Troponin T: a sensitive and specific diagnostic and prognostic marker of myocardial damage

Association between peak troponin level and prognosis among patients admitted to intensive cardiovascular care unit

INTRODUCTION

High-sensitivity cardiac troponin (hs-cTn) is a key biomarker for myocardial injury, yet its prognostic value in intensive cardiovascular care units (ICCU) remains poorly understood. We aimed to assess the association between peak hs-cTn levels and prognosis in ICCU patients.

METHODS

All patients admitted to a tertiary care center ICCU between July 2019 - July 2023 were prospectively enrolled. Patients were divided into five groups according to their peak hs-cTnI levels: A) hs-cTnI <100 ng/L; B) hs-cTnI of 100-1000 ng/L; C) hs-cTnI of 1000-10,000 ng/L; D) hs-cTnI of 10,000-100,000 ng/L and E) hs-cTnI ≥100,000 ng/L. The primary outcome was all-cause mortality at one year.

RESULTS

A total of 4149 patients (1273 females [30.7 %]) with a median age of 69 (IQR 58-79) were included. Group E was highly specific for myocardial infarction (97.4 %) and especially for ST segment elevation myocardial infarction (STEMI) (87.5 %). Patients in group E were 56 % more likely to die at 1-year in an adjusted Cox model (95 % CI 1.09-2.23, p = 0.014) as compared with group A. Subgroup analyses revealed that among STEMI patients, higher peak hs-cTnI levels were not associated with higher mortality rate (HR 1.04, 95 % CI 0.4-2.72, p = 0.9), in contrast to patients with NSTEMI (HR 7.62, 95 % CI 1.97-29.6, p = 0.003).

CONCLUSIONS

Peak hs-cTnI levels ≥100,000 ng/L were linked to higher one-year mortality, largely indicative of large myocardial infarctions. Notably, the association between elevated hs-cTnI levels and mortality differed between STEMI and NSTEMI patients, warranting further investigation.

A larval zebrafish model of cardiac physiological recovery following cardiac arrest and myocardial hypoxic damage

Contemporary cardiac injury models in zebrafish larvae include cryoinjury, laser ablation, pharmacological treatment and cardiac dysfunction mutations. Although effective in damaging cardiomyocytes, these models lack the important element of myocardial hypoxia, which induces critical molecular cascades within cardiac muscle. We have developed a novel, tractable, high throughput in vivo model of hypoxia-induced cardiac damage that can subsequently be used in screening cardioactive drugs and testing recovery therapies. Our potentially more realistic model for studying cardiac arrest and recovery involves larval zebrafish (Danio rerio) acutely exposed to severe hypoxia (PO2=5-7 mmHg). Such exposure induces loss of mobility quickly followed by cardiac arrest occurring within 120 min in 5 days post fertilization (dpf) and within 40 min at 10 dpf. Approximately 90% of 5 dpf larvae survive acute hypoxic exposure, but survival fell to 30% by 10 dpf. Upon return to air-saturated water, only a subset of larvae resumed heartbeat, occurring within 4 min (5 dpf) and 6-8 min (8-10 dpf). Heart rate, stroke volume and cardiac output in control larvae before hypoxic exposure were 188±5 bpm, 0.20±0.001 nL and 35.5±2.2 nL/min (n=35), respectively. After briefly falling to zero upon severe hypoxic exposure, heart rate returned to control values by 24 h of recovery. However, reflecting the severe cardiac damage induced by the hypoxic episode, stroke volume and cardiac output remained depressed by ∼50% from control values at 24 h of recovery, and full restoration of cardiac function ultimately required 72 h post-cardiac arrest. Immunohistological staining showed co-localization of Troponin C (identifying cardiomyocytes) and Capase-3 (identifying cellular apoptosis). As an alternative to models employing mechanical or pharmacological damage to the developing myocardium, the highly reproducible cardiac effects of acute hypoxia-induced cardiac arrest in the larval zebrafish represent an alternative, potentially more realistic model that mimics the cellular and molecular consequences of an infarction for studying cardiac tissue hypoxia injury and recovery of function.

