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Where are catheters placed for a basic diagnostic EP study?
- Right atrial apendage
- Right ventricle apex
- Across the tricuspid annulus
- Coronary sinus
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How can position of the His catheter be determined?
Relative size of the atrial and ventricular electrograms
- Atrial larger = proximal
- Ventricular larger = distal
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What are the most important features of the catheters?
position, stability, and thresholds
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When is the right bundle potential detected?
10-30 msec before ventricular electrogram in the HBE
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What is the normal AH interval?
60-125 msec
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What is the HV interval?
Time between earliest His potential to the earliest ventricular deflection (on surface ECG or His tracing)
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What is the normal HV interval?
35-55 msec (up to 60 with LBBB)
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What does a split His indicate?
His bundle disease
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What can procainamide do to the HV interval?
It specifically prolongs the HV interval
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What are three causes of an abnormally short HV interval?
- 1. Accessory pathway
- 2. PVC
- 3. Incorrect measurement of RB-V rather than HV (if atrial signal too small)
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What is the formula for pacing rate?
Pacing rate (BPM) = 60,000 / cycle length
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What is the heart rate in the following?
Cycle length: 600, 500, 400, 300, 200
100, 120, 150, 200, 300
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When performing incremental pacing, when does the operator stop bringing in S2?
Why?
when it fails to capture the myocardium
this is the tissue's refractory period
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How are refractory periods determined?
incremental pacing
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Why are beats delivered in series during incremental pacing?
refractory periods are dependant on prior cycle lengths
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What are the three types of refractory periods?
- Effective refractory period
- Functional refractory period
- Relative refractory period
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What is the effective refractory period?
The functional?
The relative?
ERP is the shortest S1-S2 that fails to depolarize the stimulated tissue
FRP is the shortest interval between two conducted beats out of the tissue (the FRP of the His is the shortest V1-V2)
RRP is the longest coupling interval that results in prolonged conduction of S2
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What channel likely results in nondecremental conduction?
IKs (delayed rectifier postassium slow channel)
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What are the three repetitive ventricular responses to VES?
- 1. Bundle branch reentry beats (50% of healthy subjects)
- 2. AV nodal echo (15% of healthy subjects)
- 3. Intraventricular reentry (<15% of healthy sujects)
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How does a bundle branch reentry beat happen?
RV stimulus blocks in the RB with transseptal conduction to the LB with retrograde HA activation with antegrade activation of the RB
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How is intrinsic heart rate determined?
Give beta blockers and atropine
IHR = 117.2 - (0.52 x age)
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How is sinus node recovery time determined?
What is normal?
Overdrive pace for > 1 minute then stop pacing
Corrected SNRT = SNRT - SCL
Normal is 500-600 msec
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How is the sinoatrial conduction time determined?
8-10 beat train followed by PAC
SACT = [(A2-A3) - (A1-A1)] /2
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In general, conduction below a cycle length of _______ means AV conduction is normal.
500 msec
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What percentage of the population has dual AV nodal pathways?
7%
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Which AV nodal pathway has the shorter refractory time?
slow pathway
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What defines an AV jump?
> 50 msec increase in A2-H2 interval in response to a 10 msec decrease in A1-A2 coupling
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What does concealed mean?
Unable to identify on the surface ECG
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What is the gap phenomenon?
It occurs when a premature stimulus blocks or delays followed by conduction without delay of a more premature stimulus
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What causes the gap phenomenon?
distal block and proximal conduction delay - longer coupling blocks in the distal segment; shorter coupling delays in the proximal segment and allows the distal segment to recover and conduct
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What is supernormal conduction?
conduction that is better than would be expected
look for it with normalization of a wide qrs complex (when aberration resolves at a fast heart rate)
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HV interval of ______ or longer is considered an indication for PPM.
100 msec
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What structure has the longest refractory period in the heart?
HPS at slow heart rates
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Which bundle has longer refractory period at slow heart rates?
At fast heart rates?
Right
Left
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What are the four common forms of aberration?
premature beat (phase 3), acceleration dependent, decceleration-dependent (phase 4), and retrograde invasion / concealment
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What is phase 3 block?
Which bundle is more often affected?
stimulation during phase 3 resulting in decreased conduction of the next action potential (long-short)
right bundle
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What is Ashman phenomenon?
aberrant RBBB with a. fib; due to Phase 3 block
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What is acceleration-dependent block?
aberration that occurs at a critical heart rate; not necessarily very rapid; occasionally with minimal (5 msec) increases in rate
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What morphology does acceleration-dependent block have?
LBBB most often
(generally associated with underlying heart disease)
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What is deceleration-dependent block?
Phase 4 block - bradycardia allows phase 4 depolarization in the Purkinje fibers which results in block or aberration
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What is retrograde invasion or concealment?
retrograde conduction into a bundle branch which causes it to be refractory to the next impulse - the most common form of perpetuation of aberration
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What are the 5 ways aberration normalizes?
- 1. "peeling back" - a VPD blocks retrograde invasion
- 2. Equal delay in both bundle branches (rare and must be accompanied by PR delay)
- 3. ipsilateral VPD to BBB
- 4. gap phenomenon
- 5. change in heart rate
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