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LETTER TO THE EDITOR

Redefinition of myocardial infarction by a consensus dissenter

^a Cardiovascular Epidemiology Unit, Ninewells Hospital and Medical School, University of Dundee, DD1 9SY Dundee, Scotland, UK

h.tunstallpedoe{at}dundee.ac.uk

Diagnosis of coronary events, including myocardial infarction, has always been dependent on the availability, frequency and timing of corroborative tests—electrocardiographic or serologic—the potential curtailment or censoring of these by death and the almost arbitrary availability/nonavailability of documentation and autopsy findings in fatal cases (3–5). In nonfatal cases, the distinction between acute and subacute or chronic, is difficult. The syndromes resemble a comet in which the front of the head is distinct but the beginning and end of the tail are not—the cut-points are arbitrary but determine relative proportions. In fatal cases, in which pathological findings are available, delayed deaths may show established infarction but no coronary thrombus, while early deaths may show the opposite, or indeed, no obvious acute event. Definition implies a rigid classification, and not, as many clinicians imagine, description of a subset of idealized cases.

After 30 years of defining, refining, coding and classifying coronary events and ensuring quality control (6–9), I had recently urged that the 20-year-old definitions of coronary events, drafted with others for the WHO MONitoring of trends and determinants in CArdiovascular disease (MONICA) Project in 1981 (3), be updated (10). I welcomed the ESC/ACC initiative and was nominated as their representative by the ESC Working Group on Epidemiology and Prevention, which includes a large number of MONICA investigators, charging me to keep them appraised of progress. I participated in the consensus meeting, co-chaired the epidemiology group, presented its written recommendations on the final day, and received some "notes" of the different group recommendations in September 1999, but nothing further. Previously assured that the July 1999 meeting was the first of a series of meetings and consultations, none has involved me. Despite use of my name, I never saw the new consensus definition for comment or approval until after it was published. I am in good company.

What happened raises two issues in accountability to the medical profession, and to the wider public interest, before consideration of the definition itself. The "consensus" committee was heterogeneous and there could be no suspicion of commercial influence. That cannot be said of a document of opaque provenance, giving a virtual monopoly to assays subject to commercial patents. The lack of a true consensus process makes the two colleges and two journals appear negligent in not asking for details of consultancies and shareholdings by those involved. Although the issue is almost certainly irrelevant, it cannot explicitly be seen to be so. There is no clear audit trail as to how these criteria were derived and approved. Due process would have ensured transparency. Senior committees asked to endorse a "consensus" will be less careful and critical than when confronted with known partisan opinions.

The public interest is also involved in the alleged "consensus" recommendation that microscopic muscle necrosis, sufficient to produce a measurable blood troponin "blip," should automatically attract the label of "myocardial infarction." If the word "consensus" means "majority," then this was true on a show of hands of the picked participants, but this was not overwhelming. A vociferous minority, including some workshop groups, argued against the proposal. It has immense consequences for potential public misunderstanding, "labeling," employment and insurance. Interventional cardiologists and cardiac surgeons will not be pleased to have to tell postoperative patients with a trivial rise in troponin levels that they had a myocardial infarction. This question is not solely of concern to cardiologists, but should involve consulting those responsible for rehabilitation, health promotion, employment and insurance and for paying medical costs, before a final decision is made. The epidemiology group preferred the term "myocardial injury" for events involving only minor damage.

The "definition" itself is flawed in two respects. It is not comprehensive for living cases and it virtually ignores fatal ones. The new definition gives a key role to an observed "rise and fall" in biochemical markers (2). In many case series, about 20% of cases of myocardial infarction take >24 h to come under care (8), by which time it would be too late to observe a rise. Cases with a "rise" would have to survive under care for several days in order to guarantee a "fall." So an ESC/ACC "myocardial infarction" is a case coming under care very early in the attack that has repeated troponin tests over many days, and is inherently unlikely to succumb for that reason alone (2,5). Other cases are excluded by this definition. What about the general practitioner’s case admitted to a cottage hospital who shows classic electrocardiographic progression but whose blood samples get lost in transit to the laboratory? Unequivocal electrocardiographic progression, without the need for serological confirmation, has always been accepted as diagnostic by clinicians (and by WHO criteria, seriously misquoted in this document) (3,4). What about the patient who dies on arrival to the coronary care unit?

