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becamemore widely used, its lack of specicity for cardiac tissue injury of LDH 1 or H subunits. Unfortunately these CK and LDH isoenzyme

International Journal of Cardiology 164 (2013) 282294

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International Journ

j ourna l homepage: www.e lwas appreciated [14].Plasma creatine kinase (CK), an enzyme that catalyzes the transfer

of high-energy phosphate from creatine phosphate to adenosine tri-phosphate, is rapidly released during muscle damage. In 1959, itwas demonstrated that CK was an extremely sensitive index of skeletalmuscle disease and one year later, it was also seen in patients with AMI[1,2,4]. In 1960, lactate dehydrogenase (LDH), an enzyme that catalysesthe reversible oxidation of lactate to pyruvate, was discovered. However,

assays remained lacking in specicity [1,2,69].Electrophoretic assayswere rst developed in 1966 but lacked sensi-

tivity. This improved with advances in chromatography in 1974 and theproduction of quantitative assays by the close of the 1970s [1,6,7,911].However, the detection and measurement of biomarkers was revolu-tionized by the development of immunoassays (initially conguredwith polyclonal antibodies and then, in the 1980s, with monoclonal an-tibodies) as well as technical advances in automation [1,6,7,911].LDH is found in all cells and, like AST, is very non

Cardiology department, Christchurch Hospital, RiccZealand. Fax: +64 33641415.

E-mail address: sally.aldous@cdhb.govt.nz.

0167-5273/$ see front matter 2012 Elsevier Irelanddoi:10.1016/j.ijcard.2012.01.081ges and elevated cardiacice [5]. As the use of AST

5. In the well-oxygenated heart, H subunits are more prominent butduring infarction they become reduced, thus lowering relative ratiosmia, ischaemic electrocardiogram (ECG) chanbiomarkers, with AST as the biomarker of choBiochemical markers of ischaemic cAMI, have been used for over half a c(AST) was found to be elevated in patithe rst cardiac biomarker to be used ithe reversible transfer of an -aminoglutamate and, as such, is an importantlism. AST is found in the heart, liver, skand is currently used clinically as a m1959, the world health organization (WAMI, dened as at least 2 out of; symptoamage, used to diagnose. Aspartate transaminaseith AMI in 1954 and wasal practice. AST catalyzesbetween aspartate ande in amino acid metabo-uscle, kidneys and brainfor liver health [14]. Inroduced a denition forgestive of cardiac ischae-

WHO recommended CK, AST and LDH as the biomarker componentsfor diagnosis of AMI. Despite this, specicity remained a problem, espe-cially in patients with muscle and hepatic diseases or injury [1,2,4].

Advances in electrophoresis allowed identication of more cardio-specic iso-enzymes of both CK and LDH. Cardiac muscle has higherCKMB levels (2530%) compared with skeletal muscle (1%), whichis mostly CKMM. The measurement of CKMB, CKMB fraction orCKMB/CKMM ratio was a more specic marker for AMI. Cardiac mus-cle is also particularly rich in LDH 1 (or HHHH) and 2 (or HHHM)compared with skeletal muscle, which contains primarily LDH 4 and1. The history of cardiac biomarkers be more specic than either AST or LDH because low levels of CK in theliver less confound results in those with hepatic dysfunction. In 1979,Review

Cardiac biomarkers in acute myocardial in

Sally J. Aldous Christchurch Hospital, Christchurch, New Zealand

a b s t r a c ta r t i c l e i n f o

Article history:Received 3 October 2011Received in revised form 16 December 2011Accepted 26 January 2012Available online 17 February 2012

Keywords:TroponinHigh-sensitivity troponinMyocardial infarctionPrognostic utilitycardiac biomarkersNovel biomarkers

