Acute coronary syndrome: biochemical strategies in the troponin era

From multi-omics approaches to personalized medicine in myocardial infarction

Myocardial infarction (MI) is a prevalent cardiovascular disease characterized by myocardial necrosis resulting from coronary artery ischemia and hypoxia, which can lead to severe complications such as arrhythmia, cardiac rupture, heart failure, and sudden death. Despite being a research hotspot, the etiological mechanism of MI remains unclear. The emergence and widespread use of omics technologies, including genomics, transcriptomics, proteomics, metabolomics, and other omics, have provided new opportunities for exploring the molecular mechanism of MI and identifying a large number of disease biomarkers. However, a single-omics approach has limitations in understanding the complex biological pathways of diseases. The multi-omics approach can reveal the interaction network among molecules at various levels and overcome the limitations of the single-omics approaches. This review focuses on the omics studies of MI, including genomics, epigenomics, transcriptomics, proteomics, metabolomics, and other omics. The exploration extended into the domain of multi-omics integrative analysis, accompanied by a compilation of diverse online resources, databases, and tools conducive to these investigations. Additionally, we discussed the role and prospects of multi-omics approaches in personalized medicine, highlighting the potential for improving diagnosis, treatment, and prognosis of MI.

Death or revascularization among nonadmitted ED patients with low-positive vs negative troponin T results

STUDY OBJECTIVE

Compare outcomes among emergency department (ED) patients with low-positive (0.01-0.02 ng/mL) vs negative troponin T.

METHODS

Retrospective cohort study of nonadmitted ED patients with troponin testing at a tertiary-care hospital. Trained research assistants used a structured tool to review charts from all nonadmitted ED patients with troponin testing, 12/1/2009 to 11/30/2010. Outcomes of death and coronary revascularization were assessed at 30 days and 6 months via medical record review, Social Security Death Index searches, and patient contact.

RESULTS

There were 57596 ED visits; with 33388 (58%) discharged immediately, 6410 (11%) assigned to the observation unit, and 17798 (31%) admitted or other. Troponin was measured in 2684 (6.7%) of the nonadmitted cases. Troponin was negative in 2523 (94.0%), low positive in 78 (2.9%), and positive (≥0.03 ng/mL) in 83 (3.1%). Of troponin-negative cases, 0.8% (95% CI, 0.4-1.1%) died or were revascularized by 30 days, vs 2.8% (95% CI, 0.0-6.7%) of low-positive cases (risk difference [RD], 2.0%; 95% CI, -1.8 to 5.9%). At 6 months, the rates were 1.7% (95% CI, 1.1-2.2%) and 12.9% (95% CI, 5.0-20.7%) (RD, 11%; 95% CI, 3.3-19.1%). Death alone at 30 days occurred in 0.4% (95% CI, 0.1-0.6%) vs 1.3% (95% CI, 0.0-3.8%) (RD, 0.9%; 95% CI, -1.6 to 3.4%). Death at 6 months occurred in 1.2% (95% CI, 0.8-1.6%) vs 11.7% (95% CI, 4.5-18.9%) (RD, 10%; 95% CI, 3.3-17.7%).

CONCLUSION

Among patients not initially admitted, rates of death and coronary revascularization differed insignificantly at 30 days but significantly at 6 months. Detailed inspection of our results reveals that the bulk of the added risk at 6 months was due to non-cardiac mortality.

Estimation of Ischemia Modified Albumin (IMA) Levels in Patients with Acute Coronary Syndrome

Myocardial ischemia produces free radicals that catalyze a series of oxidative reactions that damage healthy tissues. The N-terminal sequence of albumin is one of the proteins modified by these highly reactive oxygen species and forms the ischemia modified albumin (IMA). This study involves investigations undertaken in different study groups to assess the levels of IMA. Mean serum IMA levels (U/mL) in patients with ST-segment elevated myocardial infarction (92.1 ± 10.6), non-ST-segment elevated myocardial infarction (87.3 ± 5.95) and unstable angina (UA) (88.9 ± 6.16) were significantly higher than non-cardiac chest pain (77.9 ± 6.69) and also healthy subjects (54.7 ± 17.2) (p < 0.001). IMA is a highly sensitive marker and has a high predictive value, which might prove the usefulness of this biomarker for early detection of myocardial ischemia. These data indicate a possible role of the IMA test in the early triage of patients with chest pain.

Cardiac biomarkers in the intensive care unit

Cardiac biomarkers (CB) were first developed for assisting the diagnosis of cardiac events, especially acute myocardial infarction. The discoveries of other CB, the better understanding of cardiac disease process and the advancement in detection technology has pushed the applications of CB beyond the 'diagnosis' boundary. Not only the measurements of CB are more sensitive, the applications have now covered staging of cardiac disease, timing of cardiac events and prognostication. Further, CB have made their way to the intensive care setting where their uses are not just confined to cardiac related areas. With the better understanding of the CB properties, CB can now help detecting various acute processes such as pulmonary embolism, sepsis-related myocardial depression, acute heart failure, renal failure and acute lung injury. This article discusses the properties and the uses of common CB, with special reference to the intensive care setting. The potential utility of "multimarkers" approach and microRNA as the future CB are also briefly discussed.

