British Heart Journal, I973, 35, 6I6-622.

Incidence and presentation of myocardial infarctionin an English community

L. J. Kinlen'

From the Department of the Regius Professor of Medicine, Radcliffe Infirmary, Oxford

An attempt was made to determine the incidence and presentation of myocardial infarction in a community of375,ooo in the Oxford area. Through local general practitioners and hospital records supplemented by theOxford Record Linkage Study and certificates of sickness incapacity, 357 patients aged under 70 werefoundand divided into four categories according to the extent and type of diagnostic support. All patients or, ifdead, their relatives were interviewed soon after the attack.

The incidence of myocardial infarction in the Oxford area was appreciably lower than thatfound by similarmethods in Edinburgh, confirming the difference implied by mortality rates in these two areas. The mortalitypattern was distinctive, the likelihood of death being highest in the first few hours and quickly declining tomuch lower levels. This pattern was reflected in the high proportion offatal attacks which were medicallyunattended (65%), outside hospital (63%1), or unwitnessed and discovered after an appreciable delay (24%).Consequently, the clinician in hospital has a very limited view of myocardial infarction.

Epidemiological surveys have been used widely tostudy the aetiology of ischaemic heart disease, butfew attempts have been made to assess the incidenceof myocardial infarction in a whole community.Most clinical studies of this condition have beencarried out in hospital and take no account of casesmanaged at home or those presenting as sudden andunexpected death outside hospital. Only a studybased on a whole population will include all thesegroups and permit an examination of those factorsthat determine which cases reach hospital. It is onlywith this knowledge that the value of hospital treat-ment of myocardial infarction can be assessed. Thisapproach is also relevant to the organization andextension of resuscitation services.

MethodWith these aims in mind, a study of the incidence andpresentation of myocardial infarction was undertaken inthe Oxford area in I966-i967. The study area comprisedthe North Berkshire municipal boroughs of Abingdon,Wantage, and Wallingford, together with their associatedrural districts, and Oxfordshire except for Henley andBanbury and their rural districts. This area covered 785square miles and involved a population of about 375,000people under the age of 70.

Received I5 December 1972.1 Formerly of the Oxford Record Linkage Study and theNuffield Department of Clinical Medicine, Oxford.

Notification and ascertainment An attempt wasmade to ascertain every diagnosed case of myocardialinfarction in persons under the age of 70 in theabove area. Cases were ascertained in one or more of thefollowing ways.

i) General practitioners All but one of the I36 generalpractitioners practising in the area agreed to notify anycase of probable myocardial infarction, including suddendeath, in their patients under 70 years of age. Cases werenotified mainly by telephone and an automatic answeringdevice was used outside office hours. Co-operation wasencouraged by a fee of sop, which was paid in each caseirrespective of the final diagnosis. Regular progress re-ports were sent to the doctors co-operating in the study.

ii) Hospital admissions Only one general hospital in thearea, the Radcliffe Infirmary, normally accepts patientsfor emergency medical care and all admissions to thishospital were screened daily for possible cases of myo-cardial infarction. Contact was also maintained withcottage hospitals in the area so that the few cases ad-mitted there would not be missed.

iii) Other medical practitioners All the consultantphysicians in the area agreed to notify cases seen in pri-vate or domiciliary practice and industrial medicalofficers also co-operated.

iv) Death certificates As the area covered by the surveywas within the catchment area of the Oxford RecordLinkage Study (Acheson, I964), it was possible to

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Incidence and presentation of myocardial infarction in an English community 617

examine death certificates in respect of all deaths occur-ring during the period.

v) Coroners' cases The coroners and the forensicpathologists in the area co-operated and copies of allrelevant postmortem reports were received routinely.

vi) Other necropsies The reports of all hospital necrop-sies in the area were examined regularly.

vii) Electrocardiograms All electrocardiograms recordedin the Radcliffe Infirmary, together with the smallnumber taken by general practitioners and sent there forreporting, were examined to try to pick up additionalcases.

viii) Serun enzyme estimations All requests for serumtransaminase estimations were screened in the bio-chemistry department of the Radcliffe Infirmary, whichalso provides a service for the surrounding area.

ix) Certificates of incapacity The Ministry of SocialSecurity screened first certificates of incapacity for diag-noses suggestive of myocardial infarction.

