Rapid exclusion of acute myocardial infarction in patients with undetectable troponin using a high-sensitivity assay

High-sensitivity troponin T and C-reactive protein to identify patients without cardiac structural and functional abnormalities as assessed by cardiac CT and SPECT imaging: can biomarkers predict cardiac health?

While high-sensitivity troponin-T (hsTnT) and C-reactive protein (hsCRP) are associated with structural heart disease, we thought to determine whether biomarkers can predict which heart is healthy based on multimodality imaging. Patients from the emergency department with acute chest pain suggestive of acute coronary syndrome undergoing contrast enhanced cardiac CT and stress single photon emission computed tomography (SPECT) myocardial perfusion imaging were included. HsTnT and hsCRP were assessed at time of CT. Imaging data were assessed for coronary atherosclerosis, left ventricular hypertrophy/dysfunction and myocardial perfusion abnormalities. Patients were stratified into those with or without any cardiac findings, who were considered as cardiac healthy. For biomarkers, low cut-off corresponding to good specificity and high cut-off corresponding to good sensitivity for cardiac health were derived. Among 117 patients (52 years, 55 % male), 42 (36 %) were cardiac healthy based on cardiac CT and SPECT imaging. These patients had significantly lower hsTnT and hsCRP levels as compared to those with functional or structural abnormalities (3.58 vs. 5.63 ng/L, p = 0.002; 0.82 vs. 1.93 mg/L, p = 0.0005; respectively). Patients with both low hsTnT (<3.00 ng/L) and hsCRP (<0.45 mg/L) had a probability of 85 % for being cardiac healthy. In contrast, patients with high hsTnT (>7.00 ng/L) and hsCRP (>2.00 mg/L) had 8 % probability for being cardiac healthy. Discriminative capacity of a dual-biomarker strategy was significantly improved as compared to hsTnT or hsCRP alone or to Framingham Risk score (AUC: 0.781 vs. 0.691; vs. 0.678; vs. 0.649; all p ≤ 0.02, respectively). A dual-biomarker strategy of hsTnT and hsCRP is highly discriminative for patients with normal cardiac structure and function and provides incremental value beyond the Framingham risk score.

High-sensitive cardiac troponin T

Cardiac troponin is the preferred biomarker for the diagnosis of acute myocardial infarction (AMI). The recent development of a high-sensitive cardiac troponin T (hs-cTnT) assay permits detection of very low levels of cTnT. Using the hs-cTnT assay improves the overall diagnostic accuracy in patients with suspected AMI, while a negative result also has a high negative predictive value. The gain in sensitivity may be particularly important in patients with a short duration from symptom onset to admission. Measurement of cardiac troponin T with the hs-cTnT assay may provide strong prognostic information in patients with acute coronary syndromes, stable coronary artery disease, heart failure and even in the general population; however, increased sensitivity comes at a cost of decreased specificity. Serial testing, as well as clinical context and co-existing diseases, are likely to become increasingly important for the interpretation of hs-cTnT assay results.

Biomarkers after risk stratification in acute chest pain (from the BRIC Study)

Current models incompletely risk-stratify patients with acute chest pain. In this study, N-terminal pro-B-type natriuretic peptide and cystatin C were incorporated into a contemporary chest pain triage algorithm in a clinically stratified population to improve acute coronary syndrome discrimination. Adult patients with chest pain presenting without myocardial infarction (n = 382) were prospectively enrolled from 2008 to 2009. After clinical risk stratification, N-terminal pro-B-type natriuretic peptide and cystatin C were measured and standard care was performed. The primary end point was the result of a clinical stress test. The secondary end point was any major adverse cardiac event at 6 months. Associations were determined through multivariate stratified analyses. In the low-risk group, 76 of 78 patients with normal levels of the 2 biomarkers had normal stress test results (negative predictive value 97%). Normal biomarkers predicted normal stress test results with an odds ratio of 10.56 (p = 0.006). In contrast, 26 of 33 intermediate-risk patients with normal levels of the 2 biomarkers had normal stress test results (negative predictive value 79%). Biomarkers and stress test results were not associated in the intermediate-risk group (odds ratio 2.48, p = 0.09). There were 42 major adverse cardiac events in the overall cohort. No major adverse cardiac events occurred at 6 months in the low-risk subgroup that underwent stress testing. In conclusion, N-terminal pro-B-type natriuretic peptide and cystatin C levels predict the results of stress tests in low-risk patients with chest pain but should not be substituted for stress testing in intermediate-risk patients. There is potential for their use in the early discharge of low-risk patients after clinical risk stratification.