Each year, a large number ofinvestigation for possible acelectrocardiogram results bcally. This review summarizlished and novel) assays. Caof myocardial infarction hapatients with elevated tropoinammation and neurohormbut none have been shown tpoint of care markers may aspecic. CKwas found to

arton Road, Christchurch, New

Ltd. All rights reserved.rction

tients are seen in the Emergency Department with presentations necessitatingmyocardial infarction. Patients can be stratied by symptoms, risk factors andardiac biomarkers also have a prime role both diagnostically and prognosti-both the history of cardiac biomarkers as well as currently available (estab-c troponin, our current gold standard biomarker criterion for the diagnosisigh sensitivity and specicity for this diagnosis and therapies instituted inhave been shown to inuence outcomes. Other markers of myocardial necrosis,al activity have also been shown to have either diagnostic or prognostic utility,e superior to troponin. The measurement of multiple biomarkers and the use oferate current diagnostic protocols for the assessment of such patients.

2012 Elsevier Ireland Ltd. All rights reserved.

al of Cardiology

sev ie r .com/ locate / i j ca rdMonoclonal antibodies allowed measurement of CKMB mass. Thisenabled earlier and more rapid detection of myocardial damage andwas also more sensitive and specic than the original CKMB activityassay. However, with further research it was realized that even CKMBmass was elevated in a variety of situations as a result of skeletal muscleinjury aswell as in non-ischaemic cardiac disease and certainmalignan-cies [13,12,13].

283S.J. Aldous / International Journal of Cardiology 164 (2013) 282294Recognition of the lack of specicity of CKMB for AMI underpinnedthe search for a test with superior performance. The contractileproteins of the myobril include myosin, actin, tropomyosin and thetroponin complex. When cardiac myocytes are acutely damaged andthe integrity of the cell membrane is lost, myosin fragments are re-leased into the circulation from a soluble cytoplasmic pool of myosinlight chains. Myosin light chain release was thought to be a potentialmarker for AMI [14,15]. In itself, this discovery was disappointing, aspeak levels of myosin light chains did not signicantly vary betweenpatients presenting with AMI, unstable angina or non-cardiac chestpain. However, this improved understanding lead on to a pivotal break-through, the discovery of troponin.

Troponin has three subunits. Troponin C (TnC) binds to calciumions to produce a conformational change in troponin I (TnI), troponinT (TnT) binds to tropomyosin, interlocking them to form a troponintropomyosin complex and TnI binds to actin in thin myolaments tohold the troponintropomyosin complex in place [1619]. Troponinis found in both skeletal and cardiac muscle but cardiac TnI (cTnI)and TnT (cTnT) isotypes have additional residues on the N-aminoterminal and can therefore be readily identied as cardiac type [20].TnC cannot.

Troponin, as a constituent of themusclemyobril, was discovered inthe 1970s but sensitive radioimmunoassays for cardiac troponin (cTn)were not developed until the late 1980s. cTn was proposed as a specicmarker of myocardial necrosis but the high sensitivity of cTn comparedwith CK and CKMB had not been envisaged. Early studies showed thatcTn was raised in AMI (as diagnosed by WHO criteria) [7,2027] withhigh sensitivities and specicities [7,12,17,22,24,25,2838] and hadthe advantage over CKMB in differentiating cardiac from skeletal mus-cle injury [7,39]. Studies in the 1990s also showed that signicant num-bers of patients classed as unstable angina (as opposed to AMI) byconventional WHO criteria, had elevated cTn levels [25,26,36,3844].Furthermore, cTn positive patients exhibited an increased risk of subse-quent death [29,36,38,4550], AMI [21,38,43,44,47,5153], need forrevascularization [40,45,46,48,54] and readmission [36] than cTn nega-tive patients, even though other baseline characteristics and symptomsappearedmatched [40,52]. Thosewith unstable angina and cTn eleva-tion were thought to have unstable plaque with subsequent plateletemboli leading to micro infarcts, as opposed to stable plaque in thosewithout elevations [21,27,33,39]. Subsequent studies showed thatvarious medical and interventional techniques already instituted intopractice or under investigation, were rened as the relationships withcTn and outcomes became apparent. Such interventions included lowmolecular weight heparin [18,5560], glycoprotein llbllla inhibitors inpatients with refractory angina and in patients undergoing PCI[18,5658,60,61], antiplatelet therapy [62], 2448 h of telemetry [60],angiography as the preferred investigation [56,57] and revasculariza-tion [46,49,57,63].

