8 June 1974 S.A. MEDICAL JOURNAL 1141

Computerised Analysis, Interpretation, Storageand Retrieval of Electrocardiograms

A STUDY AND REVIEW OF AVAILABLE SYSTEMS

A. J. BRINK, C. DE W. VIVIER, J. D. N. VAN WYK

SUMMARY

A study was undertaken to determine the feasibility ofintroducing a computerised electrocardiographic analysisand interpretive system as a service to a teaching andreferral hospital.

Available computer equipment and programmes areconsidered. The accuracy and quality of the analysisand interpretation of the electrocardiographic contoursare basically dependent on such factors as pattern recog­nition, the criteria adopted for determining abnormalities,the relative values placed on scalar and orthogonal leadsand the role of review by the physician.

It is concluded that such systems are at a stage wherethey can feasibly be introduced and should be of advan­tage in freeing the physician from ,routine measuring andscreening of electrocardiograms, thus saving many hoursof professional and academic time.

Furthermore, such systems can contribute greatly as aneducational tool and increase the general knowledge ofelectrocardiography.

Systems for storage and retrieval are also being de­veloped and becoming available. The whole field is adeveloping one and continuous updating of programmesby the addition of more data, particularly for children, andthe introduction of electrocardiographic comparison pro­grammes need to be expedited.

S. Afr. Med. l., 48, 1141 (1974).

Electrocardiography can be considered as the nucleus of acardiological service in any clinical diagnostic situation,whether it be within a large teaching hospital centre,within smaller peripheral and distant rural hospitals, orwithin everyday private practice. There is an increasingawareness of the value of the electrocardiogram in theevaluation of known heart disease and in the diagnosis ofcardiac conditions, and as a baseline study for any patient

Cardiology Unit, Tygerberg Hospital, Tiervlei, CPA. J. BRINK, Head

Department of Hospital Services of the Cape ProvincialAdministration

C. DE W. \'lVIER, Deputy Director

National Electrical Engineering Research Institute, Councilfor Scientific and Industrial Research

J. D. N. VAN \WK, Director

Date received: 23 January 1974.

6

who is to undergo any major or even minor surgicalprocedure. The rapid increase in the number of coronarycare units has resulted in a further demand for electro­cardiography. During the course of the acute myocardialinfarction delayed electrocardiographic evidence of in­farction and the development of conduction and arrhyth­mic disturbances warrant repeated electrocardiographicexaminations daily or several times daily, also for pur­poses of comparison. Furthermore, general practitionersand life insurance companies are increasingly insisting onelectrocardiographic examinations. If electroca,rdiogramscould be readily taken and fully analysed without con­suming the valuable time of a physician, populationsurveys would be of great value in the early detection ofa wide variety of cardiac disorders.

An increasing and overburdening load is being placedon the electrocardiographic services of institutions; involv­ing not only technician time, but valuable physician orcardiologist time spent in the analysis, interpretation andcomparison of electrocardiograms. Mass populationsurveys are not feasible with the present-day manualapproach.

The steps taken in the conventional processing of anelectrocardiogram include the following: data acquisitionby a technician with a conventional electrocardiographicrecorder; cutting and mounting the graph; reading, analy­sis and diagnosis of the electrocardiogram (done by anelectrocardiographer); a report on the interpretation,compiled by the cardiologist; the production of a hardcopy of the electrocardiogram, with a typewritten reportdistributed to the source of request; and a system offiling and record-keeping so that electrocardiograms maylater be retrieved for purposes of comparison, review andresearch.

This whole process is time-consuming for both tech­nicians and administrative personnel, and also for thephysician/electrocardiographer; and of necessity an elec­trocardiogram and report often cannot reach the bedsideof the patient within 24 hours. Systems are now beingdeveloped which can free the physician from routinetasks, providing more time for patient care and alsoguaranteeing a certain level of quality.'-· These semi-auto­mated systems, dependent on a digital computer, facilitatethe recording of higher quality electrocardiograms, assistdiagnosis and aid follow-up management of the patient.Specialist experience can be brought within seconds toevery patient's bedside since the electrocardiographic dataare directly transmitted to the processing system by tele­phone and the signals are analysed instantaneously.

1142 S.-A. MEDIESE TYDSKRIF 8 Junie 1974

The electrocardiogram was chosen as the first signalfor automated recognition and interpretation of patternsin medicine, because physicians are most familiar with itand they have had 50 years of experience in relating thepatterns to specific and clinical purposes.

