Usefulness of detectable levels of troponin, below the 99th percentile of the normal range, as a clue to the presence of underlying coronary artery disease

Low-attenuation coronary plaque burden and troponin release in chronic coronary syndrome: A mediation analysis

BACKGROUND

Coronary low-attenuation plaque (LAP) burden is a strong predictor of myocardial infarction in patients with stable chest pain. We aimed to assess the relationship between LAP burden and circulating levels of high-sensitivity cardiac troponin T (hs-cTnT), and to explore the potential underlying etiology in patients undergoing clinically indicated coronary CT angiography (CCTA).

METHODS

A comprehensive metabolic and lipid panel, as well as C-reactive protein (CRP) and hs-cTnT tests were obtained from consecutive patients with stable chest pain at the time of CCTA. Qualitative and quantitative coronary plaque analysis, CT-derived fractional flow reserve (FFR) calculation, and pericoronary adipose tissue (PCAT) attenuation measurement around the right coronary artery were performed on CCTA images. Linear regression analyses were performed to identify independent associations with hs-cTnT concentration and mediation analysis was used to assess whether ischemia or markers of inflammation mediate hs-cTnT elevation.

RESULTS

In total, 114 patients (56.3 ​± ​10.6 years, 44.7 ​% female) were enrolled. In multivariable analysis, age (β ​= ​0.04 [95%CI: 0.02; 0.06], p ​< ​0.001), female sex (β ​= ​-0.77 [95%CI: -1.20; 0.33], p ​< ​0.001), and LAP burden (β ​= ​0.03 [95%CI: 0.001; 0.06], p ​= ​0.04) were independently associated with hs-cTnT levels. Mediation analysis, on the other hand, did not identify a significant mediating effect of lesion-specific ischemia based on CT-FFR, circulating CRP levels, or PCAT values between LAP burden and hs-cTnT levels (all p ​> ​0.05).

CONCLUSION

Although ischemia and inflammation have previously been proposed to mediate the association between LAP burden and hs-cTnT levels, our results did not confirm the role of these pathophysiological pathways in patients with stable chest pain.

Utility of cardiovascular magnetic resonance in patients with stable troponin elevation

AIMS

Cardiovascular magnetic resonance (CMR) imaging has a potential role in the evaluation of symptomatic patients with stable troponin elevation; however, its utility remains unexplored. We sought to determine the incremental diagnostic value of CMR in this unique cohort and assess the long-term clinical outcomes.

METHODS AND RESULTS

Two hundred twenty-five consecutive patients presenting with cardiac chest pain/dyspnoea, stable troponin elevation, and undergoing CMR assessment were identified retrospectively from registry database. The study cohort was prospectively followed for major adverse cardiac events (MACEs) (defined as composite of all-cause mortality and cardiovascular readmissions). The primary outcome measure was the diagnostic utility of CMR, i.e. percentage of patients for whom CMR identified the cause of stable troponin elevation. Secondary outcome measures included the incremental value of CMR and occurrence of MACE. CMR was able to identify the cause for stable troponin elevation in 160 (71%) patients. A normal CMR was identified in 17% and an inconclusive CMR in 12% of the patients. CMR changed the referral diagnosis in 59 (26%) patients. Utilizing a baseline prediction model (pre-CMR referral diagnosis), the net reclassification index was 0.11 and integrated discriminatory improvement index measured 0.33 following CMR. Over a median follow-up of 4.3 years (interquartile range 2.8-6.3), 72 (32%) patients experienced MACE.

CONCLUSION

CMR identified a cause for stable troponin elevation in 7 of 10 cases, and a new diagnosis was evident in 1 of 4 cases. CMR improved the net reclassification of patients with stable troponin elevation.

Nourin-Dependent miR-137 and miR-106b: Novel Biomarkers for Early Diagnosis of Myocardial Ischemia in Coronary Artery Disease Patients

Background: Although cardiovascular imaging techniques are widely used to diagnose myocardial ischemia in patients with suspected stable coronary artery disease (CAD), they have limitations related to lack of specificity, sensitivity and “late” diagnosis. Additionally, the absence of a simple laboratory test that can detect myocardial ischemia in CAD patients, has led to many patients being first diagnosed at the time of the development of myocardial infarction. Nourin is an early blood-based biomarker rapidly released within five minutes by “reversible” ischemic myocardium before progressing to necrosis. Recently, we demonstrated that the Nourin-dependent miR-137 (marker of cell damage) and miR-106b-5p (marker of inflammation) can diagnose myocardial ischemia in patients with unstable angina (UA) and also stratify severity of ischemia, with higher expression in acute ST-segment elevation myocardial infarction (STEMI) patients compared to UA patients. Minimal baseline-gene expression levels of Nourin miRNAs were detected in healthy subjects. Objectives: To determine: (1) whether Nourin miRNAs are elevated in chest pain patients with myocardial ischemia suspected of CAD, who also underwent dobutamine stress echocardiography (DSE) or ECG/Treadmill stress test, and (2) whether the elevated levels of serum Nourin miRNAs correlate with results of ECHO/ECG stress test in diagnosing CAD patients. Methods: Serum gene expression levels of miR-137, miR-106b-5p and their corresponding molecular pathway network were measured blindly in 70 enrolled subjects using quantitative real time PCR (qPCR). Blood samples were collected from: (1) patients with chest pain suspected of myocardial ischemia (n = 38) both immediately “pre-stress test” and “post-stress test” 30 min. after test termination; (2) patients with acute STEMI (n = 16) functioned as our positive control; and (3) healthy volunteers (n = 16) who, also, exercised on ECG/Treadmill stress test for Nourin baseline-gene expression levels. Results: (1) strong correlation was observed between Nourin miRNAs serum expression levels and results obtained from ECHO/ECG stress test in diagnosing myocardial ischemia in CAD patients; (2) positive “post-stress test” patients with CAD diagnosis showed upregulation of miR-137 by 572-fold and miR-106b-5p by 122-fold, when compared to negative “post-stress test” patients (p < 0.001); (3) similarly, positive “pre-stress test” CAD patients showed upregulation of miR-137 by 1198-fold and miR-106b-5p by 114-fold, when compared to negative “pre-stress test” patients (p < 0.001); and (4) healthy subjects had minimal baseline-gene expressions of Nourin miRNAs. Conclusions: Nourin-dependent miR-137 and miR-106b-5p are promising novel blood-based biomarkers for early diagnosis of myocardial ischemia in chest pain patients suspected of CAD in outpatient clinics. Early identification of CAD patients, while patients are in the stable state before progressing to infarction, is key to providing crucial diagnostic steps and therapy to limit adverse cardiac events, improve patients’ health outcome and save lives.