In 2000, guidelines for the diagnosis of AMI were changed withthe new denition suggesting cTn as the preferred biomarker [64].Initial scepticism, due to a signicant increase in the positive rate,a lack of assay standardization and a lack of conrmed correlationbetween cTn and histopathology, was eventually replaced by wide-spread acceptance. Assay variability was acknowledged. This led torecommendations for only cut-off values with a coefcient ofvariation (CV) of b10% to be employed. The recommended cut-offvalue was now suggested at the 99th percentile, much lower thanvalues previously used in practice. Many assays were not able tomeet precision guidelines at this level. This change in guidelineshad follow through effects. There was an increase in incidence ofdiagnosed AMI [6570] although a small proportion of patients fulll-ing WHO criteria for AMI were no longer considered AMI by the newdenition [69]. There was an increase in coronary care unit admis-sions [68], an increase in number of angiograms performed [68] anda reduction in length of stay in patients without AMI [68]. Long

term, there have possibly been decreases in post-AMI mortality[70,71] and heart failure admissions as the primary diagnosis [71].The use of cTn as the biomarker of choice in AMI was furtherendorsed in 2007, by the World Heart Federation Task Force for theRedenition of Myocardial Infarction [72].

There was and is only one manufacturer for cTnT (BoehringerMannheim, acquired by Roche Diagnostics the late 1990s, and testplatform Elecsys) and therefore the assay is standardized [7375].There are many manufacturers of cTnI assays which vary from eachother by assay format, antibodies used, specicity to differentepitopes of complexed, free and modied cTn, types of indicatormolecule and detection technique (spectrophotometric, uorescent,chemiluminescent or electrochemical) [76]. They may also have vary-ing interference from pre-analytical variables such as haemolysis,icterus, lipaemia, anticoagulant, ascorbic acid levels, biotin levels,the use of streptokinase or ruthenium, heterophile antibodies andautoantibodies, which can lead to both false negatives and false pos-itives [7678]. This leads to differences in analytical sensitivitybetween assays and therefore different levels at which there is ab10% coefcient of variation and different limits of detection (LOD)[7678]. The lack of standardization has lead to discrepancies incut-point values [74,75,79,80] with over a 3040 fold differencesdocumented [81,82] and in the past have been notorious for poorperformance at the lower end of the reference range. However, latergeneration assays are much improved and now many meet or arenear to meeting, precision guidelines [81,8385]. The early cTnTassay had slightly limited specicity in patients with skeletal muscledisease because of cross reactivity of the signal antibody with skeletalmuscle and re-expression of foetal forms of cTnT (cTnI isoforms arenot present in foetal skeletal muscle) in conditions such as rhabdo-myolysis and chronic skeletal muscle diseases such as muscular dys-trophy and myositis. These isoforms are not detected by the assayused today [73,74,79,80,86,87].

There have been many studies comparing troponin assays[74,75,79,86,8892] demonstrating that correlation and concordanceis variable [44,74,9093], however, all have been shown to be sensitiveand specic tests for the diagnosis of AMI.

