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Pre-hospital aspirin for suspected myocardial infarction and acute coronary syndromes: A headache for paramedics?
  1. M Woollard1,
  2. A Smith1,
  3. P Elwood2
  1. 1Pre-hospital Emergency Research Unit, University of Wales College of Medicine/Welsh Ambulance Services NHS Trust, Cardiff, UK
  2. 2Department of Epidemiology, Statistics, and Public Health, University of Wales College of Medicine
  1. Correspondence to: Mr Woollard, Pre-hospital Emergency Research Unit, Lansdowne Hospital, Sanatorium Road, Cardiff CF1 8UL, UK (Malcolm.peru{at}


Objective—To ascertain the frequency with which paramedics follow protocols for the administration of aspirin to patients to whom an ambulance is called for chest pain associated with suspected ischaemic heart disease.

Methods—Ambulance services in England and Wales who had conducted a recent aspirin administration audit were identified through the National Clinical Effectiveness Programme for the Ambulance Service Association. Data were requested from each of these services with a 100% return rate.

Results—Nine services out of a total of 35 had collected appropriate data. The proportion of patients who were given aspirin by a paramedic varied from 11% to 74%. The range of proportions of patients receiving pre-hospital aspirin increased after adding those patients who had already received aspirin from an alternative health provider, to 19% to 78%. It is estimated that at least 15% to 74% of patients who should have been given aspirin by the various ambulance services did not receive it. The proportion of patients for whom aspirin was judged to be inappropriate ranged from 4% to 35%. The reason for these widely varying and generally poor levels of compliance is not known. However, the range of indications and contraindications to the administration of aspirin varied considerably by ambulance service. This also made the comparison of data from different sources difficult.

Conclusions—Aspirin has been shown to be beneficial after a myocardial infarction and for other acute coronary syndromes. However, variances in the proportion of patients with suspected ischaemic heart disease given aspirin in different ambulance services indicates the need for a re-emphasis on the importance of this treatment. A standard protocol for all UK ambulance services should be devised that minimises the number of contraindications to aspirin and otherwise requires its administration to all patients with acute coronary syndromes or suspected myocardial infarction. Regular, standardised audits of compliance should also be conducted and their results widely disseminated.

  • myocardial infarction
  • aspirin

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Aspirin was first shown to be life saving in 19741 and since then its value in the reduction of risk after myocardial infarction (MI) and in other vascular diseases has been confirmed in over 150 randomised controlled trials.2

The ISIS-2 study3 identified that giving aspirin in the first 24 hours after MI resulted in a reduction in mortality at five weeks of 23%. This was similar to the 25% reduction achieved with streptokinase. Importantly, the combined administration of aspirin and streprokinase reduced mortality by 42% when compared with placebo.

A recent review of trends in treatment and survival from myocardial infarction4 concluded that “The greatest effect of any given therapy was that of aspirin, which accounted for 34% of the decrease in mortality, followed by thrombolytics (17%) . . .”

Aspirin is now widely accepted as an essential component in the early treatment of acute MI.5 The giving of aspirin by a health professional on first contact with a patient who has chest pain and who is suspected to have a MI or acute coronary syndrome is therefore recommended,6,7 and has become accepted practice. Recommendations for the pre-hospital administration of aspirin by paramedics8 and by doctors9 have also been made.

In this study we have attempted to ascertain the frequency with which paramedics follow protocols for the administration of aspirin to patients to whom an ambulance was called for chest pain believed to be related to ischaemic heart disease.


Ambulance services in England and Wales that had conducted a recent audit of aspirin administration were identified through the National Clinical Effectiveness Programme for the Ambulance Service Association.

Nine services out of a total of 35 had collected appropriate data and made these available to us. The data that had been recorded differed considerably from service to service. Relevant comparable data were extracted where possible from each services response.

The survey was completed in December 2000.


Table 1 shows the results of the audits conducted by each ambulance service. Several organisations supplied figures from more than one study, but only the data from the most recent audit are given.

Table 1

Proportion of patients receiving pre-hospital aspirin

The proportion of patients receiving pre-hospital aspirin from a paramedic or alternative health provider ranged from 19% to 78%. It is estimated that 15% to 74% of patients who should have been given aspirin before hospital admission did not receive it.

Table 2 shows the range of indications and contraindications to aspirin administration for each ambulance service.

Table 2

A comparison of indications and contraindications by ambulance service


It is widely accepted that aspirin is of value after MI. However, it is of even greater efficacy in the treatment of unstable angina. Platelet aggregation and embolisation are the important factors in this condition.10 Evidence suggests that the reduction in relative risk for subsequent non-fatal MI or death after aspirin administration is greater for unstable angina than it is for MI (51%,11,12 compared with 25%2).

