programmed lower or "fallback" rate over a programmed duration 3. When the fallback rate is reached, atrial synchrony is restored Rate smoothing - 1. Eliminated large cycle to cycle variations by preventing paced rate from changing more than a certain percentage (3%, 6%, 12%, etc) from one V-V interval to the next 2. Eliminates large fluctuations in rate during fixed-ratio or psuedo-Wenckebach block FOUND IN GDT devices sensor upper rate behavior - if the sinus rate is faster than the sensor indicated rate, P synchronous pacing occurs if the sensor indicated rate is faster, AV pacing at the sensor indicated rate occurs