br heartj electrocardiogram relevance to · myocardial infarction early administration of...

Br HeartJ 1993;70:219-225

Electrocardiogram interpretation in generalpractice: relevance to prehospital thrombolysis

W A McCrea, S Saltissi

AbstractObjective-To assess, in the context oftheir possible role in prehospital throm-bolysis, the ability of general practition-ers to recognise acute transmuralmyocardial ischaemia/infarction on anelectrocardiogram.Design-150 doctors (every fifth name)were selected from the alphabetical listof 750 on Merseyside general practitionerregister and without prior warning wereasked to interpret a series of six 12 leadelectrocardiograms. Three of theseshowed acute transmural ischaemialinfarction, one was normal, and twoshowed non-acute abnormalities. Detailsof doctors' ages, postgraduate traiming,and clinical practice were sought.Setting-General practitioners' surgeriesand postgraduate centres within theMerseyside area.Participants-106 general practitioners(mean age 45 years) agreed to partici-pate.Main outcome measure-Accuracy ofgeneral practitioners' interpretations ofthe six electrocardiograms.Results-82% of general practitionerscorrectly recognised a normal electro-cardiogram. Recognition of acute abnor-malities was less reliable. Between 33%and 61% correctly identified acute trans-mural ischaemia/infarction depending onthe specific trace presented. Accuratelocalisation of the site of the infarct wasachieved only by between 8% and 30% ofparticipants, while between 22% and 25%correctly interpreted non-acute abnor-malities. Neither routine use of electro-cardiography nor postgraduate hospitalexperience in general medicine was asso-ciated with significantly greater exper-tise.Conclusion-The current level of profi-ciency of a sample of general practition-ers in the Merseyside area in recognisingacute transmural ischaemialinfarctionon an electrocardiogram suggests thatrefresher training is needed if generalpractitioners are to give prehospitalthrombolysis.

(Br Heart J 1993;70:219-225)

It is now generally accepted that in acutemyocardial infarction early administration ofan intravenous thrombolytic agent is effective

in reducing mortality. 1-3 Furthermore, it hasbeen demonstrated that the earlier thrombo-lysis is attempted, the greater is the benefitattained."When acute myocardial infarction occurs

outside hospital there is a delay between theonset of symptoms and their assessment andtreatment by a medical practitioner.78 In theUnited Kingdom patients and their relativestake an average of up to one and a half hoursto alert medical and emergency services,8 andthe median time between the onset of symp-toms and admission to a hospital bed is gen-erally four to six hours.8 Currently, mostmedical prehospital coronary care is given bygeneral practitioners. Therefore, if thrombo-lysis is to be effective, it may well be neces-sary for this treatment to be initiated outsidehospital by the attending family doctor.

Recommendations as to which patientswith chest pain should receive thrombolyticagents have varied widely between the differ-ent reported studies, some rely on the clinicalsituation29 while most require additionalelectrocardiographic criteria of infarction.1 36Thus the ability of general practitioners tointerpret accurately electrocardiogram trac-ings may become increasingly important.However, many general practitioners quali-fied when there was little emphasis on or test-ing of electrocardiogram interpretation, andbecause most general practitioners do notregularly interpret electrocardiograms,'01'their skill at interpretation is likely to beunderdeveloped.We report the results of our study of the

current ability of a sample of Merseysidegeneral practitioners to detect acute trans-mural ischaemia/infarction on an electro-cardiogram and whether these results indicatethat general practitioners require refreshercourses in electrocardiogram interpretation.

MethodsThere are approximately 750 general practi-tioners registered in the Merseyside area. Weselected every fifth name in alphabetical orderon that register and invited these 150 familydoctors to attend one of a series of four clini-cal meetings held in different parts of theMerseyside region over a 10 day period. Allwe told these doctors was that these symposiawould entail discussions on the role of thegeneral practitioner in early thrombolysis inacute myocardial infarction. Doctors whoattended these meetings were requested,without any warning, to interpret a series ofsix 12 lead electrocardiograms (figs 1-6).

