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(Circulation. 1997;96:2953-2958.)
© 1997 American Heart Association, Inc.

Articles

Circulating Cardiac Troponin I in Severe Congestive Heart Failure

Emile Missov, MD; Charles Calzolari, PhD; ; Bernard Pau, PhD

From the Department of Cardiology and INSERM U-390, University Hospital of Montpellier (E.M.); Sanofi Recherche (C.C.); and the Faculty of Pharmacy, CNRS UMR-9921 (B.P.), Montpellier, France.

Correspondence to Emile Missov, MD, INSERM U-390, Hôpital Arnaud de Villeneuve, Centre Hospitalier Universitaire de Montpellier, 34295 Montpellier Cedex 05, France. E-mail missov{at}u390.montp.inserm.fr

	Abstract

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Background Spontaneous progression of severe congestive heart failure is structurally characterized by cellular degeneration and multiple foci of myocardial cell death. The cardiac muscle isoform of troponin I is uniquely expressed in the adult human myocardium, and an increase in its circulating levels is highly indicative of myocardial injury. Accordingly, we addressed the usefulness of cardiac troponin I as a sensitive and specific molecular marker of congestive heart failure in patients with severely reduced left ventricular performance.

Methods and Results A new generation single-step immunoenzymoluminometric assay with high analytical sensitivity was used to assess cardiac troponin I in patients with severe congestive heart failure, healthy blood donors, and hospitalized control subjects without known cardiac disease. The cardiac troponin I concentration (mean±SEM) was 72.1±15.8 pg/mL in heart failure patients and 20.4±3.2 and 36.5±5.5 pg/mL in healthy and hospitalized control subjects, respectively (P<.01 versus heart failure patients). When both control groups were considered, the mean cardiac troponin I level was 25.4±2.9 pg/mL (P<.01 versus heart failure patients). Creatine kinase MB mass and myoglobin concentrations remained within the normal range in all groups.

Conclusions These data (1) provide the first evidence for ongoing myofibrillar degradation and increased cardiac troponin I levels in patients with advanced heart failure and (2) show potential usefulness of cardiac troponin I as a specific and sensitive new serum marker molecule in severe congestive heart failure.

Key Words: cardiac troponin I • heart failure

	Introduction

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Congestive heart failure is a dynamic process with changing rate of progression and risk profile with time that adversely affects quality of life and markedly shortens survival. One-year mortality rates range from 40% to 50% in patients with NYHA functional class III and IV symptoms.^{1 2} A prominent feature of the syndrome is the dissociation between signs of congestion and exercise intolerance and the structural and functional changes in the myocardium. Heart failure relates to complex long-term neurohormonal alterations and to abnormal myocardial structure.^{3 4} The transition of asymptomatic cardiac dysfunction to symptomatic heart failure is associated with extensive remodeling of the muscular, collagenous, and vascular compartments of the myocardium. Morphological changes that are typical of advanced heart failure include noncontiguous areas of myocardial cell death and foci of replacement fibrosis.^{5 6} Irreversible progression of congestive heart failure is known to occur, but the underlying mechanisms remain unclear, possibly because of inadequate sensitivity of the measures used.

The troponin proteins are found in cardiac and skeletal muscle tissue as products of separate genes. They are located in the myofibril, where they regulate the interaction of actin monomers with the myosin heavy chain. The cAMP-dependent phosphorylation of troponin I at two adjacent serine residues in the amino-terminal of the molecule causes a decrease in the affinity of calcium for the calcium-binding troponin C and inhibition of actin-myosin interactions.⁷ Troponin I exists in three isoforms: slow skeletal, fast skeletal, and cardiac muscle–specific isoforms.⁸ The cardiac muscle isoform of troponin I is a 24-kD protein uniquely expressed in the adult human heart. It differs from the slow-twitch and fast-twitch skeletal muscle isoforms in that (1) it possesses 31 additional amino-terminal residues and (2) the remaining amino acid sequence shows 40% dissimilarity from both the slow and fast skeletal muscle isoforms. Importantly, the skeletal muscle does not express cardiac troponin I throughout ontogeny, during regenerative muscle disease, or in response to pathological stimuli, which confers to the cardiac isoform absolute specificity for the myocardium.^{9 10 11}

