Temporal Relationship between Cardiac Myosin-Binding Protein C and Cardiac Troponin I in Type 1 Myocardial Infarction

To the Editor:Although acute chest pain is a common presenting symptom, the proportion of patients with acute myocardial infarction (AMI)1 who have diagnostic electrocardiographic changes on presentation is dwindling. Consequently, early triage of chest pain patients is becoming ever more reliant on assessment of the release of cardiac troponin I (cTnI) or cTnT into the systemic circulation. However, these biomarkers are released relatively slowly, reaching their peak many hours after symptom onset (1). To achieve rapid triage, the latest guidelines recommend the use of assays for cTnI and cTnT that have very high analytical sensitivity to rule-in and rule-out AMI based on concentrations markedly above and markedly below the population-defined 99th percentiles, respectively. The use of these widely spaced decision limits improves the specificity of rule-in and the sensitivity of rule-out. However, the majority of patients presenting with chest pain have cardiac troponin concentrations that place them between these decision limits, in an indeterminate zone. These patients require repeat testing and subsequent second or third rounds of triage based on rates of change of cardiac troponin concentration over time (2). This introduces systematic delays in allocation of evidence-based treatments and prolongs stay in the pressured and precious environment of the emergency department.We have described a new biomarker of …