Patent ID: 8295929

Claim:
An implantable medical device comprising: electronic circuitry; a housing including a sidewall enclosing an interior portion of the housing, which interior portion contains the electronic circuitry, the sidewall including an exterior surface; a feedthrough assembly, the assembly comprising: a ferrule mounted to the sidewall of the housing and extending from a first end of the ferrule to a second end of the ferrule, the first end being adjacent to the exterior surface of the housing sidewall; a pin coupled to the electronic circuitry within the housing and extending through the ferrule between the first and second ends thereof; and a glass insulator containing at least approximately 20 mol % of CaO, the glass insulator surrounding the pin, within the ferrule, and being sealed to the pin and to the ferrule, the glass insulator including a surface, which is located on a side of the glass insulator that corresponds to the first end of the ferrule; wherein at least a portion of the surface of the glass insulator is exposed for contact with phosphate-containing body fluid when the device is implanted; and a second housing surrounding at least that portion of the sidewall where the ferrule of the feedthrough assembly is mounted and surrounding at least a portion of the feedthrough assembly at the exterior surface of the sidewall; wherein the second housing includes a channel extending from an opening of the channel to the feedthrough assembly, the channel opening being located at an exterior surface of the second housing, and the channel allowing the surface of the glass insulator to be exposed for contact with the body fluid when the device is implanted.