We have recently developed a new-generation, highly sensitive immunoenzymoluminometric assay for quantitative determination of the cardiac muscle isoform of troponin I in human serum. The assay operates at the picomolar concentration range and allows for the measurement of extremely low concentrations of cardiac troponin I. The lower limit of detection is 3 pg/mL. We were particularly interested in a fundamental hypothesis; specifically, whether the use of an immunoassay with high analytical performance could provide evidence for cardiac troponin I release in congestive heart failure due to systolic dysfunction of the left ventricle, reflected in a severely compromised left ventricular ejection fraction. This hypothesis is consistent with a basic biological phenomenon in the failing human myocardium, namely, myofibrilolysis, and relates to the pathophysiology of congestive heart failure.

	Methods

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Patients
This study was performed with the approval of the institutional review board, and 115 subjects gave informed consent. Thirty-five consecutive NYHA functional class III and IV patients had clinically stable severe congestive heart failure with dyspnea and fatigue at rest or modest exertion. The median duration of symptoms exceeded 6 months in all of them. Conventional therapy for congestive heart failure consisted of digoxin, diuretics, and ACE inhibitors, with long-acting oral nitrate preparations as additional vasodilator therapy and amiodarone to control ventricular rate or ectopic activity in some patients. None had suffered acute myocardial infarction or unstable angina, and none had undergone cardiac or noncardiac surgery within 30 days of inclusion. Patients with severe pulmonary disease, acute or chronic renal and liver disease, uncontrolled hypertension, or inflammatory illness were not eligible. Fifty-five healthy blood donors (28 men; mean age, 47 years) were included as control population. An additional cohort of 25 untreated patients (12 men; mean age, 52 years) had malignancies of the blood-forming tissues (leukemias and lymphomas) and no clinical, ECG, or echocardiographic evidence for cardiac disease. They were included as hospitalized control subjects.

Left ventricular ejection fraction was obtained from ECG-gated equilibrium blood pool radionuclide angiography in the best septal view in both hospitalized control subjects and heart failure patients. Venous blood for determination of cardiac troponin I, CK-MB fraction, and myoglobin was collected on dry tubes from an antecubital vein, allowed to clot for 30 minutes at room temperature, and centrifuged for 10 minutes at 4°C (3500 rpm). Sera were stored in aliquots at -80°C for subsequent analysis and were frozen and thawed only once. All biochemical markers remain stable if handled as described.

Cardiac Troponin I Immunoassay
The analytical performance of an immunoassay is usually expressed in terms of sensitivity, specificity, precision, and accuracy.

Sensitivity and specificity. Sensitivity is defined as the lowest value that can be statistically distinguished from zero concentration. In this preliminary research application, cardiac troponin I was quantitatively determined with a newly developed, highly sensitive immunoenzymoluminometric assay, which operates at the picomolar concentration range. The lower limit of detection of the assay is 3 pg/mL. This sensitivity is obtained by use of a luminescent substrate and modification of a previously described and extensively validated enzyme immunoassay based on two different monoclonal antibodies (MAbs).¹² The 8E1 and 11E12 MAbs had been selected from a library of monoclonal antibodies obtained by lymphocyte hybridization technique and paired on the basis of their high specificity and affinity for the human cardiac troponin I isoform.¹³ They recognize independent epitopes of the protein. The first epitope is mapped in the unique sequence of 31 additional amino acid residues at the amino-terminal of the molecule not found in the skeletal muscle isoforms of troponin I and is recognized by the 11E12 MAb. The second epitope is located in the carboxy-terminal half of the protein and is recognized by the 8E1 MAb.^{13 14} The specificity of these monoclonal antibodies for the human cardiac isoform of troponin I is extremely high, and there is no detectable cross-reactivity (<0.01%) with the skeletal muscle isoforms of troponin I, even for concentrations >200 ng/mL.

