Biomarkers Henry L. Green, MD, FACC, FACP December 28, 2007 Troponin Cardiac troponins are regulatory proteins that are involved in the process of cardiac contraction. Troponin I and troponin T found in cardiac muscle are sufficiently different from that in skeletal muscle that they can be used as specific markers. This is not true of troponin C, which is similar in cardiac and skeletal muscle. Troponin elevation can detect necrosis of less than 1 g. of myocardial tissue. It is released in both reversible and irreversible cell damage, and also in the setting of increased membrane permeability (sepsis, inflammation). Thus, it is not specific for coronary disease or even microcirculatory disease. In myocardial infarction The initial rise of troponin may require several hours, sometimes as long as 12 hours. However, an acute myocardial infarction, especially an ST elevation myocardial infarction, requires much more rapid treatment. Therefore, one should not rely on the troponin to determine an initial course of action. Furthermore, troponin may remain elevated for a week or more after myocardial infarction, which limits one’s ability to diagnose reinfarction Measurement of troponin also helps establish the prognosis. In unstable angina or non-ST elevation myocardial infarction, an elevated troponin indicates a risk of death or myocardial infarction that is four times as high as that in patients with negative troponins. Troponin elevation is also a useful guide to therapy. Intravenous glycoprotein IIb/IIIa inhibitors and early invasive strategy are much more beneficial in patients with positive troponins. Troponin level helps to assess reperfusion efficacy. Troponin may be elevated in a variety of other clinical settings Any degree of troponin elevation, whatever the cause, implies a worse prognosis. The degree of elevation is related to the risk of subsequent death. Demand ischemia Sepsis (myocardial depression or supply/demand mismatch) Systemic inflammatory response syndrome (myocardial depression or supply/demand mismatch) Hypotension (decreased perfusion pressure) Hypovolemia (decreased filling pressure/output) Supraventricular tachycardia, including atrial fibrillation (supply/demand mismatch) Left ventricular hypertrophy (subendocardial ischemia) 1

Myocardial ischemia Ingestion of sympathomimetic agents (direct adrenergic effects) Following PCI, a troponin elevation is probably related either to preexisting disease, or to the procedure itself. A rise in PCI after coronary bypass is usual, as there is always some myocardial damage. Coronary vasospasm (prolonged ischemia with myonecrosis) Intracranial hemorrhage or stroke (autonomic imbalance) Direct myocardial damage Cardiac contusion (traumatic) Electrical cardioversion (traumatic) Cardiac infiltrative disorders (myocyte compression) amyloid sarcoid cardiac metastases primary cardiac tumor Chemotherapy (cardiac toxicity) Myocarditis (inflammatory) including rheumatic fever Pericarditis (inflammatory) Endocarditis Drug toxicity Cardiac transplantation (inflammatory/immune-mediated) Myocardial strain Congestive heart failure (myocardial wall stretch) Pulmonary embolism (right ventricular wall stretch) Here, cardiac troponin levels increase and decrease quickly, usually peaking within the first 4 hours Pulmonary hypertension or emphysema (right ventricular wall stretch) Strenuous exercise (ventricular stretch) Unknown mechanism Chronic renal insufficiency can elevate the troponin. Earlier literature indicated that troponin elevation could occur with even mild renal impairment. However, with newer assays, the levels seem only to be elevated in severe renal disease. Even here, a troponin rise above the patient’s base line level may indicate myocardial necrosis. In dialysis patients, it is difficult to interpret the prognostic significance of troponin elevation. Interpreting troponin elevation Clearly, troponin elevation is not synonymous with an acute myocardial infarction. Its interpretation must be correlated with other clinical information. Based on an analysis of over 600 patients, Alcalai propose the following algorithm. However, it has not been validated by prospective studies.