The fact that many cases were found independentlyfrom several different sources provided a measure of theco-operation of the participants. Only one case notalready ascertained from another source was uncoveredby the screening of certificates of incapacity.

Procedure Patients found by one or more of theabove methods who were still living and who satisfiedthe diagnostic criteria were interviewed. A standardform was completed incorporating identifying details,diagnostic data, and details both of previous health andof the recent episode, including the timing of variousevents. Patients treated at home by their general prac-titioners were visited within a short time of notification,an electrocardiogram was recorded, and a blood speci-men collected for enzyme estimations. In cases of death,permission was sought from the general practitionerconcerned to approach the relatives for information.

Diagnostic criteria The electrocardiographic cri-teria for the diagnosis of recent myocardial infarctionwere taken from World Health Organization (1959).Unfortunately, however, these criteria were designedfor screening populations for evidence of previous in-farction, both recent and of long standing, and werefound to have several shortcomings in the present con-text. Thus, for example, no opportunity was allowed forassociated enzyme changes to influence the diagnosis.Even with the provision for raised enzyme levels, theseelectrocardiographic patterns were quickly found to betoo rigid and the descriptions somewhat ambiguous. Anadditional electrocardiographic category was thereforeformulated to include bundle-branch block or certainpatterns consistent with subendocardial infarction, pro-vided the clinical picture and the serum enzyme levelsupported the diagnosis. A group studying the incidenceof myocardial infarction in Edinburgh encountered the

same difficulties and added a similar category to theircriteria (A. Armstrong, 1967, personal communication).Cases were accepted if they fell into one of the followingcategories which differ in the degree of ante- or post-mortem support.

i) Any case with raised serum enzyme levels (as definedbelow) and any of the electrocardiographic abnormalities(a)-(o) described by the World Health Organization(I959); any case with raised enzyme levels and an electro-cardiogram showing T wave inversion in leads I or aVL,bundle-branch block, or ST depression. Only cases withserial electrocardiographic abnormalities of an injurycurrent pattern were acceptable in the absence of enzymechanges.2) Any case with a recent coronary thrombosis or recentmyocardial necrosis found at necropsy, if not includedin the previous category.3) Any case not included in the first category in whichdeath was sudden and a necropsy showed only long-standing changes of coronary disease (coronary atheromaor myocardial fibrosis) but no other cause for death.4) Any case not included in the first category in whichdeath was sudden and attributed (without a necropsy) toischaemic heart disease.

Cases in the last three categories are by definitionfatal, but only a proportion in the first group was fatal.All patients in the first group were seen by a doctor butwithin the other categories (2-4) a distinction was madebetween medically attended and unattended deaths,the latter being defined as cases where the patient wasnot seen by a doctor during life after the onset of theattack.

All electrocardiograms from patients notified to thestudy or admitted to hospital with suspected myocardialinfarction were classified independently by two obser-vers. Where there was disagreement a third observerarbitrated but only 7 cases gained admission to the studyas a result of his casting vote.

Serum enzyme levels The following were regardedas raised: a serum aspartate aminotransferase level ofover 40 Sigma Frankel units per ml, a lactic dehydro-genase level of over 225 mIU per ml (by the Wroblewski-La Due method), or a hydroxybutyric dehydrogenaselevel of over 125 mIU per ml (by the modified Wroblew-ski-La Due method).

ResultsTable i shows for each sex separately and for bothsexes together the numbers of patients ascertainedwho experienced at least one attack of myocardialinfarction. Cases have been separated into fourcategories according to the evidence on which thediagnosis was based. A full medical history andclinical examination, together with electrocardio-gram and serum enzyme support, were obtained for20I episodes of myocardial infarction experiencedby I94 of the 222 patients who were seen by a doctorat least once in the attack.

