Cardiac biomarkers in the intensive care unit

Blood cardiac biomarkers (CB) have become increasingly accurate for evaluating cardiac abnormalities during the past 40 years. Initially, with the focus on myocardial infarction (MI), the use of creatinine kinase-MB (CK-MB), first described in 1972, was a major step forward in the development of a highly cardiac-specific biomarker. The introduction of cardiac troponin (cTn) assays in 1989 was the next major advance, and subsequent refinement of the assays now has the definition of acute myocardial infarction (AMI) centered on it. This progression ironically has brought considerable difficulties to the critical care physician who deals with multiorgan failure rather than the patient presenting to the emergency department with chest pain or single-organ pathology. The recent penetration of high-sensitivity (hs) cTn, replacing the fourth-generation cTn assays further compounds these diagnostic challenges.Moving beyond a sole focus on MI, the search for alternative and supplementary serum markers to assist in unravelling the presence, severity, and type of cardiac injury has been intense (Figure 1). Whilst cardiac ischemia/infarction is the most prevalent cause of cardiac injury with biomarker development reflecting this, the search for more meaningful biomarkers now includes CB for inflammatory processes and myocardial wall stress (as a result of pressure or volume overload) where evaluation extends beyond myocardial necrosis. The important role of C-reactive protein (CRP) as a prognostic marker is an example of the former while natriuretic peptides are now accepted as clinically useful markers of cardiac stress.In the critical care setting, the challenge of confounding factors brings about interpretation difficulties. Clarity in diagnosis and/or guidance for management frequently present when the heart is the only organ affected, such as in the emergency department or cardiology ward, does not always hold in the intensive care unit (ICU) setting. Even so, an understan