Department ofCardiology, RoyalLiverpool Hospital,LiverpoolW A McCreaS SaltissiCorrespondence to:Dr S Saltissi,Department of Cardiology,Royal Liverpool Hospital,Liverpool L7 8XP.Accepted for publication10 February 1993

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Figure 2 Electrocardiogram demonstrating acute inferior myocardial ischaemialinfarction.

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Figure 4 Electrocardiogram demonstrating anterior myocardial ischaemialinfarction with right bundle branch block.(Reprinted with the permission ofDrM C Colquhoun and Syntex Pharmaceuticals Limited.)

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Figure 5 Electrocardiogram demonstrating left bundle branch block.

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Figure 6 Electrocardiogram demonstrating left ventricular hypertrophy and strain pattern.

Three of the six electrocardiograms showedchanges of acute transmural ischaemia/infarction, one showed left bundle branchblock, one left ventricular hypertrophy andstrain pattern, and one was normal.

Participants were informed that none of

Table 1 General practitioners' classification of electrocardiograms as either normal orabnormal

Don't know Abnormal NormalECG diagnosis (%) (%) (%)Normal 5 (5) 14 (13) 87 (82)

Myocardial infarction:Acute inferior 5 (5) 101 (95) 0Anteroseptal 7 (7) 88 (83) 11 (10)Anterior with right bundle branch block 8 (8) 94 (88) 4 (4)

Non-acute abnormnality:Left bundle branch block 5 (5) 85 (80) 16 (15)Left ventricular hypertrophy and strain 6 (6) 78 (74) 22 (20)

Table 2 Ability ofgeneral practitioners to detect myocardial infarction and offer correctdiagnosis

MI present No MI present CorrectECG diagnosis (%/) (%) diagnosis (%/)

Normnal 1 (1) 100 (94) 87 (82)

Myocardial infarction:Acute inferior 65 (61) 36 (34) 32 (30)Anteroseptal 48 (45) 51 (48) 29 (27)Anterior with right bundle branch block 35 (33) 63 (59) 9 (8)

Non-acute abnormnality:Left bundle branch block 4 (4) 97 (91) 27 (25)Left ventricular hypertrophy and atrain 10 (9) 90 (85) 23 (22)

the electrocardiograms showed arrhythmiasbut no clinical details relating to the electro-

cardiograph tracings were divulged. Doctors

were asked to indicate on an answer sheet

whether each electrocardiogram was normal

or abnormal and if they considered the trace

to be abnormal they were encouraged to

make a specific diagnosis. Doctors who were

unable to state any of the above entered

"Don't know" on their answer sheets. An

answer of "myocardial infarction" was

accepted as correct for the three electrocar-

diograms showing acute transmural ischaemia

(coved ST elevation) or typical acute myocar-

dial infarct patterns with Q waves.

Participating practitioners were asked not

to discuss their diagnoses with colleagues and

to complete a questionnaire about age, years

in general practice, postgraduate training, and

routine use of electrocardiography. The com-

pleted answer sheets and questionnaires were

then sealed in unmarked envelopes to pre-

serve anonymity. Doctors who were selected

for inclusion in this survey but who did not

attend the clinical meetings, were visited

(without notice) in their health centres during

surgery hours and invited to participate.

Those agreeing were shown the six electro-

cardiograms and asked to complete the

answer sheet and questionnaire, in the pres-

ence of one of the authors.

The x2 test, with Yates' correction, and a

significance level of 5% was used for statisti-

cal analysis.

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Electrocardiogram interpretation in general practice: relevance to prehospital thrombolysis

Table 3 Effect of six months of hospital training on ability ofgeneral practitioners todetect myocardial infarction (site not specified)

Training in medicine No training in medicine(n =51) (n =55)

ECG diagnosis MI present (%) MI present (%/o) p

Acute inferior MI 34 (67) 31 (57) NSAnteroseptal MI 22 (43) 26 (47) NSAnterior MI with right bundle branch

block 19 (37) 16 (29) NS

ECG, electrocardiogram; MI, myocardial infarction.

