Detection
How a device determines if there is a tachyarrhythmia
This is determined by
•Rate
•bpm
•CL
•Duration
•Seconds
•Interval counter
•Interval rolling window
Rate & Duration detections vary from device to device, and sometimes from zone to zone within a device.
Detection programming
Conventional ICD detection programming involved “short detections”
PREPARE trial (2006) was a leading trial in programming “long detections” specifically in primary prevention patients
•Decrease in appropriate therapies (unnecessary therapies)
•Decrease in inappropriate therapies
•no significant difference in syncopal episodes
•Lower rates of all cause mortality
ADVANCE III (2013) was a leading trial in programming “long detections” specifically in secondary prevention patients
•Decrease in appropriate therapies (unnecessary therapies)
•Decrease in inappropriate therapies
Abbott
Although the zones (both VT & VF) are programmed by one number (e.g., 16 beats) detection duration is calculated based on a rolling window.
Each current interval (CI) is compared to and average interval (AI)
•AI: last 3 intervals divided by 4
When AI & CI are different, the higher zone is prioritised
•E.g., AI indicates VT & CI indicates VF, binned as VF zone
When there is a discrepancy between AI & CI when 1 interval indicates SR (below all detection rates), the beats are not counted
•E.g., CI 200ms (VPB), AI 800ms
Biotronik
Uses 2 different methods of detection
1. Counters (e.g., 30 intervals)
Incremental (up/down) consecutive counter
•+1 point for in a zone
•-1 for outside a zone
VT1 and VT2 zones only
2. Rolling window (e.g., X/Y intervals)
VF zone only
Useful when undersensing may occur (more likely in VF)
Boston Scientific
Detection window occurs when 8/10 fast intervals occur.
A duration period is then set in seconds.
As long as 6/10 intervals remains fast, the arrhythmia is determined as sustained.
Boston Scientific - Subcutaneous ICD
Detection window occurs when 18/24 fast intervals occur. This is non programmable.
Rate is determined by a rolling average of 4 RR intervals.
Smart charge:
•If the device sees an untreated event (NSVT) the intervals are automatically lengthened by 3 extra intervals (e.g., next 21/27)
•A maximum of 15 intervals extra can be added to detection
Medtronic
Uses 2 different methods of detection
1. Counters (e.g., 30 intervals)
•Consecutive intervals (current interval only)
•Can be programmed for VT zone or FVT via VT zone
2. Rolling window (e.g., 30/40 intervals)
•Can be programmed for VF zone or FVT via VF zone
•Useful when undersensing may occur (more likely in VF)
Microport
A rolling window of 6/8 beats (75%) needs to be met in an arrhythmia zone, prior to the “persistence counter” kicking in (counter)
A rolling average interval of 4 beats determines which zone the arrhythmia falls into.