2. Current cardiac biomarkers

2.1. Biomarkers of myocardial necrosis

2.1.1. TroponinBecause of the recommendations to use only cTn assays which are

reliable (b10% coefcient of variation) at the decision limit (99th per-centile), there has been development of high-sensitivity troponinassays (hs-cTn) to increase the analytical, and thus clinical, sensitivityfor detection of myocardial injury. Such an approach may identifymore patients at risk and permit earlier diagnosis [83,94101]. Thismay allow more rapid triage to intensive and invasive treatmentstrategies in those with elevations in hs-cTn and possibly earlierstress testing or even discharge without such testing in those withoutelevations [97,102]. In the FRISC II subgroup analysis, comparing theresults of several cTnT and cTnI assays, 1012% of patients with apoor prognosis at 1-year follow-up were identied only by the cTnassay that had the highest analytical sensitivity [103]. The use oflower troponin cutoff concentrations also better separated the rateof clinical events at 1 year between groups receiving invasive versusnon-invasive treatment. Other studies conrm this prognostic utility[85,104106].

The hs-cTn assays also allow detection of circulating cTn inhealthy individuals, and therefore denition of a true normal range[99,100]. However, although hs-cTn assays will allow rened deni-tion of the upper limit of normal, their clinical application will alsorequire revisiting specicity as the upper 1% of the normal rangeand non-coronary causes of cardiac injury may now more frequently

confound the effort to rule out AMI [100].

284 S.J. Aldous / International Journal of Cardiology 164 (2013) 282294It has become evident that although elevations in cTn reect myo-cardial damage, they do not indicate its mechanism. In addition tospontaneous AMI secondary to plaque rupture and acute coronaryocclusion, AMI can be secondary to the ischaemia produced eitherby increased oxygen demand or decreased supply, e.g. coronaryartery spasm, coronary embolism, anaemia, arrhythmias, hyperten-sion or hypotension. Therefore cTn may be raised in coronary, non-coronary cardiac as well as non-cardiac conditions such as sepsis[72,82,96,107]. cTn has also been shown to be raised in patientswith renal failure without symptoms of ACS. These patients havebeen shown to have increased cardiac risk and it has been suggestedthat the marker may represent subclinical myocardial ischaemiaespecially when raised acutely. However, cTn can be raised chronicallyin these patients. Obialo et al found that 50% of patients with elevatedcTn and end-stage renal disease had coronary arteries free from owlimiting stenoses on angiography [96]. Other associations such as urae-mic myo/pericarditis, congestive cardiac failure, left ventricular hyper-trophy and diabetes suggest cTn release in these patients is not alwaysAMI related [51,74,75,86,108].

Patients with raised cTn may have normal coronary angiographyeven in a setting of apparent spontaneous AMI. Whether these repre-sent false positives or whether unstable plaque/plaque rupture withattendant microscopic myocyte ischaemia and injury has beensuccessfully treated by intensive antithrombotic/antiplatelet therapyprior to angiography is unclear. Nevertheless, cTn positive patientswith normal angiograms still have increased future risk comparedwith cTn negative patients (although lower risk than cTn positivepatients with abnormal angiograms).

Because of these facts, troponin results must be interpreted withinthe clinical context in which they are measured [108]. An elevatedvalue of cTn in the absence of clinical evidence of ischaemia shouldprompt consideration of aetiologies other than spontaneous AMI orplaque rupture [72,99], especially as cTn positive patients are treatedmore aggressively with potent antiplatelet therapies and early angiogra-phy i.e. procedures and treatments which carry risks.

In order to aid differentiation between AMI and other conditions(in particular chronic from acute elevations), it has been suggestedthat observing the pattern of cTn using serial measurements canincrease specicity as increasing values may signifying new onsetinfarction and decreasing values may signifying resolving infarction.The National Academy for Clinical Biochemistry has recommendedchanges in cTn of 20% (i.e. greater than imprecision levels assumingup to a 10% CV when levels are around the 99th percentile) fromelevated baseline values (i.e. those with pathological levels of cTn).Theymake no recommendation on a threshold change fromnormal ini-tial levels [109]. If this dynamic change is not present, other diagnosesshould be considered [84,97,100,110,111]. However, other acute ill-nesses such as myocarditis, takotsubo syndrome, pulmonary embolismand sepsis have also been associated with acute cardiac injury. Recentstudies have shown that absolute rather than delta values in cTn [112]and absolute changes rather than relative changes [113] perform betterin this setting. Also, those with increasing or decreasing cTn have beenshown tohave higher incidence of short-termadverse events comparedto patients with stable cTn [96,110].