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6I8 L. J. Kinlen

TABLE i Number of persons (attended and unattended) with myocardial infarction, by sex and type ofdiagnostic support

Type of evidence Attended cases Unattended cases Total

M F M F M F Both sexes

I) With electrocardiographic and enzyme support 14I 37 o 0 I41 37 I782) Without electrocardiographic and enzyme support:

2a) Recent thrombosis or infarction found at necropsy I2 3 53 9 65 12 772b) Long-standing changes only found at necropsy 4 0 25 6 29 6 352c) Certified without necropsy 20 7 33 I2 53 I9 72

Total I77 47 III 27 288 74 362

Presentation of myocardial infarction Thisis split into those cases who were attended and thosewho were not.

Attended cases The principal symptoms describedby I94 patients in 20i confirmed attacks of myo-cardial infarction are shown in Table 2. This in-formation was elicited at a standard interview. Infour-fifths of the episodes chest or epigastric pain(usually lasting for more than half an hour) was thepredominant feature. In two-thirds of the episodesthe pain radiated to one or more of the followingsites: neck, jaw, arms, and fingers. Pain sometimesoccurred in unusual sites. For example, in two in-stances the pain began in the back of the neck andoccipital region, while in three others pain radiatedthere from the chest. In i6 cases (8%) there wasradiation to the back.

Only one-fifth of patients described their chestpain as crushing, constricting, or vice-like, and, in-deed, burning was a more frequently used adjective.More often, however, the pain was reported as being'like indigestion' and antacids were often takenbefore calling a doctor, even by some patients witha previous history of proven peptic ulceration or byothers with a previous myocardial infarction. Thefeeling was often stressed that if only eructationwere possible the discomfort would be relieved.Others reported the wish that they could 'open theirchests' to relieve the intense feeling of pressurewhich seemed to be exerted outwards from within

TABLE 2 Predominant symptom in attended cases ofacute myocardial infarction

Symptom No. %

Pain in chest or epigastrium I76 8I-6Dyspnoea 7 3.5Syncope or collapse I6 8-oOther symptoms 2 I-0

Total episodes in 194 patients 20I

and not from outside the chest. Symptoms such asnausea, flatulence, vomiting, and diarrhoea werepresent in more than half the cases and encouragedthe hope or belief that the pain was alimentary inorigin. Sweating was reported in 63 per cent ofcases and fear admitted in 33 per cent. Yawningand hiccups were occasionally mentioned.

Occasionally pain referred to the arms was par-tially relieved by allowing the arms to hang loosely,or in other cases by pulling with both hands on afixed object. Several patients gained some relief byresting on their hands and knees.

In 69 per cent of the episodes, the attack began athome, in 8 per cent at work, in 14 per cent out ofdoors, and 9 per cent in hospital. Of those in hospi-tal, about half followed an admission on account ofsuspected myocardial infarction or because of in-creasing angina. Physical exertion is difficult toquantify in a study of this sort, but it is noteworthythat only 4 of the I94 patients were engaged in heavyexertion immediately before or at the time of theattack. Only one attack began during sexual inter-course and one during the performance of an exer-cise tolerance test.

Medically unattended cases There were I40 patientswho died before being seen by a doctor after theonset of the attack, of whom 5 had experienced aproven myocardial infarction more than one monthpreviously during the study period. Of the deathsin these medically unattended cases, 60 per centwere wimessed, in I5 per cent the deceased wasfound within minutes of death, while in 25 per centof cases the body was found after an appreciabledelay ranging from one hour to three days. Theplaces of occurrence of these sudden deaths werestrikingly similar to the location of patients at theonset of attended cases of myocardial infarctionreferred to above, and 64 per cent occurred at home,i i per cent at work, IS per cent out of doors, and 9per cent in hospital. Thirty per cent of these deathsoccurred while the patient was in bed. Three men

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Incidence and presentation of myocardial infarction in an English community 6I9

died during or immediately after sexual intercourse,while one patient died driving a car.

Information about symptoms preceding death inthese cases was necessarily indirect and was mainlyobtained from relatives. In most cases where thepatient was accompanied there was evidence ofchest or epigastric pain within a few hours of death,though sometimes this was only indicated by thepatient holding his chest.

