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Preparation of Electrocardiographic Data for Analysis by Digital Electronic Computer BY HUBERT V. PIPBERGER, M.D., EDWARD D. FREIS, M.D., B.E.E., AND HENRY TABACK, Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017 Materials and Methods Three corrected, orthogonal electrocardiographic leads (Schmitt's SVEC III system)9' 10 were recorded simultaneously on magnetic tape through FM (frequeney modulation) channels, with use of a tape recorder.* Differential preamplification with a gain of 1,000 and a frequency response flat from 0.1 to 1,250 c.p.s. was used. A fourth direct (voice) channel permitted recording of verbal information including identification of each From the Veterans Administration Hospital, the Department of Medicine, Georgetown University School of Medicine, and the National Bureau of Standards, Washington, D.C. Supported in part by a grant from the American Heart Association. Presented at the Thirty-Second Annual Scientific Sessions of the American Heart Association, Philadelphia, Pa., October 25, 1959. March 1960 LEONARD MASON, SC.D. orthogonal electrocardiographic leads into curves of spatial magnitude and orientation. Such a conversion does not necessarily lead to automatic analysis, since the newly obtained tracings must be interpreted in fashion similar to the original records. Although a few specific procedures are readily and economically accomplished by analog computation, the examination of large quantities of data for relationships that may never have been precisely formulated seems a task better suited to the digital computer. The problem of interpreting electrocardiographic wave forms is believed to be primarily one of recognition of pattern. Analog devices adapted for this use are likely to be single-purpose, and the probability is strong that a continuing development of equipment would be needed to meet drastic changes of processing procedures. On the other hand, if the researcher has access to a general purpose digital computer, an almost infinite variety of measurement and analysis can be had merely by writing a new set of instructions for the machine. Then conversion of electrical heart signals to numbers and their storage in a form acceptable to the computers becomes an essential preliminary step. In the present report, a pilot facility for accomplishing this purpose automatically is described. DIGITALI electronic computers are finding increasing applications in the analysis of medical and biologic data. The principal advantages are high speed, relatively great accuracy, and extreme versatility, especially for analytic operations that are too tedious and time-consuming for routine clinical use. Large amounts of data can be processed on a completely objective basis in a relatively short time. Thus computation by commercially available machines should facilitate extensive statistical studies, mass screening of the population, and the data handling of patient records in large organizations such as the Veterans Administration. The electrocardiogram was choseni for a pilot study in automatic data processing, since it has important clinical applications as a diagnostic aid. The electrical signals from the heart are repetitive and relatively well adapted for objective mathematical treatment. Once the feasibility of the method is established in electrocardiography, only minor modifications of the equipment would be required in other applications such as phonocardiography, ballistoeardiography, hemodynamic pressure and flow curves, electroencephalography, and electromyography. Several efforts have been made in recent years to apply analog computers to the analysis of the electrocardiogram.1-8 For example, MeFee,' Sayers et al.,5 and Abildskov et al.7 have proposed conversion of signals from 3 Circulation, Volume XXI, L. *Ampex 413 Corporation, Type FR 104. PIPBERGER, FREIS, TABACK, MASON 414 Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017 Figure 1 Equipmzeint for the neoni,ersion of electroc?ardiogralp)hic( data from th eir original analog into dliitt..l form. Th/,u eontrol unit wiith a display osc-illosc,olpe is seen on)ri the right. The elect.ocardiograp)hic signiaczls are r,etrieveed from the a-nalog tape recorder (on the left) and re-recorded thr.oiigjh a digital magnetic tape re,order (second from the right, wvith the analog- to -igital o)n,er,tehr in?iit .s lowui.er. sec(tion) The remainein q( ip)tnlent uSed in the automiatic daitac eersion pracuss is bnilt inito the nnit which is seen secoand from the left. patient. The electtro(,cartdiograllphic tracings were ca oscilloscope )0th hemonitored on ai e,ttlhode-ranfore and during, recording. Calibration