Other emerging concerns with these new hs-cTn assays includecontributions from nonspecic binding at very low cTn concentra-tions [94], contribution of biological variation in cTn over time [94]as well as the other pre-analytical factors listed previously [82].

2.1.2. MyoglobinMyoglobin, is a low molecular weight, cytoplasmic haem protein.

It has been the most sensitive conventionally assayed early markerof AMI and can be raised as early as 1 h from onset of infarction.Unfortunately, its specicity for AMI is low, being raised in other con-ditions such as skeletal muscle disease or injury, which need only be

minor, and renal impairment [1,3,7,8,12,27,114116]. Nevertheless,use of myoglobin on presentation, can aid provisional diagnosis andrisk stratication in the early hours after symptom onset. Myoglobinhas also been shown to predict mortality and still plays a role in theclinical assessment of patients with cardiac symptoms in many clini-cal centres [1,3,7,8,12,27,114116].

2.1.3. Heart fatty acid binding protein (hFABP)hFABP is a small, 132 amino acid, soluble protein, with general

characteristics resembling myoglobin. It is a cytosolic protein that isabundant in the heart and is involved in myocardial lipid homeosta-sis. Because of its low molecular weight and cytoplasmic location, itis readily released into the circulation after myocardial injury andmaybe helpful in the diagnosis of AMI in patients presenting early[118120]. It is highly but not uniquely cardiac-specic, also beingexpressed at low levels in extra-cardiac tissues including skeletalmuscle and the kidneys [117]. It is unsuitable as a test for patientspresenting >6 h from onset of symptoms due to rapid renal clearance[120122]. hFABP has also been shown to independently predictmortality in patients with ACS [123]. The use of this marker hasnever become main stream although investigations are ongoing.

2.1.4. Ischaemia modied albuminDuring acute ischaemia the N-terminal site of albumin is altered, re-

ducing its binding capacity; the modied protein is termed ischaemia-modied albumin (IMA). Although, levels of IMA are much higher inthose with ischaemia than without, the sensitivity of IMA for AMI isinsufcient to compete with other current markers and specicity islow. Overall, studies do not support its use as an effective diagnosticor prognostic marker [119,124127].

2.2. Biomarkers of Inammation

Coronary artery disease is an inammatory process. Atheroscleroticplaque formation begins with endothelial cell injury thought to be trig-gered by a range of factors including smoking, diabetes, hypertensionand dyslipidaemia. Dyslipoproteinaemias such as elevated low densitylipoprotein (LDL)-cholesterol, play a central role in atherosclerosis. Anelevated LDL concentration is pro-atherogenic because LDL is intimatelylinked to oxidative and inammatory processes in the arterial wall. Im-paired endothelial cells respond by activating adhesion molecules andsecretingpro-inammatory chemokines [128,129]. These attractmono-cytes (which thenmultiply and mature into active macrophages) and Tlymphocytes. Eventually a plaque is formed consisting of a large lipidcore, a thin brous cap, and an active inammatory cell inltrate. AMIresults from plaque rupture or supercial erosion, stimulating thesecretion of pro-inammatory and pro-coagulant substances whichmay trigger formation of occlusive thrombus [128,129]. Inammatoryprocesses therefore not only promote initiation and progression of ather-omas but also contribute to the precipitation of thrombotic complications.Consequently, it has been speculated that markers of inammation areraised in patients with AMI.

2.2.1. C-reactive proteinC-reactive protein (CRP), an acute-phase reactant produced by

hepatocytes in response to stimulation by inammatory cytokines,primarily IL-6, is the most widely used inammatory marker. In theabsence of transient acute disturbances in CRP in response to certainstimuli such as infections, injuries etc, CRP levels in individuals otherwiseremain relatively constant. CRP, in itself, also has a pro-inammatoryeffect by inducing the expression of adhesion molecules and otherinammatory cells. CRP has been implicated in vascular dysfunctionand in the progression of atherosclerosis, and subsequently has beenshown to predict future cardiovascular events, including rst-ever AMI,stroke and development of peripheral arterial disease [129].