High-sensitive cardiac troponin for the diagnosis of acute myocardial infarction in different chronic kidney disease stages

BACKGROUND

Chronic kidney disease (CKD) are associated with acute myocardial infarction (AMI). High-sensitive cardiac troponin (hs-cTn) has been evidenced to enhance the early diagnostic accuracy of AMI, but hs-cTn levels are often chronically elevated in CKD patients, which reduces their diagnostic utility. The aim of this study was to derive optimal cutoff-values of hs-cTn levels in patients with CKD and suspected AMI.

METHODS

In this retrospective paper, a total of 3295 patients with chest pain (2758 in AMI group and 537 in Non-AMI group) were recruited, of whom 23.1% were had an estimated glomerular filtration rate (eGFR) of < 60 mL min-1 (1.73 m2)-1. Hs-cTnI values were measured at presentation.

RESULTS

AMI was diagnosed in 83.7% of all patients. The optimal value of hs-TnI in diagnosing AMI was 1.15 ng mL-1, which were higher in males than females comparing different cutoff-values of subgroups divided by age, gender and renal function, and which increased monotonically with decreasing of eGFR because in patients with CKD without AMI, the correlation between hs-cTnI and renal function is low but significant (r2 = 0.067, P < 0.001).

CONCLUSIONS

Different optimal cutoff-values of hs-cTnI in the diagnosis of AMI in patients with CKD were helpful to the clinical diagnosis of AMI in various populations and were higher in males than females, but which was needed to be validated by multicenter randomized controlled clinical studies in the future.

Effect of dobutamine stress echocardiography on serum heart fatty acid binding protein levels

Objective Heart fatty acid binding protein (HFABP) is a low-molecular-weight free protein that is abundant in the intracytoplasmic space of myocytes. Due to its unique features, serum HFABP levels may increase in myocardial ischaemia. The aim of this study was to evaluate the effect of myocardial ischaemia induced by dobutamine stress echocardiography (DSE) on serum HFABP levels. Methods and results A total of 30 consecutive patients with suspected myocardial ischaemia underwent DSE examination. HFABP levels were measured immediately before and 1 hour after DSE. HFABP rose significantly in individuals in the DSE positive group (1.66 ± 1.18 ng/ml vs 2.65 ± 1.34 ng/ml, P = 0.004), but remained unchanged in the DSE negative group (1.61 ± 0.77 ng/ml vs 1.85 ± 0.76 ng/ml, P = 0.066). Conclusion Serum HFABP levels increased significantly at 1 hour in the presence of ischaemia induced by DSE in patients with stable clinical coronary syndromes. No such increase was evident in the absence of ischaemia.

Serial High-Sensitivity Troponin T in Post-Primary Angioplasty Exercise Test

BACKGROUND

The kinetics of high-sensitivity troponin T (hscTnT) release should be studied in different situations, including functional tests with transient ischemic abnormalities.

OBJECTIVE

To evaluate the release of hscTnT by serial measurements after exercise testing (ET), and to correlate hscTnT elevations with abnormalities suggestive of ischemia.

METHODS

Patients with acute ST-segment elevation myocardial infarction (STEMI) undergoing primary angioplasty were referred for ET 3 months after infarction. Blood samples were collected to measure basal hscTnT immediately before (TnT0h), 2 (TnT2h), 5 (TnT5h), and 8 hours (TnT8h) after ET. The outcomes were peak hscTnT, TnT5h/TnT0h ratio, and the area under the blood concentration-time curve (AUC) for hscTnT levels. Log-transformation was performed on hscTnT values, and comparisons were assessed with the geometric mean ratio, along with their 95% confidence intervals. Statistical significance was assessed by analysis of covariance with no adjustment, and then, adjusted for TnT0h, age and sex, followed by additional variables (metabolic equivalents, maximum heart rate achieved, anterior wall STEMI, and creatinine clearance).

