IBHRE REVIEW STUDY QUESTIONS AND ANSWERS
AV Node Reentry Tachycardia (AVNRT) - Answers-- accounts for ~60% of arrhythmias
presenting as SVT or paroxysmal atrial tachycardia (PAT)
- affects all age groups and genders equally
- no correlation with heart disease
- heart rate 150-250 bpm, palpitations, light-headedness, near-syncope, narrow QRS
complex
rheobase - Answers-lowest point on a strength duration curve at an infinitely long pulse
duration; for cardiac pacing, the rheobase is usually reached between 1-2ms
chronaxie time - Answers-pulse width at twice the rheobase value
approximates most efficient stimulation pulse duration
action potential - Answers-the cellular characteristics of depolarization and
repolarization
5 phases (0-4)
phase 0 - Answers-depolarization, rapid Na+ channels open, resting potential (-90mV)
to ~0mV
phase 1 - Answers-early repolarization; peak of depolarization
phase 2 - Answers-the "plateau phase", mediated by slow Ca2+ channels, disrupts and
delays the repolarization started in phase 1 and prolongs refractory
phase 3 - Answers-end of repolarization
phase 4 - Answers-resting phase, leaking of K+ and Na+
expanded polytetrafluoroethylene (ePTFE) - Answers-Goretex-type material that has
been shown to improve the ease of extraction due to reducing the degree of fibrous
ingrowth, especially on shocking coils
pros:
- electrically inert and does not effect DFTs
- stable biomaterial/ chemically inert
- high tear strength
- low friction coefficient
- small lead diameter
- less fibrotic
cons:
- stiff when >0.003"
- more prone to creep
, - difficult to manufacture w/o pinholes
silicone rubber insulation - Answers-pros:
- can be easily repaired
- flexible
- proven performance history
- easy to produce
cons:
- high friction coefficient
- absorbs lipids
- more thrombogenic & fibrotic
- cuts & tears easily
- large diameter (comparatively)
polyurethane 80A (pellethane) - Answers-pros:
- relatively nonthrombogenic
- thinner walls, flexible
- tougher, abrasion resistant
- resists cutting
- low friction coefficient
cons:
- adverse history
- longevity <7 years
- not repairable
- very process-dependent
recalled in 1995 by the FDA for inner insulation failure due to metal ion oxidation (MIO)
polyurethane 55D (pellethane) - Answers-pros:
- proven history
- longevity >12 years
- easy to process
- very tear-resistant and tough
- thinner walls
- abrasion resistant
cons:
- less flexible
- not repairable
environmental stress cracking (ESC) - Answers-cracks or crazing that occurs in
polyurethane in response to certain chemicals and external stresses
oxidation occurs secondary to cellular adhesion
AV Node Reentry Tachycardia (AVNRT) - Answers-- accounts for ~60% of arrhythmias
presenting as SVT or paroxysmal atrial tachycardia (PAT)
- affects all age groups and genders equally
- no correlation with heart disease
- heart rate 150-250 bpm, palpitations, light-headedness, near-syncope, narrow QRS
complex
rheobase - Answers-lowest point on a strength duration curve at an infinitely long pulse
duration; for cardiac pacing, the rheobase is usually reached between 1-2ms
chronaxie time - Answers-pulse width at twice the rheobase value
approximates most efficient stimulation pulse duration
action potential - Answers-the cellular characteristics of depolarization and
repolarization
5 phases (0-4)
phase 0 - Answers-depolarization, rapid Na+ channels open, resting potential (-90mV)
to ~0mV
phase 1 - Answers-early repolarization; peak of depolarization
phase 2 - Answers-the "plateau phase", mediated by slow Ca2+ channels, disrupts and
delays the repolarization started in phase 1 and prolongs refractory
phase 3 - Answers-end of repolarization
phase 4 - Answers-resting phase, leaking of K+ and Na+
expanded polytetrafluoroethylene (ePTFE) - Answers-Goretex-type material that has
been shown to improve the ease of extraction due to reducing the degree of fibrous
ingrowth, especially on shocking coils
pros:
- electrically inert and does not effect DFTs
- stable biomaterial/ chemically inert
- high tear strength
- low friction coefficient
- small lead diameter
- less fibrotic
cons:
- stiff when >0.003"
- more prone to creep
, - difficult to manufacture w/o pinholes
silicone rubber insulation - Answers-pros:
- can be easily repaired
- flexible
- proven performance history
- easy to produce
cons:
- high friction coefficient
- absorbs lipids
- more thrombogenic & fibrotic
- cuts & tears easily
- large diameter (comparatively)
polyurethane 80A (pellethane) - Answers-pros:
- relatively nonthrombogenic
- thinner walls, flexible
- tougher, abrasion resistant
- resists cutting
- low friction coefficient
cons:
- adverse history
- longevity <7 years
- not repairable
- very process-dependent
recalled in 1995 by the FDA for inner insulation failure due to metal ion oxidation (MIO)
polyurethane 55D (pellethane) - Answers-pros:
- proven history
- longevity >12 years
- easy to process
- very tear-resistant and tough
- thinner walls
- abrasion resistant
cons:
- less flexible
- not repairable
environmental stress cracking (ESC) - Answers-cracks or crazing that occurs in
polyurethane in response to certain chemicals and external stresses
oxidation occurs secondary to cellular adhesion