A study and investigation was undertaken (i) to deter­mine the feasibility of a computerised electrocardiographicsystem, in relation to both the hardware required and theprogrammes (software) available; and (ii) to recommend amethod for filing, storage and retrieval of electrocardio­graphic information.

FEASmILITYHardware

The feasibility of such an automated service is dependentupon the availability of suitable processing equipmentand peripheral input and output systems. A variety ofsophisticated hardware is available (International BusinessMachines Corporation (IBM); Control Data Corporation;Hewlett-Packard (HP); Siemens; Cro-Med Bionics Cor­poration; Marquette Electronics Inc).

Electrocardiograms (ECGs) can be run in batch modein an off-line system, but restriction to this system willsignificantly annul the advantage of fast computer analy­sis, which could be very valuable in emergencies. Inaddition, immediate feedback from the computer to thetechnician recording the ECG is most helpful in avoidanceof operator error. It is accepted in all computer appli­cations where raw data are fed into a computer that someform of monitoring is essential. This indicates that atleast some of the ECG information should be processedin real time with feedback to the operator.

Experience has shown that although in theory it ispossible to mix real-time applications with a large-batchcomputation load in a general-purpose, time-sharingsystem, this raises many problems in practice. Mini­computer systems, however, having been designed forreal-time processing, lend themselves ideally to thispurpose. It is possible to run more than one programmesimultaneously on such a system as well, but the differenceis that the complete mix is known beforehand and can becatered for in the executive programme. Furthermore,there are seldom more than a few programmes operativein the system at anyone time, and when the load reachessuch a magnitude that response time becomes too long,it is customary and normally quite economical to thenduplicate the system partially or entirely.

A minimum system for ECGs requires about 24 Kwords of core plus 1,25 million words of disc storage.If, however, a certain amount of patient file handling isto be included, this should be at least 32 K words ofcore storage and 2,5 million words of disc storage.

Mobile ECG data acquisition cars can accept theECG directly from the patient, make an automatic graphicrecording on three simultaneous channels and transmitthe ECG with a patient identification number on standardvoice-grade telephone lines to the comPl!ter system at aremote location; or the patient's ECG and identificationcan be recorded on site on magnetic tape, either in analogueor digital form, which is then delivered to a computer for

playback and processing. These systems are availablefrom several manufacturers (HewJett-Packard (HP);Marquette Electronics Inc.; Cambridge; Computer Instru­ments Corporation; Beckman Instruments Inc.; DexSystem).

A printed interpretive statement, either at the computersite or at the patient site, can be given in less than oneminute with a print-out in either a long form, whichincludes all the measurements and the logic _for theinterpretation, or in a short form which makes onlyan interpretive statement. The displays can include thevector loops of the XYZ orthogonal system, such as thatof Frank.

The Programme (Software)

Various programmes have been developed over the past10 years to meet the demands for accurate electrocardio­graphic analysis and interpretation.*

The accuracy and quality of the analysis and interpre­tation of the electrocardiographic contours are basicallydependent on several factors:

(i) the pattern recognition and measurements whichare made;

(ii) the criteria which are adopted for determiningabnormalities;

(iii) the relative value placed on the 12 scalar leadsOeads 1, 2, 3, aYR, aVL, aVF, VI - V6) or on anorthogonal XYZ lead system such as that of Frank;

(iv) physician review;(v) criteria for children;(vi) comparative electrocardiography;

(vii) the print-out form.Pattern recognition and measurements: The amplitudes,

slopes and durations of the various waves and segmentsof the ECG are calculated, tabulated and interpreted.The primary function is the selection of }:oints to describethe ECG wave form. Sampling is done at rates of atleast 250 per second, but it may be preferred to sampleat higher rates such as 500 per second. In the scalar leadprogramme, each simultaneous lead set (1, 2, 3; aYR, aVL,aVF; VI, V2, V3; V4, VS, V6) is recorded for up to 5seconds, allowing a typical recording time of 20 seconds.The combined scalar and orthogonal lead system alsorecords for approximately 20 seconds.

Pattern recognition -may depend on singling out themost representative cardiac cycle wave for analysis:'"labelling the onset of each of the components of theP, Q, R, Sand T waves, measuring the -amplitudes inmillivolts and constructing core-resident tables from whichan interpretation can be made. In the Pipberger"·H pro­gramme the pattern recognition depends on the average

• Caceres, C. A.-Medical Systems Development Laboratories of theUS Public Health Service, Washington DC, USA.Pordy, L.-Mount Sinai Hospital and Cro-Med Bionics Corp., ewYorK:, USA.Smith, R. E.-Mayo-IBM Electrocardiographic Computer AnalysisProgrammes, Rochester, Minnesota, USA ('I 70).