Global Longitudinal Strain and Biomarkers of Cardiac Damage and Stress as Predictors of Outcomes After Transcatheter Aortic Valve Implantation

Background Global longitudinal strain (GLS) is a sensitive measure of left ventricular function and a risk marker in severe aortic stenosis. We sought to determine whether biomarkers of cardiac damage (cardiac troponin) and stress (NT-proBNP [N-terminal pro-B-type natriuretic peptide]) could complement GLS to identify patients with severe aortic stenosis at highest risk. Methods and Results From a multicenter prospective cohort of patients with symptomatic severe aortic stenosis who underwent transcatheter aortic valve implantation, we measured absolute GLS (aGLS), cardiac troponin, and NT-proBNP at baseline in 499 patients. Left ventricular ejection fraction <50% was observed in 19% and impaired GLS (aGLS <15%) in 38%. Elevations in cardiac troponin and NT-proBNP were present in 79% and 89% of those with impaired GLS, respectively, as compared with 63% and 60% of those with normal GLS, respectively (P<0.001 for each). aGLS <15% was associated with increased mortality in univariable analysis (P=0.009), but, in a model with both biomarkers, aGLS, and clinical covariates included, aGLS was not associated with mortality; elevation in each biomarker was associated with an increased hazard of mortality (adjusted hazard ratio, >2; P≤0.002 for each) when the other biomarker was elevated, but not when the other biomarker was normal (interaction P=0.015). Conclusions Among patients with symptomatic severe aortic stenosis undergoing transcatheter aortic valve implantation, elevations in circulating cardiac troponin and NT-proBNP are more common as GLS worsens. Biomarkers of cardiac damage and stress are independently associated with mortality after transcatheter aortic valve implantation, whereas GLS is not. These findings may have implications for risk stratification of asymptomatic patients to determine optimal timing of valve replacement.

Left Ventricular Hypertrophy and Biomarkers of Cardiac Damage and Stress in Aortic Stenosis

Background Left ventricular hypertrophy (LVH) is associated with increased mortality risk and rehospitalization after transcatheter aortic valve replacement among those with severe aortic stenosis. Whether cardiac troponin (cTnT) and NT-proBNP (N-terminal pro-B-type natriuretic peptide) risk stratify patients with aortic stenosis and without LVH is unknown. Methods and Results In a multicenter prospective registry of 923 patients with severe aortic stenosis undergoing transcatheter aortic valve replacement, we included 674 with core-laboratory-measured LV mass index, cTnT, and NT-proBNP. LVH was defined by sex-specific guideline cut-offs and elevated biomarker levels were based on age and sex cut-offs. Adjusted Cox proportional hazards models evaluated associations between LVH and biomarkers and all-cause death out to 5 years. Elevated cTnT and NT-proBNP were present in 82% and 86% of patients with moderate/severe LVH, respectively, as compared with 66% and 69% of patients with no/mild LVH, respectively (P<0.001 for each). After adjustment, compared with no/mild LVH, moderate/severe LVH was associated with an increased hazard of mortality (adjusted hazard ratio [aHR], 1.34; 95% CI 1.01-1.77, P=0.043). cTnT and NT-proBNP each risk stratified patients with moderate/severe LVH (P<0.05). In a model with both biomarkers and LVH included, elevated cTnT (aHR, 2.08; 95% CI 1.45-3.00, P<0.001) and elevated NT-proBNP (aHR, 1.46; 95% CI 1.00-2.11, P=0.049) were each associated with increased mortality risk, whereas moderate/severe LVH was not (P=0.15). Conclusions Elevations in circulating cTnT and NT-proBNP are more common as LVH becomes more pronounced but are also observed in those with no/minimal LVH. As measures of maladaptive remodeling and cardiac injury, cTnT and NT-proBNP predict post-transcatheter aortic valve replacement mortality better than LV mass index. These findings may have important implications for risk stratification and treatment of patients with aortic stenosis.

Is it cardiac involvement mimicking acute myocardial infarction in idiopathic inflammatory myopathy?

