Confirmation+ Feature

The Confirmation+ algorithm confirms the presence of an arrhythmia by comparing the rhythm cycle length to a calculated confirmation interval. After VT/VF detection, but before a shock is delivered following the device charge, the device monitors the rhythm to confirm the presence of VT/VF. If the presence of VT/VF is not confirmed, then the shock therapy will be aborted and the device will either redetect an arrhythmia, if present, or declare the episode terminated. Confirmation+ helps to improve shock delivery specificity.1

This feature can be found in some Medtronic ICD and CRT-D devices. Please go to or consult with your local Medtronic representative regarding device models available in your geography.

Confirmation+ is nominally On and can also be programmed to Off.

To program this feature, go to Params -> Therapies -> Shared Settings.

VF is confirmed with Confirmation+ using one of the following confirmation intervals:

  • Confirmation+ On: The confirmation interval equals the ventricular cycle length + 60 ms (minimum of the programmed VF detection interval (FDI)). When an unstable arrhythmia is detected in the VF zone, the confirmation interval equals FDI + 60 ms.
  • Confirmation+ Off: The confirmation interval equals the programmed VT Interval + 60 ms (or the programmed VF Interval if VT Detection is programmed to Off).

Confirmation+ begins the confirmation process during the charge. If ATP During Charging is programmed On, confirmation will begin once the ATP therapy is complete.

The device classifies any ventricular sensed interval that is less than the confirmation interval as an “arrhythmic event” and any ventricular sensed interval that is longer than the confirmation interval as a “normal event.” With each ventricular event, the device reviews the previous 5 ventricular events. If the previous 5 ventricular events include 4 “normal events,” the device aborts the therapy.

The specific confirmation interval used for Confirmation+ depends on which zone the rhythm is occurring in and if the rhythm is regular. The following table indicates the confirmation interval that is calculated.

Detected Zone
Rhythm Stable
(Regular RR intervals)
Confirmation Interval
VF Zone
Tachycardia Rhythm Cycle Length + 60 ms or FDI
(whichever is the longer interval)
FDI + 60 ms
VT Zone
Not Applicable
Tachycardia Rhythm Cycle Length + 60 ms
(minimum of FDI)


  • Tachycardia Rhythm Cycle Length is calculated using the six intervals prior to detection. The maximum and minimum intervals are eliminated and the average is taken of the remaining four intervals.
  • The device uses the four intervals used to calculate the Tachycardia Rhythm Cycle Length to determine if the rhythm is stable or not.
    • The rhythm is considered stable (monomorphic) if the change in the maximum interval minus the minimum interval is less than or equal to 50 ms.
    • The rhythm is not considered stable (polymorphic) if the change in the maximum interval minus the minimum interval is greater than 50 ms.
    • Confirmation+ applies to CV, non-committed defib Rx (i.e. Rx#1) and during redetection in Rx#1.
  • Enhancements over prior Confirmation criteria include:
    • Confirmation Interval now based on arrhythmia cycle length.
    • Able to abort the first defibrillation Rx more than once per episode.
    • Provides confirmation in combination with ATP During Charging.

The example below displays an episode where Confirmation+ aborts a shock in case of a dirty break or PVCs after ATP During Charging. Only a single VF Zone is programmed to 320 ms. In this case, the confirmation interval is the FDI or 320 ms. Therefore, the first four intervals after the first VS are non-arrhythmic and the shock is aborted.


  1. Volosin K, Exner DV, Wathen MS et al., Virtual ICD: A Model to Evaluate Shock Reduction Strategies, HRS Conference, May 2010.

Sources: Medtronic Protecta XT DR Clinician Manual; Medtronic Protecta XT CRT-D Clinician Manual.

Last updated: 
03 Apr 2013