Discriminators Flashcards
What criteria must be present for PR Logic to deem an arrhythmia “AF” or “AFl”?
Ratio of sensed A/V events is >1:1, and v cycle rate is not regular (indicating AF) OR when AV pattern shows regular 2:1 or 3:2 conduction (indicating AFl).
What criteria must be present for PR Logic to deem an arrhythmia “Sinus Tach”?
1:1 AV ratio with a gradual Onset
What criteria must be present for PR Logic to deem an arrhythmia “Other 1:1 SVT’s”?
1:1 AV ratio when there are consistent, near-simultaneous depolarizations in both chambers (indicating an accelerated junctional rhythm or AV nodal re-entrant tachycardia.
What criteria must be present for PR Logic to deem an arrhythmia “Double Tachycardia”?
Rhythms are dissociated, indicating VT+SVT, VF+SVT, or FVT+SVT
What are PR Logic elements?
Rate, pattern, regularity, AV dissociation, AF evidence, and presence of far-field R-waves
How does PR Logic calculate rate?
Rate is calculated by looking at the median interval of the last 12 atrial events and the last 12 ventricular events. When the median of the last 12 ventricular events is longer than the programmed SVT limit, PR Logic will analyze the rate.
How does PR Logic use pattern when categorizing an arrhythmia?
Pattern examines the position and number of P waves relative to R waves and is used to examine A:V pattern information.
What discriminators are applied during sensing?
RV Lead Noise, Lead Integrity Alert, and TWOS
How does RV Lead Noise work?
Recognizes if lead noise is occurring by observing sensed events on the near-field signal, then checking the far-field signal to determine if there was an actual intrinsic event or not. If 3 out of 12 beats are classified as noise, the whole set of 12 will be classified as noise. If three out of the last twelve sets are classified as noise, detection will be withheld.
What feature is programmable within RV Lead Noise?
Timeout (15 sec - 2 min), nom 45 seconds
What clinical data is important to know about RV Lead Noise Timeout?
With a 45 sec timeout, device will correctly withhold therapy in 85% of lead failures.
How will you know if RV lead noise has been activated?
“VOS” under observation on QuickLook screen, also recorded in text of an episode.
What are the markers for RV lead noise?
N=noise and NT=noise discrimination time out
How does Lead Integrity Alert (LIA) work?
Needs 2/3 conditions to be met: sensing integrity counter >/= 30 for the last 3 days, at least 2 NSVT’s < 220 ms, and/or high lead impedance. Once condition is met an audible tone will sound from device and NID will increase to 30/40.
What factors does TWOS discriminator take into consideration when analyzing rhythms?
Amplitude, frequency content and pattern
Does the SVT limit apply to TWOS?
No
What discriminators are applied pre-counting?
Onset
What discriminators are applied at NID?
Wavelet, PR Logic, RVN and TWOS withhold therapy
What are the characteristics considered for PR Logic?
(FRRAPAFib) Far-field R waves, Rate, Regularity, AV dissociation, Pattern, and A Fib evidence
What is ventricular rate stabilization?
Rate smoothing algorithm for PVC’s. A minimum interval is added to last interval until Vs occurs
What discriminators are most useful for sinus tach?
Onset, Wavelet and ST rule in PR Logic
What discriminators are most useful for atrial tachycardia?
Wavelet, PR Logic
What discriminators are most useful for atrial fibrillation?
PR Logic AF, Wavelet, Stability
What discriminators are most useful for exercise rates?
Onset, Wavelet, PR Logic Sinus Tach Rule
What discriminators are most useful for RVR?
Wavelet
What discriminators are most useful for RV noise?
RVN algorithm, LIA, NID
What discriminators are most useful for T waves?
TWOS, sensitivity, sensing configuration
What discriminators are most useful for FFRW?
PR Logic
What discriminators are applied during counting?
Stability
What is the nominal setting for SVT Limit?
260ms
How is the SVT limit represented on the diagram detailing the detection zones?
A blue box
How does PR Logic determine pattern?
Looks at 2 Vs intervals and counts the number and position of the atrial events between them, then labels them as one of nineteen pattern codes
How does the PR Logic Sinus Tach rule work?
Compares R-R intervals that contain one to two atrial events and a recent history of 1:1 AV conduction against the adaptive “expected range”.
How does PR Logic determine regularity?
Looks at the V cycle length variability in a window of the most recent 18 intervals, then sorts into bins based on cycle length and calculates the percentage of how often the two most frequent intervals occur; >50% = regular, <50% = irregular
How does PR Logic determine AV dissociation?
When four of the last 8 V-V intervals either lack an atrial event or contain PR intervals that vary more than 40 ms compared to the previous 8, AV is considered disassociated.
How does PR Logic determine if far-field R waves are present?
When 4/12 R-R intervals have a FFRW pattern, indicated by: short long pattern of A-A intervals, a short PR interval (<160 ms)
What two oversensing situations look like train tracks on an interval plot?
FFRW and TWOS
How does Wavelet work?
If 3 out of the last 8 comparisons between the current morphology and the template morphology do not match (<70%), therapy is withheld at NID
When should you change the Wavelet EGM 2 source?
If peak to peak R wave amplitudes are less than 3mV, consider changing source. If R waves are too large (> 6mV, consider changing to a larger range value (+/-16mV),
What considerations should be taken concerning Wavelet for patients who have a concurrent pacemaker?
Since Wavelet cannot distinguish between paced and sensed R waves, changing Wavelet to MONITOR or turning OFF Auto Collection may be prudent to ensure an accurate template is collected.
What affect does increasing or decreasing the Wavelet match threshold have on detection?
Decreasing the match threshold makes it less likely to incorrectly deliver therapy for an SVT, but it makes it less likely for the device to recognize true VT. Increasing the match threshold increases VT specificity, but may incorrectly deliver therapy to an SVT.
How should Wavelet be reprogrammed in the event that the QRS is being clipped?
Change EGM 2 range to +/-16mV
When does TWOS operate?
On detection and redection.
Before TWOS algorithms, what methods were used to deal with TWOS?
Adjusting sensitivity, adjusting RV sensing vector, changing to V blanking or repositioning the leads
How does the TWOS algorithm work?
It uses signal-frequency content and pattern analysis to distinguish R-T pattern. If 4 of the last 20 intervals meet the TWOS criteria, therapy is withheld.
Does Onset apply to initial and redetection?
No, only initial detection.
How does PR Logic determine rate?
Looks at a rolling window of 12 beats and takes the larger of the two median values.
How does the Sinus Tach Rule work pre-Protecta?
Device looks at where P waves fall in relationship to R wave and labels them “antegrade,” “junctional” or “retrograde.” The boundary for where each category lies in relation to the R waves: pre-Gem III, the boundary was set to 50% of the distance between the R waves. Post Gem III, this boundary is programmable, nominally set at 50%. For patients with first degree block, the antegrade boundary would need to be increased.
Discuss the details behind how the TWOS algorithm works.
First, the sensing signal is differential filtered for six cycles, this will diminish the size of the T waves because of their frequency, allowing R and T waves to be distinguished by their amplitude. Then, the maximum value between adjacent R and T waves is measured for the six differential ventricular events. The three maximum values are averaged and used as the threshold for discrimination of R and T waves.