Sensible use of high-sensitivity troponin assays

The first intracellular Ca(2+)-sensor protein to be described was the troponin complex. Only later it was -discovered that cardiac-specific isoforms of troponin I (cTnI) and troponin T (cTnT) exist, and nowadays, measurement of cardiac troponins is a corner stone in the diagnosis of patients with acute coronary syndrome (ACS). High-sensitivity (hs-) assays have been developed that can record slightly elevated plasma concentrations of cardiac troponins as early as 3 h after onset of clinical symptoms. International guidelines defined a diagnostic cut-off at cardiac troponin levels corresponding to the 99th percentile of a healthy reference population and require that hs-assays measure this concentration with an interassay coefficient of variation ≤10%. This review provides an overview of the diagnostic and prognostic use of cardiac troponins.

Current applications of cardiac troponin T for the diagnosis of myocardial damage

Biochemical markers of myocardial injury play an important role in the diagnosis of cardiovascular diseases. Measurement of cardiac biomarkers is one of the most important diagnostic tests in acute myocardial infarction (AMI), heart failure, and other cardiovascular disorders. Recently, the European Society of Cardiology, the American College of Cardiology Foundation, the American Heart Association, and the World Heart Federation have published a consensus definition of AMI that includes a detailed guideline for the assessment of biochemical markers in suspected disease. The cardiac troponins (cTI and cTnT) were recommended as preferred markers of myocardial necrosis in this setting. Herein, we review cardiac troponin biochemistry, the performance characteristics of cTnT assays, and optimal utilization of troponin in patients with proven or possible cardiovascular disease. We also discuss the use of troponin tests, with emphasis on cTnT, in different clinical situations in which its levels may be elevated.

A novel approach to cardiac troponins to improve the diagnostic work-up in chest pain patients

In patients with acute chest pain, current guidelines recommend serial measurements of cardiac troponins at predefined and partly late time points. Consequently, diagnostic assessment in these patients tends to be lengthy and often results in unnecessary admissions. We, therefore, evaluated whether an approach integrating troponin results into the clinical context provided by the individual patient's presentation might facilitate the early diagnostic work-up. In 197 chest pain patients, cardiac troponin I (cTnI; Stratus CS) was measured serially within 12 hours after hospital admission. In patient cohorts with different chances of having myocardial infarction (MI) according to clinical data, electrocardiographic findings, and admission biomarker results, pretest probabilities for MI were calculated and compared with posttest probabilities derived from subsequent cTnI results after admission. Elevated cTnI levels at 1 to 2 hours after admission revealed ≥95.0% posttest probabilities for MI in cohorts with intermediate or high chances of having MI. The posttest probabilities for the absence of MI were 94.7% to 98.2% in cohorts with low or intermediate chances of having MI when cTnI was negative at 2 hours. Troponin testing considering the individual patient's pretest probability of MI seems, in conclusion, to provide clinically useful information already 1 to 2 hours after admission. Such an approach has the potential to identify both patient cohorts in whom early discharge or admittance for further evaluation would be appropriate. This could facilitate the early diagnostic work-up of chest pain patients, thereby improving patient flow and reducing overcrowding in healthcare facilities.

High Sensitivity Troponins — Translating Research into Practice

Troponin is vital in the evaluation of acute coronary syndrome. Decision limits, based on the 99th percentile upper reference limit derived from a sufficiently large normal reference population, must be determined for each specific troponin method. The new troponins exhibit high-sensitivity performance – assay precision at less than 10% coefficient of variation (at the 99th percentile upper reference limit) and ability to detect measurable values in healthy subjects. The troponin literature has reached a tipping point necessitating guidance on its use from specialist societies.