RESULTS

This study included 95 patients. The highest geometric means were observed at 5 hours (TnT5h). After adjustments, peak hscTnT, TnT5h/TnT0h and AUC were 59% (p = 0.002), 59% (p = 0.003) and 45% (p = 0.003) higher, respectively, in patients with an abnormal ET as compared to those with normal tests.

CONCLUSION

Higher elevations of hscTnT may occur after an abnormal ET as compared to a normal ET in patients with STEMI.

Clinical benefit of high-sensitivity cardiac troponin I in the detection of exercise-induced myocardial ischemia

BACKGROUND

A pilot study using a novel high-sensitivity cardiac troponin I (hs-cTnI) assay suggested that cTnI might be released into blood during exercise-induced myocardial ischemia. We investigated the potential clinical value of this signal.

METHODS

We included 819 patients with suspected exercise-induced myocardial ischemia referred for rest/bicycle myocardial perfusion single-photon emission computed tomography. The treating cardiologist used all available clinical information to quantify clinical judgment regarding the presence of myocardial ischemia using a visual analog scale twice: prior and after stress testing. High-sensitivity cTnI measurements were obtained before, immediately after peak stress, and 2 hours after stress testing in a blinded manner. Myocardial ischemia was adjudicated using perfusion single-photon emission computed tomography and coronary angiography findings.

RESULTS

Exercise-induced myocardial ischemia was detected in 278 (34%) patients. High-sensitivity cTnI levels were significantly higher at all time points in patients with myocardial ischemia as compared with those without (P < .001 for all). Combining clinical judgment prior exercise testing with baseline hs-cTnI levels increased diagnostic accuracy as quantified by the area under the receiver operating characteristics curve (AUC) from 0.672 to 0.757 (P < .001). Combining clinical judgment after exercise testing (AUC 0.704) with baseline or poststress hs-cTnI levels also increased the diagnostic accuracy (AUC 0.761-0.771, P < .001 for all). In contrast, exercise-induced changes in hs-cTnI during exercise did not seem useful, as they were small and similar in patients with or without myocardial ischemia.

CONCLUSIONS

High-sensitivity cTnI concentrations at rest and after exercise, but not its exercise-induced changes, provide substantial incremental value to clinical judgment including exercise electrocardiography regarding the presence of myocardial ischemia.

Troponin T and N-terminal pro B-Type natriuretic peptide and presence of coronary artery disease

BACKGROUND

We tested the effects of exercise intensity, sampling intervals, degree of coronary artery stenosis, and demographic factors on circulating N-terminal pro B-Type natriuretic peptide (NT-pro-BNP) and cardiac Troponin T (cTnT) in subjects suspected of coronary artery disease (CAD).

MATERIALS AND METHODS

A total of 242 subjects referred for diagnostic evaluation of possible CAD had blood samples obtained before, 5 min after, and again 20 h after a symptom-limited exercise test.

RESULTS

Totally 40 subjects had CAD with ≥ 50% stenosis, 115 subjects had no stenosis and 87 subjects served as controls. In univariate analysis CAD-subjects had higher median baseline NT-pro-BNP-levels (85.3 ng/L) compared with non-CAD-subjects (41.3 ng/L) and controls (40.1 ng/L), both p < 0.001, but the association disappeared in multivariate analysis adjusted for age and gender. NT-pro-BNP increased similarly after exercise in CAD-subjects, non-CAD-subjects, and controls (median increase 8.14 ng/L) and the increase was positively associated with baseline NT-pro-BNP but not presence of CAD. Median baseline cTnT was 6.25 ng/L in CAD-subjects and 3.00 ng/L in non-CAD-subjects as well as controls, both p < 0.0001. Median ΔcTnT (baseline to 20 h after exercise) was higher in CAD-subjects than non-CAD-subjects and controls (0.62 ng/L vs. 0.0 ng/L, p < 0.001). A linear relationship between ΔcTnT and 'percent of predicted maximal heart rate achieved' was found in subjects with ≥ 70% stenosis (n = 24, r = 0.4067 p = 0.046).

CONCLUSIONS

Baseline cTnT and ΔcTnT were found to be independently associated with CAD and also with exercise intensity in stable chest pain subjects. These properties were not identified for NT-pro-BNP.

Glycogen phosphorylase BB in myocardial infarction

Early experimental and clinical reports on glycogen phosphorylase BB (GPBB) kinetics following myocardial ischemic injury suggested that it could be a useful diagnostic marker for early detection of acute myocardial infarction (AMI). After more than two decades of investigation, there is now overwhelming body of evidence that do not support the use of GPBB measurement in diagnosis of acute AMI in patients presenting with acute chest pain. Currently, GPBB cannot be recommended as a diagnostic marker of AMI either as a stand-alone test or as an addition to (high-sensitive) troponin testing. It should be noted that these considerations apply to the early diagnosis of AMI, not to the prognostic stratification, which is also suggested but it warrants further investigation. The aim of this review is to summarize available evidence of GPBB measurement in early diagnosis of myocardial infarction.

Glycogen phosphorylase isoenzyme BB plasma kinetics is not related to myocardial ischemia induced by exercise stress echo test

BACKGROUND

Glycogen phosphorylase BB (GPBB) is released from cardiac cells during myocyte damage. Previous studies have shown contradictory results regarding the relation of enzyme release and reversible myocardial ischemia. The aim of this study was to determine the plasma kinetics of GPBB as a response to the exercise stress echocardiographic test (ESET), and to define the relationship between myocardial ischemia and enzyme plasma concentrations.