Isolated creatine kinase-MB rise with normal cardiac troponins: a strange occurrence with difficult interpretation

A 37-year-old man is admitted to the hospital for retrosternal chest pain lasting more than 30  min and nonspecific ECG findings. Serial assays of cardiac biomarkers reveal an isolated elevation of creatine kinase-MB and negative troponin levels. A coronary angiography shows normal vessels in the presence of a Thrombolysis in Myocardial Infarction (TIMI) 2 flow. How should this patient be managed and treated? Is it a myocardial infarction? We here provide a review of the relevant literature and suggest that such a strange condition, for which several explanations are possible, involves a worse prognosis than for normal creatine kinase-MB and troponins.

Heart-type fatty acid binding protein as an adjunct to cardiac troponin-I for the diagnosis of myocardial infarction

We hypothesized that when used in combination with cardiac troponins, heart-type fatty acid binding protein (H-FABP) would have greater diagnostic value than conventional markers for the early diagnosis of myocardial infarction (MI). Patients with typical chest pain at a single emergency department were consecutively enrolled. Initial blood samples were drawn for H-FABP, myoglobin, creatine kinase isoenzyme MB (CK-MB), and cardiac troponin-I (cTnI) measurements. MI was defined by serial cTnI measurements. To evaluate the adjunctive role of biochemical markers, we derived and compared logistic regression models predicting MI in terms of their discrimination (area under the receiver operating characteristics curve, AUC) and overall fit (Bayesian information criterion, BIC). Seventy-six of 170 patients were diagnosed as having MI. The AUC of cTnI, H-FABP, myoglobin, and CK-MB were 0.863, 0.827, 0.784, and 0.772, respectively. A logistic regression model using cTnI (P = 0.001) and H-FABP (P < 0.001) had the biggest AUC (0.900) and the best fit determined by BIC. Sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio of this model at 30% probability were 81.6%, 80.9%, 4.26, and 0.23, respectively. H-FABP has a better diagnostic value than both myoglobin and CK-MB as an adjunct to cTnI for the early diagnosis of MI.

Current Trends in Diagnostic Biomarkers of Acute Coronary Syndrome

The diagnosis and management of patients with acute coronary syndrome (ACS) have evolved dramatically over the past decade. Biomarkers play an important role in the diagnosis of ACS, especially in unstable angina and non-ST-segment elevation myocardial infarction. Among these, cardiac troponin and creatine kinase appear to be the most sensitive and specific markers of myocardial injury. Recent studies have revealed several novel biomarkers. Elevated levels of C-reactive protein and interleukin-6 are strong independent markers of increased mortality among patients with ACS. However, the ideal biomarkers that offer early detection, risk stratification, selection of therapy, monitoring disease progression, and treatment efficacy remain to be elucidated. This review assesses limitations and contemporary needs for biomarkers in the context of diagnosis of ACS. It also discusses the newly developing technologies for novel biomarkers or novel biomarker protein signatures discovery, and importance of point-of-care testing for future management. Key words: Cardiac troponin, Creatine kinase, NSTEMI

Neuregulin-1 attenuated doxorubicin-induced decrease in cardiac troponins

Neuregulin-1 (NRG1) is a potential therapeutic agent for the treatment of doxorubicin (Dox)-induced heart failure. NRG1, however, activates the erbB2 receptor, which is frequently overexpressed in breast cancers. It is, therefore, important to understand how NRG1, via erbB2, protects the heart against Dox cardiotoxicity. Here, we studied NRG1-erbB2 signaling in Dox-treated mice hearts and in isolated neonatal rat ventricular myocytes (NRVM). Male C57BL/6 mice were treated with recombinant NRG1 before and daily after a single dose of Dox. Cardiac function was determined by catheterization. Two-week survival was analyzed by the Kaplan-Meier method. Cardiac troponins [cardiac troponin I (cTnI) and cardiac troponin T (cTnT)] and phosphorylated Akt protein levels were determined in mice hearts and in NRVM by Western blot analysis. Activation of caspases and ubiquitinylation of troponins were determined in NRVM by caspase assay and immunoprecipitation. NRG1 significantly improved survival and cardiac function in Dox-treated mice. NRG1 reduced the decrease in cTnI, cTnT, and cardiac troponin C (cTnC) and maintained Akt phosphorylation in Dox-treated mice hearts. NRG1 reduced the decrease in cTnI and cTnT mRNA and proteins in Dox-treated NRVM. Inhibition of erbB2, phosphoinositide 3-kinase (PI3K), Akt, and mTOR blocked the protective effects of NRG1 on cTnI and cTnT in NRVM. NRG1 significantly reduced Dox-induced caspase activation, which degraded troponins, in NRVM. NRG1 reduced Dox-induced proteasome degradation of cTnI. NRG1 attenuates Dox-induced decrease in cardiac troponins by increasing transcription and translation and by inhibiting caspase activation and proteasome degradation of troponin proteins. NRG1 maintains cardiac troponins by the erbB2-PI3K pathway, which may lessen Dox-induced cardiac dysfunction.