Precision and accuracy. Precision refers to the magnitude of random errors and the reproducibility of measurements. Intra-assay and interassay precision testing resulted in coefficients of variation of 11% for within-run reproducibility and of 15% for run-to-run reproducibility. These coefficients describe the variability of data points with the SD as a percent of the average value. Accuracy refers to the extent to which all measurements agree with a true concentration value. Accuracy was assessed by a standard dilution test with satisfactory results, and the spiking test showed a recovery close to 100%, which is particularly important in measurement of serum or plasma samples because of their heterogeneity.

Principle of the immunoassay. Briefly, the solid phase of the assay is a polystyrene tube coated with the 8E1 anti–cardiac troponin I MAb. Revelation is performed with the peroxidase-labeled MAb 11E12. The samples and standards and the labeled tracer antibody are incubated in the coated tubes at room temperature. After washes, the enzymatic activity is revealed by addition of a luminescent substrate. The generated signal is directly proportional to the concentration of cardiac troponin I available in the sample. All samples were run in quadruplicate, and the average value is reported.

Cardiac Troponin I Standard Assay, CK-MB Isoenzyme, and Myoglobin Assays
In addition to the new-generation, highly sensitive immunoassay, cardiac troponin I concentration was also assessed by an established assay (upper reference limit, 0.1 ng/mL) simultaneously with CK-MB isoenzyme mass (upper reference limit, 6 ng/mL) and myoglobin concentrations (upper reference limit, 90 ng/mL) on an Access immunoassay system analyzer (all from Diagnostics Pasteur). Results from highly hemolyzed and severely lipemic samples were not used for statistical purposes. All measurements were performed blindly without knowledge of patients' history or clinical data.

Statistical Analysis
All statistics were performed with the SAS version 6.08 statistical package (SAS Institute Inc). Data are expressed as mean±SEM. The 95% CIs of the mean and the median (25th, 75th percentile) values are also provided. Nonparametric Kruskall-Wallis ANOVA was used to test between-group differences. Post hoc comparisons were performed by the Mann-Whitney U test and adjusted for multiple tests. The null hypothesis was rejected for values of P<.01.

	Results

Top Abstract Introduction Methods Results Discussion References

 
Severe congestive heart failure was the final clinical pathway in patients with ischemic and idiopathic dilated cardiomyopathies. Their radionuclide left ventricular ejection fraction was abruptly and similarly decreased regardless of the underlying cause and, not surprisingly, tended to be somewhat higher in patients with class III symptoms. The characteristics of congestive heart failure patients are detailed in Table 1. Left ventricular ejection fraction was within the normal range in all hospitalized control patients (0.69±0.01).

View this table: [in this window] [in a new window]   Table 1. Characteristics of Congestive Heart Failure Patients

Cardiac Troponin I Levels
The use of a highly sensitive immunoassay permitted the detection of cardiac troponin I in sera from healthy and hospitalized control subjects. The mean cardiac troponin I mass concentrations were 20.4±3.2 and 36.5±5.5 pg/mL in the healthy population and in the hospitalized control subjects, respectively. When both control groups were considered, the mean cardiac troponin I value was found to be 25.4±2.9 pg/mL in this cohort of 80 control subjects. In patients with congestive heart failure, the mean cardiac troponin I concentration was 72.1±15.8 pg/mL, significantly higher (P<.01) than in healthy blood donors, hospitalized control subjects, and the entire control population. These results are detailed in Table 2. No clear differences were seen between patients with idiopathic and ischemic cardiomyopathies or between NYHA class III and class IV patients in this population sample, despite a moderate increase of all biochemical markers in patients with idiopathic dilated cardiomyopathy and in patients with NYHA class IV symptoms (data not shown).

View this table: [in this window] [in a new window]   Table 2. Biochemical Markers of Myocardial Injury in the Study Population

When cardiac troponin I levels were assessed with the standard cardiac troponin I assay (upper reference limit, 0.1 ng/mL), in 8 of 35 congestive heart failure patients (23%), the assay failed to provide any evidence for a measurable protein concentration; in 26 patients, the cardiac troponin I values were below the upper reference limit; and in only 1 patient, a clearly positive cardiac troponin I value of 0.206 ng/mL was detected. The mean cardiac troponin I concentrations were virtually identical in heart failure patients and in the control population with this standard assay (0.02±0.01 versus 0.01±0.002 ng/mL).

