Magnet Feature

Positioning a magnet over a Medtronic pacemaker/CRT-P device switches the device to an asynchronous mode and pacing at the magnet rate.

Positioning a magnet over a Medtronic ICD/CRT-D device suspends tachyarrhythmia detection, causing no therapies to be delivered.

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

Medtronic pacemakers/CRT-P devices

A magnet over a Medtronic pacemaker causes the pacemaker to:

  1. Switch to an asynchronous mode and pace at the magnet rate:
    • DOO in modes with dual chamber pacing, VOO in the VDD mode, and VOO/AOO in single chamber modes.
    • Magnet rate for normal operation is 85 ppm for all modes.
    • Magnet rate is 65 ppm when Recommended Replacement Time (RRT/ERI) has occurred or a full electrical reset has occurred.
    • If the pacemaker is in a sensing mode only; for example ODO, the device will switch to OOO mode with a magnet.
    • The device ignores the magnet in the programmer head when telemetry communication is established.

    Note: For the purpose of determining Magnet Modes, the AAI<=>DDD and AAIR<=>DDDR modes are considered dual chamber modes. 
     
  2. Perform a Threshold Margin Test (TMT). This allows a check for loss-of-capture by pacing at 100 bpm with the amplitude reduced by 20% on the third pulse.

    Warning: A loss-of-capture at a 20% reduction in amplitude indicates that the threshold safety margin is inadequate. As soon as possible, reevaluate the patient’s threshold and reprogram outputs for 2x safety margin. Imminent loss of ventricular capture for a pacemaker-dependent patient may constitute an emergency situation. The Threshold Margin test is not available starting in EnRhythm pacemakers.

When the magnet is removed, the pacemaker resumes programmed operation within 2 seconds.

Medtronic ICDs/CRT-D

Positioning a magnet over a Medtronic ICD suspends tachyarrhythmia detection, and no tachyarrhythmia therapies will be delivered. However, it does not alter bradycardia therapy (pacing mode does not change).

A steady tone emits for 10 seconds when a magnet or the programming head is applied over the device to verify that notifications are operational and no alert conditions are met. A dual high-low or intermittent on-off tone emits when a magnet or programming head is applied and a patient alert condition has been met. The device should be interrogated to determine reasons for alert.

If you place a programming head over the device during a wireless telemetry session, the magnet in the programming head always suspends tachyarrhythmia detection. If you place a programming head over the device and establish a nonwireless telemetry session, tachyarrhythmia detection is not suspended.

When the magnet is removed, the ICD resumes tachyarrhythmia detection and therapy delivery as programmed.

Pacemaker/CRT-P

Below is an example of a magnet placed over a Medtronic pacemaker. After the magnet is placed, a Threshold Margin Test is conducted with the first 3 intervals at 100 bpm with 100 ms AV delay. Pacing output in the third interval (blue box) is decreased by 20% in the A and V. In this scenario, capture remains. If capture was lost in the AP or VP, there would not be a 20% safety margin in that chamber. At the completion of the TMT, pacing is forced to a rate of 85 bpm in the magnet mode. If RRT/ERI or an electrical reset had occurred, pacing would be forced to 65 bpm in the magnet mode.

References

Sources: Medtronic Adapta/Sensia Reference Guide; Medtronic Consulta CRT-P Clinician Manual;Medtronic Protecta XT DR Clinician Manual; Medtronic Protecta XT CRT-D Clinician Manual.

Last updated: 
27 Mar 2013