ICDs Flashcards
What are two common areas for idiopathic ventricular tachycardia?
RVOT
Fascicular VT
How does ventricular scar cause VT?
Scar tissue blocks or slow the normal conduction and creates electrical channels
Late activations can initiate reentry pattern resulting in monomorphic VT
Monomorphic VT is usually associated with what?
Scar
Idiopathic
What is polymorphic VT usually associated with?
Ischemia
Long QT syndrome
What phase of the action potential do class I AADs affect?
Phase 0
How do class I AADs work?
block sodium channels therefore slowing depolarization and slowing conduction speed of ventricular tachycardias
What phase of the action potential do class III AADs affect?
Phase 3
How do class III AADs work?
block potassium channels and prolong the ventricular refractory period
How does ATP work?
Delivers a pacing impulse during a certain point in the action potential while different parts of the myocardium are excitbale
SCD represents what percentage of all deaths worldwide?
15-20%
What is an integrated bipolar ICD lead?
Distal RV coil acts as the anode and electrode tip is the cathode
What are the potential causes of high impedance on ICD lead?
Conductor fracture
Loose connector
Unipolar leads programmed bipolar
What are the potential causes of low impedance on ICD lead?
Insulation degradation
Y-adaptor or parallel pathways
Loos connection maintaining contact with body fluids
What lead connectors are used for RV ICDs?
DF-1 and DF-4
What ICD connectors are used for LV ICDs (BiV)?
IS-4
What is a potential fall back to integrated bipolar leads?
Oversensing due to larger surface area on the anode
Diaphragmatic myopotential oversensing
What is a unique algorithm for sensing amongst ICDs?
Auto-adjusting sensing algorithm
Following a sensed/paced event, device becomes increasingly more sensitive until threshold is reached
Other than changing sensing values, what is another way to adjust sensing?
Change polarity of device from true bipolar to integrated bipolar
What type of counter is used for ventricular tachycardia detection?
Consecutive counter
All beats in VT zone must be consecutive for programmed length (NID) for device to recognize and begin to deliver therapies
What type of counter is used for ventricular fibrillation detection?
Probabilistic counter
Uses a ratio of VF intervals to consecutive intervals due to low amplitude in VF and to avoid withholding therapies due to undersensing
How are interval counters different during redetection phase following therapy delivered by ICD?
NID becomes smaller during redetection phase
Define combined count
Used when a rhythm switches between VT and VF zones and classifies rhythm as VF even though there are not technically enough NID to satisfy either individual zone
What are the main SVT discriminators?
Onset
Stability
Morphology
A-V association
How does use of “onset” work for programming purposes?
An onset percentage is assigned and represents the change in ventricular rate required to enable VT even counting
How does MDT PRLogic algorithm work to identify SVT vs VT?
Analyzes both atrial and ventricular chambers and assess characteristics including:
Pattern of A and V events
A and V rates
Regularity of ventricular rhythm
Association vs dissociation
Far-field R wave
How do stability algorithms work?
Device compares most recent VT interval to the previous 3. If difference between most recent interval and any of the preceding three intervals exceeds the stability threshold, the VT counter resets to zero.
What is the most accurate SVT discriminator in single chamber devices?
Morphology template
What is the approximate success rate of ATP?
85%
How does ATP work?
Delivers pacing impulses during the refractory period within the re-entrant circuit of ventricular tachycardia
What are the two main types of ATP?
Burst pacing
Ramp pacing
Burst ATP
delivers pacing stimuli at equal intervals
Ramp ATP
therapy delivers stimulus at decremental or progressively shorter intervals by subtracting, per pulse, the programmed interval decrement
Brugada patients are at increased risk for inappropriate ICD therapies due to what?
T wave oversensing
Where is the lead for S-ICDs placed?
1-2 cm left of the sternal midline
Vertically positioned in the subcutaneous tissue of the chest
How is screening done for candidacy of S-ICD?
Utilize the automated screening tool (AST 2.0)
What are the three SVT discriminators used in S-ICD devices?
Static morphology analysis
Dynamic Morphology analysis
QRS width analysis
What is the average time to shock in S-ICDs?
20 seconds, allows for longer delays to avoid shocks for rhythms that would otherwise self-terminate
