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Publication Date: 2005-Oct-05
Document File: 5 page(s) / 32K

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An implantable medical device has a field-programmable sensitivity to the presence of a magnet provided to trigger a magnet mode of the device. The implantable medical device includes a magnetic sensor that is capable of measuring magnetic field strength and has a programmable field-detection threshold. During a field calibration procedure, the magnetic sensor measures the magnetic field strength created by the magnet. The measured magnetic field strength is used to reprogram the field-detection threshold when necessary. Such a field calibration procedure can be performed to change a preprogrammed default field-detection threshold, to re-calibrate the field-detection threshold on a regular basis or as needed, or to reprogram the field-detection threshold when a new magnet is provided.

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Field Calibration of magnet detection sensitivity for implantable medical device

            Medical devices are implanted in human bodies for monitoring physiological conditions, diagnosing diseases, treating diseases, or restoring functions of organs or tissues.  Examples of such implantable medical devices include cardiac rhythm management (CRM) devices, neurological stimulators, neuromuscular stimulators, drug delivery devices, and physiological monitors.  An implantable medical device often communicates with one or more external devices.  Examples of such external devices include programmers, network-based patient management systems, and hand-held controllers.  Implantable medical devices of certain types are each provided with a magnet used as a simple hand-held external controller.  The presence of the magnet next to such an implantable medical device may force the implantable medical device to operate in a particular mode referred to as the magnet mode.

            One particular example of implantable medical devices is an implantable CRM device that treats irregular or other abnormal cardiac rhythms by delivering electrical pulses to a patient’s heart.  Such abnormal cardiac rhythms result in diminished blood circulation.  Implantable CRM devices include pacemakers and defibrillators.  A pacemaker is often used to treat a patient with bradyarrhythmias, that is, hearts that beat too slowly or irregularly.  A pacemaker may also coordinate atrial and ventricular contractions to improve the heart’s pumping efficiency.  A defibrillator delivers higher energy electrical stimuli to the heart to terminate tachyarrhythmias, that is, hearts that beat too quickly.  A defibrillator may also include a cardioverter, which synchronizes the delivery of such stimuli to portions of sensed intrinsic heart activity signals.  In addition to pacemakers and defibrillators, implantable CRM devices also include pacer/defibrillators that combine the functions of pacemakers and defibrillators, drug delivery devices, and any other implantable systems or devices for diagnosing or treating cardiac disorders.  One example for a magnet mode of an implantable CRM device is a constant-rate pacing mode such as an AOO or VOO mode.  Such a magnet mode is used, for example, to identify an implanted device, to provide essential life support when the implanted device fails to operate properly at a programmed mode due to environmental noise, or to test an operational status of the device such as the battery status.  Another example for a magnet mode of an implantable CRM device is a defibrillation inhibition mode, which allows inhibition of automatic delivery of defibrillation shocks when the environmental noise may cause false detections of tachyarrhythmia.  Yet another example for a magnet mode of an implantable CRM device is an electrogram recording mode, which allows a patient to record an electrogram for diagnostic purposes wh...