RF filter for an active medical device (AMD) for handling high RF power induced in an associated implanted lead from an external RF field

Abstract

An RF filter for an active medical device (AMD), for handling RF power induced in an associated lead from an external RF field at a selected MRI frequency or range frequencies includes a capacitor having a capacitance of between 100 and 10,000 picofarads, and a temperature stable dielectric having a dielectric constant of 200 or less and a temperature coefficient of capacitance (TCC) within the range of plus 400 to minus 7112 parts per million per degree centigrade. The capacitor's dielectric loss tangent in ohms is less than five percent of the capacitor's equivalent series resistance (ESR) at the selected MRI RF frequency or range of frequencies.

Description

FIELD OF INVENTION[0001]This invention generally relates to the problem of RF energy induced into implanted leads during medical diagnostic procedures such as magnetic resonant imaging (MRI), and provides methods and apparatus for redirecting RF energy to locations other than the distal tip electrode-to-tissue interface. In addition, the present invention provides electromagnetic interference (EMI) protection to sensitive active implantable medical device (AIMD) electronics.BACKGROUND OF THE INVENTION[0002]Compatibility of cardiac pacemakers, implantable defibrillators and other types of active implantable medical devices with magnetic resonance imaging (MRI) and other types of hospital diagnostic equipment has become a major issue. If one proceeds to the websites of the major cardiac pacemaker manufacturers in the United States, which include St. Jude Medical, Medtronic and Boston Scientific (formerly Guidant), one will see that the use of MRI is generally contra-indicated for pati...

AI Technical Summary

Benefits of technology

[0028]In a second embodiment, the AIMD diverter capacitor 140 comprises at least ten interleaved active and ground electrode plates designed to minimize the capacitor's high frequency ESR while maximizing internally generated heat flow from the capacitor. The ground electrode plates are conductively connected to an energy dissipating surface (EDS). In preferred embodiments of the invention, the EDS surface comprises a housing of the AMD and / or a ferrule conductively attached to both the ground electrode plates and the housing for the AMD.

Problems solved by technology

Compatibility of cardiac pacemakers, implantable defibrillators and other types of active implantable medical devices with magnetic resonance imaging (MRI) and other types of hospital diagnostic equipment has become a major issue.

There have been reports of latent problems with cardiac pacemakers or other AIMDs after an MRI procedure sometimes occurring many days later.

Moreover, there are a number of recent papers that indicate that the SAR level is not entirely predictive of the heating that would be found in implanted leads or devices.

It is speculated that SAR level alone is not a good predictor of whether or not an implanted device or its associated lead system will overheat.

These antennas are not very efficient due to the damping effects of body tissue; however, this can often be offset by extremely high power fields (such as MRI pulsed fields) and / or body resonances.

Subjected to RF frequencies, the lead itself can exhibit complex transmission line behavior.

The effects of this heating are not readily detectable by monitoring during the MRI.

Such long term heating effects of MRI have not been well studied yet for all types of AIMD lead geometries.

There can also be localized heating problems associated with various types of electrodes in addition to tip electrodes.

While these anecdotal reports are of interest, they are certainly not scientifically convincing that all MRI can be safe.

For example, just variations in the pacemaker lead length and implant trajectory can significantly affect how much heat is generated.

Most experts still conclude that MRI for the pacemaker patient should not be considered safe.

It is well known that many of the undesirable effects in an implanted lead system from MRI and other medical diagnostic procedures are related to undesirable induced EMFs in the lead system and / or RF currents in its distal tip (or ring) electrodes.

This can lead to overheating of body tissue at or adjacent to the distal tip.

Excessive current at the distal electrode to tissue interface can cause excessive heating to the point where tissue ablation or even perforation can occur.

This can be life threatening for cardiac patients.

For neurostimulator patients, such as deep brain stimulator patients, thermal injury can cause coma, permanent disability or even be life threatening.

Similar issues exist for spinal cord stimulator patients, cochlear implant patients and the like.

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