was ob tained by recording leriodieally a 2-millivolt peaiksignal oni a,ill 3 FM clhanneXls to-peak square of the tal.pe -recorder. Tracingsi, of approxiima tely < 2v0 cardiae elc>es from each of ahbout 100 patients hlaive been recorded on eaeh tape teel. The equipmenit for conversion of analog-to-dig,ital data was operlited by a technician sitting at the control un-iit (figs. 1 and 2). The electrical hea rt signals were ietrieved,as voltages fronti the magnetie tape by usingi the play-back mechanism of the analog recorder. The operator examined these records nit aall oscilloscope screen, ac high-speed eleetrolic switch providing hint with sinmculta neous dispLays of all 3 leads automatically tinted to the heart rlate and synclhronized successively to show similar intervals of a,is many beats a,s 111ig-ht be desired. In (ca-ises witlh uinoai l sins rhlythm,i each cycele will comiiprise the familiar P-QTiS-T eonp)lex. The operaitor, after viewing severa.l cycles to clheck the essential uniformaitv of successive complexes, pressed a "irecor.d' switch that initiated the coinversion of the next cycle, and moniitored it on the osc,illoscope. [f it al)lpeaxed to be nontypical (e.g.,an extr(asystole), lie backed up tlhe analog--. tape drive and recorded an earlier (ycle. Circulatton, Volume XXI, March 1960 COMPUTER FOR ELECTROCARDIOGRAPHIC DATA 415 Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017 ANALOG TO DIGITAL CONVERSION SYSTEM FOR ELECTROCARDIOGRAPHIC DATA Figure 2 Block diagram of the equipment used for the analog-to-digital data conversion for electrocardiograms. The remainder of the process was completely automatic, requiring no further manipulations by the operator. The control unit first sets the digital tape transport into motion. After a brief delay to bring the tape up to proper speed, the format control is activated. This apparatus fulfills several functions: (1) by controlling the analog switch it samples each of the 3 leads X, Y, and Z 1,000 times a second; (2) it initiates the operation of the analog-to-digital converter' which converts the analog voltages to binary digits represented by sets of pulses, and feeds these pulses to a buffer which amplifies them and feeds them back to the format control unit; (3) the latter delivers them serially to the digital "write" electronic unit for re-recording on digital nmagnetic tape. The digital write electronic unit provides proper data form and power level for energizing the "record" heads of the digital tape recorder. At the end of a cardiac cycle the conversion equipment receives a stop signal from the control unit, *Epsco '"Datrac. ' Circulation, Volume XXJ, March 1960 and is then ready for the next patient's record. Records of 1 cardiac cycle of each of approximately 1,000 patients can be stored on one reel of digital magnetic tape. The digital tape format was designed to be compatible with one of the digital computers available at the National Bureau of Standards." Consequently, the information thus stored can be fed directly into any digital computer of this type for further processing and analysis of the electrocardiographic data as may be desired. Results Records of 988 patients with a variety of electrocardiographic abnormalities were proc- essed through the described analog-to-digital conversion equipment and a digital computer.* An obvious test for the proper functioning of the automatic equipment is the conformity between the original records and graphs of the 3 processed electrocardiographic *IBM Type 704. 416 416)) PIPRGER FREIS, TlA\l3iCIK MASON 1^~ :--- .1 --- -- -. ill,-------- 11 C ---f . Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017 Figure 3 RecordI.4ooi fi gure 1 uif./ j JJt ti through '('it 479v ) e+ll((Jic)tu'' itt and dljital 'ou iputer. The trueciug wos printed ouit Min nit Oi(tn c(td furorm a0(d ye ]plotted 01 hleIvusis o f 1/is dligitail inf ot motion. A tii}JilttidfC1ftQJ5,C 44(47 ( , ((461( tiite re Ititiotishipweire titonitoined s/eisfetrdteJ. Thisi, ti(me slto is. ct poi tf? 4 d47t10 i'( 1l /Il 1lt fJof/ -. lactas ott tIil basis of Ithe digitl i)tiilt-out received froim tle coin-puter. FigTure 3 is a graphi. of a 3-1lcatl cletrteardiogratu (pcatient C-21 ) after its conversin from tle anialogo record o07 ma-gtnetic tape, Its recad-in to tlhe diogital eorniputer, and its p)r'ini.t -otut as a colutIn of numiihers at millisecond interivals. Except where greater resolution was reqluired acecurately to delineate thIe ctirve oilly every fifth iiumber. Wx as plotted. ''lhe origillnal electrocardiogram was a sequelnee of 22 successive beats but the l)attern of figure 3 was suifficienitly distinctive to perllmit a sing{le tbeadit to be seleete(l from