What happens to an implantable cardioverter defibrillator (ICD) when a magnet is placed over the device?

Effect of Magnet Placement on an ICD

Placing a magnet over an implantable cardioverter defibrillator temporarily disables or suspends the antitachycardia (shock) function only—it does NOT change the pacing function or convert the device to pacemaker mode. 1

Key Mechanism of Magnet Effect on ICDs

A magnet placed over an ICD affects ONLY the defibrillation/shock therapy, not the pacing function. This is fundamentally different from how magnets affect standard pacemakers. 1

What Actually Happens:

• The antitachycardia (shocking) function is temporarily suspended while the magnet remains in place over the device 1
• The pacing function remains completely unchanged by magnet application—the ICD continues to pace according to its programmed settings 1, 2
• The device does NOT convert to asynchronous pacing mode with magnet placement alone 1

Critical Device-Specific Variations

The response to magnet placement varies significantly by manufacturer and model, making this approach unpredictable and potentially dangerous without prior knowledge of the specific device: 1, 2

Two Main Magnet Response Patterns:

1. Some ICD models: The magnet first suspends antitachycardia function, then actually turns the therapy OFF completely 1
2. Other ICD models: The magnet only temporarily disables shock function while in place, and therapy becomes active again immediately upon magnet removal (whether intentional or unintentional) 1, 3

Why This Matters for Your Patient

For a patient experiencing frequent ICD shocks, simply placing a magnet will:

• Stop the device from delivering further shocks while the magnet is properly positioned 1
• NOT address any underlying pacing needs if the patient is pacemaker-dependent 1, 2
• Require the magnet to remain in place until formal device interrogation and reprogramming can occur 1

Critical Safety Considerations

Programming the shock function off with an ICD programmer (and turning it back on after addressing the issue) is the preferred and most reliable method rather than relying on magnet placement alone. 1, 2

Common Pitfalls to Avoid:

• Never assume magnet placement provides adequate long-term management, as magnet effects are variable and unpredictable across device models 2, 4
• The magnet must be secured with adhesive tape to prevent unintentional displacement, which could immediately restore shock therapy 1
• Magnets may not be effective in obese patients or if continuous generator contact cannot be ensured 1
• Some devices can have programmable magnet responses disabled, meaning the magnet may elicit no response at all 1
• Inappropriate magnet use has caused device damage, loss of antitachycardia therapies, and inadvertent shocks in documented cases 4, 5, 6

Immediate Management for Frequent Shocks

For your patient experiencing frequent ICD discharges:

1. Place a doughnut magnet directly over the device to temporarily suspend shock therapy 1
2. Secure the magnet with adhesive tape to maintain proper positioning 1
3. Arrange urgent device interrogation by qualified personnel with an ICD programmer to determine the cause of frequent shocks and formally reprogram the device 1, 2
4. Maintain continuous cardiac monitoring throughout the period when shock therapy is disabled 1, 2
5. Have external defibrillation immediately available in case life-threatening arrhythmias occur while the ICD is disabled 1, 2

The magnet should remain in place until the device can be formally evaluated and appropriately reprogrammed, as removing it may immediately restore shock capability. 1