METHODS

We studied 46 consecutive patients undergoing ESET, with recent coronary angiography. In all patients, a submaximal stress echo test according to Bruce protocol was performed. Concentration of GPBB was measured in peripheral blood that was sampled 5 min before and 10, 30 and 60 min after ESET.

RESULTS

There was significant increase of GPBB concentration after the test (p=0.021). Significant increase was detected 30 min (34.9% increase, p=0.021) and 60 min (34.5% increase, p=0.016) after ESET. There was no significant effect of myocardial ischemia on GPBB concentrations (p=0.126), and no significant interaction between sampling intervals and myocardial ischemia, suggesting a similar release profile of GPBB in ischemic and non-ischemic conditions (p=0.558). Patients in whom ESET was terminated later (stages 4 or 5 of standard Bruce protocol; n=13) had higher GPBB concentrations than patients who terminated ESET earlier (stages 1, 2 or 3; n=33) (p=0.049). Baseline GPBB concentration was not correlated to any of the patients' demographic, clinical and hemodynamic characteristics.

CONCLUSIONS

GPBB plasma concentration increases after ESET, and it is not related to inducible myocardial ischemia. However, it seems that GPBB release during ESET might be related to exercise load/duration.

Serial measurements of high-sensitivity cardiac troponin T after exercise stress test in stable coronary artery disease

OBJECTIVE

The aim was to assess serial measurements of high-sensitivity cardiac troponin T (hs-cTNT) post-exercise in patients with stable coronary artery disease (CAD).

METHODS

Twelve patients with positive coronary angiograms (CAD positives) and 12 controls performed an exercise stress test.

RESULTS

CAD positive had higher baseline and peak concentrations of hs-cTNT than controls. Significant increases in hs-cTNT were seen in both groups after exercise. In two-third of patients the peak in hs-cTNT was above the 99th percentile.

CONCLUSION

hs-cTNT is higher in patients with stable coronary disease than in controls and exceeds the diagnostic cut-off value for myocardial infarction in a majority of patients with CAD after exercise.

Determinants of high-sensitivity troponin T among patients with a noncardiac cause of chest pain

BACKGROUND

It is unknown to what extent noncardiac causes, including renal dysfunction, may contribute to high-sensitivity cardiac troponin T levels.

METHODS

In an observational international multicenter study, we enrolled consecutive patients presenting with acute chest pain to the emergency department. Of 1181 patients enrolled, 572 were adjudicated by 2 independent cardiologists to have a noncardiac cause of chest pain. Multiple linear regression analyses were used to determine the important predictors of log-transformed high-sensitivity cardiac troponin T. Kaplan-Meier curve was used to assess the prognostic significance of high-sensitivity cardiac troponin T>0.014 μg/L (99th percentile).

RESULTS

A total of 88 patients (15%) had high-sensitivity cardiac troponin T>0.014 μg/L. Less than 50% of cardiac troponins could be explained by known cardiac or noncardiac diseases. In decreasing order of importance, age, estimated glomerular filtration rate, hypertension, previous myocardial infarction, and chronic kidney disease (adjusted r(2) 0.44) emerged as significant factors in linear regression analysis to predict high-sensitivity cardiac troponin T. High-sensitivity cardiac troponin T was best explained by a linear curve with age as ≤0.014 μg/L. Patients with high-sensitivity cardiac troponin T levels>0.014 μg/L were at increased risk for all-cause mortality (hazard ratio 3.0; 95% confidence interval, 0.8-10.6; P=.02) during follow-up.

CONCLUSION

Among the known covariates, age and not renal dysfunction is the most important determinant of high-sensitivity cardiac troponin T. Because known cardiac and noncardiac factors, including renal dysfunction, explain less than 50% of high-sensitivity cardiac troponin T levels among patients with a noncardiac cause of chest pain, unknown or underestimated cardiac involvement during the acute presenting condition seems to be the major cause of elevated high-sensitivity cardiac troponin T.

The combined prognostic potential of serum high-sensitivity cardiac troponin I and N-terminal pro-B-type natriuretic peptide concentrations in dogs with degenerative mitral valve disease

BACKGROUND

Identification of factors associated with decreased survival in dogs with degenerative mitral valve disease (DMVD) will allow more accurate prognosis. N-terminal pro-B-type natriuretic peptide (NT-proBNP) is negatively associated with survival in dogs with DMVD. In human patients, multimarker strategies provide superior risk stratification compared with single markers.

HYPOTHESIS

High-sensitivity cardiac troponin I (hscTnI) and other clinical variables will be associated with survival time in dogs with DMVD. Measuring hscTnI and NT-proBNP in combination will be prognostically superior to measurement of either marker alone. The rate of change of these markers will vary according to cause of death.

ANIMALS

Client-owned dogs (n = 202) with DMVD of varying severity and age-matched healthy control dogs (n = 30) recruited from first opinion private practice.

METHODS

Prospective cohort study relating clinical variables at enrollment in dogs with DMVD to survival time (all-cause, cardiac, and noncardiac mortality). Multivariable Cox regression analysis was used to identify factors associated with survival. Measurements were obtained approximately every 6 months. Repeated measures models were constructed to assess changes over time.

