Systematic review, meta-analysis and economic modelling of ...

DOI: 10.3310/hta17010 Health Technology Assessment 2013 Vol. 17 No. 1Chapter 1 BackgroundDescription of health problemAcute coronary syndrome (ACS) typically occurs when coronary artery disease (CAD) leads to obstructionof a patient’s coronary arteries. This can lead to myocardial infarction (MI), heart failure (HF), arrhythmia,cardiac arrest and death. ACS has a 6-month mortality of up to 20%, 1 and one-fifth of patients arerehospitalised within 6 months of their initial admission. 2Acute coronary syndrome usually presents as chest pain and must be differentiated from other commoncauses of chest pain, such as muscular pain, gastro-oesophageal pain and anxiety. Differentiation isdifficult because clinical assessment is unreliable and the electrocardiogram may be normal in the presenceof ACS. Patients with suspected ACS therefore constitute a large and varied population, many of whomwill not have ACS or CAD, but have non-cardiac causes for their chest pain. Accurate identification of ACSand CAD is therefore required to guide subsequent intervention.The health-care burden of suspected acute coronary syndromeSuspected ACS represents a substantial health-care problem and investigation represents a substantialchallenge. Chest pain is responsible for around 700,000 emergency department (ED) attendances inEngland and Wales, 3 with the main reason for attendance being suspected ACS. Hospital EpisodesStatistics for England (1998–2010) 4 report 253,765 emergency admissions with chest pain (code R07),63,082 with angina (I20) and 50,386 with MI. Table 1 shows how emergency admission rates, length ofstay (LoS) and bed-days for these three codes have changed over the last 10 years and Figure 1 shows thechange in admission rates.Hospital Episodes Statistics for England 4 show that emergency admission rates have been falling forangina and MI, but more than doubled for chest pain between 1998 and 2010. This was accompaniedby falls in LoS for chest pain and angina, and, since 2004, for MI. As a result, bed-days are falling for allthree conditions. The changes in admissions and LoS for angina and MI probably reflect the decreasingincidence of these conditions and changes in practice that have resulted in shorter hospital stay. 5 Thechanges in admissions and LoS for chest pain probably reflect changes in service delivery to promoteemergency hospital attendance with chest pain 1 and changing threshold for decision-making, leading tomore admissions with chest pain and a low risk of ACS for diagnostic assessment. 6Investigation for suspected acute coronary syndromeInvestigation for suspected ACS has two main elements: (1) diagnosis of MI and (2) diagnosis ofunderlying CAD. Diagnosis of unstable angina is another consideration but of decreasing importance forreasons outlined below.In the context of investigating suspected ACS the term MI usually refers to non-ST elevation MI (NSTEMI).Although ST-elevation MI (STEMI) is included in the definition of ACS it can usually be identified on thepresenting electrocardiogram and thus does not form part of the typical diagnostic challenge of suspectedACS, although electrocardiography (ECG) interpretation and differentiation from other causes of STelevation may present separate challenges.Clinical diagnosis of NSTEMI, according to the universal definition of MI, 7 is based on a troponin elevationabove the 99th percentile of the upper reference limit for the normal population. Patients with elevatedtroponin levels have an increased risk of adverse outcome 8 and are more likely to benefit from treatmentsusually provided in hospital. 9 However, testing troponin does not achieve optimal sensitivity for MI untilseveral hours after the symptoms of MI, 10 so guidelines typically recommend delaying sampling until© Queen’s Printer and Controller of HMSO 2013. This work was produced by Goodacre et al. under the terms of a commissioning contract issued by the Secretary of Statefor Health. This issue may be freely reproduced for the purposes of private research and study and extracts (or indeed, the full report) may be included in professional journalsprovided that suitable acknowledgement is made and the reproduction is not associated with any form of advertising. Applications for commercial reproduction should beaddressed to: NIHR Journals Library, National Institute for Health Research, Evaluation, Trials and Studies Coordinating Centre, Alpha House, University of Southampton SciencePark, Southampton SO16 7NS, UK.1