Prodromal symptoms of myocardial infarction Table3 shows that in both attended and unattended cases,chest or epigastric pain occurred in the previousmonth in more than half of all cases. The frequencyof premonitory pain in the unattended group isprobably an underestimate due to the source of thedata. In 49 per cent of attended cases and 33 percent of unattended sudden deaths, the pain eitherbegan in the previous month or changed signifi-cantly in severity or frequency in this period.

It was common for wives of men who had diedsuddenly to describe spontaneously an increase intiredness or progressive loss of energy in the weeksor months before death. This applied to 4I per centof such cases (Table 3) while in over 20 per cent arecent change in appearance was noted. This wasvariously described as looking older, drawn,pinched, grey, or pale.

Characteristics of patients with myocardialinfarction In about I7 per cent of cases bothof attended proven myocardial infarction and un-attended sudden deaths, there was a previous historyof proven myocardial infarction. The frequency of adiagnosis of previous angina and high blood pressurereported by the patient is shown in Table 4. Adiagnosis of angina was accepted ifmade by a doctoror if chest pain was characteristically related toexertion and relieved by rest.

TABLE 3 Symptoms in month before myocardialinfarction or unattended death

Myocardial Unattendedinfarction death

No. % No. %

Onset of pain 46 23.7 26 i8-6Significant change in

previous pain 49 25-3 20 14-3Previous pain unchanged 33 I7.O 32 22-9No pain 5I 26-3 44 314Tiredness 38 I9-6 57 40°7Dyspnoea 37 I9-I 30 2I-4Change in appearance 5 2-6 30 2I.4

Total patients 194 140

TABLE 4 Frequency of known coronary heart diseaseand 'high blood pressure' in patients with myocardialinfarction and unattended death

Myocardial Unattendedinfarction death

No. % No. %

Angina 85 43-8 45 32-IDefinite or probable

myocardial infarction 37 I91I 28 20-0High blood pressure 59 30°4 35 25-0

Total patients 194 140

Of the I94 attended patients with proven myo-cardial infarction, 6 (3%) gave a history of gout, IO(5%) of diabetes, while 3 (Ip5%) had proven hyper-cholesterolaemia under treatment. Of unattendedsudden deaths, I5 (8%) had diabetes and i patienthad known hypercholesterolaemia. Of the womenin the study, three-quarters had not menstruated forIO years or more, and only 3 women had had amenstrual period within 2 months of the attack. In6 cases, menstruation had ceased as a result ofhysterectomy.

Incidence Table 5 shows the number of cases ofmyocardial infarction in men by age and type ofcase as ascertained during the 9 months of the study,together with the estimated total annual incidencerates. The corresponding data for women are givenin Table 6. It will be noted that only in about halfof all cases was the diagnosis confirmed during lifeby electrocardiographic and serum enzyme changes.Among the remaining (all fatal) cases, the diagnosiswas often unsupported by any specific findings sincenecropsy was either not performed or showed norecent myocardial necrosis or coronary thrombosis.In such cases the diagnosis was based on a historyof chest pain or the manner of death, in the absenceof other evident cause. The validity of this practiceis discussed later in this paper. Incidence increasedconsiderably with age and was appreciably greaterin men than in women.

Mortality pattern in myocardial infarction Itcan be seen from Table i that the confirmation byelectrocardiogram or enzyme changes in only halfof the cases of myocardial infarction is largely dueto the large proportion of deaths (64 8%) whichoccurred before a doctor reached the patient. Ob-viously, these investigations are only possible inliving patients. What determines whether a patientwith acute myocardial infarction is seen by a doctorduring life ? Two relevant factors are the promptness

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TABLE 5 Number of cases and incidence of myocardial infarction, by age, in the Oxford area: men

Age Confirmed Presumed Total (rate per 0OOO- ~~~~~peryear)

Electrocardiogram Necropsy Only long-standing coronary Other deathsand enzymes disease found at necropsy (no necropsy)

30-39 5 2 I 0 8 (0o4)40-49 24 I3 5 5 47 (2 7)50-59 58 I9 9 I3 99 (5*7)60-69 54 3I I4 35 I34 (I30)

Total I4I 65 29 53 288 (4p5)

TABLE 6 Number of cases and incidence of myocardial infarction, by age, in the Oxford area: women

Confirmed Presumed Total (rate per zoooAge per year)

