Given the complexity of this question, we’ll answer it in three parts: 1) a discussion of troponins; 2) a discussion of atypical symptoms or anginal equivalents; and 3) a discussion of what it means to put these two together.
PART I – THE POWER AND PITFALLS OF TROPONIN
Troponin is a complex of three proteins (troponin C, troponin I, and troponin T) involved in calcium processing in skeletal and cardiac muscle. While skeletal and cardiac muscle share troponin C isoforms, the troponin I and T isoforms are found exclusively in cardiac muscle. Cardiac Troponin I, also known as cTnI, exists in myocytes in two forms: bound and cytoplasmic. When myocytes are damaged or undergo apoptosis, the cytoplasmic cTnI spills into the blood, where it can be measured by assay. Modern cTnI assays are highly sensitive for myocardial damage, to the point where serum cTnI measurement has become the gold standard for differentiating unstable angina from NSTEMI in patients undergoing an ACS workup.
- Macrae AR1, Kavsak PA, Lustig V, Bhargava R, Vandersluis R, Palomaki GE, Yerna MJ, Jaffe AS Assessing the requirement for the 6-hour interval between specimens in the American Heart Association Classification of Myocardial Infarction in Epidemiology and Clinical Research Studies. Clin Chem. 2006 May;52(5):812-8. Epub 2006 Mar 23.
- Jaffe AS1. Use of biomarkers in the emergency department and chest pain unit. Cardiol Clin. 2005 Nov;23(4):453-65, vi.
- Anderson JL, Adams CD, Antman EM, Bridges CR, Califf RM, Casey DE Jr, Chavey WE 2nd, Fesmire FM, Hochman JS, Levin TN, Lincoff AM, Peterson ED,Theroux P, Wenger NK, Wright RS, Smith SC Jr, Jacobs AK, Halperin JL, Hunt SA, Krumholz HM, Kushner FG, Lytle BW, Nishimura R, Ornato JP, Page RL,Riegel B. ACC/AHA 2007 guidelines for the management of patients with unstable angina/non ST-elevation myocardial infarction: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 2002 Guidelines for the Management of Patients With Unstable Angina/Non ST-Elevation Myocardial Infarction): developed in collaboration with the American College of Emergency Physicians, the Society for Cardiovascular Angiography and Interventions, and the Society of Thoracic Surgeons: endorsed by the American Association of Cardiovascular and Pulmonary Rehabilitation and the Society for Academic Emergency Medicine. Circulation. 2007 Aug 14;116(7):e148-304. Epub 2007 Aug 6.