-Bonner, R. E.-IBM Health Care Support/Electrocardiogram (ECG)Analysis ProR!'am, New York, USA. -Pipberger. H. V.-Veterans Administration Centre for Cardiac Pro·cessing, Washington DC, USA.Riedl, H.-Siemens Akliengesellschaft Medical Engineering Group,Erlangen, Germany.Ducinmetiere, P.-Unite de Recherche Statistique de LN.S.E.R.M.,Paris, France.

8 June 1974 S.A. MEDICAL JOURNAL 1143

of measurements made on all recorded cycles of the ECGand not on the most representative cycle.

A noise factor is calculated, and if in any lead thisexceeds a present value, the ECG is considered too noisyfor further analysis and is rejected.

Rhythm analysis is obtained from the logic devoted tobasic pattern recognition in addition to logic devoted tothe recognition of arrhythmias.

Adjacent pairs of QRS complexes are organised into'units', a concept which permits separation of basic fromectopic rhythm. For each set of three R-wave peaks, thereare two RR intervals. If the smaller one is less thanthree-quarters of the larger, an arrhythmia is flagged.Further detailed analysis of arrhythmias is dependent onsearching, identifying and typing the P waves, determiningthe presence or absence of a regularly spaced train of Pwaves, and the application of special tests for arrhythmiassuch as atrial fibrillation. This complex computer activityof measurement, pattern recognition and arrhythmiadetermination is described in different publications.'-·

The criteria: The parameters (amplitudes, duration, axes,etc.) are compared against limits or other parameters foreach lead. The final interpretation will therefore be theproduct of the comparison of the established valuesobtained for the particular ECG and criteria for diagnosisincorporated into the programme. Different sets of criteriahave been programmed, based on available knowledge fromthe electrocardiographic literature, the combined viewsof panels of cardiologists and, in the case of the Pipbergerprogramme, on observations on a bank of patients withheart disease with diagnoses proved by autopsy or specialinvestigation.

Scalar and ortbogonal leads: At the Mount SinaiHospital in New York, Pordy has developed an operationalon-line electrocardiographic analysis and interpretivesystem based on the 12 scalar leads. He is convinced, andpresents supporting evidence, that the scalar leads aresuperior to the vectorcardiographic leads, and he believesthat the vectorcardiogram misreads about 25 % of contourdiagnosis. 1

The IBM Health Care Support/Electrocardiogram(ECG) programme, the new programme of Bonner, basedon the 12 scalar leads plus 3 orthogonal leads not usedfor interpretation but for rhythm diagnosis, is in use atseveral centres in the USA and in Europe. The programmeis claimed to be highly accurate. Since no dedicatedcomputer is known to us to be available for this pro­gramme, one is limited to a batch mode interpretive system.Moreover, some evidence from a comparison ofinterpretations made with the Pordy programme suggeststhat it is capable of erroneous diagnosis.' It was alsostated that the Bonner programme tends to read anegative P wave lying close to QRS in standard lead Ias a Q wave, and that in the presence of left ventricularhypertrophy anteroseptal infarction can be missed."

The 12-lead scalar electrocardiogram is used by Caceres,who has an ongoing programme improvement project andwill release a new programme by 1974.9 The quality isclaimed to be such that it would make it quite unnecessaryfor a physician to review the product. This new programme.

7

like the Pordy programme, includes the capability ofcomparative electrocardiography. Contour analysis is nowpossible in the presence of arrhythrnias. The new pro­gramme has a capability of diagnosing the 15 mostcommon arrhythmias with considerable accuracy.

Pipberger has developed a programme which up to thisstage has been of a developmental and research nature,with the emphasis on the orthogonal lead system ofFrank. The ECG is produced and displayed as vectorloops, together with an interpretive statement derivedfrcm the 3 XYZ leads. The measurements are calculatedon the mean values of all the complexes registered, andnot based on the most representative complex such as isthe case in the Bonner, Caceres and Pordy programmes.The measurements made are analysed by multivariantanalysis, and the interpretive statement is expressed in aform of probabilities in such a way that a diagnosis wouldbe given, for instance, as left ventricular hypertrophy64% probability, myocardial infarction 40% probability.The multivariant analysis of the measurements is aprocedure which is followed by only one other group, inJapan.'·' The criteria in the Pipberger programme havebeen painstakingly developed on the basis of electrocardio­graphic findings in cases of proven diagnosis, proved eitherby autopsy or by special cardiological investigations suchas cardiac catheterisation and angiocardiography. The databank for this purpose is now based on records of about28000 patients."