CK-MB Mass and Myoglobin Levels
CK-MB mass and myoglobin concentrations were in the normal reference range for each immunoassay in all groups. However, congestive heart failure patients demonstrated an absolute increase in the CK-MB and myoglobin levels that paralleled the increase of cardiac troponin I (Table 2). Of the 35 congestive heart failure patients, 8 (23%) had CK-MB levels that exceeded the assay upper reference limit of 6 ng/mL. Importantly, when patients were stratified according to the CK-MB cutoff, all markers of myocardial injury clearly tended to be increased in the group of CK-MB–positive heart failure patients (Table 3).

View this table: [in this window] [in a new window]   Table 3. Biochemical Markers of Myocardial Injury in CK-MB Positive and Negative Congestive Heart Failure Patients

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
This study is the first written report to provide evidence for substantially increased levels of a myofibrillar protein in patients with advanced heart failure (Figure, panel A). However, the reported levels for cardiac troponin I both in the control population and in heart failure patients are far below the levels presently in use to diagnose acute myocardial infarction,^{12 15 16} to document perioperative myocardial injury,¹⁷ or to detect myocardial injury in critically ill patients.¹⁸ They are sensitively detected only because of the high analytical performance of the immunoassay and are expressed in units of picograms per milliliter. Otherwise, cardiac troponin I levels remain undetectable or far below the upper reference limit of 0.1 ng/mL when sera are assessed with a conventional cardiac troponin I assay. Importantly, the increase in the absolute CK-MB and myoglobin concentrations reported in heart failure patients in the present study is subtle compared with the multiples of upper reference limit increase usually seen in patients with acute myocardial injury (Table 2).

View larger version (13K): [in this window] [in a new window]   Figure 1. Box-and-whisker plots illustrate serum concentrations of cardiac troponin I, creatine kinase (CK)-MB, and myoglobin in congestive heart failure patients (CHF, n=35), normal healthy blood donor control subjects (nCTL, n=55), hospitalized control patients (hCTL, n=25), and both control groups (nCTL and hCTL, n=80). Line within box is mean value, upper and lower box values represent ±1 SEM, whiskers in plot are defined as mean±1.96 SEM, and solid circles are individual data points exceeding this specified value. A, *P<.01 vs all groups. B, Cutoff of CK-MB immunoassay is 6 ng/mL; *P<.01 vs hCTL and (nCTL and hCTL). C, Cutoff of myoglobin immunoassay is 90 ng/mL; *P<.01 vs all groups.

Cardiac Troponin I in Blood Donors and Hospitalized Control Subjects
Studies of protein metabolism are important because of the continuous turnover of cardiac proteins and the central role of protein synthesis and degradation in physiological and pathological conditions. The intracardiac proteolytic events that commit a structurally bound protein to complete hydrolysis to free amino acids have not been unambiguously delineated in the normal myocyte. However, protein breakdown seems to be dependent on two basic mechanisms. One is lysosomal and involves proteolytic enzymes. The second is cytosolic and requires ATP and conjugation of proteins to ubiquitin.^{19 20} A third and unsuspected possibility is suggested by the reported cardiac troponin I values in the healthy blood donor control population. These values imply leakage of intracellular compounds from terminally differentiated cardiomyocytes and might suggest programmed cell death at some constitutive level, with regeneration of myocytes in the normal myocardium. The hypothesis is consistent with an extracardiac physiological turnover process for the protein, a similar pathway being described for low-molecular-weight proteins, including myoglobin.²¹ However, it is difficult to provide a definite interpretation of these data. An alternative explanation would suggest that the values of cardiac troponin I in the control population reflect minor analytical fluctuation of the results and an unspecific seric effect in the very low range of detection due to the high sensitivity of the immunoassay. Improving the operating characteristics of the assay most likely will result in a very low background and in an increased signal-to-noise ratio, further reducing the fluctuation of the generated signal in the low end of the standard curve. These are exciting hypotheses, and future work will be aimed at arbitrating between them.

