Cardiac pacer with rate limiting means

Claim 1

A cardiac pacer for producing stimulation pulses for delivery to electrodes adapted to be connected to a heart, comprising: (1) a stimulation pulse generator, comprising a one-shot multivibrator for producing a stimulation pulse, including: (a) first and second gates of the type which produce an output state coinciding with selected coinciding input states, each gate having first and second inputs and an output the output of said second gate being connected to the first input of said first gate, (b) a capacitor interconnecting the output of said first gate to the first input of said second gate, and (c) resistor means connected to discharge said capacitor to time the width of the pulse produced by said stimulation pulse generator, (2) a source of clock pulses, (3) a counter connected to receive said clock pulses for applying an output state to the second input of said first gate after counting a number of said clock pulses corresponding to a stimulation pulse interval to trigger said stimulation pulse generator, and having a reset terminal connected to the output of said second gate, (4) a monostable multivibrator having an input operative to reinitiate a timing period thereof less than the stimulation pulse interval, and having an output which changes state for said timing period after a signal is applied to the input, (a) the input being connected to the output of said second gate, (b) the output being connected to the second input of said second gate, (c) whereby when said monostable multivibrator is triggered, the output thereof disables said stimulation pulse generator for the timing period thereby limiting the rate of said stimulation pulse generator to the timing period, (5) and means for amplifying the pulse from the output of said second gate for delivery to said electrodes.