Electrocardiogram Necropsy Only long-standing coronary Other deathsand enzymes disease found at necropsy (no necropsy)

30-39 0 0 0 0 0 0

40-49 4 I O 0 5 (0o2)50-59 9 4 3 2 I8 (Ito)60-69 24 7 3 I7 5I (3 9)

Total 37 12 6 I9 74 (I.I)

of patients in seeking medical help and that of doc-tors and other medical services in responding. Themost important factor, however, is the frequentsupervention of death soon after the apparent onsetof the attack, as shown in the Fig. This shows thepercentage distribution of patients who died withinone month of the attack at various intervals afterthe onset of symptoms, though an important qualifi-cation needs to be made in this connexion. In thecases where death occurred before a doctor couldattempt to determine the time of onset of symptoms,the approximate hour of onset could only be inferredfrom the highly variable testimony of relatives. Ifthe onset in unattended cases of sudden death istaken to be the time these patients first reportedtroublesome symptoms in the I2 hours before theircollapse, halfofall deaths in the first month occurredwithin an hour of the onset (curve A). Curve Bshows the distribution of deaths when the onset isdefined as the time of collapse or when incapacitatingsymptoms developed, according to which 64 percent of all deaths occurred in the first hour. Theonset in unattended fatal attacks was taken (as inthe surviving attended cases) as being the timethose symptoms began which prompted the call tothe doctor. The distribution of these cases is shownin curve C.

DiscussionIncidence This study represented the first attemptto assess the overall incidence of myocardial infarc-

tion (including unattended deaths) in a whole com-munity in which the diagnosis in home treated caseswas placed on a firm basis comparable with thatmore usually applied in hospital. Shortly after itwas begun, a somewhat similar project was mountedin Edinburgh though not all general practices inthe city participated in the comprehensive part ofthe study (Armstrong et al., 1972). Before the Ox-

100 All cases. Distributedby definition of

90- onset A and B (see text)------ Medically attended

80 - cases only

370 - B

| 60 /

X50.- /,o /'00 40 -

1J30- ,,"

20 -

10

001 05 1 2 4 8 3hr hr hr hr hr hr day days wk mthInterval from onset to deoth (log scale)

FIGURE

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Incidence and presentation of myocardial infarction in an English community 62I

ford study, only 4 total incidence studies in thegeneral population had been reported, 3 in Scan-dinavia - in Malmo, Sweden (Bj6rck, Blomqvist,and Sievers, I959; Sievers, I963), in Oslo (Westlundand Hougen, I956, I96I), and in Denmark (Mos-bech and Dreyer, I966), while a fourth was in NorthDakota, U.S.A. (Painter et al., I960). However,these differed in design and diagnostic criteria fromthe present study. Thus the Scandinavian studiesdid not include home-treated cases (unless fatal),the diagnostic criteria in the Danish study (whichcovered only the months March and April, I963)were not standardized, and the Swedish study tookno account of serum enzyme changes. Cases in thelatter study with possibly long-standing electro-cardiographic abnormalities accompanied by 'un-usually severe anginal pain' were accepted. Simi-larly, the Oslo survey included cases with theresidual changes of old infarction if these were firstnoted during the study period. The Dakota studywas carried out in a relatively small population usingdiagnostic criteria which included coronary in-sufficiency. A five-year incidence study by Mc-Whinney (I968) in a group practice in Stratford-upon-Avon was limited by the population beingsmall (8000) and representing only part of thattown.

Unlike large-scale prospective studies such asthat in Framingham, incidence studies of the presenttype provide no information on aetiology but givedata which may be helpful for the planning of medi-cal services. In addition, if carried out in differentparts of the country, studies of this sort may confirmor refute the suggestion provided by death rates thatthere may be interregional variation in the incidenceor fatality of the disease. Thus death rates forarteriosclerotic heart disease in Oxford are amongthe lowest in the United Kingdom (Registrar-General, I970), whereas the rate in Scotland is muchhigher. Though in theory this difference could beexplained by a higher fatality rate in Scotland, thepresent results suggest that it may be due at leastin part to a higher incidence in that country. Theannual incidence of myocardial infarction in theOxford area was 4.5 per Iooo men aged under 70in contrast with a figure of 8 4 found by similarmethods in Edinburgh (Armstrong et al., I972; B.Duncan, 1972, personal communication).

