Raised troponin: non-invasive cardiac investigations

The first of a two part series looking at troponin and cardiac investigations A borderline troponin result is a potential minefield for the student and junior doctor alike. Similarly, patients with chest pain but without a rise in troponin concentration (“a negative troponin”) need further investigations to assess their cardiac risk. This first part of these two articles covers the non-invasive investigations that may be ordered if troponin concentrations are raised. Part two will look at invasive investigations. Patients who attend hospital with chest pain are common and account for 700 000 emergency department attendances (6% of total) and as many as a quarter of acute admissions in England and Wales.1 The principal differential diagnoses have cardiac, respiratory, and gastrointestinal causes. The key diagnosis of concern is myocardial infarction, and this depends on a history of cardiac sounding chest pain, electrocardiographic features, and changes in troponin concentration above the 99th centile of the upper recommended limit. Myocardial infarction is part of the umbrella term of the acute coronary syndromes (ACS). These consist of ST elevation myocardial infarction (STEMI), non-ST elevation myocardial infarction (NSTEMI; raised troponin), and unstable angina (normal troponin) (box 1).2 ACS represent unstable coronary atheroma that may be acutely enlarging because of rupture and platelet activation (unstable angina) or because of acute total occlusion of a vessel (STEMI). STEMI and NSTEMI are generally a type 1 myocardial infarction, but there is substantial overlap with types 2 and 3 myocardial infarction. The universal definition of myocardial infarction (the five types) is used mainly in research, but clinically most doctors use STEMI and NSTEMI. #### Box 1: Classification of myocardial infarction2