Different collection tubes in cardiac biomarkers detection

The role played by different collection tubes is one of the more frequently forgotten parameters, which influences the quality of laboratory results.We aimed to determine whether there is a significant difference in assay of myoglobin, cardiac troponin I, and CK-MB depending on the presence of anticoagulant and gel separator in the collecting tubes.Blood samples were collected in 40 consecutive patients admitted for acute coronary syndrome. The samples were taken at the same moment in three different tubes (tubes without anticoagulant and with gel separator, heparin tubes with gel separator and heparin tubes without gelseparator;Venosafe, Terumo Europe, Leuven Belgium). Myoglobin, CK-MB and cardiac troponin I were measured with a double side (sandwich) chemiluminescent immuenzymatic assay (Access Myoglobin, Access CK-MB, Access AccuTnI).Cardiac troponin I was not influenced by the type of collection tube used. On the contrary, myoglobin and CK-MB showed a statistical difference depending on the test tube. In particular, there was a significant difference between tubes without anticoagulant and with gel separator and tubes with heparin and without gel.

Elevated serum cardiac troponin in non-acute coronary syndrome

Cardiac troponins (CTn) are the most sensitive and specific biochemical markers of myocardial injury and risk stratification. The assay for troponin T (cTnI) is standardized, and results obtained from different institutions are comparable. This is not the case with troponin I (cTnT), and clinicians should be aware that each institution must analyze and standardize its own results. Elevated cTn levels indicate cardiac injury, but do not define the mechanical injury. The differentiation of cTn elevation caused by coronary events from those not related to an acute coronary syndrome (ACS) is tiresome, at times vexing, and often costly. Elevation of cTn in non-ACS is a marker of increased cardiac and all-cause morbidity and mortality. The cause of these elevations may involve serious medical conditions that require meticulous diagnostic evaluation and aggressive therapy. At present, there are no guidelines to treat patients with elevated troponin levels and no coronary disease. The current strategy of treatment of patients with elevated troponin and non-ACS involves treating the underlying causes.

Bench-to-bedside review: the value of cardiac biomarkers in the intensive care patient

The use of cardiac biomarkers in the intensive care setting is gaining increasing popularity. There are several reasons for this increase: there is now the facility for point-of-care biomarker measurement providing a rapid diagnosis; biomarkers can be used as prognostic tools; biomarkers can be used to guide therapy; and, compared with other methods such as echocardiography, the assays are easier and much more affordable. Two important characteristics of the ideal biomarker are disease specificity and a linear relationship between the serum concentration and disease severity. These characteristics are not present, however, in the majority of biomarkers for cardiac dysfunction currently available. Those clinically useful cardiac biomarkers, which naturally received the most attention, such as troponins and B-type natriuretic peptide, are not as specific as was originally thought. In the intensive care setting, it is important for the user to understand the degree of specificity of these biomarkers and that the interpretation of the results should always be guided by other clinical information. The present review summarizes the available biomarkers for different cardiac conditions. Potential biomarkers under evaluation are also briefly discussed.

Influence of acute physical exercise on emerging muscular biomarkers

: Although there is comprehensive information on traditional biomarkers of muscle and cardiac damage following exercise, less is known on the kinetics of innovative markers, including ischemia modified albumin (IMA), glycogen phosphorylase isoenzyme BB (GPBB), carbonic anhydrase III (CAIII) and heart-type fatty acid-binding protein (H-FABP) in athletes performing a sub-maximal exercise.

: A total of 10 healthy trained Caucasian males performed a 21-km run. Blood samples were collected before the run, immediately after (post), 3, 6 and 24 h thereafter. Cardiac troponin I (cTnI), myoglobin, creatine kinase isoenzyme MB (CK-MB), GPBB, CAIII and H-FABP were assayed using a new diagnostic system based on protein biochip array technology. IMA was measured by a commercial colorimetric assay on a Roche Modular system P.

: Significant variations by one-way analysis of variance were observed for CK-MB (p=0.013), myoglobin (p<0.001), GPBB (p=0.029), H-FABP (p<0.001), CAIII (p=0.006), but not for cTnI (p=1.00) and IMA (p=0.881). In particular, values of all the biomarkers tested, but cTnI and IMA, increased significantly immediately after the run. GPBB and H-FABP values returned to baseline 6 and 3 h thereafter, those of CAIII, CK-MB and myoglobin remained significantly elevated from the pre-run value up to 24 h after the run. The major variation over pre-run values was recorded for myoglobin (nearly 4-fold increment), whereas CAIII, CK-MB, GPBB and H-FABP increased by 2.9-, 1.8-, 1.4- and 1.2-fold, respectively.

: We conclude that a sub-maximal aerobic exercise influences the concentration of several markers of muscle damage. Except for IMA, not one of the emerging biomarkers tested can be safely used to rule out myocardial damage as well as cardiospecific troponins in patients who had undergone recent physical activity.

Clin Chem Lab Med 2008;46:1313–8.