the orig,itl recorli of 22 ceardiae eve les. Wlhe the graphi was overlaid by the filmri recoi.cl of that ori cinl enlarged 1 2 timles as in figure 4. the amiplituides of the 2 (lliagralmlls were founid to Coeille(le Withinl a trlace width a (discrel)aney far less than the heat-to-beat variabilitx Figure 4 SttnipbJI 47e<es( off a 01[ii oyoiioi 4(1)01it'ciioljr'pin 7 front to]) to bottouit) ieployed Ifrom Z Icads (X., unulog)(J t}itoyit C?tic' to rind1)110t]ioto i'ttphir(1 front all suc i os eo pe seercn. of alln average11 eel ltclLogtai. A n umber of other diatients (liitizedl records. )lotteCl1 a1t 10-mlillist leod intervals, showeed eqiuallv coodclorrespondene. Thlins, it hias been dentrou.stcateh thalt tlhe faeility used for eonversro and lligital storagi)e of eleearlliographie data performs satisfactorily an1d eliably. Discussion As i)oilnted otut above, logical anid miathe-mcatical operattionis Oni electrocardiogralphic dlata in digital formn afford a high degree of fiexibilitv O nce the sitgllnls are stored on digital magnetli tape iii a suiitable format, onlyl ptroper progriamming of a digital eomnputer is requirll tto pr.ovide a great xariiety of anialytic procedrles. rT is flexibility appears espeeially iiutporta i-t for the establishlment of clinlic(al norms and the discovery of inew diagnostic Circulation, Volume XXI, March 1960 COMPUTER FOR ELECTROCARDIOGRAPHIC DATA Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017 procedures. Wheln these have been tested by experience, a special-purpose computer for electrocardiographic data might then be designed, to replace the general purpose equipment described in this report. The size and cost of the required apparatus might then be brought down within the reach of an average hospital. Objective data analysis with computers could provide a considerable increase in diagnostic accuracy, since subjective and descriptive criteria for electrocardiographic interpretation can be replaced by quantitative statements. Rather elaborate analytic and statistical procedures take only a few seconds on a digital computer and so pose no major problems. Also the electrocardiographic information can be supplemented by salient facts from the patient's history and physical examination, which can be entered into the digital computer on punched cards. There are no instrumental limitations, therefore, for providing a more broadly based computer program as an aid in electrocardiographie diagnosis. The total information thus available would greatly facilitate statistical correlations of various parameters. Magnetic tape provides a convenient medium for recording and storing electrocardiographic tracings. The original analog tape can be used at any time for the display of old records either on an oscilloscope in scalar or vectorial form or, if so desired, for re-recording old tracings on paper. Considerably less storage space is required for magnetic tape than for conventional recording media. The described equipment requires only minor changes to make possible the inclusion of other diagnostic methods for cardiac evaluation. Modifications for phonocardiography, respiratory volume curves, and pulse tracings are presently being made. Summary A pilot facility for automatic processing of electrocardiograms leading to their analysis by digital computer has been described. Wave forms from orthogonal electrocardiographic leads were recorded on magnetic tape. By Circulation, Volume XXI, March 1960 417 means of newly designed conversion equipment these records have beern converted from their original analog form into digital form. The further processing and analysis of the data thus becomes feasible through the use of commercially available digital electronic computers. It has beeln demonstrated that the electrocardiographic tracings as recorded from patients can be reproduced from the resulting numerical print-outs in their original and undistorted formn. The further analysis of these records theii requires only proper programming of a digital computer. The same equipment with minor modifications can be used for automatic processing of other analog data such as phonocardiograms, pulse tracings, and ballistocardiograms. Summario in Interlingua Es describite un arrangiamento de dispositivos pro le manipulation automatic de electrocardiogrammas preparatori a lor analyse per medio de un computator digital. Formas de unda ab orthogone derivationes electrocardiographic esseva registrate in bandas magnetic. Per medio de un novemente elaborate dispositivo de conversion iste registratioiies esseva convertite ab lor forma original analoge a in un forma digital. Le cetere processage e le analyse del datos deveni assi effectuabile