Diagnostic criteria It is clear that the more re-stricted the diagnostic criteria, the lower will be theestimated incidence rate, and vice versa. One of thedistinctive features of myocardial infarction is thatit may present with death, or at least cause deathso quickly that there is no time to substantiate the

diagnosis during life. Adherence exclusively to ante-mortem criteria would exclude this important andconsiderable group of cases. Even the inclusion ofall cases proven at necropsy, however, still leaves asubstantial group of cases in which necropsy was notperformed or in which no evidence of thrombosis orinfarction was found at necropsy. These negativefindings raise a more basic problem. Absence ofmyocardial necrosis may be due to the superventionof a fatal arrhythmia before the macroscopicalchanges ofinfarction have developed, which may takeup to 3 days (Mallory, White, and Salcedo-Salgar,I939; Lodge-Patch, 195I); failure to find a recentthrombosis may simply be due to the limited natureof the search. When neither a thrombosis normuscle necrosis is found, however, the justificationfor attributing death to an unobserved arrhythmiaprecipitated by an undetected thrombosis cannotbe taken for granted. Coronary atheroma is anexpected finding in adults in Western society, whilemyocardial fibrosis is not uncommon. Moreover, insome reported cases of sudden death attributed tomyocardial ischaemia, the cardiac findings may beindistinguishable from those found in cases ofaccidental death (Mason, I963; Rigal, Lovell, andTownsend, I960). In this study there were 35 casesof this type, all of which were attributed by coroners'pathologists to myocardial ischaemia, which untilrecently was allocated to the same code (420o i) asfrank myocardial infarction. In this group the meancardiac weight, the degree of myocardial fibrosis,and the frequency of angina and hypertension werenot significantly different from proven cases, sug-gesting that this certification practice is on the wholecorrect. Nevertheless, in any individual case thediagnosis is unproven and may be wrong.

Identification of onset The definition of theonset is relevant to any discussion of prodromalsymptoms, since what is regarded as the onset willnecessarily demarcate the premonitory symptomsfrom those of the attack itself. In this study theonset was regarded in interviewed cases as the timethose symptoms began which prompted the patientto seek help. In some cases a later sudden increasein the chest pain or a similar pain the previous daymight with equal validity be considered as the onseteven though the patient had not called a doctor.There is, however, no accurate means of determiningthe time of onset in myocardial infarction, or indeedany means of establishing the precise relation be-tween pathology and symptoms. Investigations pro-vide little help in this matter and even the shape ofthe curve of serial enzyme estimations cannot beused reliably to identify the time when the infarct

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occurred (Whitby, i968). Similarly, electrocardio-grams may be normal in the early stages, even justbefore a cardiac arrest (Lawrie et al., i968). Necrop-sies are even more unsatisfactory and conventionaltechniques may be unable to demonstrate any recentchange. Moreover, more refined studies are greatlyaffected by the interval between death and fixingthe tissue. The difficulties in defining the onsetwere among the reasons which made Lown (i968)reluctant to give data on the intervals between onsetand admission to his unit. In spite of this un-certainty, there is no doubt that the early mortalityof myocardial infarction in relation to the onset ofsymptoms is considerable.

Prodromal symptoms Premonitory chest painsare well known before many attacks of myocardialinfarction and were frequent in the present series.Their predictive value, however, is difficult toevaluate because they often only come to noticewhen reported by patients later presenting withestablished infarcts. Consequently there is no meansof knowing the prevalence of symptoms of this sortwhich are not followed by infarction.

Still more difficult to evaluate is the tiredness re-ported by relatives in the weeks or months beforedeath in 40 per cent of sudden and unexpecteddeaths. It is possible that the judgment of theseobservers would often be clouded by their recentbereavement. Nevertheless, the extent of the tired-ness described, sometimes causing the person to fallasleep at meals, could be striking. Oliver (i966) hasreported that abnormal tiredness quite often pre-cedes the development of overt features of ischaemicheart disease, but most of the standard textbooks oncardiology make no mention of this symptom.

