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Indications, Safety, and Warnings

Sensing Assurance Feature

Sensing Assurance allows for automatic adjustments to programmed sensitivity in pacing devices, aiding in appropriate sensing during AF and preventing oversensing due to large T-waves. It allows for the automatic adjustment of atrial and ventricular sensitivity levels in IPGs by monitoring P- and R-wave values.

This feature can be found in some Medtronic Pacemakers. Please go to manuals.medtronic.com or consult with your local Medtronic representative regarding device models available in your geography.

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Sensing Assurance will adjust sensitivity only if the programmed mode allows both sensing and pacing in a chamber, with the exceptions that adjustments are allowed in the VDD, AAI<=>DDD, and AAIR<=>DDDR modes, and are not allowed in the AAT/VVT modes. It is nominally On.

To program this feature, go to Params -> Atrial / Ventricular Sensitivity.

Considerations:

  • While Sensing Assurance is On, there are limits to manually programming sensitivity values (reference table below).
  • Ventricular Safety Pacing ((VSP) must be programmed On for ventricular Sensing Assurance operation in dual chamber modes (DDD, DDDR).

The following steps describe how Sensing Assurance operates.
 
Step 1: Device calculates Target Sensing Margin
Each nonrefractory sensed event (AS or VS) is measured and compared to the Target Sensing Margin, which varies depending on the sensitivity setting, the type of lead (A and V) and its polarity. See table:
Chamber and Sensing Polarity
Target Sensing Margin
Atrial Bipolar
4.0 - 5.6 x (programmed value)
Atrial & Ventricular Unipolar
or Ventricular Bipolar
2.8 - 4.0 x (programmed value)
Example: A bipolar atrial lead set to 0.5 mV yields a target Atrial Sensing margin = 2.0 mV to 2.8 mV (4 x 0.5 mV to 5.6 x 0.5 mV).
 
Step 2: Classification of each P or R-wave
The sensed P wave is then classified as either a low, adequate, or high amplitude.
 
Classification of each R-wave is similar, except with a 2.8x minimum and 4.0x maximum Target Sensing Margin.
 
 
Step 3: Reprogramming sensitivity
If 17 consecutive beats are “Low,” the sensitivity is adjusted to the next programmable value that is more sensitive. If 36 consecutive beats are “High,” the sensitivity is adjusted to the next less sensitive value.
 
Sensing Assurance will not adjust Sensitivity during temporary operation.
 
Sensing Assurance also adjusts the Sensitivity Threshold, based on the number of paced events and whether the paced events resulted from noise reverson. While Sensing Assurance is designed to adapt sensitivity margins in response to changes in sensed event amplitudes, Sensing Assurance may not eliminate all sources of oversensing.

Sensing Assurance Off: When P-wave amplitudes decrease during atrial flutter, the smaller P-waves could be undersensed (as shown in the ECG below).


Sensing Assurance On: When P-wave amplitude decreases during atrial flutter, sensing assurance will readjust the sensitivity level to sense smaller P-waves.

The following clinical data supports the need for an automatic sensing feature:

  • Changes in P and R wave signal amplitudes may occur with lead maturation, myocardial infarction, antiarrhythmic medications, atrial arrhythmias, and exercise.1
  • Atrial arrhythmias and exercise have been shown to affect signal amplitudes.2
  • Programming the sensitivity threshold and safety margin using the sinus rhythm signal amplitude may not be adequate to sense the atrial events during the atrial arrhythmias.3

References

  1. Castro A, Liebold A, Vincente J, Dungan T, Allen JC Jr. Evaluation of autosensing as an automatic means of maintaining a 2:1 sensing safety margin in an implanted pacemaker. Autosensing Investigation Team. PACE. November 1996;19(11, Part II):1708-1713.
  2. Frohlig G, Schwerdt H, Schieffer H, Bette L. Atrial signal variations and pacemaker malsensing during exercise: a study in the time and frequency domain. J Am Coll Cardiol. April 1988;11(4):806-813.
  3. Wood MA, Moskovljevic P, Stambler BS, Ellenbogen KA. Comparison of bipolar atrial electrogram amplitude in sinus rhythm, atrial fibrillation, and atrial flutter. PACE. February 1996;19(2):150-156.

Source: Micra™ MC1VR01 Clinician Manual, Medtronic Adapta™/Versa™/Sensia™ Reference Guide.

Last updated: 
20 Jun 2016