RESULTS

hscTnI, LVEDDN, heart rate, and age were independently associated with decreased survival time (all-cause mortality). Survival times were shortest in dogs in which both serum hscTnI and NT-proBNP were increased. hscTnI and NT-proBNP increased more rapidly in dogs that died of cardiac disease.

CONCLUSIONS AND CLINICAL IMPORTANCE

Serum hscTnI has prognostic value in dogs with DMVD. Measurement of NT-proBNP and hscTnI is prognostically superior to measuring either alone. Serial measurement strategies provide additional prognostic information.

High sensitivity troponin outperforms contemporary assays in predicting major adverse cardiac events up to two years in patients with chest pain

Background

Previous studies have shown a risk of subsequent major adverse cardiovascular events (MACEs) in patients with suspected acute coronary syndromes (ACSs) and elevated cardiac troponin. The aim of this study was to compare prognostic utility of high-sensitivity troponin with contemporary troponin assays in such patients.

Methods

In total, 332 patients with suspected ACS were investigated between November 2006 and April 2007; all were followed for two years. Blood samples were analysed to compare Roche Elecsys high-sensitivity troponin T (hsTnT), Abbott Architect troponin I 3rd generation (TnI 3) and Roche Elecsys troponin T (TnT), for the prediction of MACE (composite of cardiovascular death, non-fatal myocardial infarction and revascularization).

Results

Sixty-eight patients (20.5%) experienced MACE between discharge and two years. Receiver operating characteristic (ROC) curve derived area under the ROC curve (95% confidence intervals) for baseline hsTnT were 0.70 (0.63–0.76), TnI 3 0.66 (0.59–0.73) and TnT 0.61 (0.53–0.69). hsTnT ( P = 0.001) was superior to TnT and TnI 3 trended ( P = 0.094) to superiority but were equivalent to each other. hsTnT best stratified patients with cumulative event rates for two-year MACE of 35.6% for levels ≥99th percentile, 17.9% for levels between the limit of detection (LOD) and 99th percentile and 5.4% for levels <LOD compared with TnI 3: 33.0%, 31.1% and 10.9%, respectively. TnT had MACE rates of 36.7% when ≥99th percentile and 15.4% when <99th percentile (=LOD).

Conclusions

hsTnT outperformed contemporary TnI and TnT assays for the prediction of MACE at two years. Those with levels below the LOD for hsTnT identified a group of patients at very low risk for adverse events.

Cardiac troponin T measured with a highly sensitive assay for diagnosis and monitoring of heart injury in chronic Chagas disease

CONTEXT

Chronic Chagas disease (15 million patients; annual incidence, 40, 000 patients; annual mortality, 12 ,500 patients) is the most serious parasitic disease in Latin America. Between 10 and 30 years after infection, 30% of patients with Chagas disease develop heart injury, which is the main reason for its high mortality. Consequently, frequent cardiac diagnostics are required for patients with Chagas disease.

OBJECTIVE

To minimize time-intensive and cost-intensive diagnostics, such as electrocardiography, echocardiography, and radiologic imaging, we tested the effect of measuring serum cardiac troponin T (cTnT) with a highly sensitive assay. To indicate the pathophysiologic background for cTnT release in Chagas heart injury, inflammation markers, such as C-reactive protein and interleukin 6, were measured in parallel.

DESIGN

Serum cTnT was measured in 26 healthy subjects and in 179 patients with chronic Chagas disease who were asymptomatic (indeterminate stage, n  =  86), who were suffering from cardiomyopathy with or without megacolon (n  =  71), or who were suffering from megacolon exclusively (n  =  22).

RESULTS

Serum cTnT was significantly higher in patients with cardiomyopathy with or without megacolon than in healthy subjects, asymptomatic subjects, and patients with megacolon, and the cTnT value was correlated with the severity of the cardiomyopathy. The lower limit of detection for the highly sensitive assay (3 ng/L) was best at distinguishing patients with, and without, heart injury. C-reactive protein and interleukin 6 were found to parallel cTnT changes in both the different Chagas groups and the cardiomyopathy groups separated by disease severity.

CONCLUSIONS

Highly sensitive cTnT measurement has the potential to contribute to diagnosis and monitoring of heart injury in patients with chronic Chagas disease. The highly sensitive assay of cTnT release seems to be related to Chagas heart disease-specific inflammation.

Recommendations for the use of cardiac troponin measurement in acute cardiac care

The release of cardiomyocyte components, i.e. biomarkers, into the bloodstream in higher than usual quantities indicates an ongoing pathological process. Thus, detection of elevated concentrations of cardiac biomarkers in blood is a sign of cardiac injury which could be due to supply-demand imbalance, toxic effects, or haemodynamic stress. It is up to the clinician to determine the most probable aetiology, the proper therapeutic measures, and the subsequent risk implied by the process. For this reason, the measurement of biomarkers always must be applied in relation to the clinical context and never in isolation. There are a large number of cardiac biomarkers, but they can be subdivided into four broad categories, those related to necrosis, inflammation, haemodynamic stress, and/or thrombosis. Their usefulness is dependent on the accuracy and reproducibility of the measurements, the discriminatory limits separating pathology from physiology, and their sensitivity and specificity for specific organ damage and/or disease processes. In recent years, cardiac biomarkers have become important adjuncts to the delivery of acute cardiac care. Therefore, the Working Group on Acute Cardiac Care of the European Society of Cardiology established a committee to deal with ongoing and newly developing issues related to cardiac biomarkers. The intention of the group is to outline the principles for the application of various biomarkers by clinicians in the setting of acute cardiac care in a series of expert consensus documents. The first of these will focus on cardiac troponin, a pivotal marker of cardiac injury/necrosis.