Idiopathic inflammatory myopathy (IIM) comprises a group of rare systemic diseases characterized by progressive weakness of the symmetrical proximal limb muscles, elevated muscle enzymes, inflammation or necrosis on muscle biopsy. IIM may impair the function of multiple organs, particularly the heart. However, it rarely manifests as acute myocardial infarction (AMI) at initial presentation. The present study described the case of a 39-year-old woman with AMI, whose muscle biopsy on the left arm conformed to polymyositis. Coronary arteriography showed irregularities in the left descending and right coronary artery (25% diameter reduction in middle segment). It was concluded that AMI was the chief manifestation of IIM at initial presentation. Furthermore, to the best of our knowledge, the present study was the first to provide a systematic literature review to assess AMI in IIM patients and discuss the possible causes of AMI.

Human epididymis protein 4 (HE4) in laboratory medicine and an algorithm in renal disorders

Over the past three decades, cancer antigen (CA) 125 has been utilized for monitoring women who were treated for ovarian cancer. However, this tumor marker showed several limitations such as false elevation in benign pelvic diseases and, in turn, no alterations in ovarian tumors at early stages with a relatively high ratio. For more than ten years, the human epididymis protein 4 (HE4) has become available for the routine laboratory repertoire, showing a higher sensitivity and specificity compared to that of CA125 in ovarian malignancies, but also in other types of tumors based on recently accumulated clinical data. Despite its remarkable diagnostic characteristics, in certain cases, the evaluation of HE4 results may be problematic when patients suffer from additional conditions that may alter HE4 level. Besides the direct effects of age and smoking, menopause status and decreased renal function also show a substantial impact on HE4 values, which should be considered in each patient. For this purpose, we attempted to create a new formula and an algorithm that may be helpful to predict the probability of the presence of ovarian tumor by using the concentrations of HE4 and CA125.

Effects of tyrosine kinase inhibitors on rat isolated heart function and protein biomarkers indicative of toxicity

INTRODUCTION

Cardiac toxicity, manifested as diminished contractility, ischemic heart disease, and heart failure is a major issue in drug safety. Concerns revolve around targeted drugs (TKIs) where contractility effects were not anticipated. The ability to predict cardiac toxicity early would help to de-risk drugs in development and prepare physicians to manage risk in the clinic. Issues with current preclinical studies include insufficient testing with informative, translatable models, and predictive biomarkers. The isolated heart model is amenable to multiple assessments which can be combined with current technologies to assess toxicity on a multi-scale level.

METHODS

Rat isolated heart model was used to assess changes in left ventricular (LV) contractility and protein biomarkers BNP, IL6, TNFα, and cardiac troponins T (TnT) and I (TnI). Responses were assessed during perfusion with modified Henseleit Krebs (MHK), and 20 min concentration escalations of verapamil, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), isoproterenol, or 20 min escalations bracketing clinical blood concentrations of sunitinib, sorafenib, and erlotinib. LV parameters and effluent for biomarkers were collected before and during escalating drug concentrations.

RESULTS

Verapamil reduced inotropy with no change in biomarkers, FCCP and isoproterenol reduced and increased heart function respectively and increased TnT and TNFα. Erlotinib had no significant effects on function or biomarkers. Sunitinib diminished function, increased TNFα at 0.1 μM, and increased TnT at higher concentrations. Sorafenib dose dependently increased TNFα beginning at 0.1 μM, reducing contractility and flow rate at 0.6 μM.

DISCUSSION

The ex-vivo assay is a sensitive and predictive model for assessing changes in heart function and biomarkers of toxicity and injury. This assay demonstrates the potential for sunitinib and sorafenib to cause cardiac toxicity in humans. Also, TNFα appears to be a biomarker in the heart prior to injury. Due to its versatility, the isolated heart assay has potential to fill gaps in cardiac safety testing early in drug development.

