GDT ICD 3

This page is for patients who have one of the following devices made by Guidant: Contak Renewal 3 AVT, Contak Renewal 4 AVT, Contak Renewal RF

The Issue: These devices contain a magnetic switch known in the industry as a reed switch. Application of a magnet to the devices will normally activate this switch and turn therapy in these devices for life threatening heart rhythm problems off. This feature (when it's working correctly) enables doctors, through the simple application of a magnet on top of the device, to either temporarily or permanently turn off the defibrillator. For example this feature might prove useful if a patient was getting shocked by a defibrillator for the wrong reasons and an emergency room doctor wanted to turn the shocks off but did not have access to a Guidant programming computer. Application of a magnet to a Guidant defibrillator will either temporarily or permanently shut the device down depending on how long the magnet was applied for. During magnet application, these devices normally will emit beeping sounds on every heart beat which is detected to alert the physician that the device is reading the magnet and is being inhibited. Pacing is not affected by a magnets application in these devices, only therapies like shocks for treatment of ventricular arrhythmias. The failure with these devices that has been seen is that the reed switch can stick closed and tell the device it thinks a magnet has been applied to the device when in fact none has been. This has the effect of making the device beep for a short period of time and, if the switch stays closed long enough, permanently shut down therapies in this device.

The Consequences: Should inappropriate reed switch closure occur, the following will occur:

The patient will hear a series of beeps coming from the defibrillator. These beeps are soft in volume and in a noisy environment or if the patient is hard of hearing he may never know his reed switch closed incorrectly

Due to the above, these devices may reprogram themselves into a mode which will fail to deliver any therapy for life threatening fast heart rhythm disorders

Pacing for slow heart rhythm disorders will still occur in these devices -even if the reed switch incorrectly closes.

Accelerated depletion of the devices batteries will occur should the devices reed switch inappropriately close.

The Risks: Four and possibly five occurrences of this phenomena have been reported in 46,000 of these types of devices implanted making this a rare problem.

Our Recommendations: All patients with these devices need to have consultations with their doctors for individualized medical advise. In general however, we suggest the following steps to take

	Interrogation of the device needs to be done by your doctor to verify normal device function
	Assuming the device is functioning normally, it should be reprogrammed to change "ENABLE MAGNET USE" mode to "OFF". This reprogramming of the device should completely eliminate the issues seen with this faulty switch.
	Once reprogrammed, the device will no longer be able to sense magnetic fields. For most patients however this is of no clinical consequences.