While the proportion of patients eligible for aspirin in hospital who receive the drug is high, there remains room for further improvement. The gap between the need for aspirin and the proportion of patients who actually receive it could, therefore, be reduced via pre-hospital administration by paramedics. A 1992 to 1993 inhospital study of aspirin administration to 10 108 patients with MI and aged 65 or over found treatment rates of only 61% in the first two days. However, it also determined that aspirin administration was significantly associated with a lower mortality (odds ratio 0.78; 95% confidence intervals 0.70 to 0.89).13 Other authors have reported inhospital aspirin administration rates ranging from 45.1% (4052 elderly Medicare patients, USA, 1992/1993)14 to 87.8% to 91.3% (1737 patients, USA, 1997).15 European authors have reported similar aspirin administration rates after MI.16 But administration rates of aspirin after episodes of unstable angina are much lower. A review of practice against guidelines in nine European countries reported antiplatelet administration rates of only 70.2%.17 While inhospital compliance rates are high after MI, pre-hospital administration of aspirin by paramedics does, therefore, have the potential to help reduce the number of eligible patients who do not receive it and who forgo its benefits. It is not possible to definitively diagnose MI in the pre-hospital arena according to standard criteria, and consequently administration of aspirin to all patients with chest pain suggestive of ischaemic heart disease seems to be a reasonable recommendation.

The data we present come from ambulance services that had conducted an audit of aspirin administration to patients with chest pain suspected to be associated with ischaemic heart disease. The proportion of patients who received aspirin from any source varied from 19% to 78%. These figures are disappointing, but the reasons for these low levels of compliance to protocol are unclear. The proportion of subjects with chest pain for whom aspirin is contraindicated is likely to be around 5%–7%.18 Typically, therefore, 93% of patients with chest pain arising from suspected ischaemic heart disease might safely be given aspirin. This implies that, in the samples reported in this study, from 15% to 74% of suspected ischaemic chest pain patients who were potentially eligible for aspirin did not receive it.

The protocols followed by each ambulance services differed, but the description of patients to whom aspirin is to be given is typically “a patient presenting with signs and symptoms of ischaemic chest pain”. One service gives a more detailed list of signs and symptoms and required evidence of infarction from an ECG before aspirin was given. This is of some concern, as it has been shown that early in the infarction process diagnostic ECG changes may not be present initially, but might develop later.19 Perhaps even more importantly, aspirin is also of benefit (and is recommended) for patients suffering from a range of acute coronary syndromes, not just those with confirmed MI.20

The protocols from each ambulance service all listed criteria that defined patients to whom aspirin should not be given, but these differed greatly. Allergy to aspirin, current use of anticoagulants, haemophilia and other bleeding disorders were present in all the protocols. But in two protocols the taking of aspirin within the previous 24 hours constituted a contraindication. The wisdom of this criterion can be questioned as, even if a prophylactic dose of aspirin had been taken earlier, fresh platelets may have entered the circulation since this time and it is important to reduce the proportion of un-acetylated platelets and maintain these at the lowest possible level. A further dose of 300 mg of aspirin may therefore be beneficial and is unlikely to do harm; it should not be withheld. It seems reasonable to argue that contraindications should be kept to an absolute minimum in a situation where a relatively safe drug could be life saving.

The variability identified between the various services indicates the need for an UK standard protocol based on the available evidence from trials. In formulating this it should be borne in mind that a rigid approach, restricting aspirin only to those patients with definitive evidence of acute MI may deprive many others of the benefits of aspirin treatment. Patients who report having had chest pain but who are later judged not to have had an infarct do, in fact, have an increased mortality.21 Undoubtedly some of these will indeed not have had an infarct, but even in those in whom the pain is muscular aspirin may have a useful role. In a small proportion the chest pain may arise from a stomach lesion, and there is a risk that the questions which paramedics ask may not reveal this. Nevertheless, while aspirin would be best withheld in such patients, it could be argued on the basis of relative risks that where the diagnosis is uncertain, aspirin should be given.

Further UK wide standardised audits of aspirin administration should be conducted, as poor compliance to this aspect of paramedic treatment protocols may indicate poor compliance to other aspects of the treatment of chest pain. While early administration of aspirin is important there is no strong evidence to suggest that its effectiveness is increased by giving it at the earliest possible time. Other forms of treatment may be considerably more time sensitive (such as the administration of fibrinolytics). The Royal College of Physicians (RCP) has developed a core dataset for documenting the treatment of MI, and has collaborated with the Joint Royal Colleges Ambulance Liaison Committee and the Ambulance Service Association in defining its ambulance related aspects. The RCP is also conducting a national audit of MI (MINAP). Ambulance services must audit and report every administration of a thrombolytic by a paramedic, and may be required to audit other treatments in the future. These initiatives may well meet the need for ongoing audit.


We would like to thank Stuart Nicholls, Manager of the National Clinical Effectiveness Programme for the Ambulance Service Association, and the Ambulance Service NHS Trusts for their cooperation in the provision of data for this publication. Our thanks also go to Tom Quinn and Professor Douglas Chamberlain whose helpful comments resulted in substantial improvements to an earlier draft of this paper.

Contribution Peter Elwood conceived the study, and helped write and edit the paper. Anna Smith collected and analysed the data, and helped write and edit the paper. Malcolm Woollard developed the study methodology and wrote and edited the paper.


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  • Funding: none.

  • Conflicts of interest: none.