In a comparison of the computer diagnosis of the ECGwith the individual diagnosis of cardiologists in cases ofproven diagnosis, the cardiologist's performance was 54%accurate, against the 80% accuracy of the computer.This programme has been adopted by Hugenholtz inRotterdam, Holland." The programme is to be madeoperational as a service for the Veterans AdministrationHospital in Washington, and will also be coupled to achildren's hospital and an additional hospital during1973.14

The Smith programme, which has been developed atthe Mayo Clinic, is based on the analysis of the 12 scalarreads and the 3 orthogonal XYZ leads of Frank.lO

,,,

Measurements from the 12 scalar leads are presented inthe print-out report of the analysis, but the interpretationis made from the orthogonal leads.

Smith is confident that there is no significant differencebetween the use of the scalar leads compared with thevectorcardiogram with regard to accuracy. The vector­cardiogram may be better than the scalar leads in perhaps1:20000 instances. The two systems give the same in­formation; there is only a difference in presentation.Smith also believes that the multivariant analysis usedby Pipberger tends to diffuse the diagnostic criteria andto make diagnosis less definite." Expressing these diagnosesin the form of probabilities is in fact confusing for theconsumer, who would prefer to have a definite electro­cardiographic interpretation to fit into the general clinicalpicture with other laboratory findings for diagnosis.Comparative electrocardiography is also possible and thenew programme will be released in 1973. Pipberger'6stresses the point that the ultimate test for a particularprogramme is diagnostic accuracy.

1144 S.-A. MEDIESE TYDSKRIF 8 Junie 1974

Physician review: Whether or not the interpreted ECGshould undergo physician review, or to what extent itshould be reviewed, is a matter of great difference ofopinion. Pordy' is categorical about the fact that everyBCG should be reviewed before it is finally released.His on-line system makes provision for review after pro­cessing by a panel of physicians! cardiologists. Any correc­tions are then introduced into the further processing, sothat the final hard copy and print-out is an amendedversion. He is of the opinion that normal and abnormalBCGs must be reviewed in this fashion. The fact thatPipb~rger has demonstrated to his own mtisfaction thatcomputer diagnosis is superior to that of a cardiologist!physician," leads him to the conclusion that there is noneed for a review, since the accuracy of human interpre­tation is so much less than that of the automated machine.

It is Caceres's view: too, that the new programm~ whichwill shortly be released by him will make a 'centralreview' of the ECG unnecessary. The question of 'centralreview' is emphasised, because the review may be doneat the consumer end and there should be no need for acentral point where all or any BCGs are first reviewedand corrected. This will allow the individual physician!cardiologist to make his own assessment, and where otherhospitals are linked to the central system, such hospitalscan organise their own reviewing system if they so wish.

A general system of surveillance of the quality of theelectrocardiographic interpretation is the requirement ofSmith. ll In his view it is unnecessary to review normalBCGs and in his experience perhaps one out of everythousand interpretations subjected to review by a cardio­logist is altered. This alteration does not necessarily meanan improvement. Consequently Smith states that (a) nor­mal BCGs need not be reviewed; (b) abnormal BCGs inwhich the type of abnormality is of a kind where thereis a 100% agreement as to the nature of the abnormality,for instance the diagnosis of a pure posterior myocardialinfarction, need not be reviewed; (c) where the diagnoseshave a wider variety of interpretive possibilities the BCGsshould be reviewed. The programme should thereforeinclude a certain quality control for the different diagnoses;and the greater the degree of agreement with regard tocriteria for a diagnosis, the less the need for reviewexists, so that an increasingly large number of abnormalECGs can be included in the mainstream of records whichneed not be reviewed. The higher the possible diagnosticerror, the more a physician's review becomes necessary.

Criteria for children: The various programmes havethus far not included sufficient criteria to meet the demandsfor the various ages from 0 to 20 years. However, thenewer programmes of Caceres' will have sufficient criteriafor interpretation from the age of 5 years. Pipberger willinclude criteria for children, once they are linked up witha children's hospital." The Smith programme is nowmaking provision for the addition of criteria in relationto children, and normal values are being fed into theprogramme to include the ages 0 - 20 years in differentcategories."