It has also been shown that CRP is raised in patients with unstable

coronary syndromes, but specicity and sensitivity are not sufcient

285S.J. Aldous / International Journal of Cardiology 164 (2013) 282294for use as a reliable diagnostic marker. It is, however, a signicantpredictor of poor outcome. Studies including the TIMI 11B sub-studyin 1998 and GUSTO IV analysis in 2003 conrmed the short-term prog-nostic value of CRP in acute coronary syndromes even in patients withnegative cTn results [129131]. Treatment of healthy individuals withRosuvastatin (Justication for the Use of statins in Prevention: an Inter-vention Trial Evaluating Rosuvastatin study) in response to elevationsin high-sensitivity CRP, even in those without hyperlipidaemia, signi-cantly reduced the incidence of major cardiovascular events [132].

However, in assessing outcome in patients with ACS studiesshowed that cTn out-performed CRP for mortality prediction. In addi-tion to this, it was found that CRP has no relationship with the early orlate occurrence of AMI, unlike cTn, and more importantly, only cTnbut not CRP is helpful in therapeutic triage of such patients by identi-fying those who will benet from an invasive over a conservativestrategy or antithrombotic treatment [129,133,134].

Nevertheless, in 2003, the American Heart Association (AHA) andthe Centres for Disease Control and Prevention issued a scienticstatement that suggested the use of high-sensitivity CRP as an optionalrisk factormeasurement in patientswithACS [128].With this interest ininammation andACS, attention turned to other candidate inammato-ry biomarkers.

2.2.2. Pro-inammatory markersThe major pro-inammatory markers include IL-6 and TNF-. The

immuno-inammatory response to injury resulting from ischaemiaand reperfusion of infarcted myocardium is associated with the in-duction of many cytokines including IL-6 and TNF-. IL-6 is involvedin inammatory cell recruitment and activation, stimulates the liverto produce acute-phase proteins such as CRP and may also have anegative inotropic effect mediated through myocardial nitric oxidesynthase [135,136]. TNF- is a cytokine found in endothelial cells,smooth muscle cells and macrophages. TNF- is a cardio-inhibitory cy-tokine that depresses cardiac contractility either directly or throughinduction of nitric oxide synthase [137].

2.2.3. Markers of plaque destabilizationCell adhesion molecules (CAM) are produced by the arterial wall

and include inter-cellular adhesion molecules (ICAM), endothelialadhesion molecules (ELAM) and vascular adhesion molecules(VCAM). Myocardial necrosis induces complement activation andfree radical generation, triggering a cytokine cascade. Interleukinsare activated and recruit neutrophils in the ischaemic myocardium.Neutrophil inltration is regulated through a complex sequence ofmolecular steps involving the selectins and the integrins, whichmediate leukocyte adhesion to the endothelium. Marginated neutro-phils exert potent cytotoxic effects through the release of proteolyticenzymes and adhere to ICAM expressing cardiomyocytes. Also,atherosclerosis in itself appears to be modulated by soluble forms ofadhesion molecules. CAMs are therefore involved both in the acutephase of AMI and chronic process of atherosclerosis [15,138,139].