The elevated serum S100A8/A9 during acute myocardial infarction is not of cardiac myocyte origin

Overproduction of circulating S100A8/A9 occurs in patients following acute myocardial infarction (AMI). It remains unclear whether ischemia insult per se induces S100A8 and S100A9 expression in cardiac myocytes or even whether the cardiac myocytes participate as a source of these proteins. In this study, western blot analysis and quantitative real-time reverse transcription polymerase chain reaction were used to test samples obtained from isolated spontaneously hypertensive rat hearts and Wistar-Kyoto rat hearts subjected to global normothermic ischemia and from neonatal Wistar rat cardiac myocytes undergoing hypoxia. Ischemia did not increase the expression of S100A8 and S100A9 proteins and mRNA in the myocardium either from the spontaneously hypertensive rat hearts or the Wistar-Kyoto rat hearts. In addition, the levels of S100A8 and S100A9 proteins were unchanged in the neonatal rat cardiac myocytes undergoing hypoxia. However, both ischemia and hypoxia activated NF-kappaB in ischemic myocardium and in hypoxic cardiac cells in a time-dependent manner. The results suggest that the increased serum S100A8/A9 concentrations following AMI were not of cardiac myocyte origin.

[Cardiac biomarkers in perioperative medicine : significance for noncardiac surgery patients]

Perioperative detection of cardiac biomarkers may help to identify patients at risk. Whether detection of these markers will be recommended in the preoperative setting for patients with cardiac diseases in the future has to be discussed as large prospective trials on this topic are missing. For preoperative evaluation of cardiac insufficiency quantification of brain natriuretic peptide (BNP) and amino-terminal pro-brain natriuretic peptide (NT-proBNP) are useful markers. Troponin is the marker of choice for detection of myocardial ischemia/infarction in the postoperative setting. In unstable patients coronary angiography and/or percutaneous coronary intervention (PCI) are indicated. However, in stable patients the decision for coronary angiography and/or PCI has to be made in each patient individually after interdisciplinary discussion between anesthesiologists, cardiologists and surgeons.

The relationship between cardiac troponins and left ventricular mass index in patients with chronic renal failure

The abstract of this study was accepted as an oral presentation in the 10(th) Annual Meeting of the ESC Working Group on Echocardiography, December 6-9, 2006, Prague, Czech Republic.

Cardiac Troponin T as a Prognostic Marker in Patients With Heart Failure : A 3-Year Outcome Study

Cardiac troponin T (cTnT), a highly sensitive and specific indicator of myocardial cell death, may be elevated in congestive heart failure (CHF). The aims of this study were to test the hypothesis that decompensated CHF may be associated with an increase in cTnT release and to correlate between cTnT levels and patient outcomes. The authors studied 55 patients aged between 38 and 86 years (30 women and 25 men) who were hospitalized for CHF. Left ventricular ejection fraction (EF) was calculated by using modified Simpson's rule by echocardiography. cTnT levels were assessed. Troponin T ≥0.1 ng/mL was considered as positive. All patients were contacted by phone annually during the next 3 years, and their history of subsequent hospital admissions and current health status were recorded. cTnT was negative in 44 (80%) and positive in 11 (20%) patients. EF was significantly lower and NYHA was higher in cTnT-positive patients. During the 3-year follow-up period, 25 patients died from CHF. The mortality rate was 8/11 (72.7%) among cTnT-positive patients, whereas the mortality rate was 17/44 (38.6%) among cTnT-negative patients. There were significant relationships among positivity of cTnT, NYHA, EF, and mortality rate. Multivariate regression analysis yielded an independent relationship between positivity of cTnT, NYHA classification, and mortality rate. The percent of hospital admissions due to CHF was also higher in patients with cTnT positive (63.6% versus, 27.3%, p <0.05). In conclusion, this study shows that cTnT positivity is an independent risk factor in predicting the long-term mortality and morbidity rate in patients with CHF. Patients with worsening CHF may possibly be identified early on the basis of their elevated serum cTnT levels.

Two cases of inflammatory muscle disease presenting with raised serum concentrations of troponin T

Troponins T and I are highly sensitive markers of myocardial injury. However, non-cardiac disorders, such as pulmonary embolism, renal failure, subarachnoid haemorrhage, sepsis, eclampsia, chemotherapy, and inflammatory muscle conditions (dermatomyositis and polymyositis), can also result in raised serum troponin concentrations. This article describes two cases that occurred within a month of each other in Craigavon Area Hospital, whereby conditions unrelated to myocardial ischaemia resulted in raised concentrations of cardiac markers. The first patient, in retrospect, underwent unnecessary investigation as an inpatient in the cardiac ward. Experience gained from this case led to more appropriate consultation and management of the second patient.

