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

[0027]The present invention relates to an RF filter for an active medical device (AMD) for handling high RF power induced in an associated lead from an external RF field at a selected MRI frequency or range of frequencies. In a preferred embodiment, the RF filter comprises a capacitor having a capacitance generally between about 10 to about 20,000 picofarads, and a temperature stable dielectric having a dielectric consta

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 pr

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