Patent GB-1502331-A (GB)
Title: Cardiac function monitoring system and method for use in association with cardiac pacer apparatus
IPC: A61B5/0452
Filed: 1975-05-13
Abstract: 1502331 Remote monitoring of the condition of a patient's heart and/or his pacemaker PACEMAKER DIAGNOSTIC CLINIC OF AMERICA Inc 13 May 1975 20092/75 Heading G1N(E) In a system for remotely monitoring the condition of a pacemaker within the patient, the cardiac electrical waveform picked up from electrodes L, G R , R on the patient is processed in such a way that the bandwidth of the pacemaker pulsewidth signal is compressed. This enables the pulsewidth signal and other pacemaker parameter signals to be transmitted through a telephone 33 line by way of a voltage controlled audio oscillator 20 supplying a speaker 32. In the preferred embodiment, Figs. 1-14, (Figs. 2-14 not shown) a patient identification code (in a store 18), an E.C.G. signal, a signal representing the area of the pacemaker pulse, and a signal representing the height of the cardiac pacemaker pulse are transmitted in a particular sequence to the V.C.O. 20 by means of a commutator 4. The commutator 4 is controlled by a "4 Bit counter and decoder" 26 in conjunction with an associated commutator clock 17 and logic circuitry which also starts and stops the information transmission. The measured pacemaker parameters are used to provide information about the condition of the pacemaker battery. Pacemaker signal analysis. The signals are derived from the patient by way of metal wrist bands Fig. 1A (not shown) and the amplified 1 signals pass via a 60 Hz notch filter 2 to a pacemaker analysis channel A and to an ordinary E.C.G. signal channel B. In the pacemaker channel A the signal passes via a potentiometer 6 and an amplifier 5 and a positive pulse selector 7. The resulting signal is further split into two channels, C and D, one D going to a Keying logic system 10 and 11 with associated switches 12 and 13, designed to recognize and pass only pacemaker signal parameters, while the other branch C is conducted to area and height analyzers 14 and 15 via the switches 12 and 13. The keying and analysis circuit comprises a differentiator 8 for a pulse having a fast rise time and an integrator 9 including a capacitor C I  which only passes signals with widths in excess of 250 Ás. If the rise time is sufficiently high, pacer pulse selection logic 10 forces the switches 12, 13 into a sample mode. This permits the electronic impulse to pass into both area integration amplifier 14 and high amplifier 15 during that period. If at the end of a 250 Ás sample period the input signal still persists the switches 12, 13 are charged to a hold position causing signals representing the pacemaker pulse area and height to be presented to the commutator 4. Bandwidth compression. The length of time that the area and height output is displayed i.e. the length of the hold period, depends on the actual width of the cardiac pacer impulse as measured at same fixed percentage of the maximum impulse amplitude. This width is multiplied by 100 so that the hold period is 100 times that of the cardiac width, since the actual width is too narrow for telephone transmission. The multiplication by 100 is achieved by feeding the pulse width data into a shift register under the control of a clock Fig. 6A (not shown) and then reading the data out 100 times slower by dividing the clock signal by 100 and using the result to read out the shift register. The description explains the electronics of the system in great detail Figs. 2-14 (not shown) including a station for processing the signals as picked up at the other end of the telephone line, possibly using a computer.