Comparative electrocardiography:' The' comparison ofECGs taken in the immediate follow-up period, parti­cularly in the intensive care units, and baseline ECGs done

pre-operatively, is becoming an increasingly importantfacet of clinical electrocardiography. The programmesof Pordy, Caceres and Smith allow for the possibility ofcomparison, but this requires an increase in active storagespace in the computer system. This type of storage is mostefficiently supplied by means of disc storage.

The print-out fonn: All available programmes permitthe option of having a print-out in a long or a short form.The long form includes the actual measurements to anydegree of detail required. This is then followed by aninterpretive statement with reasons for arriving at theparticular diagnosis. The form in which the interpretationis required will depend lJn the type of consumer.

Firstly, the cardiologist requiring the ECG will wishto have the complete information, including the graph andall the measurements, as well as the analysis and the reas­ons for the interpretive statement. He would then probablyassess the BCG for himself and compare this with thecomputer diagnosis, and if there is a difference of inter­pretation he would most likely prefer his owninterpretation.

Secondly, the general physician or postgraduate studentand the undergraduate student will perhaps also requirethe long form, but would have more interest in theinterpretive statement and the logic for the conclusionsarrived at. They would tend to accept the computerdiagnosis.

Thirdly, the general practitioner and non-internistspecialist in hospital service would have most interest incomputer diagnosis and none in details.

Storage

The storage of electrocardiographic information mustbe viewed on a functional rather than an encyclopaedicbasis:

Short-tenn: Short-term storage is required for theperiod in which the ECG will be active and may haveto be retrieved rapidly for comparative purposes, or forinclusion in the patient file, or when taken on an out­patient awaiting admission to hospital. This type ofstorage is best done on magnetic disc, which is expensiveand can be used t;) only a limited extent. It is thereforenecessary to decide how long the ECG should stay inthis form. An arbitrary time of, say, the average hospitalstay or the average time of awaiting admission from aclinic, may be set-a period of 3 weeks may be reasonable.

Intennediate tenn: An intermediate period of storage isrequired in which the ECG may be called for" becauseof the possible readmission of a patient. This is a difficultlength of time to determine. It is fairly certain, howeve.r,that only a small percentage of EeGs need be stored ID

this form for more than a year. Magnetic tape storagecould be considered for this purpose. Digital tape wouldmake an ECG more rapidly retrievable and has fewerproblems than analogue tape. A magnetic data card systemhas been developed and appears to be close to ideal forintermediate and long-term storage (Marquette ElectronicsInc.). The card has magnetic tape strips which can recordin both a digital and an analogue form. The system

8 June 1974 S.A. MEDICAL JOURNAL 1145

automatically receives ECGs, along w:th pat'ent identifi­cation data, by telephone or from tape cas'ettes. As eachrecord is received, it is transcribed onto a magnetic datacard. Later diagnostic codes and computer commentarycan be recorded or corrected on the same card. Automat;creproduction of recorded data is qu;ck:y accomplished.Recorded data cards can be stored. 2 000 cards perdrawer. This file can be extended.

Raw digitised ECG, contain from is COO to 60000"bytes' (8-bit characters). An accumulation of 100000ECGs would represent some 1,5 - 6 billion bytes. A discpack of 731-metre reel of digital tape can store 5 - 20million bytes. As a result it would require seVEral hundreddisc packs or tape reels to store these records.

Five minutes are required to load and ,earch digitaltape, somewhat less for a disc pack. If I00 o~d tracingsper day have to be located, 2 full-time computer techniciansare required. It is claimed that 100 magnEtic data cardscan be retrieved from the fi~es in less than one hour andcan be converted into hard copy in IS minutes. A com­puter is not required for such a procedure. This newcentral magnetic data card system appears to be a veryvaluable adjunct for storage and retrieval pUipcses, whichcould serve both intermediate and the long-term needs.

L~Dg-term: A less costly but also less useful form ofstorage is the microfilm card storage (3M Brand FilmsortCards, 3M Co., St Paul, Minn., USA). The ECG is ina form in which it cannot be reanalysed or compared bymeans of the computer.