per le uso de commercialmente disponibile computatores electronic digital. Il ha essite demonistrate que le registrationes electrocardiographic obtenite ab le patientes pote esser reproducite ab le resultante configuration numeric in lor forma original sin ulle distorsion. Le ainalyse additional de iste registrationes require alora solmente le appropriate programmation del computator digital. Le mesme apparatura con minor modificationes pote esser usate pro le processage automatic de altere datos analoge como per exemplo illos del phonocardiogramma, de registrationes de pulso, e del ballistocardiogramma. References 1. MCFEE, R.: A trigonometric computer with electrocardiographic applications. Rev. Scient. Inst. 21: 420, 1950. 2. JOHNSTON, F. D., MCFEE, R., AND BRYANT, J. M.: An integration circuit for measurement of the areas of the wxaves in the electrocardiogram. Circulation 2: 5, 1950. 3. BRILLER, S. A., MARCHAND, N., AND KOSSMANN, C. E.: A differential vectoreardiograph. Rev. Scient. Inst. 21: 805, 1950. 4. SIMONSoN, E., SCIIMITT, 0. H., DAHL, J., FRY, PIPBERGER, FREIS, TABACK, MASON 418 D., AND BAKKEN, E. E.: The theoretical and experimental bases of the frontal plane ventricular gradient and its spatial counterpart. Am. Heart J. 47: 122, 1954. 5. SAYERS, B. MCA., SILBERBERG, F. G., AND DURIE, D. F.: The electrocardiographic spatial magnitude curve in man. Am. Heart J. 49: 323, 1955. 6. NEWMAN, E. V., McGOVERN, J. F., AND ARNOLD, T. G.: The important recent advances in electrocardiography. Arch. Int. Med. 96: 591, 1955. 7. ABILDSKOV, J. A., INGERSON, W. E., AND HISEY, B. L.: A linear time scale for spatial vectorcardiographic data. Circulation 14: 556, 1956. 8. BRILLER, S. A.: The integrated electrocardiogram. Ann. New York Acad. Se. 65: 894, 1957. 9. SCHTUITT, 0. H., AND SIMONSON, E.: The present status of vectorcardiography. Arch. Int. Med. 96: 574, 1955. 10. PIPBERGER, H. V.: Current status and persistent problems of electrode placement and lead systems for vectoreardiography- and electrocardiography. Progress in Cardiovase. Dis. 2: 248, 1909. Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017 Dollery, C. T., Harington, M., and Kaufmann, G.: The Mode of Action of Chlorothiazide in Hypertension. Lancet 1: 1215 (June 13), 1959. In a series of experiments it was demonstrated that chlorothiazide potentiates the ganglion-blocking agents (as exemplified by pentolinium) by causing a reduction in plasma volume. A negative sodium balance was observed in 11 patients, but the extent of this did not correlate well with the development of increased sensitivity to pentoliniuim. There was better correlation with the changes in plasma volume. In 8 of 13 patients studied, 3 days' treatment with chlorothiazide produced a fall in plasma volume and all of them showed an increased sensitivity to pentolinium. In 4 out of 5 in whom there was no significant change in plasma volume, the effect of pentolinium was unchanged. Replacement of the calculated loss in plasma volume with salt-free Dextran in 7 patients was followed by reduction in sensitivity to pentolinium to about the pre-chlorothiazide level in all except 1. It was thought unlikely that chlorothiazide had any direct hypotensive action, since no change in blood pressure nor potentiation of ganglion blockade was observed after intravenous injection of large single doses. The sensitivity to pentolinium did not develop until the second day. This was not true with the non-quaternary ailmonium compounds such as Mecamylamine and Pempidine. Since there was a slight shift of the urinary pH toward the alkaline side on first giving chlorothiazide, there was a resultant reduction in the renal excretion of these latter drugs, and therefore an increased hypotensive effect. The potentiating effect of chlorothiazide on pentolinium particularly affected the postural drop of blood pressure. Some postural hypotension was observed as a response to chlorothiazide itself in 4 of 13 patients. Three of these had a considerable fall in plasma volume while the fourth had an extensive sympathectomy previously. The postural response was abolished in each case by the infusion of sufficient Dextran to replace lost plasma volume. SHEPS Circulation, Volume XXI, March 1960 Preparation of Electrocardiographic Data for Analysis by Digital Electronic Computer HUBERT V. PIPBERGER, EDWARD D. FREIS, LEONARD TABACK and HENRY L. MASON Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017 Circulation. 1960;21:413-418 doi: 10.1161/01.CIR.21.3.413 Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 1960 American Heart Association, Inc. All rights reserved. Print ISSN: 0009-7322. 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