High-Sensitivity Cardiac Troponin T for Early Prediction of Evolving Non–ST-Segment Elevation Myocardial Infarction in Patients with Suspected Acute Coronary Syndrome and Negative Troponin Results on Admission

Background: We sought to determine the diagnostic performance of the new high-sensitivity cardiac troponin T (hs-cTnT) assay for early detection of non–ST-segment myocardial infarction (NSTEMI) in patients with acute coronary syndrome.

Methods: We enrolled patients with retrospectively confirmed unstable angina or NSTEMI and an initially negative cTnT concentration and compared the performance of baseline concentrations and serial changes in concentration within 3 and 6 h. Percentage change criteria included ≥20% δ change and ROC-optimized value.

Results: Based on the standard fourth-generation cTnT result of ≥0.03 μg/L, an evolving NSTEMI was diagnosed in 26 patients, and 31 patients were classified as having unstable angina. With the use of the hs-cTnT assay at the 99th-percentile cutoff, the percentage of NSTEMI cases detected increased gradually from 61.5% on presentation to 100% within 6 h, and the overall number of MI diagnoses increased by 34.6% (35 vs 26 cases). A δ change ≥20% or ≥ROC-optimized value of &gt;117% within 3 h or ≥243% within 6 h yielded a specificity of 100% at sensitivities between 69% and 76%. The standard cTnT at the 99th percentile was less sensitive than hs-cTnT for early diagnosis of MI on presentation, and follow-up samples obtained within the initial 3 h demonstrated very low specificity of cTnT compared with hs-cTnT.

Conclusions: The high-sensitivity cTnT assay increases the number of NSTEMI diagnoses and enables earlier detection of evolving NSTEMI. A doubling of the hs-cTnT concentration within 3 h in the presence of a second concentration ≥99th percentile is associated with a positive predictive value of 100% and a negative predictive value of 88%.

Analytical Validation of a High-Sensitivity Cardiac Troponin T Assay

Background: We report the development of a novel high-sensitivity cardiac troponin T (hs-cTnT) assay, a modification of the Roche fourth-generation cTnT assay, and validation of the analytical performance of this assay.

Methods: Validation included testing of analytical sensitivity, specificity, interferences, and precision. We established the 99th percentile cutoff from healthy reference populations (n = 616). In addition, we studied differences in time to a positive result when using serial measurements of hs-cTnT vs cTnT in patients with a confirmed diagnosis of non-ST elevation myocardial infarction (non-STEMI).

Results: The hs-cTnT assay had an analytical range from 3 to 10 000 ng/L. At the 99th percentile value of 13.5 ng/L, the CV was 9% using the Elecsys® 2010 analyzer. The assay was specific for cTnT without interferences from human cTnI or cTnC, skeletal muscle TnT, or hemoglobin concentrations up to 1000 mg/L, above which falsely lower values would be expected. When the assay was evaluated clinically, a hs-cTnT higher than the 99th percentile concentration identified a significantly higher number of patients with non-STEMI on presentation (45 vs 20 patients, P = 0.0004) compared with cTnT, and a final diagnosis of non-STEMI was made in 9 additional patients (55 vs 46 patients, P = 0.23) after serial sampling. Time to diagnosis was significantly shorter using hs-cTnT compared with cTnT [mean 71.5 (SD 108.7) min vs 246.9 (82.0) min, respectively; P &lt; 0.01].

Conclusions: The analytical performance of hs-cTnT complies with the ESC-ACCF-AHA-WHF Global Task Force recommendations for use in the diagnosis of MI.

Coronary microembolization: from bedside to bench and back to bedside

Coronary microembolization from the erosion or rupture of a vulnerable atherosclerotic plaque occurs spontaneously in acute coronary syndromes and iatrogenically during percutaneous coronary interventions. Typical consequences of coronary microembolization are microinfarcts with an inflammatory response, contractile dysfunction, and reduced coronary reserve. Apart from transient elevations of creatine kinase and troponin, microemboli can be visualized by intracoronary Doppler and the resulting microinfarcts by late-enhancement nuclear magnetic resonance. Statins, antiplatelet agents, and coronary vasodilators protect against microembolization and microinfarction when started before percutaneous coronary interventions. Distal protection devices can retrieve atherothrombotic debris and prevent its embolization into the microcirculation, but their effect on clinical outcome has been disappointing so far, except for saphenous vein bypass grafts. Devices for aspiration of thrombi and thrombus-derived vasoconstrictor, thrombogenic, and inflammatory substances, however, reduce thrombus burden, improve perfusion, and provide protection in patients with acute myocardial infarction.

Subclinical myocardial necrosis and cardiovascular risk in stable patients undergoing elective cardiac evaluation

OBJECTIVE

The presence of subclinical myocardial necrosis as a prodrome to longer-term adverse cardiac event risk has been debated. The debate has focused predominantly within patients with acute coronary syndrome, and on issues of troponin assay variability and accuracy of detection, rather than on the clinical significance of the presence of subclinical myocardial necrosis (ie, "troponin leak") within stable cardiac patients. Herein, we examine the relationship between different degrees of subclinical myocardial necrosis and long-term adverse clinical outcomes within a stable cardiac patient population with essentially normal renal function.

