Patent GB-1493531-A (GB)
Title: Apparatus for the analysis and display of electrocardiographic waveforms
IPC: A61B5/336
Filed: 1975-01-15
Abstract: 1493531 Electrocardiographs AMERICAN OPTICAL CORP 15 Jan 1975 [15 April 1974] 1826/75 Heading G1N [Also in Division H4] Electrocardiogram (ECG) cathode-ray tube display apparatus reads ECG signals from a recording medium at a faster rate than that at which they were recorded, temporarily stores the complete signals and then recirculates them and displays all of the signals superimposed on each other at a faster rate than that at which they were read (top trace, Fig. 1) and should a premature beat be detected, a portion of the signals read from the recording medium, long enough to include two normal heart beat cycles and previously temporarily stored in a separate temporary store, is recirculated independently of the recirculation of the complete signals and displayed, also at a faster rate than that at which they were read, as a separate display (bottom trace, Fig. 1). Referring to Figs. 2, 3, and 4, a tape play-back unit 200 containing a previously recorded continuous ECG signal is read at sixty times the realtime recording rate and supplied to an R-wave detector 244 (which produces a basic synchronizing signal) and to an analogue-to-digital conversion system operating according to a known technique and comprising a comparator 218, a successive approximation register 220 and a digitalto-analogue converter 224. The output of register 220 comprising eight-bit signals representative of the instantaneous value of the ECG signal is then supplied to the BO-A....B7-A inputs of two digital multi-plexers 226, 310 each of which has a second group of inputs BO-B .... B7-B connected to ground. When the select A input to multi-plexer 226 is "high" its output comprising the eight-bit signal is transferred to respective 256-bit shift registers 228-0.... 228-7 and then rapidly transferred to respective shift registers 304-0 ... 304-7 via a multi-plexer 302 which receives at its B input the outputs of the registers 304-0 .... 304-7 and so constitutes a recirculating memory. The output of the latter, as it is recirculated, D0-D7 is supplied to the B inputs of a multi-plexer 418. When a premature heart beat is detected (by known detecting means 314) the eight-bit signals already supplied to multi-plexer 310 and already transferred to respective 1024 bit (about four seconds of real time) shift registers 312-0 .... 312-7 are then rapidly transferred to a second recirculating memory, similar to the first recirculating memory, and comprising multi-plexer 400 and shift registers 402-0 .... 402-7 the output of which, as it is circulated is supplied to the A inputs of multiplexer 418. Multi-plexer 418 then transfers the A and B input, alternately, to an eight-bit latch 422 which is strobed at the rate at which new bit samples are transferred. Thus the 256 bits in the recirculating registers 304-0 ....304-7, which form the B input, are strobed at 115-2KH z  (the recirculation rate) whilst the 1024 bits in the recirculating registers 402-0 .... 402-7, which form the A input, are strobed at 460.8 KH z  (the recirculation rate) the data for the A and B inputs then being both recirculated at a rate of 450 complete recirculations per second. The output of latch 422 is then supplied via a digital-to-analogue converter 424 to the vertical deflection input of the CRT 430 via a summing junction 433 together with a 225H z  squarewave signal see Fig. 6 which causes alternate horizontal deflection traces (occurring at 450H z ) to be shifted vertically. Thus the B input to multi-plexer 418 is displayed on the upper trace and the A input (if any, i.e. if a premature heart beat is detected) is displayed on the lower trace Fig. 6. A short persistence phosphor tube together with a high recirculation rate results in a display free from flicker and from smearing. A potentiometer 436 allows the vertical position of the whole display to be adjusted.