CT coronary angiography: new risks for low-risk chest pain

Widespread conservative management of low-risk chest pain has motivated the development of a rapid triage strategy based on CT coronary angiography (CTCA) in the Emergency Department (ED). Recently, three prominent trials using this technology in the ED setting have presented results in support of its routine use. However, these studies fail to show the incremental prognostic value of CTCA over clinical and biomarker-based risk-stratification strategies, demonstrate additional downstream costs and interventions, and result in multiple harms associated with radio-contrast and radiation exposure. Observing the widespread overdiagnosis of pulmonary embolism following availability of CT pulmonary angiogram as a practice pattern parallel, CTCA use for low-risk chest pain in the ED should be advanced only with caution.

For a rapid diagnosis of acute myocardial infarction, a sensitive troponin assay is needed in the near-patient testing setting

An early diagnosis of myocardial infarction in the emergency setting would be advantageous for both patients and the physicians treating these patients. Guidelines currently recommend serial samples that are drawn at presentation and 6-9 h later to be measured for cardiac troponin to aid in this diagnosis. However, much effort has been directed to decrease the time to make a diagnosis in this setting, and there has been renewed interest in shortening the time between serial measurements as well as the turnaround time for reporting the results. By eliminating the blood sample transit time to the central laboratory, point-of-care testing or near-patient testing can reduce the turnaround time for reporting the results, however this is possibly at the cost of decreased diagnostic performance. In this article, we discuss the recent results from the RATPAC study, which evaluated whether the combination of myoglobin, the MB isoenzyme of creatine kinase (CKMB) and a sensitive troponin assay would be superior to troponin alone.

Usefulness of high-sensitivity troponin T for the evaluation of patients with acute chest pain and no or minimal myocardial damage

BACKGROUND

Although high-sensitivity troponins allow early diagnosis of acute myocardial infarction, their role for identification of acute coronary syndrome in patients with normal conventional troponin remains unclear.

METHODS AND RESULTS

A total of 446 patients presenting to the emergency department with chest pain and normal troponin (common practice assays) in 2 serial samples were included. Both samples were also centrally analyzed for high-sensitivity troponin T (hs-TnT) (Roche Diagnostics, Basel, Switzerland). Detection (>3 ng/L) and 99th percentile (≥ 14 ng/L) cutoffs of the maximum hs-TnT levels (hs-TnTmax) were considered. The end points were acute coronary syndrome diagnosis and the composite of in-hospital revascularization or 30-day cardiac events.

RESULTS

Acute coronary syndrome was adjudicated to 84 patients (19%), and 62 (14%) had the composite end point. In univariate setting, hs-TnTmax >3 ng/L exhibited high sensitivity (87% and 92%, respectively) and negative predictive value (93% and 97%) for both end points, whereas hs-TnTmax ≥ 14 ng/L provided high specificity (90% and 89%), although low positive predictive values (40% and 33%). After adjusting for clinical (pain characteristics and risk factors) and electrocardiographic data, there was a stepped increase of risk across hs-TnTmax categories (≤ 3, >3 but <14, and ≥ 14 ng/L) for both end points; however, the discriminative capacity added was marginal (integrated discrimination improvement of 2.6% and 3.5%, respectively).

CONCLUSIONS

Clinical and electrocardiographic data remain the most important tools for the evaluation of patients with chest pain and with no or minimal myocardial damage. The main contribution of hs-TnT is the high negative predictive value of undetectable levels (≤ 3 ng/L).

Clinical Use and Measurement of Cardiac Troponin (cTn)

Cardiac troponins are cardio-specific and are widely used for the early diagnosis and triage of patients with acute coronary syndromes in conjunction with clinical history, electrocardiographic changes and imaging. Troponin is also useful for the prediction of outcomes in acute coronary syndromes, renal failure, sepsis, and critically ill patients. New developments in assay technology, designated as high sensitivity troponins, permit detection of lower levels of troponin in most healthy individuals, earlier diagnosis of myocardial infarction, and prognosis of stable coronary disease in the community.

