Miniaturization of package for an implantable heart monitoring device

摘要

A myocardial-implantable accelerometer device used for monitoring heart activity is presented in this paper. It is a device built around a commercially available MEMS accelerometer, packaged for use inside the body. Myocardial fixation is desired from a surgical point of view because it truly represents heart motion without interfering with surrounding tissue. It requires miniaturization in order not to damage heart tissue. An integration of polyimide-based substrate and cable has been proposed as a unique flexible printed circuit system with high aspect ratio (2.2/500 mm-width/length). Procedures of design, fabrication, assembly and testing of the prototypes are detailed and a design with a 3 mm diameter has been obtained. This study also suggested specific experimental set-ups for qualifying essential safety requirements based on the standards and regulations for implantable devices. Several compliance tests have been done successfully and achieved very promising results: The measured leakage currents are 1,000 times below the maximum allowed limit, insulation resistance between the conductors is well within the safety limits, the tensile strength is suitable for implantable devices, flexural endurance is good, and the performance was maintained after a 7-days soak test. The prototype has been used in animal trials, giving high-quality acceleration signals.