Ultra-High-Efficiency Strong Cation Exchange LC/RPLC/MS/MS for High Dynamic Range Characterization of the Human Plasma Proteome

High-efficiency nanoscale reversed-phase liquid chromatography (chromatographic peak capacities of approximately 1000: Shen, Y.; Zhao, R.; Berger, S. J.; Anderson, G. A.; Rodriguez, N.; Smith, R. D. Anal. Chem. 2002, 74, 4235. Shen, Y.; Moore, R. J.; Zhao, R.; Blonder, J.; Auberry, D. L.; Masselon, C.; Pasa-Tolic, L.; Hixson, K. K.; Auberry, K. J.; Smith, R. D. Anal. Chem. 2003, 75, 3596.) and strong cation exchange LC was used to obtain ultra-high-efficiency separations (combined chromatographic peak capacities of >10(4)) in conjunction with tandem mass spectrometry (MS/MS) for characterization of the human plasma proteome. Using conservative SEQUEST peptide identification criteria (i.e., without considering chymotryptic or elastic peptides) and peptide LC normalized elution time constraints, the separation quality enabled the identification of proteins over a dynamic range of greater than 8 orders of magnitude in relative abundance using ion trap MS/MS instrumentation. Between 800 and 1682 human proteins were identified, depending on the criteria used for identification, from a total of 365 microg of human plasma. The analyses identified relatively low-level (approximately pg/mL) proteins (e.g., cytokines) coexisting with high-abundance proteins (e.g., mg/mL-level serum albumin).

Cardiac troponin T and malondialdehyde modified plasma lipids in haemodialysis patients

BACKGROUND

In patients with end-stage renal disease (ESRD), treated with haemodialysis, a high overall mortality is observed. A previous study showed that cardiac troponin T (cTnT) is a strong independent predictor of outcome in this population. In this study we investigated possible causes of cTnT increase and its relationship with a marker of oxidative stress.

METHODS

In a group of 71 haemodialysis patients (36 male, 35 female, mean age 68.7+/-1.5 years) we determined cTnT and compared its presence with several biochemical parameters and with malondialdehyde (MDA), which is an indicator of oxidative stress. None of the patients suffered an acute coronary event during the observation period. Three measurements of cTnT and MDA were performed with a 2-week interval. Forty-nine patients underwent a transthoracic echocardiography.

RESULTS

Twenty-nine patients (or 40.8%) had a positive cTnT determination (defined as cTnT >/=0.10 ng/ml). cTnT positive patients had significantly higher levels of MDA (P=0.0125), C-reactive protein (CRP) (P=0.04) and pre-dialysis urea (P=0.04). Regression analysis showed that both pre-dialysis urea and MDA independently influenced cTnT. No correlation was found with age, dialysis adequacy, post-dialysis urea, total cholesterol, white blood cell count, fibrinogen or any of the echocardiographical parameters. Presence of heart failure, diabetes or use of medication could not discriminate between cTnT positive and cTnT negative patients. MDA levels correlated positively with time on haemodialysis (P=0.0021). Echocardiography showed left ventricular hypertrophy in 88% of the examined patients and impaired wall motion in 35%. Patients with clinical signs of heart failure had a lower ejection fraction and worse wall motion score index. No correlation existed between echocardiographic findings and cTnT or MDA. Survival was independently predicted by cTnT (P=0.0025), MDA (P=0.0007), CRP (P=0.006) and age (P=0.0143). Patients with both cTnT and CRP increase had a survival of <50% at 1 year, compared with 90% in patients with both cTnT and CRP within the normal range and 80% when either CRP or cTnT was increased (chi(2)=12.127; P=0.0023).

CONCLUSIONS

This study confirms that the presence of cTnT predicts prognosis in ESRD. The presence of cTnT is linked to oxidative stress, inflammation and uraemia. The absence of specific findings on EKG and echocardiography points towards subclinical myocardial damage caused by endothelial disturbances.