The levels of cardiac troponin I in hospitalized control patients appeared to be slightly increased compared with the healthy blood donor control population (Table 2). Hospitalized control subjects have the characteristic features of hematologic malignancies, including severe anemia and hypoxemia, hypotension and tachycardia, and increased cardiac output. The myocardium of these patients is therefore exposed to a large spectrum of stresses that is likely to induce some level of subtle cardiac injury by chronically decreasing myocardial oxygen supply and/or increasing myocardial oxygen consumption. These patients are also at an age when atherosclerosis is likely to be present, and some of them may have had some degree of unsuspected intrinsic coronary artery disease. The cardiac troponin I level for the entire cohort of control subjects provides an estimate of what a reference mean cardiac troponin I value could be in a large and unselected control population with the use of this new, highly sensitive assay. Once again, it should be emphasized that this value is close to the low end of the standard curve and does not necessarily represent a definite reference value. Improved analytical performance of the immunoassay and a larger control population will most likely further refine this value.

Cardiac Troponin I in Heart Failure Patients
None of the heart failure patients included in the present study had evidence of acute myocardial infarction or injury. The serum concentrations of CK-MB mass and myoglobin were not significantly increased above the upper reference limits for both assays in any patients. Importantly, the reported clearly positive cardiac troponin I levels, detected by a highly sensitive assay, are far below the 0.1 ng/mL cutoff limit presently in use to diagnose acute myocardial injury with a standard cardiac troponin I assay.^{12 17} However, we have previously shown that increased cardiac troponin I levels can be sporadically measured in some severe congestive heart failure patients even with such an assay,²² and in the present study, we also detected a patient with a clearly positive cardiac troponin I value. Taken together, these data provide strong evidence that the level of the marker protein measured in any sample depends on the sensitivity and specificity of the assay used to detect it.

Severe congestive heart failure is associated with noncontiguous areas of myocardial cell death, structural abnormalities in viable myocytes, and progressive interstitial fibrosis, which lead to worsening heart failure through cardiac remodeling.^{5 6 23} We theorize that the levels of cardiac troponin I in heart failure patients reflect cellular injury and ongoing degradative processes of the contractile apparatus. These levels are most likely part of the remodeling of the myocardium, and they sensitively monitor the cell death that accompanies the spontaneous progression of heart failure. The progressive impairment of cardiac structure and function occurs through a number of putative processes that include neurohormonal factors, oxidative stress, and a number of cytokines. Each of these factors can promote cardiac cell death by producing either myocyte necrosis^{5 23 24} or myocyte apoptosis through activation of specific genetic pathways.^{25 26} Both processes may be more common forms of myocardial cell death than initially believed, because focal and diffuse loss of contractile units constitutes the major structural characteristic of advanced heart failure and conditions the progression of the disease.

The presence of myofibrillar proteins in sera from congestive heart failure patients suggests that these myofibrils are degraded within the myocardium before their protein content is subsequently released into the circulation. Myocyte injury results in damage to contractile proteins and is a key mechanism responsible for the release of the structurally bound cardiac troponin I.²⁴ Experimental data further support this hypothesis and provide a plausible explanation for impaired contractility.²⁷ Extensive and functionally significant breakdown and release of cardiac troponin I, tropomyosin, -actinin, and myosin light chain 1 have also been demonstrated in tissue and effluent samples in a rat cardiac model of ischemia-reperfusion injury.²⁸ These data strengthen our fundamental hypothesis of myofibril degradation and strongly support the finding of increased cardiac troponin I circulating levels in patients with a chronically injured myocardium. Another potential mechanism for release of cardiac troponin I might be dependent on leakage of a cytosolic pool of functionally unbound protein, because the membranes of injured myocytes lose their properties of semipermeability and allow exposure of the intracellular milieu to the extracellular environment. However, such a possibility has not been definitively proved for cardiac troponin I,^{16 29} and the cytosolic pool, if any, of the protein can be estimated at <2%.