Benefits of an Automated ECG System

Experience has taught that once an analytical andinterpretive electrocardiographic system becomes opera­tional, it greatly contributes to the elevation of the generalknowledge of electrocardiographic interpretation:, .. ,1' Ithas turned out to be a powerful educational instrument.Wright" of the Haylor College of Medicine, Houston,Tex;s. states that their senior medical students becomeas w~1I versed in the interpretation of ECGs within 5-!­weeks of exposure to this system as their senior residentstaff. The fact that the interpretive statement is presentedtogether with the reasoning for the diagnosis, means thatthe reviewing physician can look at the tracing criticallyand study the unknown facets in depth.

Great advantage is derived from freeing the physicianand the cardiologist from routine measuring and screeningof ECGs, and thus many hours of professional andacademic time are saved.

The service aspect of an automated system is notlimited to large teaching institutions, but applies particu­larly to institutions, whether they be large or small, wherethere may be few if any cardiologists or internists availableto read and interpret ECGs. Ideally, such a centralisedsystem can be linked with peripheral and rural hospitalsand even mission stations and general practitioner groupsin outlying areas.

The storage of the vast amount of accumulated e!ectro­cardiographic data in a form in which it is retrievable andcomparable, can also be best accomplished hy this means.

9

There can then be little doubt that provided the criteriaof accuracy are ensured. the installation of such accmputeris~d sj::tem for electrocardiographic analysisand interpretation can be justified. The direct and indirectbenefits, consisting of the educational value, service valueand the storage facility. would outweigh the fiscalconsiderations.

DISCUSSION

The general conclusion is that a cardiographic analysisand interpretive system can be installed and made opera­tional to the benefit of any teaching hospital and itsenvironment. The 12-lead scalar electrocardiographicprogramme appears at prEsent to be most suitable to ourlocal requirements and will provide an acceptable form ofelectrocardiographic presentation. With the increasingtrend towards the use of an orthogonal lead system,a programme which includes both the 12 leads and theorthogonal leads may be preferable. An on-line systemis functionally preferable and can be readily installed ina central complex and linked with peripheral hospitals, bymeans of the telephone network. However, it does seemnecessary to make provision for an off-line possibility asa back-up facility and for the purpose of surveys inoutlying areas. Storage facilities must be provided on ashort-term basis, during which ECGs are actively required,particularly for comparative purposes, and also onintermediate and long-term bases. Disc capacity fs tl:ere­fore necessary for short-term purposes, and the most suit­able long-term system is one in which a single manualstep is required, but which is both economical andefficient, such as the magnetic data card system.

The form which the print-out takes is optional and canbe varied according to consumer requirement.

All the available programmes are ,till being improvedupon, but have reached a general state of maturity whichmakes them acceptable for routine service. It can bereasoned that the electrocardiographic interpretation isbetter done by a computer than by an individual cardio­logist. Programmes will soon include criteria for children,and provision is made for comparative electrocardiography.No programme can thus far be regarded as infallible, butrecognition of the normal ECG has a degree of accuracyof more than 99°0. The accuracy w;th abnormalities varies,depending upon the degree of consensus regarding thecriteria for a particular diagnosis and on the measurementsdecided upon to indicate abnormality. The scalar leads areperhaps inferior to vectorcardiogram leads as regardsaccuracy, but opinions differ. Since the scalar leads aremore widely acceptable in this country, as is the case inmost other parts of the world, and the vector leads are notso familiar to most cardiologists and practising physicians,a programme at this stage would include the 12 scalarleads. If the vector leads were more familiar, they wouldc~rtainly be more economical, because measurements inonly 3 leads are required for interpretative purposes.Rhythm analysis has been brought to a stage where thebulk of arrhythmias are diagnosed accurately, and prevail­ing opinion is that great progress in accuracy has beenm:td~ with regard to arrhythmias.

S.-A. MEDIESE TYDSKRIF 8 Junie 1974

The avaiiable programmes are of such quaiity at presentthat a complete review of all ECGs is not necessary. Anincreasingly larger number of abnormal ECGs may infuture be included in the mainstream of normal ECGswhich are not reviewed. The diametr:caIly opposed viewsof Pordy and Pipberger, the former being in favour ofreview on every ECG, and the latter advocating nointerference from the physician/cardiologist because ofsuperior performance by the computer, cannot be com­pletely accep:ed. There need be no objection to havingan organisation run on the lines suggested by Caceres;where review is done at the receiving end of the inter­pretative statement.

We wish to thank the Provincial Administration of theCape Province and in particular the Department of HospitalServices for sponsoring this investigation.