Clinical and Experimental Results on Cardiac Troponin Expression in Duchenne Muscular Dystrophy

Background: Because of controversial earlier studies, the purpose of this study was to provide novel experimental and additional clinical data regarding the possible reexpression of cardiac troponin T (cTnT) in regenerating skeletal muscle in Duchenne muscular dystrophy (DMD).

Methods: Plasma from 14 patients (mean age, 7.5 years; range, 5.7–19.4 years) with DMD was investigated for creatine kinase (CK), the CK MB isoenzyme (CKMB), cTnT and cardiac troponin I (cTnI), and myoglobin. cTnT concentrations were measured by an ELISA (second-generation assay; Roche) using the ES 300 Analyzer. cTnI, myoglobin, and CKMB were measured by an ELISA using the ACCESS System (Beckman Diagnostics). Troponin isoform expression was studied by Western blot analysis in remnants of skeletal muscle biopsies of three patients with DMD and in an animal model of DMD (mdx mice; n = 6).

Results: There was no relation of cTnT and cTnI to clinical evidence for cardiac failure. cTnI concentrations remained below the upper reference limit in all patients. cTnT was increased (median, 0.11 μg/L; range, 0.06–0.16 μg/L) in 50% of patients. The only significant correlation was found for CK (median, 3938 U/L; range, 2763–5030 U/L) with age (median, 7.5 years; range, 6.8–10.9 years; r = −0.762; P = 0.042). Western blot analysis of human or mouse homogenized muscle specimens showed no evidence for cardiac TnT and cTnI expression, despite strong signals for skeletal muscle troponin isoforms.

Conclusions: We found no evidence for cTnT reexpression in human early-stage DMD and in mdx mouse skeletal muscle biopsies. Discrepancies of cTnT and cTnI in plasma samples of DMD patients were found, but neither cTnT nor cTnI plasma concentrations were related with other clinical evidence for cardiac involvement.

Validation of NACB and IFCC guidelines for the use of cardiac markers for early diagnosis and risk assessment in patients with acute coronary syndromes

BACKGROUND

International guidelines have been established for the use of cardiac markers in the early diagnosis and risk assessment of patients with acute coronary syndromes.

METHODS

A single center, prospective observational study was conducted in a tertiary care university hospital on 200 consecutive patients with suspected acute myocardial infarction (AMI). Blood was drawn on admission and after 2, 4, 8, 12 and 24 h for the measurement of CK-MB/CK activity, myoglobin, CK-MB mass and troponin I. A 6-week follow-up was undertaken for the combined end point of acute coronary syndrome and death.

RESULTS

Myoglobin showed an early diagnostic sensitivity of 0.65 on admission, 0.90 after 2 h and 0.92 after 4 h compared with 0.46, 0.74 and 0.88 for CK-MB/CK activity. The combination of myoglobin and cTnI increased the diagnostic value compared with myoglobin alone on admission, 2 and 4 h later. In multivariate analysis, cTnI and CK-MB/CK mass, but not myoglobin and CK-MB/CK activity, were shown to be independent predictors on the 6-week follow-up.

CONCLUSIONS

Repetitive myoglobin measurements within 4 h of admission, combined with at least one early troponin test, was shown to be the strategy of choice in early AMI diagnosis and prognosis assessment.

Evaluation of a point-of-care system for quantitative determination of troponin T and myoglobin