Multi-marker strategy of natriuretic peptide with either conventional or high-sensitivity troponin-T for acute coronary syndrome diagnosis in emergency department patients with chest pain: from the "Rule Out Myocardial Infarction using Computer Assisted Tomography" (ROMICAT) trial

BACKGROUND

Compared to troponin alone, a dual-marker strategy with natriuretic peptides may improve acute coronary syndrome (ACS) diagnosis with a single blood draw and provide physiologic information regarding underlying heart disease. We evaluate the value of adding natriuretic peptides (myocyte stress markers) to troponins (myocardial injury markers) for diagnosing ACS in emergency department patients with chest pain.

METHODS

In 328 patients (53 ± 12 years, 63% men) with an initially negative conventional troponin and nonischemic electrocardiogram who underwent 64-slice cardiac computed tomography (CT), we measured conventional troponin-T (cTnT), high-sensitivity troponin-T (hsTnT), N-terminal pro-B type natriuretic peptide, and mid-regional pro-atrial natriuretic peptide. ACS was defined as myocardial infarction or unstable angina. CT was evaluated for coronary plaque, stenosis, and regional wall motion abnormality.

RESULTS

Patients with ACS (n = 29, 9%) had higher concentrations of each biomarker compared to those without (all P < .01). Adding natriuretic peptides, especially N-terminal pro-B type natriuretic peptide, to both cTnT or hsTnT improved the C-statistics and net reclassification index for ACS, largely driven by correctly reclassifying events. Dual-negative marker results improved sensitivity (cTnT 38% to 83%-86%, hsTnT 59% to 86%-90%; all P < .01) and negative predictive value (cTnT 94% to 97%-98%, hsTnT 96% to 97%-98%) for ACS. Patients with dual-negative markers had the lowest percentage of CT coronary plaque, stenosis, and regional wall motion abnormality (all P-trend <.001).

CONCLUSION

Among emergency department patients with low-intermediate likelihood of ACS, combining natriuretic peptides with either conventional or highly-sensitive troponin improved discriminatory capacity and allowed for better reclassification of ACS, findings supported by structural and functional CT results.

A new improved accelerated diagnostic protocol safely identifies low-risk patients with chest pain in the emergency department

OBJECTIVES

To assess whether the accelerated diagnostic protocol (ADP) studied in the Asia Pacific Evaluation of Chest Pain Trial (ASPECT) could be optimized to effectively risk stratify patients with symptoms suggestive of acute coronary syndrome (ACS) and allow early discharge of very-low-risk patients.

METHODS

Patients presenting to the emergency department (ED) with chest pain were prospectively enrolled between November 2007 and April 2010. Blood samples were analyzed at 0 and 2 hours postpresentation with a point-of-care multimarker panel (POC-MMP; troponin I [TnI], creatine kinase myocardial band [CKMB] isoenzyme fraction, and myoglobin) and a high-sensitivity cardiac troponin T assay (hsTnT). Patients received standard care. The original ADP (Thrombolysis in Myocardial Infarction [TIMI] risk score = 0, no ischemic electrocardiogram [ECG] changes, and the multimarker panel negative) was compared with an ADP using the point of care TnI only, hsTnT only, or TIMI risk score = 0 to 1. Primary outcome was ACS within 30 days.

RESULTS

Of the 1,000 patients recruited, 362 (36.2%) had ACS. There were 12.3% identified as low risk by the original ADP with a sensitivity for ACS of 99.2% (95% confidence interval [CI] = 97.5% to 99.8%). The ADP with the point of care TnI only or hsTnT had the same sensitivity, but identified more patients for discharge (15.0% vs. 12.3%). Including patients with a TIMI risk score of 1 identified more patients as low risk (19.7%), but with a lower sensitivity (97.0% vs. 99.2%).

CONCLUSIONS

An ADP consisting of a TIMI risk score of 0, no new ECG changes, and negative troponin at 0 and 2 hours postpresentation safely identifies patients at low risk of ACS, in whom discharge without further evaluation can be considered.

