System and method for responding to pulsed gradient magnetic fields using an implantable medical device
First Claim
1. In an implantable medical device, a method comprising:
- operating in a first pacing mode to deliver pacing therapy using a first set of device outputs and a first pacing vector defined by a first pair of electrodes;
detecting magnetic fields;
detecting for static component of the magnetic fields and if any are detected, determining a value representative of the strength of the static component and comparing the static component value to a static magnetic field threshold;
detecting for pulsed gradient components of the magnetic fields and if any are detected, determining a value representative of the strength of the pulsed gradient components and comparing the pulsed gradient component value to a pulsed gradient threshold; and
controlling device functions differently based on whether both the static component value and the pulse gradient component value exceed their respective threshold, only one of the static component value and the pulse gradient component value exceed their respective threshold, and neither of the static component value and the pulse gradient component value exceed their respective threshold.
1 Assignment
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Accused Products
Abstract
Implantable medical devices, such as pacemakers or implantable cardioverter defibrillators (ICDs), are vulnerable to the powerful magnetic fields associated with magnetic resonance imaging (MRI). In particular, pulsed gradient components, if strong enough, can induce parasitic currents that may damage the device or cause parasitic pacing that may trigger an arrhythmia in the patient. The static magnetic field components of the MRI typically do not induce parasitic currents, even though they may be as strong as the pulsed gradient components. Accordingly, techniques are described herein for specifically addressing the pulsed gradient components of the MRI fields so as to reduce the risk of parasitic currents. In one example, a pacemaker switches to tri-state pacing outputs in the presence of strong pulsed gradient magnetic fields. The device continues with normal bi-state pacing outputs so long as the pulsed gradient fields are not strong, even in the presence of a strong static magnetic field. As an added safety feature, the pacemaker switches to fixed-rate ventricular pacing whenever strong static MRI fields are detected.
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Citations
15 Claims
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1. In an implantable medical device, a method comprising:
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operating in a first pacing mode to deliver pacing therapy using a first set of device outputs and a first pacing vector defined by a first pair of electrodes;
detecting magnetic fields;detecting for static component of the magnetic fields and if any are detected, determining a value representative of the strength of the static component and comparing the static component value to a static magnetic field threshold; detecting for pulsed gradient components of the magnetic fields and if any are detected, determining a value representative of the strength of the pulsed gradient components and comparing the pulsed gradient component value to a pulsed gradient threshold; and controlling device functions differently based on whether both the static component value and the pulse gradient component value exceed their respective threshold, only one of the static component value and the pulse gradient component value exceed their respective threshold, and neither of the static component value and the pulse gradient component value exceed their respective threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An implantable medical device comprising:
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means for operating in a first pacing mode to deliver pacing therapy using a first set of device outputs and a first pacing vector defined by a first pair of electrodes means for detecting magnetic fields; means for detecting for static component of the magnetic fields and if any are detected, determining a value representative of the strength of the static component and comparing the static component value to a static magnetic field threshold; means for detecting for pulsed gradient components of the magnetic fields and if any are detected, determining a value representative of the strength of the pulsed gradient components and comparing the pulsed gradient component value to a pulsed gradient threshold; and means for controlling device functions differently based on whether both the static component value and the pulse gradient component value exceed their respective threshold, only one of the static component value and the pulse gradient component value exceed their respective threshold, and neither of the static component value and the pulse gradient component value exceed their respective threshold.
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15. In an implantable cardiac stimulation device having a voltage generator for applying a voltage across a first electrode and a second electrode for pacing the heart of a patient, a method comprising:
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detecting magnetic fields associated with magnetic resonance imaging (MRI); detecting a strength of pulsed gradient components of the magnetic fields; and if the strength of the pulsed gradient components of the magnetic field is above a predetermined parasitic current risk threshold level, establishing current paths between the voltage generator and first and second electrodes only during pace pulse delivery, otherwise opening the current path between the voltage generator and one of the first and second electrodes.
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Specification