Impedance compensated passive implantable atrial defibrillator

An impedance compensated passive implantable atrial defibrillator is reported. The two-part system consists of a handheld lithium-ion powered base unit (external power transmitter) and a passive (battery free) implantable coil (power receiver), with integrated rectifilter and power control unit, electrocardiogram (ECG) and bioimpedance measurement circuits, data communications circuitry and atrial connection leads. The system is designed to operate in two distinct modes: cardiac sense mode (wake-up, measure the impedance of the cardiac substrate and communicate data to the external base unit) and shock mode (delivery of an ECG synchronised impedance compensated monophasic very low tilt rectilinear shock waveform). A prototype was implemented and tested. In the sense mode, up to 5 W of sustained DC power was delivered across a 2.5 cm air–skin barrier with approximately 40% DC-to-DC power transfer efficiency at a transmission frequency of 185 kHz achieved, thereby providing 15.9 VDC (320 mA) to the implant side for measurement and communication at 433 MHz with the base unit. In the shock delivery mode, >186.9 W (rectilinear monophasic shock pulse: 100 V, 1.9 A, 12 ms duration) was repeatedly and reliably delivered transcutaneously to a 50 Ω cardiac load. Further testing in ten porcine models verified the in vivo operation, with inter-catheter impedance variations of ±20.1% measured between successive defibrillation attempts.