Noninvasive positive airway pressure and risk of myocardial infarction in acute cardiogenic pulmonary edema: continuous positive airway pressure vs noninvasive positive pressure ventilation

BACKGROUND

The addition of both noninvasive continuous positive airway pressure (n-CPAP) or noninvasive intermittent positive pressure ventilation (n-IPPV) to medical treatment has been shown to improve the outcome of patients with acute cardiogenic pulmonary edema (ACPE). Previous studies indicated a potential risk of new-onset acute myocardial infarction (AMI) associated with the use of n-IPPV. Although further studies did not confirm this observation, a few recent metaanalyses could not eliminate all the doubts at this regards because of the paucity of data available and the presence of confounding factors. This study aims to assess whether the application of n-IPPV, as opposed to n-CPAP, increases the rate of AMI in ACPE patients.

METHODS

Fifty-two patients with severe hypoxemia consequent to ACPE were randomized to receive n-CPAP (n = 27) or n-IPPV (n = 25) in addition to medical therapy. Patients with signs of acute coronary syndrome on hospital admission were excluded from the study. Cardiac markers, ECG, and clinical/physiologic parameters were assessed at study entry, after 30 and 60 min, and every 6 h for the first 2 days.

RESULTS

No significant difference was observed in the rate of AMI (26.9% and 16% with n-CPAP and n-IPPV, respectively, p = 0.244). Rate of intubation (p = 0.481), death (p = 0.662), and hospital stay (p = 0.529) were not different between the two groups. Both techniques were effective in improving gas exchange and vital signs in patients with ACPE.

CONCLUSIONS

The AMI rate was not different with n-CPAP and n-IPPV, which resulted to be equally effective in the treatment of ACPE.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT00453947.

Earlier detection of myocardial infarction by an improved cardiac TnI assay

OBJECTIVES

The aim of this study was to establish the diagnostic sensitivity of combinations of well-selected monoclonal antibodies (mAbs) against cardiac troponin I (cTnI) to allow an earlier rule-in of acute coronary syndrome (ACS) patients.

DESIGN AND METHODS

Using several combinations of mAbs, four new experimental cTnI immunoassays were evaluated to analyze plasma samples from 62 patients suffering from angina (16/62), patients having a chest pain of extracardiovascular origin (19/62) and ACS without ST elevation (NSTE-ACS) (27/62).

RESULTS

Assay 2, which relies on a capture mAb directed against the central part of cTnI and two conjugated mAbs directed against the N-ter region, provided the best clinical sensitivity. In 11 out of 27 patients with NSTE-ACS, it detected an early rise of cTnI within 0 and 1 h upon admission, contributing to the detection of 53% of samples found to be negative by the reference AccuTnI Assay upon admission (Beckman Coulter), thereby reducing the delay in diagnosis.

CONCLUSIONS

Assay 2 can identify early cTnI elevation in NSTE-ACS, possibly facilitating the rule-in procedure for these patients once the assay is automated.

Rapid diagnosis of myocardial injury with troponin T and CK-MB relative index

BACKGROUND

Current hospital practice involves protracted observation of chest-pain patients to rule out myocardial infarction. Concurrent measurement of multiple biomarkers may increase sensitivity and make rapid diagnosis feasible.

OBJECTIVE

We sought to determine the optimal biomarker strategy for highly sensitive, early diagnosis of myocardial injury.

STUDY DESIGN

A prospective evaluation of 171 acute coronary syndrome patients admitted to a single university medical center was performed. Blood tests for creatine kinase (CK), CK myocardial band isoenzyme (CK-MB), and troponin T were obtained at 0, 3, 6, 8, and 16 hours after presentation to the emergency department. Myocardial injury was defined as a troponin T level of >or=0.03 ng/mL.

RESULTS

Troponin T had sensitivities of 79.7%, 95.7%, and 98.4% at the time of initial presentation, 3 and 6 hours after presentation, respectively. Using a combination of troponin T and CK-MB relative index, sensitivity on presentation was increased to 90.6%. The sensitivity was improved to 97.9% and 100% at 3 and 6 hours, respectively.

CONCLUSION

This study demonstrates that the diagnosis of myocardial injury can be accurately excluded within 6 hours of admission with high sensitivity using troponin T. The combination of troponin T and CK-MB relative index provided the largest improvement in diagnostic sensitivity at patient arrival. These results support the feasibility of rapid, efficient triage for the emergent presentation of patients with chest pain.

The value of bedside cardiac multibiomarker assay in rapid and accurate diagnosis of acute coronary syndromes

For emergency department physicians, timely triage and risk stratification of chest pain patients remains a challenge. Faced with an aging population and the growing prevalence of heart disease, clinicians are seeking more effective ways to diagnose acute coronary syndromes rapidly and accurately. Emergency department physicians must make critical and time-sensitive decisions based on patient history, physical examination, and 12-lead electrocardiogram as justification for diagnosis of acute coronary syndromes. But because most of these tools are not reliable independently, these incomplete strategies can result in costly and inappropriate treatment decisions.