A different sequence of events in cardiac protein degradation is likely to occur in the normal and in the failing human myocardium. Changes in the cardiac protein composition occur under pathophysiological conditions and are accompanied by modifications in protein synthesis and breakdown.³⁰ These processes are controlled by substrate and energy availability and by mechanical factors.¹⁹ Increased proteolytic rate has been documented in animal models of heart failure.³¹ In the failing human myocardium, the degradation of cardiac troponin I might promote a compensatory upregulation of the synthesis rate in the cytosol and speed up the turnover of the protein. As a consequence, a constitutive increase of the myocardial cardiac troponin I content is likely to occur. Eventually, the deficient regulation of synthesis and breakdown of different myocardial proteins, including cardiac troponin I, could provide a mechanistic explanation for the deficient contraction in the chronically injured myocardium.

CK-MB and Myoglobin in Heart Failure Patients
CK-MB and myoglobin lack the absolute specificity of cardiac troponin I for the myocardium. Both are cytosolic enzymes that are not intrinsically linked to the myofibril. They appear only transiently in plasma after injury, and an increase in their concentration could result from membrane damage or even from cytosolic leakage only. Neither CK-MB mass nor myoglobin reflects the low-level but chronic structural degradation of the contractile apparatus involved in the remodeling process that ultimately produces a mechanically inefficient heart. Regardless of these considerations, the absolute increases in both CK-MB mass and myoglobin mean concentrations (Figure, panels B and C) strongly support the finding of high cardiac troponin I in patients diagnosed with severe congestive heart failure.

Clinical Implications
The cardiac troponin I levels in heart failure patients raise several important hypotheses: specifically, whether serial cardiac troponin I measurements could be beneficial for managing congestive heart failure and preventing progression of disease. Optimal treatment might seek to normalize cardiac troponin I levels in patients with increased baseline values, and future studies will be necessary to determine whether normalization is associated with better compensation of heart failure and/or a better prognosis. Cardiac troponin I could be used to assess the effects of different treatment approaches, including inotropic drug support, and monitor their therapeutic effectiveness. If this hypothesis gains support, it would provide a clearer rationale for early or even prophylactic strategies. This novel approach is likely to be more sensitive, convenient, and cost-effective in providing a cardiac-specific tool for refinement of the clinical assessment of risk and follow-up of patients diagnosed with severe congestive heart failure. Studies also have to be focused on cardiac troponin I levels in a population of patients with mild to moderate symptomatic heart failure. They might add substantial novelty to our understanding of the remodeling process at the cellular and subcellular levels and the timing and rate of progression of chronic congestive heart failure.

	Acknowledgments

 
We are grateful to Dr Allan Jaffe for critical review of the manuscript and many helpful suggestions and to Dr Véronique Bourgeois and Dr Marie-Christine Picot for statistical advice.

Received April 23, 1997; revision received June 9, 1997; accepted June 19, 1997.

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				N. A. Abbas, R. I. John, M. C. Webb, M. E. Kempson, A. N. Potter, C. P. Price, S. Vickery, and E. J. Lamb Cardiac Troponins and Renal Function in Nondialysis Patients with Chronic Kidney Disease Clin. Chem., November 1, 2005; 51(11): 2059 - 2066. [Abstract] [Full Text] [PDF]

				D. L. Mann and M. R. Bristow Mechanisms and Models in Heart Failure: The Biomechanical Model and Beyond Circulation, May 31, 2005; 111(21): 2837 - 2849. [Full Text] [PDF]

				J. J. Kottwitz, D. E. Preziosi, M. A. Miller, J. A. Ramos-Vara, D. J. Maggs, and J. D. Bonagura Heart Failure Caused by Toxoplasmosis in a Fennec Fox (Fennecus zerda) J. Am. Anim. Hosp. Assoc., November 1, 2004; 40(6): 501 - 507. [Abstract] [Full Text] [PDF]

				E. R. Perna, S. M. Macin, J. P. C. Canella, N. Augier, J. L. R. Stival, J. R. Cialzeta, A. E. Pitzus, E. H. Garcia, R. Obregon, M. Brizuela, et al. Ongoing Myocardial Injury in Stable Severe Heart Failure: Value of Cardiac Troponin T Monitoring for High-Risk Patient Identification Circulation, October 19, 2004; 110(16): 2376 - 2382. [Abstract] [Full Text] [PDF]

