Cardiac troponin and the diagnosis of type 2 myocardial infarction and acute non-ischaemic myocardial injury

Cardiac troponin is integral in the diagnosis of myocardial injury and infarction. The Fourth Universal Definition recommends a classification by aetiology, in order to encourage clinicians to consider the mechanism of myocardial injury, and its influence on treatment. The development of high-sensitivity cardiac troponin assays has led to an increase in the amount of myocardial injury we identify in clinical practice. Acute non-ischaemic myocardial injury and type 2 myocardial infarction are responsible for around half of all measurable cardiac troponin elevations in unselected hospitalised patients presenting with suspected acute coronary syndromes. Despite the high incidence of noncardiovascular death in this population, major adverse cardiovascular events rates are similar to those with atherothrombotic type 1 myocardial infarction. However, despite attempts to further characterise these conditions there remains a paucity of evidence in patients with type 2 myocardial infarction or acute non-ischaemic myocardial injury to support diagnosis, investigation or treatment strategy. Current proposed treatment approaches revolve around the identification of coronary artery disease and left ventricular dysfunction and optimisation of therapies for these conditions. This review explores the clinical presentation of these conditions, the proposed cellular mechanisms of cardiac troponin release and the current direction of research efforts to help clinicians understand, risk stratify and treat patients with secondary myocardial injury and infarction.