We present the results of a multicenter evaluation of a new point-of-care system (Cardiac Reader) for the quantitative determination of cardiac troponin T (CARDIAC T Quantitative test) and myoglobin (CARDIAC M test) in whole blood samples. The Cardiac Reader is a CCD camera that optically reads the immunochemical test strips. The measuring range is 0.1 to 3 microg/l for CARDIAC T Quantitative and 30 to 700 microg/l for CARDIAC M. Both tests are calibrated by the manufacturer. The reaction times of the tests are 12 or 8 minutes, respectively. Method comparisons were performed with 281 heparinized blood samples from patients with suspected acute coronary syndromes. The results obtained with CARDIAC T Quantitative showed a good agreement compared with cardiac troponin T ELISA (r = 0.89; y = 0.93x + 0.02). The method comparison between CARDIAC M and Tina-quant Myoglobin also showed a good agreement between both assays (r = 0.98; y = 0.92x + 1.6). Test lot-to-lot comparisons yielded differences of 2% and 6% for CARDIAC T Quantitative and of 0 to 11% for CARDIAC M. The within-run imprecision with blood samples and control materials was acceptable for CARDIAC T Quantitative (CV 10 to 15%) and good for CARDIAC M (CV 5 to 10%). The between-instrument CV was below 7% for CARDIACT Quantitative and below 5% for CARDIAC M. The cross-reactivity of CARDIAC T Quantitative with skeletal troponin T was approximately 0.003%. No significant analytical interference was detected for any of the assays in investigations with biotin (up to 100 microg/l), hemoglobin (up to 0.125 mmol/l), hematocrit (26 to 52%), bilirubin (up to 340 micromol/l), triglycerides (up to 5.0 mmol/l), and 18 standard drugs. With the Cardiac Reader reliable quantitative results can be easily obtained for both cardiac markers. The system is, therefore, particularly suitable for use in emergency rooms, coronary care units and small hospitals.

Laboratory diagnosis of patients with acute chest pain

The enzyme activities of creatine kinase (CK), its isoenzyme MB (CK-MB) and of lactate dehydrogenase isoenzyme 1 (LD-1) have been used for years in diagnosing patients with chest pain in order to differentiate patients with acute myocardial infarction (AMI) from non-AMI patients. These methods are easy to perform as automated analyses, but they are not specific for cardiac muscle damage. During the early 90's the situation changed. First creatine kinase MB mass (CK-MB mass) replaced the measurement of CK-MB activity. Subsequently cardiac-specific proteins troponin T (cTnT) and troponin I (cTnI) appeared on the scene, displacing LD-1 analysis. However, troponin concentrations in blood increase only from four to six hours after onset of chest pain. Therefore a rapid marker such as myoglobin, fatty acid binding protein or glycogen phosphorylase BB could be used in early diagnosis of AMI. On the other hand, CK-MB isoforms alone may also be useful in rapid diagnosis of cardiac muscle damage. Myoglobin, CK-MB mass, cTnT and cTnI are nowadays widely used in diagnosing patients with acute chest pain. Myoglobin is not cardiac-specific and therefore requires supplementation with some other analyses such as troponins to support the myoglobin value. Troponins are very highly cardiac-specific. Only the sera of some patients with severe renal failure, which requires hemodialysis, have elevated cTnT and/or cTnI without there being any evidence of cardiac damage. On the other hand, the latest studies have shown that elevated troponin levels in sera of hemodialysis patients point to an increased risk of future cardiac events in a similar manner to the elevated troponin values in sera of patients with unstable angina pectoris. In addition, the bedside tests for cTnT and cTnI alone or together with myoglobin and CK-MB mass can be used instead of quantitative analyses in the diagnosis of patients with chest pain. These rapid tests are easy to perform and they do not require expensive instrumentation. For routine clinical laboratory practice we suggest that in diagnosis of patients with chest pain, myoglobin and CK-MB mass measurements should be performed whenever they are requested (24 h/day) and cTnT or cTnI on admission to the hospital and then 4-6 and 12 hours later.

Release of cardiac troponin in acute coronary syndromes: ischemia or necrosis?

Analysis of cardiac troponin T and I have been shown to be effective in detecting minor myocardial injury in cardiac patients who present with acute coronary syndromes (ACS). Determination of minor myocardial injury is significant, as these patients have a higher short-term morbidity and mortality than other unstable angina patients with normal concentrations for these markers. In this report, two theories are given as to why cardiac troponin is superior to other markers such as CK-MB for risk stratification. The 'low cut-off concentration model' is based on the fact that troponin is not increased in patients with skeletal muscle disease or injury, resulting in low baseline concentrations of the cardiac isoforms in the absence of active cardiac disease. This enables the use of low decision limits. Troponin also has a higher myocardial tissue content relative to CK-MB, thereby also increasing its clinical sensitivity to irreversible injury. In the 'reversible ischemia model', cytoplasmic free troponin T and I leak across the membrane of myocytes as the result of reduced coronary blood flow. Jeopardized myocardial tissue can recover with acute recanalization. Support for this model comes from clinical observations and animal studies.