Magnet Mode 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 may also apply to select pacemakers. See the feature operation section for details.
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:
- 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.
The device ignores the magnet in the programmer head when telemetry communication is established. When the magnet is removed, the pacemaker resumes programmed operation within 2 seconds. The pacemaker automatically suspends all diagnostic data collection while a magnet is applied to the pacemaker. Data collection resumes when the magnet is removed. Applying a magnet does not clear diagnostic data. In devices with the MRI SureScan™ feature, the device ignores the magnet if MRI SureScan mode is programmed On.
Medtronic Adapta™/Versa™/Sensia™ Pacemakers
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.
Medtronic Advisa™/Revo™ Pacemakers
When a magnet is placed near the device, the pacing mode changes from the programmed mode to DOO, VOO, or AOO, and the pacing rate changes to 85 bpm or 65 bpm, depending on the battery status.
Medtronic Azure™/Astra™ Pacemakers
When a magnet is placed near the device, the pacing mode changes from the programmed mode to DOO, VOO, or AOO, and the pacing rate changes to 100 bpm for 5 beats and then changes to 85 bpm or 65 bpm, depending on the battery status.
Medtronic Azure/Astra/Advisa/Revo Pacemakers
To suspend detection, place a magnet over the device. To resume detection, remove the magnet from the device.
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 non-wireless telemetry session, tachyarrhythmia detection is not suspended.
When the magnet is removed, the ICD resumes tachyarrhythmia detection and therapy delivery as programmed.
In devices with the MRI SureScan™ feature, the device ignores the magnet if MRI SureScan mode is programmed On.
Adapta Pacemaker Threshold Margin Test Example
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.
This course covers:
- How the magnet affects Medtronic devices
- Clinical scenarios in which the magnet can be used
- How to prepare and monitor a patient once the determination is made to use the magnet
This course is designed for medical personnel...
This tip card covers:
- How magnets affect Medtronic devices
- Perioperative management when using a magnet
- How to prepare and monitor a patient once the determination is made to use a magnet
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.