Implications of lowering threshold of plasma troponin concentration in diagnosis of myocardial infarction: cohort study

OBJECTIVE

To assess the relation between troponin concentration, assay precision, and clinical outcomes in patients with suspected acute coronary syndrome.

DESIGN

Cohort study.

SETTING

Tertiary centre in Scotland.

PARTICIPANTS

2092 consecutive patients admitted with suspected acute coronary syndrome were stratified with a sensitive troponin I assay into three groups (<0.012, 0.012-0.049, and ≥0.050 µg/L) based on the 99th centile for troponin concentration (0.012 µg/L; coefficient of variation 20.8%) and the diagnostic threshold (0.050 µg/L; 7.2%).

MAIN OUTCOME MEASURE

One year survival without events (recurrent myocardial infarction, death) in patients grouped by troponin concentration.

RESULTS

Troponin I concentrations were <0.012 µg/L in 988 patients (47%), 0.012-0.049 µg/L in 352 patients (17%), and ≥0.050 µg/L in 752 patients (36%). Adoption of the 99th centile would increase the number of people receiving a diagnosis of myocardial infarction from 752 to 1104: a relative increase of 47%. At one year, patients with troponin concentrations of 0.012-0.049 µg/L were more likely to be dead or readmitted with recurrent myocardial infarction than those with troponin concentrations <0.012 µg/L (13% v 3%, P<0.001; odds ratio 4.7, 95% confidence interval 2.9 to 7.9). Compared with troponin ≥0.050 µg/L, patients with troponin 0.012-0.049 µg/L had a higher risk profile but were less likely to have a diagnosis of, or be investigated and treated for, acute coronary syndrome.

CONCLUSION

Lowering the diagnostic threshold to the 99th centile and accepting greater assay imprecision would identify more patients with acute coronary syndrome at risk of recurrent myocardial infarction and death but would increase the diagnosis of myocardial infarction by 47%. It remains to be established whether reclassification of these patients and treatment for myocardial infarction would improve outcome.

Diagnostic and prognostic utility of early measurement with high-sensitivity troponin T assay in patients presenting with chest pain

BACKGROUND

High-sensitivity troponin assays are now available for clinical use. We investigated whether early measurement with such an assay is superior to a conventional assay in the evaluation of acute coronary syndromes.

METHODS

Patients presenting to an emergency department with chest pain who did not have ST-segment elevation were prospectively recruited from November 2007 to December 2010. Patients underwent serial testing with a conventional cardiac troponin I assay. Samples were also obtained at presentation and two hours later for measurement of troponin T levels using a high-sensitivity assay. The primary outcome was diagnosis of myocardial infarction on admission; secondary outcomes were death, myocardial infarction and heart failure at one year.

RESULTS

Of the 939 patients enrolled in the study, 205 (21.8%) had myocardial infarction. By two hours after presentation, the high-sensitivity troponin T assay at the cut-off point of the 99th percentile of the general population (14 ng/L) had a sensitivity of 92.2% (95% confidence interval [CI] 88.1%-95.0%) and a specificity of 79.7% (95% CI 78.6%-80.5%) for the diagnosis of non-ST-segment myocardial infarction. The sensitivity of the assay at presentation was 100% among patients who presented four to six hours after symptom onset. By one year, the high-sensitivity troponin T assay was found to be superior than the conventional assay in predicting death (hazard ratio [HR] 5.4, 95% CI 2.7-10.7) and heart failure (HR 27.8, 95% CI 6.6-116.4), whereas the conventional assay was superior in predicting nonfatal myocardial infarction (HR 4.0, 95% CI 2.4-6.7).

INTERPRETATION

The high-sensitivity troponin T assay at the cut-off point of the 99th percentile was highly sensitive for the diagnosis of myocardial infarction by two hours after presentation and had prognostic utility beyond that of the conventional assay. To rule out myocardial infarction, the optimal time to test a second sample using the high-sensitivity troponin T level may be four to six hours after symptom onset, but this finding needs verification in future studies before it can become routine practice.