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1. If symptoms and ECG are suggestive of an acute coronary syndrome, then an acute coronary syndrome is likely. 2. In the absence of supportive symptoms or ECG findings. a. If the troponin T is > 1.0 ng/ml i. If GFR is over 50, then acute coronary syndrome is likely ii. If GFR ≤ 50, diagnosis is uncertain b. If troponin T is ≤ 1.0 i. If GFR is >50 or age < 70 diagnosis is uncertain ii. If GFR ≤ 50 or age ≥ 70, diagnosis is unlikely Brain Natriuretic Peptide The diagnosis of heart failure can be difficult, especially in the elderly, the obese, and in patients with underlying lung disease. Even echocardiography may not help, since as many as 50% of patients with heart failure have preserved systolic function. In addition, many patients with a low ejection fraction do not have heart failure. A and B natriuretic peptides are released in response to myocardial stretch. BNP is of myocardial origin and is produced by the ventricles. ANP is of myocardial origin and is produced by the atria. CNP is of endothelial origin. The steps in generation of BNP consist of an initial release of preproBNP that is then cleaved into proBNP. ProBNP is cleaved into BNP and N-terminal BNP. BNP is a neurohormone, whereas N-terminal BNP is inactive. The half-life of BNP is 22 minutes. Over 90% of young, healthy adults have BNP levels of under 25 pg/ml. The BNP level rises with age, but generally stays below 100 unless the patient reaches heart failure stage C. The levels may be elevated in women without heart failure. In women over 65, it can be as high as 155 pg/ml. Interpretation of BNP levels The commonest application is in the diagnosis of heart failure. Levels of under 100 pg/ml generally exclude the diagnosis, whereas values of over 500 are usually indicative of it. The “gray area” is between 100 and 500. It is elevated in both systolic and diastolic heart failure, as well as right heart failure. BNP can also be elevated in conditions other than heart failure: Renal failure with a GFR of under 60. Acute coronary syndrome without heart failure (due to left ventricular dysfunction?) Pulmonary disease, such as obstructive lung disease (usually within the “gray zone” unless there is concomitant heart failure. Pulmonary embolism (right heart strain) Primary pulmonary hypertension 3

High output states, e.g. hyperthyroidism, cirrhosis, sepsis (usually does not exceed the diagnostic threshold, but it can be very high in sepsis or shock.) Atrial fibrillation one author suggests using a cut point of 200 rather than 100 BNP can be unexpectedly low in certain settings: Obesity – probably should use lower cut points in the obese patient Flash pulmonary edema Heart failure due to mitral stenosis or acute mitral regurgitation Cardiac tamponade Constrictive pericarditis BNP is also used as a therapeutic agent (nesiritide) in the management of heart failure. Its measurement in the plasma may be misleading in this setting. Once the infusion is terminated, the short half-life of BNP permits its use as a diagnostic or prognostic too. Alternatively, N-terminal proBNP can be used as a marker. BNP as a guide to therapy and prognosis In the management of heart failure, the BNP can be used to guide therapy. It should be obtained early during the hospitalization. It is reasonable to repeat the test during the hospital stay when there is a change in the patient’s condition. It should be rechecked just before discharge. If it is still significantly elevated at that time, then more aggressive outpatient therapy may be indicated. One study showed that a pre-discharge level of over 700 portends a poor prognosis, whereas a level of under 350 is more favorable. BNP is potentially useful in the outpatient setting as well. It is helpful to estimate what the patient’s optimum level is, in order to appreciate the significance of changes. While there is spontaneous variation even in stable patients, a rise of 50% over the steady state level is a warning sign. The BNP level is also a good prognostic tool in patients without heart failure. In cardiomyopathy, a high level indicates increased risk of sudden death. The prognosis in patients with pulmonary embolism also correlates with BNP. Similar relationships exist in acute coronary syndromes, and even in patients with stable angina. N-Terminal BNP This marker performs similarly to BNP. It has a half-life of 1 to 2 hours. 90% of young healthy adults have levels ≤ 70 pg/ml. Values under 300 pg/ml argue against heart failure, whereas levels over 900 favor it. The “gray zone” is between those figures. Like BNP, it also correlates with prognosis in pulmonary embolism and other conditions.