In vitro and in vivo examination of cardiac troponins as biochemical markers of drug-induced cardiotoxicity

Cardiac troponin T (cTnT) and troponin I (cTnI) are becoming acknowledged as useful biochemical markers of drug-induced cardiotoxicity. In this study we examined the release kinetics of cTnT and cTnI using an in vitro model of isolated rat neonatal ventricular cardiomyocytes (NVCM, 72h treatment with 0.1-3microM of daunorubicin) and compared it with data from a rabbit model of chronic anthracycline-induced cardiomyopathy in vivo (3mg/kg of daunorubicin weekly, 10 weeks). In cell-culture media, the cTnI and cTnT concentrations were concentration- and time-dependently increasing in response to daunorubicin exposure and were negatively exponentially related to cardiomyocyte viability. With 3microM daunorubicin, the relative increase of AUC of cTnT and cTnI was 2.4- and 5.3-fold higher than the increase of LDH activity, respectively. In rabbits, the daunorubicin-induced cardiomyopathy was associated with progressive increase of both cTnT and cTnI. Although the correlation between cTnT and cTnI cumulative release (AUCs) was found (R=0.81; P<0.01) and both cardiac troponins corresponded well with the echocardiographically-assessed systolic dysfunction (R=0.83 and 0.81 for cTnT and cTnI, respectively; P<0.001), the first significant increase in cTnI levels was observed earlier (at a cumulative daunorubicin dose of 200mg/m(2)) than with cTnT (350mg/m(2)). In conclusion, our study has confirmed cTnT and cTnI as very sensitive and specific markers of anthracycline-induced cardiotoxicity. The troponins can become not only the bridge between the clinical and experimental studies of drug-induced cardiotoxicity but also the linkage between the preclinical experiments in vitro and in vivo.

The exciting story of cardiac biomarkers: from retrospective detection to gold diagnostic standard for acute myocardial infarction and more

This paper reviews the history of the contribution of the laboratory medicine to clinical cardiology and discusses the most important steps in this field. Until 20 years ago, the clinical laboratory only placed at the cardiologist's disposal a few assays for the retrospective detection of cardiac tissue necrosis, such as enzymatic methods for creatine kinase and lactate dehydrogenase activities. However, in the latter part of the 20th century, highly sensitive and specific assays, such as cardiac troponins, as well as assays for markers of myocardial function, such as cardiac natriuretic peptides, rapidly changed the scenario of clinical management of patients with cardiac diseases, assigning to the laboratory a pivotal role in the overall diagnostic flow. This is witnessed by the recent incorporation of these markers into international guidelines and in the redefinition of myocardial infarction. For the foreseeable future, new serum markers of myocardial ischemic, i.e. reversible, injury or related to coronary plaque instability and disruption are expected.

The influence of cardiopulmonary resuscitation without defibrillation on serum levels of cardiac enzymes: A time course study of out-of-hospital cardiac arrest survivors

BACKGROUND

The serum concentration of cardiac enzymes may be influenced by mechanical and electrical trauma due to cardiopulmonary resuscitation (CPR) attempts. This could complicate the determination of whether an acute myocardial infarction (AMI) had occurred. In this study, only patients without any of the known confounding factors affecting cardiac enzyme release were included, and the specific time course and patterns of serum cardiac enzyme levels after resuscitation were evaluated. The purpose is to help clinicians distinguish between spontaneous myocardial damage and that induced by CPR.

METHODS AND RESULTS

This prospective, observational study was performed in the emergency department on eight patients surviving cardiac arrest. They were selected for not having heart disease, chest trauma or septic shock; and not receiving defibrillation. The median (range) duration of return of spontaneous circulation (ROSC) was 13 min (5-30 min). Cardiac enzyme measurements were taken immediately after ROSC and every 6h thereafter. Although cardiac troponin I (cTnI) level reached as high as 62.6 ng/ml at 24 h in one patient, five of the eight (62.5%) patients had their cTnI level fall below the normal reference range (i.e. 2 ng/ml) by 30 h. The time to maximum and peak concentration of cTnI was 16.50+/-10.99 h and 16.85+/-21.50 ng/ml, respectively. Both MB creatine kinase (CKMB) and total creatine kinase (CK) levels were above their normal reference ranges. In addition, the CKMB/CK ratio exceeded 5% in all patients at any time point during this study.

CONCLUSION

In this study, the influence of resuscitative procedures - defibrillation excluded - on the release of cardiac enzymes were examined. During 30 h after ROSC cTnI level exhibited a bell-shaped configuration, which is distinct from that after AMI; whereas the enzymatic activities of CKMB and CK, as well as CKMB/CK ratio, were constantly higher than normal. This chronological pattern of cardiac enzyme levels may help physicians differentiate primary cardiac disease from other aetiologies in out-of-hospital cardiac arrests.