METHODS AND RESULTS

Sequential consenting patients (N=3828; median creatinine clearance, 100 mL/min/1.73m(2)) undergoing elective diagnostic coronary angiography with cardiac troponin I (cTnI) levels below the diagnostic cut-off for defining myocardial infarction (<0.03 ng/mL) were evaluated. The relationship of subclinical myocardial necrosis with incident major adverse cardiovascular events (defined as any death, myocardial infarction, or stroke) over 3-year follow-up was examined. "Probable" (cTnI 0.001-0.008 ng/mL) and "definite" (cTnI 0.009-0.029 ng/mL) subclinical myocardial necrosis were observed frequently within the cohort (34% and 18%, respectively). A linear relationship was observed between the magnitude of subclinical myocardial necrosis and risk of 3-year incident major adverse cardiovascular events, particularly in those with cTnI 0.009 ng/mL or higher (hazard ratio, 3.00; 95% confidence interval, 2.4-3.8), even after adjustment for traditional risk factors, C-reactive protein, and creatinine clearance. The presence of subclinical myocardial necrosis was associated with elevations in acute phase proteins (C-reactive protein, ceruloplasmin; P<0.01 each) and reduction in systemic antioxidant enzyme activities (arylesterase; P<0.01) but showed no significant associations with multiple specific measures of oxidant stress, and showed borderline associations with myeloperoxidase, a marker of leukocyte activation.

CONCLUSIONS

In stable cardiology patients, prodromal subclinical myocardial necrosis is associated with substantially higher long-term risk for major adverse cardiovascular events. The underlying mechanisms contributing to this minimal troponin leak phenomenon warrants further investigation.

Will the universal definition of myocardial infarction criteria result in an overdiagnosis of myocardial infarction?

The Universal Definition of Myocardial Infarction (acute myocardial infarction [AMI]) requires detection of increasing or decreasing cardiac biomarkers (preferably cardiac troponin) with >or=1 value >99(th) percentile, together with either clinical symptoms, new ischemic electrocardiographic changes, or typical imaging findings indicative of myocardial necrosis as diagnostic criteria for AMI. However, a small cardiac troponin elevation together with ST-T segment abnormalities may also occur in clinically stable populations. Accordingly, 0.6% of elderly subjects from a community sample (PIVUS Study) and 6.7% of patients stabilized after an acute coronary syndrome (FRISC II Study) would have been labeled AMI following the Universal Definition of AMI when diagnostic classification had been based on a single cardiac troponin I result. In conclusion, our results emphasized the importance of a significant change in cardiac troponin to avoid misdiagnosis of AMI.

Value of Cardiac Troponin I Cutoff Concentrations below the 99th Percentile for Clinical Decision-Making

Background: The aim of this study was to evaluate factors influencing the 99th percentile for cardiac troponin I (cTnI) when this cutoff value is established on a highly sensitive assay, and to compare the value of this cutoff to that of lower cutoffs in the prognostic assessment of patients with coronary artery disease.

Methods: We used the recently refined Access AccuTnI assay (Beckman-Coulter) to assess the distribution of cTnI results in a community population of elderly individuals [PIVUS (Prospective Study of the Vasculature in Uppsala Seniors) study; n = 1005]. The utility of predefined cTnI cutoffs for risk stratification was then evaluated in 952 patients from the FRISC II (FRagmin and Fast Revascularization during InStability in Coronary artery disease) study at 6 months after these patients had suffered acute coronary syndrome.

Results: Selection of assay results from a subcohort of PIVUS participants without cardiovascular disease resulted in a decrease of the 99th percentile from 0.044 μg/L to 0.028 μg/L. Men had higher rates of cTnI elevation with respect to the tested thresholds. Whereas the 99th percentile cutoff was not found to be a useful prognostic indicator for 5-year mortality, both the 90th percentile (hazard ratio 3.1; 95% CI 1.9–5.1) and the 75th percentile (hazard ratio 2.8; 95% CI 1.7–4.7) provided useful prognostic information. Sex-specific cutoffs did not improve risk prediction.

Conclusions: The 99th percentile of cTnI depends highly on the characteristics of the reference population from which it is determined. This dependence on the reference population may affect the appropriateness of clinical conclusions based on this threshold. However, cTnI cutoffs below the 99th percentile seem to provide better prognostic discrimination in stabilized acute coronary syndrome patients and therefore may be preferable for risk stratification.

Detection of acute changes in circulating troponin in the setting of transient stress test-induced myocardial ischaemia using an ultrasensitive assay: results from TIMI 35

AIMS

To determine whether an ultrasensitive assay can permit quantification of changes in circulating cardiac troponin (Tn) in the setting of stress test-induced myocardial ischaemia.