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Inflammatory Markers Inflammation plays a major role in atherogenesis. Proinflammatory cytokines recruit smooth muscle cells and stimulate collagen formation. In addition, inflammation drives plaque degradation, an important step in intravascular thrombosis. Measurement of inflammatory markers may provide a means to identify patients at higher risk for coronary artery disease. High-Sensitivity C-reactive protein (hsCRP) C-reactive protein is the marker most commonly used. The Framingham risk score has been disappointing as a predictor of cardiovascular risk in women. The hsCRP identifies a significant number of women at risk who would otherwise be missed. It is probably the best supported inflammatory marker. Results less than 1.0 mg per dL (9.5 nmol per L) represent low risk; 1.0 to 3.0 mg per dL (9.5 to 28.6 nmol per L), average risk; and greater than 3.0 mg per dL, high risk. Results greater than 10 mg per dL (95.2 nmol per L) may represent a chronic inflammatory or infectious process. In addition to its utility in predicting cardiovascular disease, it also has prognostic implications in individuals who already have the condition. Since the CRP is actually a nonspecific marker of inflammation, a high level should be rechecked several weeks later to determine whether it is chronically elevated or simply due to an intercurrent infection. Whether it takes part in the pathogenesis of coronary artery disease or is merely a surrogate marker is still debated. Some authors currently propose targeting the CRP level in titrating the dose of statin drugs. Ineterleukin-6 (IL-6) IL-6 is another inflammatory marker that may be involved in atherogenesis. It may have a procoagulant effect as well. Ridker et al demonstrated that, in apparently healthy men, elevated IL-6 is a marker for future myocardial infarction. Others have found it to correlate with mortality.

Myeloperoxidase (MPO) Myeloperoxidase is a leukocyte enzyme that promotes oxidation of lipoproteins in the atheroma. MPO levels correlate with the prevalence of coronary artery disease. Fibrinogen The fibrinogen level also correlates with cardiovascular disease.

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References Antman EA. Decision making with cardiac troponin tests. N Engl J Med 2002; 346:20792082 Jeremias A and Gibson CM. Narrative review: Alternative causes elevated cardiac troponin levels when acute coronary syndromes are excluded. Ann Intern Med 2005; 142;786-791 Alcalai R et al. Acute coronary syndromes vs nonspecific troponin elevation: clinical 3predictors and survival analysis. Arch Int Med 2007; 167:276-281 Shapiro BP et al. Use of plasma brain natriuretic peptide concentration to aid in the diagnosis of heart failure. Mayo Clin Proc 2003; 78L481-486 Hobbs RE. Using BNP to diagnose, manage and treat heart failure. Cleve Clin J Med 2003; 70:333-336. Rodeheffer RJ. Measuring plasma B-type natriuretic peptide in heart failure. JACC 2004; 44:740-749. Spevack DM and Schwartzbard A. B-type natriuretic peptide measurement in heart failure. Curr Journal Rev 2004; 27:489-494. Mark DB and Felker MG. B-type natriuretic hormone - a biomarker for all seasons? N Engl J Med 2004; 350:718-720 Sabatine MS and Brauwald E. Another look at the age-old question. JACC 2005;45:244-245 Ridker PM et al. Plasma concentration of interleukin-6 and the risk of future myocardial infarction among apparently healthy men. Circulation. 2000;101:1767-1772 Bellasi A et al. New insights into ischemic heart disease in women. Cleve Clin J Med 2007;74:585-594 Vorchheimer DA and Fuster V. Inflammatory markers in coronary artery disease. JAMA 2001; 286:2154-2156. in women. Cleve Clin J Med 2007;74:585-595. Daniels LB and Maisel AS. Natriuretic peptides. JACC 2007;50:2357-2368

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