Metalloproteinases are also markers of plaque destabilization.Myeloperoxidase, (MPO) is the most abundant metalloproteinaseand is an enzyme produced by polymorphonuclear neutrophils andmacrophages. It catalyzes the conversion of chloride and hydrogenperoxide to hypochlorite and is involved in the oxidation of lipidscontainedwithin LDL particles. It generates an array of reactive oxidantsand radical species that contribute to the development of atheroma andsubsequent plaque rupture [140143]. Myeloperoxidase is not specicto cardiac diseases, as activation of neutrophils and macrophages canoccur in infectious, inammatory and inltrative disease processes.Studies have shown that myeloperoxidase is inferior to current bio-markers for diagnostic purposes but elevated levels independentlypredict future risk of coronary artery disease in both healthy individuals

and those with ACS [143].Pregnancy associated plasma protein A (PAPPA) is another metal-loproteinase, originally discovered as a glycoprotein in pregnantwomen, produced by the syncytiotrophoblasts of the placenta. How-ever, it is also produced by non-placental cell types, including bro-blasts, vascular endothelial cells, and vascular smooth muscle cells.It is responsible for the cleavage of insulin-like growth factor bindingprotein-4. The insulin-like growth factors are important regulatoryproteins involved in cell proliferation and metabolism and havebeen implicated in atherosclerotic plaque progression and instability[144147].

Matrix metalloproteinases, in particular matrix metalloproteinases2 and 9, play an important role in the collagen breakdown and structur-al changes associated with ventricular remodeling after AMI. MMPshave been shown to correlate with Nt-proBNP levels [148,149].

2.2.4. Markers of myocyte ruptureCD40L is a cytokine belonging to the TNF- family and CD40 is its

receptor. CD40L is up-regulated on platelets within fresh thrombus.Delivery into the peripheral circulation is thought to occur when acti-vated platelets are released from the intracoronary thrombus that hasformed at the site of the unstable/ruptured plaque [135,150]. In additionto the cell-associated form, CD40L is also present in plasma as the biolog-ically active fragment, soluble CD40L, which is pro-inammatory andpromotes coagulation [151153].

Platelet derived growth factor (PDGF) is a glycoprotein found inplatelets, macrophages, smooth muscle cells and endothelial cells.Its main function involves wound repair by causing mitosis of smoothmuscle cells and broblasts and attracting other cells such as mono-cytes, neutrophils and platelets [154,155].

Placental growth factor (PGF) is a member of the vascular endo-thelial growth factor family and acts as a specic ligand for vascularendothelial growth factor receptor-1. It has been implicated in neo-vascularization in ischaemic myocardium and promoting atherosclero-sis. Themajor site of augmented expression of PGF has been found to bethe endothelium of vessels within an infarcted region [156,157].

Many of these biomarkers sparked interest and evidence wasobtained from both large scale trial sub studies such as the OptimalTrial in Myocardial Infarction with the Angiotensin II AntagonistLosartan (OPTIMAAL) and Cholesterol and Recurrent Events (CARE)trials (TNF-), the CAPTURE trial (PGF, CD40L, myeloperoxidase),the FRISC ll sub-study (CD40L) and the Fast ASsessment of Thoracicpain by nEuRal networks (FASTER Imyeloperoxidase) study as wellas smaller targeted studies. Although these biomarkers are raised inpatients with AMI, the spread of values limits their use for diagnosis.Many also are related to risk of adverse events, particularly of deathand heart failure, rather than ischaemic events, but there is no consis-tent evidence to show any of these markers are independently predic-tive variables or convey additional information to cTn which maytherefore inuence treatment. Hence they have not evolved to becomemainstream markers in ACS [137,138,142,143,153,158,159].

2.3. Neuro-endocrine biomarkers

2.3.1. BNP/NT-proBNPThe predominant site of BNP gene expression is the heart and is

translated to a parent peptide, preproBNP. This peptide is translo-cated across the lumen of the cellular endoplasmic reticulum whereit is cleaved to form proBNP and BNP-signal peptide. proBNP iscleaved into an amino-terminal product (NT-proBNP) and the physio-logically active BNP. NT-proBNP has a longer half life (70 to 120 min)than BNP (20 min) in part due to the fact it is actively degraded bycirculating endopeptidases as well as cleared by cellular binding recep-tors. Due to the clearance of BNP and NT-proBNP partially by renalexcretion, either may accumulate in patients with renal insufciency

creating false positive results.

