Tachy Episode Detection Feature

Tachy Episode Detection is an Insertable Cardiac Monitor (ICM) feature that detects fast heart rates. This feature is appropriate for patients experiencing, palpitations, dizziness or shortness of breath which may be symptoms associated with a fast heart rate and/or tachycardia.

This feature can be found in some Medtronic insertable cardiac monitor (ICM) devices. Please go to manuals.medtronic.com or consult with your local Medtronic representative regarding device models available in your geography.

To program this feature in Reveal LINQ go to Params ->Tachy Detection, which is nominally On.

  1. Tachy Interval (Rate): Programmable range of 270 – 520 msec, in 10 msec intervals. (Nominal is the closest value that is (230 bpm minus the Patient’s age). Patient age is based on the data entered in Patient Date of Birth
  2. Tachy Duration: Programmable number of beats (5,12,16,24,32,48)

Note: Nominals are in bold.

The automatic detection and ECG storage of Tachy episodes is turned on when Device Data Collection is activated. The Tachy Detection Interval is programmed automatically to 230 bpm minus the patient’s age and rounded to the nearest programmable value. This value is calculated from the information entered in Patient Date of Birth found in Patient Details, and for all Reasons for Monitoring located in Device Data Collection. For example, if the patient is 54 years of age, the Tachy Detect Interval would be calculated as 230 bpm – 54 = 176 bpm (340 ms).

An automatically detected Tachy episode starts when: 

  1. The ventricular intervals are occurring at shorter intervals or a faster rate than the programmed Tachy interval or rate.
    AND
  2. The number of Tachy sensed events is greater than the programmed Tachy Duration and the ECG noise level is not excessive, a Tachy episode is marked and stored.

In addition, very fast rates will cause a Tachy episode to be stored when 30 of the last 40 ventricular events have an interval < 260 ms. These episodes are marked as Tachy. This is non-programmable in Reveal LINQ. If the noise level is excessive, as indicated by the presence of very short ventricular intervals and high frequency content in the ECG, the ventricular tachyarrhythmia is rejected.

Tachy Detection Noise Algorithm
Reveal LINQ utilizes a noise rejection algorithm to reduce the incidence of short or nonphysiologic signals contributing to the detection of a tachy episode. When Tachy detection criteria is met, and at least one of the last 12 non-noisy R-R intervals is less than 220 ms, the device will "look back" and count the number of signal inflections in the 781 ms window preceding the Tachy Detection. If the number of inflections is > 20, a Tachy episode is not detected and the Tachy counter is reset.

Tachy Detection Noise Algorithm Example

Overrange interaction

If a noise interval occurs during the detection of a Tachy episode, the following occurs:

  • If the VT event counter is 0 and the FVT event counter is > than 0, then the FVT event counter is decremented by 1.
  • If the VT event counter is > 0, then this counter is decremented by 1 and the FVT event counter remains unchanged.
  • If both VT and FVT counters are 0, then both counters remain unchanged.

The Tachy episode ends when one of the following criteria is met:

  • Eight consecutive R-waves are detected with an interval  the programmed Tachy interval.
  • The median ventricular interval is  the programmed Tachy interval during a period of 20 seconds.
  • No R-wave is detected during a period of 10 seconds.

If Tachy detection is programmed Off, the device stops detection and recording of the episode is terminated.

Viewing Episodes

Arrhythmia episode data is stored in an episode log. This includes up to 60 episodes for tachy. When the log is full, data from the most recent episode may overwrite the oldest stored episode data. For each tachy episode, the ECG recording consists of 30 seconds of ECG prior to episode detection and up to 27 seconds of ECG prior to episode termination. The Arrhythmia Episodes window displays a list of all episodes currently stored in device memory. The log includes the following summary information:

  • Type of episode – this will say "Tachy" for a Tachy event.
  • The date, time, and duration of the episode.
  • The highest ventricular rate (automatically detected episodes only).
  • The median ventricular rate at detection (automatically detected episodes only).
  • Whether ECG data is available for the episode.

For a particular episode, you can display the following information:

  • An interval (or rate) plot
  • A strip chart of the stored ECG (if available)
  • A text summary

Marker Channel Annotation for Tachy Episodes

Note: If the patient uses the Patient Assistant while an automatically detected episode is in progress, both episodes are stored. The device records "Symptom (Patient Activated) occurred during episode" in the text of the automatically detected episode.

Programming Considerations

  1. Reveal LINQ allows for programming of one tachy detection zone but the device further separates VT from FVT based on non-programmable detection criteria stated above.
  2. The Noise Rejection Algorithm and Overrange Interaction work behind the scene in the device and are not programmable.
  3. No morphology algorithm (Wavelet) is used.
  4. Since there is no therapy delivery, there is no possibility of redetection, high-rate time-out, or other therapy-related interactions with detection.
  5. Select the length of the blanking period that is started after the detection of a sensed R-wave. During the blanking period, sensing is inhibited to prevent the multiple sensing of the R-wave due to a broad QRS complex. If the blanking period is programmed too long, tachy events may be blanked.
  6. A Tachy Episode CareAlert Notification may be enabled when monitoring Reveal LINQ patients remotely. The ICM sends a daily wireless audit transmission to the patient's MyCareLink monitor. If the following criteria are met:
    1. Tachy detection is programmed "On".
    2. The CareAlert Notification for a Tachy episode is enabled in CareLink.
    3. The Tachy episode is the highest priority event of the day per the Wireless Data Priority setting.

    Then, the Tachy event details will be sent to the CareLink Network in the daily wireless audit by the MyCareLink monitor. As a result, CareLink will generate the CareAlert Notification and the Tachy will be displayed in the Event Report. The episode details include 30 seconds of the detected event’s ECG. The clinician is notified of the CareAlert based on clinic defined methods.

The example below demonstrates an Event Report derived from a CareAlert Notification of a Symptomatic Tachy episode. The Tachy episode was automatically collected when the patient's heart rate increased above the programmed Tachy detect rate for the programmed duration of beats. Approximately 80 seconds after the rate increase occurred, the patient used their patient assistant to mark the event as symptomatic. The ECG from the Tachy event and the interval (rate) plot from the symptom event were transmitted wirelessly to the patient’s home monitor that night at the programmed wireless time. A CareAlert Notification was generated once the data was received by the CareLink network. The report shows 20 seconds of ECG at the time of Tachy episode detection and 10 seconds of ECG at the time of episode termination. The episode lasted nearly 2 minutes.

References

Sources: REVEAL LINQ LNQ11 Clinician Manual, Reveal XT 9529 Clinician Manual.

Last updated: 
23 Dec 2014