METHODS AND RESULTS

Blood samples were obtained before, immediately after, and 2 and 4 h after stress testing with nuclear perfusion imaging in 120 patients. Troponin was measured using commercial assays as well as with a novel, ultrasensitive cardiac TnI assay with a limit of detection of 0.2 pg/mL. Using the ultrasensitive assay, TnI was detectable in all patients before stress testing (median 4.4 pg/mL, interquartile range 3.1-8.6 pg/mL). By 4 h, troponin levels were unchanged in patients without ischaemia, whereas circulating levels had increased by a median of 1.4 pg/mL (24% increase) in patients with mild ischaemia (P = 0.002) and by 2.1 pg/mL (40% increase) in patients with moderate-to-severe ischaemia (P = 0.0006). In contrast, changes in troponin levels across patients in different ischaemic categories were indistinguishable using commercial troponin assays. When added to clinical factors, a >1.3 pg/mL increase in TnI using the ultrasensitive assay was an independent predictor of ischaemia (odds ratio 3.54, P = 0.007).

CONCLUSION

Transient stress test-induced myocardial ischaemia is associated with a quantifiable increase in circulating troponin that is detectable with a novel, ultrasensitive TnI assay.

Biomarkers of atherosclerosis: clinical applications

Current cardiovascular risk prediction models incorporate traditional risk factors to estimate 10-year cardiovascular risk. Numerous blood-based biomarkers have been identified that are associated with increased cardiovascular risk after adjusting for traditional risk factors. Many of these biomarkers, alone or in combination, have been incorporated into risk prediction models to determine whether their addition increases the model's predictive ability. We review the recently published literature on blood-based biomarkers and examine whether incorporating these markers may improve clinical decision making.

Highly Sensitive Cardiac Troponin T Values Remain Constant after Brief Exercise- or Pharmacologic-Induced Reversible Myocardial Ischemia

Background: Using a new precommercial high-sensitivity cardiac troponin T (hsTnT) assay, we evaluated whether hsTnT increases after reversible myocardial ischemia.

Methods: In 195 patients undergoing nuclear stress testing (ST) using single-photon emission computed tomography (SPECT) for suspected ischemic heart disease, we measured hsTnT before and 18 min, 4 h, and 24 h after the stress test. Thirty patients were excluded before ST because of cardiac troponin T (cTnT) &gt;30 ng/L (0.03 μg/L) as measured by the fourth-generation commercial test. Another 65 patients were excluded because of a combination of fixed and reversible perfusion defects (PDs) after SPECT.

Results: We studied 18 patients with reversible PDs, 41 patients with fixed PDs, and 41 patients without any PDs. Of these 100 patients, 61 received dynamic ST and 39 pharmacological ST. Median baseline hsTnT concentrations (25th, 75th percentile) were comparable in patients with reversible, fixed, and no PDs [5.57 (2.47, 12.60), 8.01 (4.55, 12.44), and 6.90 (4.63, 10.59) ng/L, respectively]. After ST, median hsTnT concentrations did not change in the reversible, fixed, or no PD groups from baseline to 18 min [−0.41 (−0.81, 0.01), 0.01 (−0.75, 0.79), and 0.36 (−0.42, 1.01) ng/L] or from baseline to 4 h [−0.56 (−1.82, 0.74), 0.24 (−0.60, 1.45), and 0.23 (−0.99, 1.15) ng/L]. Median baseline hsTnT concentrations tended to be higher in patients undergoing pharmacological vs dynamic ST; however, there were no significant increases in hsTnT concentrations after either type of ST.

Conclusions: Elevation of cTnT is rather a consequence of irreversible myocyte death than reversible myocardial ischemia after exercise or pharmacologic myocardial ischemia.

The clinical need for high-sensitivity cardiac troponin assays for acute coronary syndromes and the role for serial testing

BACKGROUND

Cardiac troponin is the biomarker of choice for the serologic diagnosis of acute coronary syndromes. International cardiology and laboratory medicine guidelines have suggested that the cutoff concentration be set at the 99th percentile of a healthy population, with an assay imprecision of 10% or less. Unfortunately, most commercial troponin assays do not have the sensitivity and precision to reliably detect troponin in sera of healthy subjects. Therefore, there is a need to develop troponin assays with higher sensitivity, which cannot be achieved while also improving the assay's precision.

METHODS AND RESULTS

Novel prototype analytical testing devices have been developed that are 5- to 10-fold more sensitive than existing commercial troponin assays. These tests should enable an earlier detection of myocardial infarction relative to the time of presentation and detect a higher percentage of emergency department chest pain patients who are at risk for short-term major adverse cardiac events. However, use of a high-sensitivity troponin assay will also result in detection of more patients who have cardiac necrosis due to a nonischemic etiology.

CONCLUSIONS

Serial troponin testing will be necessary to determine the clinical significance of low levels of troponin release with use of high-sensitivity assays. Guidelines will need to be established to determine a change in troponin results that is statistically and clinically significant, and new considerations for the time interval needed between blood collections. This will enable the use of future high-sensitivity troponin assays to be more valuable.

New potential uses for cardiac troponins

This review briefly synthesizes the molecular biology of troponin, which is currently the best biochemical marker for the detection of cardiac injury and, thus, acute myocardial infarction as well. Potential new uses for the marker based on these insights, with a specific interest in cardiac troponin fragments that potentially could be linked to distinct clinical conditions, are described. Some of the clinical problems clinicians are faced with including how to use the markers in renal failure and the difficulties associated with the heterogeneity of current troponin assays are also discussed. Finally, we present the possibility of specific cardiac troponin fragments resulting from modification or degradation, associated with distinct pathological processes, as new potential uses for this biomarker.