Sequential cardiac troponin T following delivery and its relationship with myocardial performance in neonates with respiratory distress syndrome

We measured serial cardiac troponin T in babies with respiratory distress syndrome and in "healthy" controls (no cardiorespiratory support required). We investigated relationships between cardiac troponin T and myocardial performance in respiratory distress syndrome. This was a prospective observational study at a large tertiary maternity unit that recruited 104 "healthy" babies from whom individual samples were collected. A further 24 infants with respiratory distress syndrome and 14 "healthy" preterm infants had serial sampling over the first three days. We measured fractional shortening in 14 of the infants with respiratory distress syndrome. Cardiac troponin T rose from a median (interquartile range) of 10 (10-11) pg/mL on day one to 34 (22-46) pg/mL by day three, p=0.005, in "healthy" babies. In respiratory distress syndrome levels were higher, 91 (46-135) pg/mL at 6 (5-7) hours of age, p<0.001, and remained so for all three days. In babies with respiratory distress syndrome on day one cardiac troponin T correlated negatively with fractional shortening, Rho=-0.831, p<0.001, but this correlation did not persist. In "healthy" babies there is a minimal rise of cardiac troponin T by day 3. In respiratory distress syndrome there is an early and sustained elevation of cardiac troponin T, with a negative relationship with fraction shortening, suggesting significant myocardial damage of antenatal/intrapartum origin, giving rise to measurable dysfunction.

The new definition of myocardial infarction and the impact of troponin determination on clinical practice

OBJECTIVE

To discuss the more controversial clinical and laboratory aspects in the application of the new biochemical diagnostic standard for myocardial infarction, 4 years after its introduction, and to make some suggestions, which could allow for a more realistic application of the new definition in the current clinical practice.

METHODS

Studies published in the last 4 years in the most important cardiology and laboratory medicine journals (including proceedings of the international meetings), discussing advantages and limits of the new definition of myocardial infarction, were reviewed and pertinent data were discussed and compared with similar information available in literature.

RESULTS AND CONCLUSIONS

Although the exact status of implementation of the new definition of myocardial infarction cannot yet be known, the trend toward such recommendation is evolving significantly, even if at different rates in different countries. To make the transition smoother, major educational efforts are required to disseminate the conceptual reasoning behind the new guidelines. On the other hand, more knowledge is needed for some relevant issues, such as the different analytical performance of cardiac troponin assays or the prognostic significance of biomarker changes after a percutaneous coronary intervention.

Point-of-Care Testing and Cardiac Biomarkers: The Standard of Care and Vision for Chest Pain Centers

Point-of-care testing (POCT) is defined as testing at or near the site of patient care. POCTdecreases therapeutic turnaround time (TTAT), increases clinical efficiency, and improves medical and economic outcomes. TTAT represents the time from test ordering to patient treatment. POC technologies have become ubiquitous in the United States, and, therefore,so has the potential for speed, convenience, and satisfaction, strong advantages for physicians, nurses, and patients in chest pain centers. POCT is applied most beneficially through the collaborative teamwork of clinicians and laboratorians who use integrative strategies, performance maps, clinical algorithms, and care paths (critical pathways). For example, clinical investigators have shown that on-site integration of testing for cardiac injury markers (myoglobin, creatinine kinase myocardial band [CKMB],and cardiac troponin I [cTnI]) in accelerated diagnostic algorithms produces effective screening, less hospitalization, and substantial savings. Chest pain centers, which now total over 150 accredited in the United States, incorporate similar types of protocol-driven performance enhancements. This optimization allows chest pain centers to improve patient evaluation, treatment, survival, and discharge. This article focuses on cardiac biomarker POCT for chest pain centers and emergency medicine.

Advances in cardiac biomarkers

The diagnostic and prognostic roles of new and established cardiac biomarkers are continually changing. This update article discusses clinical diagnosis as a framework for directing biomarker testing. Markers are reviewed in the settings of acute coronary syndromes, decompensated heart failure, and noncardiac clinical scenarios.

Circulating cardiovascular markers and mediators in acute illness: an update

An update is given of the circulating markers and mediators of cardiovascular dysfunction in acute illness. Some of these circulating markers reflect mediator action on the peripheral vasculature, such as endothelium-derived endothelin and nitrite/nitritate, the stable end products of nitric oxide. Other markers mainly reflect actions on the heart, such as the natriuretic peptide family, released from the heart upon dilatation, serving as a marker of congestive heart failure and potentially having negative inotropic effects. Indeed, some factors may be both markers as well as mediators of cardiovascular dysfunction of the acutely ill and bear prognostic significance. Assessing circulating levels may help refine clinical judgment of the cardiovascular derangements encountered at the bedside, together with clinical signs and hemodynamic variables. For instance, assessing natriuretic peptides in patients with pulmonary edema of unclear origin may help to diagnose congestive heart failure and cardiogenic pulmonary edema, when the pulmonary capillary wedge pressure is not measured or inconclusive. Future aligning of hemodynamic abnormalities with patterns of circulating cardiovascular markers/mediators may help to stratify patients for inclusion in studies to assess the causes, response to therapy and prognosis of cardiovascular derangements in the acutely ill.

Induction and detection of disturbed homeostasis in cardiopulmonary bypass

During cardiopulmonary bypass (CPB) haemodynamic alterations, haemostasis and the inflammatory response are the main causes of homeostatic disruption. Even with CPB procedures of short duration, the homeostasis of a patient is disrupted and, in many cases, requires intensive postoperative treatment to re-establish the physiological state of the patient. Although mortality is low, disruption of homeostasis may contribute to increased morbidity, particularly in high-risk patients. Over the past decades, considerable technical improvements in CPB equipment have been made to prevent the development of the systemic inflammatory response syndrome (SIRS). Despite all these improvements, only the inflammatory response, to some extent, has been reduced. The microcirculation is still impaired, as measured by tissue degradation products of various organs, indicating that CPB may still be considered as an unphysiological procedure. The question is, therefore, whether we can detect the pathophysiological consequences of CPB in each individual patient with valid bedside markers, and whether we can relate this to determinant factors in the CPB procedure in order to assist the perfusionist in improving the adequacy of CPB. The use of these markers could play a pivotal role in decision making by providing an immediate feedback on the determinant quality of perfusion. Therefore, we suggest validating the proposed markers in a nomogram to optimize not only the CPB procedure, but also the patient's safety.