Table 4 Effect ofsix months of hospital training on ability ofgeneral practitionersaccurately to locate site of myocardial infarction (that is, offer correct diagnosis)

Training in medicine No training in medicineECG diagnosis (n = 51) (%) (n = 55) (%) p

Myocardial infarction:Acute inferior 15 (29) 17 (31) NSAnteroseptal 14 (27) 15 (27) NSAnterior with right bundle branch

block 5 (10) 4 (7) NS


Table 5 Effect of routine use of electrocardiography on ability ofgeneral practitioners todetect myocardial infarction (site not specified)

Routine use ofECG No routine use ofECGECG diagnosis (n = 31) (n = 75) p

Acute inferior MI 22 (71%) 43 (57%) NSAnteroseptal MI 15 (48%) 33 (44%) NSAnterior MI with right bundle branch

block 13 (42%) 22 (29%) NS


Table 6 Effect of routine use of electrocardiography on ability ofgeneral practitioners tooffer correct diagnosis

Routine use ofECG No routine use ofECGECG diagnosis (n = 31) (%) (n = 75) (%) p

Normal 28 (90) 59 (79) NS

Myocardial infarction:Acute inferior 12 (39) 20 (27) NSAnteroseptal 8 (26) 21 (28) NSAnterior with right bundle branch

block 2 (6) 7 (9) NS

Non-acute abnormality:Left bundle branch block 10 (32) 17 (23) NSLeft ventricular hypertrophy and strain 9 (29) 14 (19) NS

ECG, electrocardiogram.

Table 7 Effect of routine use of electrocardiography and six months of hospital trainingon ability ofgeneral practitioners to detect myocardial infarction (site not specified)

Routine use ofECG and No routine use ofECGtraining in medicine and no training in medicine

ECG diagnosis (n = 13) (%) (n = 37) (%) p

Myocardial infarction:Acute inferior 10 (77) 19 (51) NS

Anteroseptal 5 (38) 16 (43) NSAnterior with right bundle branch

block 8 (26) 12 (32) NS


ResultsOne hundred and six of the 150 doctorsselected for inclusion actually participated inthis survey (52 attended one of the fourclinical meetings and 54 were visited at theirsurgeries). Of the 44 doctors who did nottake part in this study, 30 were unavailable attime of visit (on leave or on a domiciliaryconsultation), 10 refused, and four hadretired or were dead. The mean age of partic-ipating doctors was 45 (range 28-74) andthey had been general practitioners for amean of 15 years (range 1-46). Fifty one(48%) had had at least six months of post-registration hospital training in general medi-cine before their entry into general practice,but only 31 (29%) claimed to carry routinelyor to have immediate access to an electrocar-diograph machine while on emergency calls.Most doctors correctly classified an

electrocardiogram as either normal (82%) orabnormal (range 74-95%) (table 1). Whenpressed to make a specific diagnosis (table 2),however, approximately half (range 34-59%)the respondents did not recognise evidence ofacute transmural ischaemia/infarction on anelectrocardiogram. Between 33% and 61%,depending on the specific trace presented,correctly identified such changes though only8-30% could accurately localise its site (table2). Respondents were least able to identifyanterior myocardial infarction in the presenceof right bundle branch block. None of therespondents gave a completely correctanswer, only 33% recognised an acute infarctpattern and only 8% localised it correctly(table 2).Very few of the 106 doctors diagnosed

myocardial infarction when it was not pre-sent, even when other electrocardiographicabnormalities were present (table 2). Whenshown an ECG demonstrating left bundlebranch block, only four (4%) doctors diag-nosed infarction and only 10 (9%) misinter-preted an ECG pattern of left ventricularhypertrophy and strain as showing changestypical of infarction (table 2). However, only22% of respondents (for left ventricularhypertrophy and strain) and only 25% (forleft bundle branch block) could correctlydiagnose these non-acute abnormalities(table 2).

Six months of post-registration hospitaltraining in general medicine neither signifi-cantly increased ability to recognise myocar-dial infarction on an electrocardiogram (table3) nor conferred greater diagnostic skill inaccurately locating the site of infarction com-pared with those doctors without such post-graduate experience (table 4). Similarly,doctors who claimed either routinely to carry,or to have immediate access to an electrocar-diograph machine while on emergency calls(that is, routine ECG users) did not showgreater expertise in identifying the presence ofinfarction on an electrocardiogram than theircolleagues who did not (table 5).

