PR-Logic

Question 1

What are the 6 criteria used by PR-logic to differentiate SVT from true VT?

Answer 1

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

Question 2

What is the fastest rate both PR-logic and Wavelet be applied to?

Answer 2

SVT Limit - if rhythm is faster, PR-logic and wavelet will not be applied

Question 3

What is the nominal value the SVT Limit is set to?

Answer 3

260ms or 231 bpm

Question 4

How does PR-Logic calculate/analyze the rate or cycle length?

Answer 4

• 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

Question 5

How does PR-Logic analyze the pattern of a rhythm?

Answer 5

• 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

Question 6

What is the Sinus Tachycardia rule used by PR-Logic?

Answer 6

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

Question 7

When would PR-Logic determine that AV dysinchronization has occurred?

Answer 7

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

Question 8

Why does Pr-Logic look for AV dissociation?

Answer 8

To determine if a double tachycardia is present

Question 9

PR-Logic is able to differentiate true VT from which rhythms?

Answer 9

• A-Fib (AF) / Atrial Flutter (Afl)
• Sinus Tach
• Other 1:1 SVT’s
• Double tachycardias

Question 10

How does the PR-Logic algorithm determine the regularity of an algorithm?

Answer 10

• 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%

Question 11

What regularity percentage is needed for PR-Logic to to determine if a rhythm is regular?

Answer 11

≥ 75%

Question 12

What regularity percentage is needed for PR-Logic to to determine if a rhythm is irregular?

Answer 12

≤ 50%

Question 13

How does the PR-Logic algorithm identify far-field R waves?

Answer 13

• 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

Question 14

When would the PR-Logic algorithm determine if Far Field R-Waves (FFRW) are present?

Answer 14

• 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

Question 15

When does the PR-Logic Algorithm detect A-Fib?

Answer 15

• AF counter criteria is satisfied with score of 6 ≤ 10
• regularity percentage ≤ 50% (irregular rhythm)
• A rate is 6% faster than the V rate

Question 16

What is required for the PR-Logic algorithm to identify sinus tachycardia with FFRW sensing?

Answer 16

• a FFRW on 4/12 of the most recent ventricular intervals

Question 17

What is the maximum duration PR-Logic and other SVT discrimination features can withhold detection and therapy?

Answer 17

High Rate Timeout

Question 18

How many beats does PR-Logic evaluate when determining if FFRW are present?

Answer 18

• looks at 12 intervals

- if 4/12 are FFRW, than all are

Question 19

How many intervals does PR-Logic evaluate when determining the rate?

Answer 19

• rolling 12 intervals

Question 20

What is the purpose of PR Logic?

Answer 20

to discriminate between rapidly conducted SVT’s and true ventricular arrhythmias and avoid inappropriate ventricular therapy

Question 21

Why does PR logic use the median rate instead of the average?

Answer 21

because the average rate can be influenced by outliers such as PVC’s, making the median more representative of the true rate

Question 22

Where can you see both the median and mean/avg rates calculated by PR Logic?

Answer 22

in the episode summary in the Episode Text and Log

Question 23

How many pattern codes can PR Logic apply?

Answer 23

19 codes

Question 24

When does PR Logic determine that an AF episode has terminated?

Answer 24

when the AF counter gets to ≤ 5

Question 25

How does the AF counter work?

Answer 25

• 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)

Question 26

Why does the AF counter max out with a value of 10?

Answer 26

• 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.

Question 27

When will PR Logic determine that AV dissociation if present?

Answer 27

• 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

Question 28

When will Wavelet be applied if it is programmed on with PR Logic?

Answer 28

• when PR Logic does not classify rhythm as an SVT and the atrial rate ≥ ventricular rate

Question 29

When would PR Logic label an atrial event as “Junctional”?

Answer 29

• when the atrial event falls in the “junctional zone”

- 80ms before and 50ms after the ventricular event

Question 30

What will be seen in the channel marker if PR Logic withholds therapy and classifies a rhythm as an “other 1-1 SVT”?

Answer 30

SV

Question 31

When should the PR Logic “other 1:1 SVT” feature be turned on and why?

Answer 31

• 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