Cardiac pacer with improved battery system, output circuitry, and emergency operation

摘要

A fully implantable programmable cardiac pacer includes two main pacing channels driven by a crystal oscillator circuit. For each channel, amplitude and pulse width are programmed in paired combinations corresponding to monotonically increasing charge density. Selectively combinable constant current sources are shared by each channel. A low battery indicator system samples battery voltage relative to two threshold levels. In magnet rate, if the main battery voltage is above the first threshold, the fixed pacer output will be 70 beats per minute. If the battery voltage is between the first and second threshold levels, the fixed pacer output will be 62.5 beats per minute. An emergency RC oscillator continuously produces an output at 52.5 beats per minute and one millisecond pulse width. The emergency output is switched directly to the output of channel 2 when either the low battery voltage falls below the second threshold or the crystal oscillator frequency changes when tested by a frequency checking circuit using the output of the RC oscillator as a reference clock. An emergency battery is coupled to the main battery via a diode steering circuit which allows the remaining capacity to be combined with that of the emergency battery.