Glycogen phosphorylase BB in acute coronary syndromes

The diagnosis of myocardial damage is preferably based on measurement of the cardiac-specific troponins. However, there is an emerging need for early, specific cardiac markers. One potential candidate is the glycogen phosphorylase BB isoenzyme (GPBB). We investigated the use of a new, commercially available GPBB ELISA assay in 61 patients presenting with an acute coronary syndrome (37 acute myocardial infarction, 24 unstable angina pectoris) in comparison to established cardiac markers such as troponin T, creatine kinase isoenzyme MB (CKMB) mass, and myoglobin. Blood samples were obtained on arrival, as well as 1, 2, 3, 4, 8, 12 and 24h later. GPBB plasma concentrations were elevated in 90.9% of patients 1h after onset of chest pain and increased to 100% at 4–5h. Within the first 6h, GPBB showed the highest sensitivity (95.5–100%) and high specificity (94–96%) compared to myoglobin (85–95% sensitivity) and CKMB mass (71.4–91.3% sensitivity). As expected, troponin T showed high specificity (100%) and sensitivity >95% later in the time course (≥3h). In un-stable angina pectoris patients, a very high rate of elevated GPBB was observed (93.9% at 3h) compared to myoglobin (66.7%). Cardiac troponin T and CKMB were only elevated in 33.8% and 55.0% of these patients, respectively. In conclusion, GPBB is a promising marker for the early diagnosis of acute coronary syndromes and could probably act as a marker of ischemia. However, further studies on specificity and development of a fast, automated assay are necessary before GPBB can be recommended as a routine diagnostic tool.

What's new in acute coronary syndrome?

Patients presenting with ACS are an exciting challenge for health care providers. It has been documented that hospitals that carry out evidence-based therapies related to ACS have reduced mortality rates and better outcomes in general. The use of evidence-based practices has been shown to be more difficult in women, the elderly, and nonwhite patients. This suggests that there are opportunities to make more substantial improvements in outcomes for these groups of individuals. There is a tremendous need to use the knowledge gained in treating patients with ACS. Surprisingly little is known about why health care professionals do not institute therapies that are based on quality evidence. What could the quality outcomes such as mortality rate be for ACS persons if there were widespread use of the knowledge already in the literature regarding the care of ACS clients?

Effect of sarcolemmal rupture on myocardial electrical impedance during oxygen deprivation

Plasma membrane disruption is a characteristic feature of cell death induced by hypoxia or ischemia. Here, we investigated whether analysis of tissue electrical impedance allows detection of ongoing cell membrane rupture and necrotic cell death in hypoxic or ischemic myocardium. Twenty-eight isolated rat hearts were submitted to 5 h of ischemia (n = 8) or hypoxia (n = 20). Myocardial electrical impedance and lactate dehydrogenase (LDH) release were monitored. The time course of hypoxia-induced cell death was modified by altering pH (pH 7.4 or 6.4, 5 h) or by adding 3 or 10 mM glycine. Ischemia and hypoxia induced an increase in electrical impedance, followed by a plateau, and later a reduction. During hypoxia, LDH release started after a prolonged lapse of time (80.00 +/- 8.37 min at pH 7.4 and 122.50 +/- 11.82 min at pH 6.4). The onset of LDH release was followed by the onset of the late reduction in electrical impedance, and both were delayed by acidic pH (P < 0.05) and by glycine (P < 0.05). The times of onset of LDH release and of late electrical changes were significantly correlated (r = 0.752, P < 0.001). In separate experiments, induction of sarcolemmal rupture with Triton X-100 (n = 6) mimicked the late effects of ischemia or hypoxia on tissue impedance. The protective effects of glycine and acidosis on membrane disruption were confirmed (propidium iodide) in energy-deprived HL-1 cardiomyocytes. These results describe for the first time a late fall in electrical impedance in myocardium submitted to prolonged oxygen deprivation and demonstrate that this fall allows detection of ongoing cell necrosis.

Myocardial infarction rate in acute pulmonary edema: noninvasive pressure support ventilation versus continuous positive airway pressure

OBJECTIVE

Noninvasive pressure support ventilation (NIPSV) delivered by face mask has proved an effective treatment for patients with acute pulmonary edema. However, an increase in acute myocardial infarction rate has been reported with this ventilation modality. We investigated whether the use of NIPSV increases the incidence of acute myocardial infarction compared with continuous positive airway pressure (CPAP) in patients with acute pulmonary edema.

DESIGN

Randomized, prospective, controlled study.

SETTING

Emergency Department, Niguarda Hospital of Milano (Italy).