Similarly, neither localisation of infarctionnor the correct interpretation of non-acutelyabnormal electrocardiograms was signifi-

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Table 8 Effect of routine use of electrocardiography and six months of hospital trainingon ability ofgeneral practitioners to offer correct diagnosis

Routine use ofECG and No routine use ofECGtraining in medicine and no training in medicine

ECG diagnosis (n = 13) (%/) (n = 37) (%) p

Normal 11 (85) 31 (84) NSMyocardial infarction:

Acute inferior 5 (38) 10 (27) NSAnteroseptal 3 (23) 10 (27) NSAnterior with right bundle branch

block 1 (7) 3 (8) NS

Non-acute abnormality:Left bundle branch block 6 (46) 8 (22) NSLeft ventricular hypertrophy and

strain 4 (31) 3 (8) NS

ECG, electrocardiogram.

cantly better by routine users of electrocar-diograph machines than non-users (table 6).

Furthermore, when users of electrocardio-graph machines who also had experience inhospital medicine (n = 13) were comparedwith non-users with no such hospital training(n = 37), no significant difference was foundin ability either to detect acute transmuralmyocardial ischaemia/infarction (table 7) or

to offer the correct electrocardiogram diagno-sis (table 8).

DiscussionThe principal aim of this study was toassess whether a representative sample ofMerseyside general practitioners could accur-

ately identify electrocardiographic patternswhich, in the appropriate clinical setting,would help them to correctly use throm-bolytic therapy. The test electrocardiogramswere therefore deliberately chosen to includeexamples highly suggestive of acute trans-mural ischaemia/evolving infarction (covedST elevation with or without T wave

changes). Such electrocardiographic changeswould be expected to prompt the use ofthrombolytic agents (in the absence ofcontraindications) whereas recognition of theelectrocardiographic patterns of non-acuteabnormality (left bundle branch block andleft ventricular hypertrophy and strain) or

normality would support a decision to with-hold thrombolytics. The results showed thatthough most family doctors recognisedwhether or not an electrocardiogram was

abnormal, about half of them did not recog-nise changes on an electrocardiogram thatindicated myocardial infarction and only a

third of our respondents were proficient ininterpreting a non-acutely abnormal electro-cardiogram. Skill at electrocardiogram diag-nosis was not significantly greater in thosewith postgraduate hospital experience (atleast six months of general medicine) nor was

it improved by regular use of electrocardio-graphy or by a combination of these two

factors.It was not easy for the 150 doctors we

selected to opt out of the study because thosewho did not attend the clinical meetings were

subsequently approached individually in theirsurgeries. Approximately 70% of the sample(106 out of 150) eventually participated. We

expect that those who participated were likelyto be more proficient and/or interested thanthose who did not. So the observed resultswere probably an over rather than under esti-mate of the electrocardiograph interpretationskills of the sample.

In addition, participating doctors were notalerted beforehand that their ability to inter-pret electrocardiograph tracings was to beassessed and neither discussion nor groupconferring was possible because of closescrutiny by the authors. This contrasts withprevious studies of electrocardiogram inter-pretation in general practice that were per-formed without invigilation and which, bytheir nature, involved doctors who were nottruly representative of the general practitionerpopulation. Such factors may well accountfor the higher level of diagnostic expertisereported.'I 12

We consider that our results accuratelyreflect the current, average level of generalpractitioners' expertise in electrocardiograminterpretation within the Merseyside area andare thus applicable to the acute clinical situa-tion outside hospital.

