Change in cardiac troponin T to differentiate acute from chronic myocardial injury in the Emergency Department

INTRODUCTION: Persistently elevated cardiac troponin (cTn) values are observed in many patients with suspected acute coronary syndrome (ACS) in the absence of myocardial infarction and may reflect underlying cardiac disease. Chronic myocardial injury is defined where cTn values are elevated and vary by ≤ 20 % on sequential measurements. We aimed to evaluate whether these criteria are reliable over short intervals applied in accelerated diagnostic pathways. METHODS: In a secondary analysis of a prospective, multi-centre cohort study of patients with suspected ACS, cTnT was measured at presentation, 1, 2 and 6-36 h, and the final diagnosis adjudicated according to the Fourth Universal Definition of Myocardial Infarction. Two criteria for chronic myocardial injury were compared: a relative change in cTn of ≤ 20 % and an absolute change < 3 ng/L, and the findings externally validated. RESULTS: At presentation cTnT was elevated in 242 of 1,000 (24 %) patients (73 years, 42 % female), of whom 94/242 (39 %), 13/242 (5 %) and 137/242 (56 %) had myocardial infarction, acute or chronic myocardial injury, respectively. A relative change of ≤ 20 % misclassified 58 % (59/101) and 49 % (48/98) of patients with a final diagnosis of acute myocardial injury or infarction at 1 and 2 h, respectively, whereas an absolute change of < 3 ng/L misclassified 22 % (22/101) and 15 % (15/98). In the validation cohort (n = 621), the relative and absolute change criteria at one hour misclassified 43 % (13/30) and 17 % (5/30) of those with myocardial infarction. CONCLUSIONS: Chronic myocardial injury cannot reliably be differentiated from acute myocardial injury or infarction by recommended criteria over short remeasurement intervals in the Emergency Department. Longer intervals between sampling and absolute rather than relative criteria may reduce the risk of misclassification.