I am indebted to Professor E. D. Acheson, who sug-gested and supervised the study and was also mosthelpful in his criticism of this manuscript. I am also verygrateful to many others in the Oxford area who made thisstudy possible: the general practitioners, physicians,pathologists, medical officers of health, and industrialmedical officers; the chief ambulance officers of the area,the biochemistry department of the Radcliffe Infirmary,the staff of the Oxford Record Linkage Study, and toDr. P. Dandona who reviewed all the electrocardio-grams. The work was carried out in the Oxford RecordLinkage Study and the Nuffield Department of ClinicalMedicine with financial support from the Departmentof Health and Social Security and the Nuffield ProvincialHospitals Trust.

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British J'ournal of Preventive and Social Medicine, I8, 8.Armstrong, A., Duncan, B., Oliver, M. F., Julian, D. G.,

Donald, K. W., Fulton, M., Lutz, W., and Morrison, S. L.(I972). Natural history of acute coronary heart attacks. Acommunity study. British Heart3journal, 34, 67.

Bjorck, G., Blomqvist, G., and Sievers, J. (I959). Studies onmyocardial infarction in Malmo I935 tO 1954: IV. Myo-cardial infarcts in the hospital in relation to coronary heartdisease in the population. Acta Medica Scandinavica, 165,I.

Lawrie, D. M., Higgins, M. R., Godman, M. J., Oliver, M.F., Julian, D. G., and Donald, K. W. (I968). Ventricularfibrillation complicating acute myocardial infarction.Lancet, 2, 523.

Lodge-Patch, I. (I95i). The ageing of cardiac infarcts, and itsinfluence on cardiac rupture. British Heart_Journal, 13, 37.

Lown, B. (1968). Coronary care units: current policies andresults. In Acute Myocardial Infarction, p. 20. Ed. by D. G.Julian and M. F. Oliver. Livingstone, Edinburgh.

Mason, J. K. (I963). Asymptomatic disease of coronaryarteries in young men. British Medical3Journal, 2, I234.

McWhinney, I. R. (I968). Incidence of ischaemic heart-disease in a county-town group practice. Lancet, 2, 342.

Mallory, G. K., White, P. D., and Salcedo-Salgar, J. (I939).The speed of healing of myocardial infarction. AmericanHeart Journal, i8, 647.

Mosbech, J., and Dreyer, K. (I966). Coronary occlusion inDenmark: morbidity and mortality. Acta Medica Scan-dinavica, I80, 429.

Oliver, M. F. (I966). Presymptomatic diagnosis of precociousischaemic heart disease. Symposium of 5th World Congressof Cardiology, p. 377. Acta Cardiologica, Brussels.

Painter, R. C., Ralston, L. S., Fawcett, R. M., Zukel, W. J.,and Lewis, R. H. (I960). Short-term study of coronaryheart disease in a North Dakota community. J'ournal of theAmerican Medical Association, 172, I26I.

Registrar-General (1970). Decennial Supplement, England andWales, I96I. Area Mortality Tables. H.M.S.O., London.

Rigal, R. D., Lovell, F. W., and Townsend, F. M. (I960).Pathologic findings in the cardiovascular systems of mili-tary flying personnel. American_Journal of Cardiology, 6, I9.

Sievers, J. (I963). Myocardial infarction. Acta Medica Scan-dinavica, Suppl. 406.

Westlund, K., and Hougen, A. (I956). Myocardial infarction:an epidemiologic and prognostic study of patients fromfive departments of internal medicine in Oslo, I935-I949.Acta Medica Scandinavica, Suppl. 3I5.

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Whitby, G. (I968). The enzyme response of the myocardiumto ischaemia and infarction. In Acute Myocardial Infarction,p. 272. Ed. by D. G. Julian and M. F. Oliver. Livingstone,Edinburgh.

World Health Organization (1959). Hypertension and coron-ary heart disease: classification and criteria for epidemio-logical studies. World Health Organization. TechnicalReport Series, No. I68.

Requests for reprints to Dr. L. J. Kinlen, Departmentof the Regius Professor of Medicine, Radcliffe Infirmary,Oxford OX2 6HE.

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