REFERENCES

1. Caceres, C. A. (1972): Prog. Cardiovasc. Dis., 15, 25.2. Wartak, J. (1971): Compwers in ElecIrocardiography. Springfield.

Ill.: Charles C. Thomas.3. US Department of Health, Education and Welfare (undated): Com­

puters, Eleccrocardiography and Public Health (Public Health ServicePublication Nu. 1644). WashlIlgton, DC: US Govt Printer.

4. Caceres, C. A. and Hochberg, H. M. (1971): Computers in theSen';ce 0/ Clinical EleclTocardiography. (Roche Medical ElectronicsDivision.) Cranbury, N. J.: Hoffmann-La Roche.

5. Cudahy, M. J. (1973): Computer ECG Studies, 6th ed. Milwaukee.Wise.: Marquette Electronics.

6. Pordy, L., Jaffe, H. and Chesky, K. (1967): J. Mt Sinai Hosp.,24, 69.

7. Pordy, L. (1973): Personal communication.8. Bonner, R. E. (1973): Personal communication.9. Caceres, C. A. (1973): Personal communication.

10. Hu Kuang-Chi, Francis, D. B., Gau, G. T. and Smith, R. E.(1973): Proc. Mayo Clin., 48, 260.

11. Smith, R. E. (1973): Personal communication.12. Pipberger, H. V., Stallman, F. W. and Berson, A. S. (1962): Ann.

Intern. Med., 57, 776.13. Stallman, F. W. and Pipberger, H. V. (1961): Circulat. Res., 9, 1138.14. Pipberger, H. V. (1973): Personal communication.15. Wright, T. (1973): Personal communication.16. Pipberger, H. V. and Cornfield, J. (1973): Circulation, 47, 918.

Variant (Prinzmetal's) Form of Angina PectorisManifesting in Complicating Ventricular

ExtrasystolesL. SCHAMROTH,

SUMMARY

A case of the variant (Prinzmetal's) atypical form ofangina pectoris is presented. Secondary and primarychanges affecting the S-T segment and T wave arediscussed.

The features were also present, and indeed moremarked, in complicating ventricular extrasystoles, one ofwhich reflected the infarction pattern.

S. A/I'. Med. l., 48. 1146 (1974).

In 1959 Prinzmetal et alY focused attention on an unusualform of angina pectoris, which has been termed thevariant or atypical form of angina pectoris.

The distribution of the pain is identical with the classicform of angina pectoris, being substernal with radiationto the jaw and down the ulnar surfaces of the arms andbeing oppressive in character. Unlike the cla>:sic form ofangina pectoris, however, the pain frequently occurs

Baragwanath Hospital and University of tl!e Witwatersrand,Johannesburg

L. SCHAMROTH. :\f.D.. D.SC., F.R.C.P., F.R.. (S.AF.)

Cape Town.L H. LEVENSTEIN, l\f.B. CH.B., l\!.F.G.P. (S.A.)

-----Date received: 24 January 1974.

J. H. LEVENSTEIN

spontaneously and is not necessarily related to effort oremotion. The pain is usually severe and of longer duration.It usually presents with a series of attacks which tend tobe cyclical, recurring every few minutes with peaks ofremarkab!e constancy, and frequently at the same timeor times of each day. The waxing and waning periods ofchest pain are often of equal duration, unlike the typicalform of angina pectoris where the waning period is shorterand more abrupt than the waxing period. The attacksfrequently progress to myocardial infarction, and it isnoteworthy that the .severe angina pectoris frequentlydisappears dramatically after such an infarction. Thecondition is usua!.Iy associated with a grave prognosis.Recent reports have indicated that the variant anginapectoris with the typical electrocardiographic changes mayalso be precipitated by effort.3

Electrocardi :Jgraphically, the variant form of anginapectoris has the fo~!owing characteristics. There is transientelevation of the SoT ~egment in leads orientated to theapex and the adjacent anteroseptal region, viz. leads V2to V6, particular:y leads V4 and VS. Occasiona]:y. andespecially with vertical hearts, the manifestation appearspart:cularly in standard leads n, III and lead AVF.The associated T waves are usually upright. but may beinverted. When the T wave is upright. the elevated SoTsegment will have a concave-upward or upward slopingappearance. This manifestation is similar to the hyper­acute early injury phase of acute myocardial infarction.When the a,sociated T wave is inverted. the elevated SoT