The squeamishness of Dr. Alpert’s and Dr. Thygesen’s definition concerning fatal cases creates immense problems for the utility of these criteria. Epidemiologists are made of stronger stuff (3,4). There is a need for diagnostic criteria and definitions that can be used generally, not only by epidemiologists but also in the modern enthusiasm for league tables and performance indicators, beloved of health service administrators. You cannot have criteria covering nonfatal cases alone. Imagine two hospitals following identical criteria for nonfatal cases, but applying their own arbitrary criteria for what is a fatal case. Their statistics would be given false respectability by the standardization of nonfatal criteria, but their reported fatality rates could appear to be very different, when in reality they were exactly the same. Not all fatal cases show demonstrable myocardial infarctions, which is why MONICA calls heart attacks coronary events, and fatal events coronary deaths.

The new criteria may be suitable for recruiting coronary care unit survivors into clinical trials: one apparent rationale (2). They are unusable for general diagnostic use. They are not incorporated into a diagnostic classification which is comprehensive. They do not cover early and other fatal cases, and nonfatal cases in which tests are partial, delayed, missing or curtailed. Therefore, they are not applicable to more than a proportion of coronary events in the real world. New criteria need to be field tested and related either to the current, or a modified version, of the International Statistical Classification of Diseases and Health Problems (11) before they are adopted, or there will be diagnostic confusion and chaos in hospital and regional morbidity statistics. Comparative figures could reflect the frequency and intensity of troponin measurement, rather than the underlying disease burden.

None of this denies the immense value of the newer biochemical markers such as troponins (12) in increasing the sensitivity and specificity of diagnosis of coronary events; nor the consequent need for older definitions and classifications to be revised for the modern era, and for the purposes specified by the college presidents in their accompanying editorial (1). The WHO MONICA Project criteria were drafted 20 years ago (3) with strong transatlantic collaboration to marry older European qualitative criteria (4), for classifying myocardial infarction and coronary deaths, with American precision. These criteria mapped trends in coronary disease incidence and case fatality across four continents for over a decade, in a third of a million cases (9). It is time they were updated by those with expertise in the field. The names of epidemiologists involved in this recent "consensus" exercise have been used, while they themselves have been kept at arm’s length. Diagnosis means more than recruitment to clinical trials. We are discussing among ourselves how to carry the need for revised criteria forward from this brave but flawed attempt. We hope to have the help of national and international organizations.

	References

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3. WHO MONICA ProjectTunstall-Pedoe H, Kuulasmaa K, Amouyel P, Arveiler D, Rajakangas AM, Pajak A. Myocardial infarction and coronary deaths in the World Health Organization MONICA Project: Registration procedures, event rates, and case fatality rates in 38 populations from 21 countries in 4 continents. Circulation. 1994;90:583–612[Abstract/Free Full Text]

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7. Tunstall-Pedoe H. Problems with criteria and quality control in the registration of coronary events in the MONICA study. Acta Med Scand. 1988;(Suppl 728):17–25

8. Tunstall-Pedoe H, Morrison C, Woodward M, Fitzpatrick B, Watt G. Sex differences in myocardial infarction and coronary deaths in the Scottish MONICA population of Glasgow 1985–91: presentation, diagnosis, treatment and 28-day case fatality of 3,991 events in men and 1,551 events in women. Circulation. 1996;93:1981–1992[Abstract/Free Full Text]

9. WHO MONICA (MONitoring trends and determinants in CArdiovascular disease) ProjectTunstall-Pedoe H, Kuulasmaa K, Mahonen M, Tolonen H, Ruokokoski E, Amouyel P. Contribution of trends in survival and coronary-event rates to changes in coronary heart disease mortality: 10-year results from 37 WHO MONICA Project populations. Lancet. 1999;353:1547–1557[CrossRef][Medline]

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