PATIENTS

Forty-six patients affected by acute pulmonary edema.

INTERVENTIONS

The patients received either NIPSV (24 patients) or CPAP (22 patients) through a face mask.

MEASUREMENTS AND MAIN RESULTS

Cardiac enzymes (myoglobin, creatine kinase isoenzyme MB, and troponin I) were determined and electrocardiographic and physiologic measurements made over the subsequent 36 hrs. No significant differences were observed in the incidence of acute myocardial infarction in the CPAP group (13.6%) compared with the NIPSV group (8.3%). Both modalities of noninvasive ventilation improved ventilation and vital signs in patients with acute pulmonary edema. Two patients of the NIPSV group (8.3%) and one of the CPAP group (4.5%) required endotracheal intubation because vital signs and arterial blood gases worsened 1 hr after the start of noninvasive ventilation. No significant differences were found in in-hospital mortality rate.

CONCLUSIONS

NIPSV proved to be equally effective in improving vital signs and ventilation without increasing acute myocardial infarction rate in patients with nonischemic acute pulmonary edema in comparison to CPAP alone. However, because the study lacked statistical power and excluded patients with acute coronary syndromes, caution is still advised when applying NIPSV to the latter subgroup of patients.

Multicenter evaluation of analytical performance of the Liaison® troponin I assay

OBJECTIVES

This study evaluated the analytical characteristics of the Liaison immunoassay for cardiac troponin I (cTnI).

DESIGN AND METHODS

The protocol consisted of eight sections: evaluation of antibody specificity, linearity, detection limit and imprecision, method comparison, evaluation of endogenous interferents, anticoagulant interference, sample stability, and reference values.

RESULTS

The assay equally measured free and complexed cTnI. The minimum detectable cTnI concentration was 0.021 microg/l. The cTnI concentration corresponding to a total CV of 10% was 0.056 microg/l. Linearity of response was demonstrated along the entire dynamic range of the assay. Assay interferences were minimal. cTnI concentrations in serum and heparinized plasma were significantly different. Values in EDTA plasma were on average approximately 5% higher than in matched serum, but this difference was not significant. The 99th percentile cTnI value in healthy subjects was 0.036 microg/l.

CONCLUSIONS

Being sensitive, specific, and precise, the Liaison cTnI assay meets current requirements to aid in the diagnosis of myocardial necrosis.

Current concepts in standardization of cardiac marker immunoassays

Cardiac markers are measured by a number of different immunoassays using specific antibodies directed to the respective antigens. Lacking assay standardization, different results from different assays measuring the same marker may be obtained and this problem may cloud interpretations of reported data. Presently, there are no reference procedures for cardiac markers; certified reference materials should still be established and, at least for cardiac troponins, the analyte in the patients' blood is significantly different from newly synthesized protein. It is therefore clear that the problems of cardiac marker standardization will not be quickly solved. A number of projects are, however, underway under the auspices of the IFCC and other organizations. The aim of this opinion is to reflect on some concepts related to the implementation of a metrologically correct measurement system, giving practical examples on how these concepts can be applied to immunoassays measuring cardiac markers.

Biochemical markers of cardiac diseases

This article reviews the current contribution of the determination of biochemical markers to clinical cardiology and discusses some important developments in this field. Biochemical markers play a pivotal role in the diagnosis and management of patients with acute coronary syndrome (ACS), as witnessed by the incorporation of cardiac troponins into new international guidelines for patients with ACS and in the redefinition of myocardial infarction. Despite the success of cardiac troponins, there is still a need for development of early markers that can reliably rule out ACS from the emergency room at presentation and detect myocardial ischemia also in the absence of irreversible myocyte injury. Under investigation are two classes of indicators: markers of early injury/ischemia and markers of coronary plaque instability and disruption. Finally, with the characterization of the cardiac natriuretic peptides, Laboratory Medicine is also assuming part in the assessment of cardiac function.

Troponin testing: an audit in three metropolitan hospitals

OBJECTIVE

To audit the appropriateness of use of a troponin I assay in three hospitals.

DESIGN

Cross-sectional survey of use of a troponin assay.

SETTING

Three hospitals in Melbourne, Victoria, each with an emergency department and a coronary care unit.

PARTICIPANTS

Patients for whom a troponin I assay was requested between 1 and 7 May 2002, 27-42 months after introduction of the assay.

INTERVENTIONS

User-focused dissemination of relevant information, including protocols for use, from opinion leaders when the assay was introduced; continuous reinforcement of information in pathology reports.

MAIN OUTCOME MEASURES

Adherence to protocol for assay use.

RESULTS

Troponin assays were requested for 333 patients during 351 symptom episodes. A single assay was used in 194 symptom episodes (55%), and serial assays in 157 (45%); proportions were statistically indistinguishable across all three hospitals (chi(2); P = 0.71). Of the 194 single assays, 13 (7%) diagnosed a myocardial infarction. Serial troponin testing in all three hospitals followed the suggested protocol, with mean time between serial assays being more than 6 hours at all hospitals.

CONCLUSIONS

Adherence to the protocol for serial troponin assay intervals was adequate, but single troponin assays were used extensively and probably inappropriately.