PR-Logic Flashcards
What are the 6 criteria used by PR-logic to differentiate SVT from true VT?
1) Rate (A and V)
2) Pattern (atrial to ventricular events)
3) Ventricular Regularity
4) AV dissociation
5) Far Field R-Wave (FFRW)
6) AF evidence
What is the fastest rate both PR-logic and Wavelet be applied to?
SVT Limit - if rhythm is faster, PR-logic and wavelet will not be applied
What is the nominal value the SVT Limit is set to?
260ms or 231 bpm
How does PR-Logic calculate/analyze the rate or cycle length?
- once VT NID is met
- algorithm looks back 12 intervals (Atrial and Vent)
- sorts low to high
- uses the median or the 7th interval as the rate
- if rate is = or > SVT limit, PR logic is applied
How does PR-Logic analyze the pattern of a rhythm?
- uses 2 ventricular intervals or 3 VS beats
- counts number of atrial events
- assess the position of the atrial events (junctional, retrograde..)
- then assigns 1 of 19 pattern codes
What is the Sinus Tachycardia rule used by PR-Logic?
Rhythm is Sinus Tachycardia if all the below is present:
- 1:1 AV conduction
- has < 15% change in R-R intervals
- has < 15% change in P-R intervals
When would PR-Logic determine that AV dysinchronization has occurred?
When 4/8 of the most recent V-V intervals show either:
- no atrial event within V-V intervals
- an AV interval that differs from the average previous intervals by >40ms
Why does Pr-Logic look for AV dissociation?
To determine if a double tachycardia is present
PR-Logic is able to differentiate true VT from which rhythms?
- A-Fib (AF) / Atrial Flutter (Afl)
- Sinus Tach
- Other 1:1 SVT’s
- Double tachycardias
How does the PR-Logic algorithm determine the regularity of an algorithm?
- looks at rolling 18 V-V intervals
- places intervals into 10ms bins
- counts # of times the 2 most common intervals occur
- # is divided by 18 to calculate a regularity percentage
- regular = ≥ 75%
- irregular = ≤ 50%
What regularity percentage is needed for PR-Logic to to determine if a rhythm is regular?
≥ 75%
What regularity percentage is needed for PR-Logic to to determine if a rhythm is irregular?
≤ 50%
How does the PR-Logic algorithm identify far-field R waves?
- when exactly 2 A-events occur within a single V-V interval, device further analyzes the P-R pattern to determine if one of the atrial events is far field
When would the PR-Logic algorithm determine if Far Field R-Waves (FFRW) are present?
- if there are exactly 2 atrial events for each R-R interval with consistent R-P or P-R intervals AND a short-long pattern of A-A intervals with either:
] an A-V (PR) interval < 60 ms
] a V-A (RP) interval < 160 ms
When does the PR-Logic Algorithm detect A-Fib?
- AF counter criteria is satisfied with score of 6 ≤ 10
- regularity percentage ≤ 50% (irregular rhythm)
- A rate is 6% faster than the V rate
What is required for the PR-Logic algorithm to identify sinus tachycardia with FFRW sensing?
- a FFRW on 4/12 of the most recent ventricular intervals
What is the maximum duration PR-Logic and other SVT discrimination features can withhold detection and therapy?
High Rate Timeout
How many beats does PR-Logic evaluate when determining if FFRW are present?
- looks at 12 intervals
- if 4/12 are FFRW, than all are
How many intervals does PR-Logic evaluate when determining the rate?
- rolling 12 intervals
What is the purpose of PR Logic?
to discriminate between rapidly conducted SVT’s and true ventricular arrhythmias and avoid inappropriate ventricular therapy
Why does PR logic use the median rate instead of the average?
because the average rate can be influenced by outliers such as PVC’s, making the median more representative of the true rate
Where can you see both the median and mean/avg rates calculated by PR Logic?
in the episode summary in the Episode Text and Log
How many pattern codes can PR Logic apply?
19 codes
When does PR Logic determine that an AF episode has terminated?
when the AF counter gets to ≤ 5
How does the AF counter work?
- adds 1 for every V-V interval with 2 ≤ A events
- subs 1 for every V-V interval with 1 A event unless the previous interval added to the counter, then will only hold value (+0)
Why does the AF counter max out with a value of 10?
- b/c the counter will continue to increment while the patient is in AF and may calculate in the thousands nd the counter needs to decrement to a value of 5 for the episode to be labeled as terminated.
When will PR Logic determine that AV dissociation if present?
- if 4/8 of the last V-V intervals have:
) no Atrial events
OR
) has PR intervals that vary by > 40ms when compared to the last 8
When will Wavelet be applied if it is programmed on with PR Logic?
- when PR Logic does not classify rhythm as an SVT and the atrial rate ≥ ventricular rate
When would PR Logic label an atrial event as “Junctional”?
- when the atrial event falls in the “junctional zone”
- 80ms before and 50ms after the ventricular event
What will be seen in the channel marker if PR Logic withholds therapy and classifies a rhythm as an “other 1-1 SVT”?
SV
When should the PR Logic “other 1:1 SVT” feature be turned on and why?
- turn on after atrial lead has matured, approximately 1 month after implant, because if the atrial lead falls into the ventricle, therapy might be withheld inappropriately