Interpretation of electrocardiograms is nota skill that general practitioners are requiredto use regularly, nor is it usually taughtformally at post-graduate meetings so thelevels of skill that we found are expected andpredictable.A British Heart Foundation Working

Group report on the role of general practi-tioners in the management of patients withmyocardial infarction recommended that onlythose proficient in interpretation of electro-cardiograms should administer thrombolytictreatment.8 The results of our study suggestthat, at present, this would exclude mostfamily doctors. Furthermore, the workinggroup recommended that electrocardio-graphic evidence of infarction should besought by general practitioners before theydecided whether thrombolysis was needed.8However, our data indicate that manypatients with suspected acute myocardialinfarction who present with chest pain and acorroborative electrocardiogram might re-main unrecognised. This means that throm-bolysis in the community or after promptreferral to hospital will be delayed if its initia-tion depends on the recognition of electro-cardiographic changes of infarction.The British Heart Foundation Working

Group also recommended that educationalprogrammes in electrocardiogram interpreta-tion should be available to general practition-ers." It is worrying that we showed thatneither shortlived hospital training in generalmedicine nor routine (though probably infre-quent) use of electrocardiography conferredany greater ability to detect myocardialinfarction on an electrocardiogram. There-fore, it is questionable whether the simpleprovision of a circumscribed course in elec-trocardiogram interpretation will produce anylong-term improvement in the level of exper-tise among general practitioners. To achievethis would probably require prolonged tuition

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repeated at frequent intervals to maintainadequate standards.Our results indicate that at least half of the

general practitioners in the Merseyside arearequire such tuition, which would be expen-sive and time consuming. Similar educationalexercises are likely to be needed throughoutthe United Kingdom.

If proficiency at interpretation of an elec-trocardiogram by general practitioners is aprerequisite for thrombolytic administrationoutside hospital, then either expensive, con-tinuing educational programmes will need tobe initiated or for the foreseeable futurepatients with acute myocardial infarction willcontinue to be denied the proven benefits ofthrombolysis.

We thank Dr M C Colquhoun for his permission to repro-duce the electrocardiogram demonstrating anterior myocar-dial infarction in the presence of right bundle branch block(fig 4).

1 GISSI-Effectiveness of intravenous thrombolytic treat-ment in acute myocardial infarction. Lancet 1986;i:397-402.

2 ISIS-2 (Second International Study of Infarct Survival)Collaborative Group. Randomised trial of intravenousstreptokinase, oral aspirin, both, or neither among

17,187 cases of suspected acute myocardial infarction.ISIS-2. Lancet 1988;ii:349-60.

3 AIMS Trial Study Group. Effect of intravenous APSACon mortality after acute myocardial infarction: prelim-inary report of a placebo-controlled clinical trial. Lancet1988;i:545-9.

4 McNeill A, Cunningham S, Flannery D, Dalzell G,Wilson C, Tsoi E, et al. Pre-admission recombinanttissue plasminogen activator (abstr). Eur Heart J 1988;9(suppl I):214.

5 Koren G, Weiss AT, Hasin Y, Appelbaum D, Welber S,Rozenman Y, et al. Prevention of myocardial damage inacute myocardial ischaemia by early treatment withintravenous streptokinase. N Engl J Med 1985;313:1384-9.

6 Van de Werf F, Arnold AER, for the European StudyGroup for recombinant tissue type plasminogen activa-tor. BMJ' 1988;297:1374-9.

7 Rawles JM, Haites NE. Patient and general practitionerdelays in acute myocardial infarction. BMJ 1988;296:882-4.

8 Report of a British Heart Foundation Working Group.Role of the general practitioner in managing patientswith myocardial infarction: impact of thrombolytictreatment. BMJ 1989;299:555-7.

9 Wilcox RG, Olsson CG, Skene AM, von der Lippe G,Jensen G, Hampton JR. Trial of tissue plasminogenactivator for mortality reduction in acute myocardialinfarction. Anglo-Scandinavian study of early thrombo-lysis (ASSET). Lancet 1988;ii:525-30.

10 Colquhoun MC. General practitioners' use of electro-cardiography: relevance to early thrombolytic treatment.BMJ 1989;299:433.

11 Macallan DC, Bell JA, Braddick M, Endersby K,Rizzo-Naudi J. The electrocardiogram in general prac-tice: its use and its interpretation. J R Soc Med 1990;83:559-62.

12 Rawles JM. General practitioners' management of acutemyocardial infarction and cardiac arrest: relevance tothrombolytic treatment. BMJ 1987;295:639-40.

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