				Y Sato, T Kita, Y Takatsu, and T Kimura Biochemical markers of myocyte injury in heart failure Heart, October 1, 2004; 90(10): 1110 - 1113. [Abstract] [Full Text] [PDF]

				C. Roongsritong, I. Warraich, and C. Bradley Common Causes of Troponin Elevations in the Absence of Acute Myocardial Infarction: Incidence and Clinical Significance Chest, May 1, 2004; 125(5): 1877 - 1884. [Abstract] [Full Text] [PDF]

				S. A. Jortani, S. D. Prabhu, and R. Valdes Jr Strategies for Developing Biomarkers of Heart Failure Clin. Chem., February 1, 2004; 50(2): 265 - 278. [Abstract] [Full Text] [PDF]

				D. Ritter, P. A. Lee, J. F. Taylor, L. Hsu, J. D. Cohen, H. D. Chung, and K. S. Virgo Troponin I in Patients without Chest Pain Clin. Chem., January 1, 2004; 50(1): 112 - 119. [Abstract] [Full Text] [PDF]

				M. Imazio, B. Demichelis, E. Cecchi, R. Belli, A. Ghisio, M. Bobbio, and R. Trinchero Cardiac troponin i in acute pericarditis J. Am. Coll. Cardiol., December 17, 2003; 42(12): 2144 - 2148. [Abstract] [Full Text] [PDF]

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				T Goto, H Takase, T Toriyama, T Sugiura, K Sato, R Ueda, and Y Dohi Circulating concentrations of cardiac proteins indicate the severity of congestive heart failure Heart, November 1, 2003; 89(11): 1303 - 1307. [Abstract] [Full Text] [PDF]

				T. B. Horwich, J. Patel, W. R. MacLellan, and G. C. Fonarow Cardiac Troponin I Is Associated With Impaired Hemodynamics, Progressive Left Ventricular Dysfunction, and Increased Mortality Rates in Advanced Heart Failure Circulation, August 19, 2003; 108(7): 833 - 838. [Abstract] [Full Text] [PDF]

				C. P. Cannon and A. G.G. Turpie Unstable Angina and Non-ST-Elevation Myocardial Infarction: Initial Antithrombotic Therapy and Early Invasive Strategy Circulation, June 3, 2003; 107(21): 2640 - 2645. [Full Text] [PDF]

				R. Labugger, J. A. Simpson, M. Quick, H. A. Brown, C. E. Collier, I. Neverova, and J. E. Van Eyk Strategy for Analysis of Cardiac Troponins in Biological Samples with a Combination of Affinity Chromatography and Mass Spectrometry Clin. Chem., June 1, 2003; 49(6): 873 - 879. [Abstract] [Full Text] [PDF]

				C. M. O'Connor, W. A. Gattis, K. F. Adams Jr, V. Hasselblad, B. Chandler, A. Frey, I. Kobrin, M. Rainisio, M. R. Shah, J. Teerlink, et al. Tezosentan in patients with acuteheart failure and acute coronary syndromes: Results of the randomized intravenous tezosentan study (ritz-4) J. Am. Coll. Cardiol., May 7, 2003; 41(9): 1452 - 1457. [Abstract] [Full Text] [PDF]

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				M. E. Bertrand, M. L. Simoons, K. A.A. Fox, L. C. Wallentin, C. W. Hamm, E. McFadden, P. J. De Feyter, G. Specchia, and W. Ruzyllo Management of acute coronary syndromes in patients presenting without persistent ST-segment elevation Eur. Heart J., December 1, 2002; 23(23): 1809 - 1840. [Full Text] [PDF]

				A. van der Laarse Hypothesis: troponin degradation is one of the factors responsible for deterioration of left ventricular function in heart failure Cardiovasc Res, October 1, 2002; 56(1): 8 - 14. [Abstract] [Full Text] [PDF]

				D. A. Colantonio, W. Pickett, R. J. Brison, C. E. Collier, and J. E. Van Eyk Detection of Cardiac Troponin I Early after Onset of Chest Pain in Six Patients Clin. Chem., April 1, 2002; 48(4): 668 - 671. [Full Text] [PDF]

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