286 S.J. Aldous / International Journal of Cardiology 164 (2013) 282294BNP has a constitutive release with a background homeostatic andcardio-protective role. However, at times of wall stress/dysfunction ofthe ventricles, it is produced in higher levels in response to neurohor-monal signals from the adrenergic and reninangiotensinaldosterone(RAA) systems. BNP production has also been shown to be stimulatedby hypoxia suggesting that ischaemia can directly induce BNP releasein addition to the effects infarction has on regional left ventricularfunction [160163]. The function of BNP includes vasodilatation, natri-uresis and inhibition of the RAA and sympathetic nervous systems[160165]. BNP levels trend upward to a peak between 14 and 40 hafter an ischaemic event. Some patients have a biphasic release withsecond peak at 73120 h thought to reect the long term adverse effectof left ventricular remodelling and has been shown to be prognosticallyadverse compared with the monophasic response [160163,166169].BNP/NT-proBNP are higher in patients with more severe coronaryartery disease, greater extent of ischaemic territory, left ventriculardysfunction (systolic and diastolic), regional wall motion abnormalitiesand heart failure/cardiogenic shock [116,159,166,169175].

Although BNP/NT-proBNP are increased in those with ACS, theyare not useful diagnostic markers with levels being raised in otherconditions with similar symptoms such as heart failure and pulmo-nary embolus. They can aid diagnosis of heart failure in patientswith cardiac ischaemia [116,166,168]. Their usefulness, however,lies in risk stratication, shown in large trials such as Orboban inPatients with Unstable coronary Syndromes (OPUS)-TIMI 16 and TAC-TICS TIMI 18 as well as smaller trials. BNP/NT-proBNP are independentpredictors of death [116,160,164,167,168,170181] and heart failure[116,159161,166,174,179,182] independent of left ventricular ejectionfraction and this risk is graduated. They predict thosewho incur adverseleft ventricular remodelling (progressive dilatation and cardiac dys-function) [161,172,183], with a correlation better than for cTn [165].BNP/NT-proBNP have been found to predict recurrent ischaemia insome but not all trials [116,160,161,166,173,174,181,182,184] andparticularly in subjects with impaired left ventricular function [160].

Once BNP/NT-proBNP were identied as risk stratication tools,analyses directed at assessing their potential in guiding treatmentwere undertaken. Studies have tested the benets of ACE inhibitors,ARBs and renin inhibitors in patients with and without raised BNP/NT-proBNP. They have been shown to be of benet to patients withAMI and heart failure and/or left ventricular dysfunction but evidencein patients without heart failure and with normal left ventricularfunction is less strong [160162]. One sub-study analysis suggestedthat those with high but not low levels of NT-proBNP benet fromtreatment with tiroban but this association was lost after correctionfor cTn levels [185]. Some studies have also shown that early revascu-larization in patients with high but not low levels of BNP/NT proBNPsignicantly reduce rates of mortality and heart failure [131,133] butothers did not [186,187].

In conclusion, both BNP and NT-proBNP are excellent markers ofadverse events post-AMI, (death, heart failure and less strongly forrecurrent cardiac ischaemia) but, in contrast to their proven role inthe diagnosis and management of acute and chronic heart failure, asyet there is no consensus they can be used to guide early treatmentin AMI in order to improve outcomes.

2.3.2. ANPANP is a peptide, stored and released by cardiac myocytes in the

atria. It is released in response to atrial stretch and a variety ofother signals induced by hypervolaemia, exercise or caloric restric-tion. ANP is constitutively expressed in the ventricle and is releasedin response to stress induced by increased afterload or injury (e.g.AMI). ANP stimulates a reduction in blood volume via extravasationof uid into the extracellular space and therefore a reduction in cardiacoutput and systemic blood pressure. It also directly vasodilates,suppresses pressor hormones including the RAA system and reduces

sympathetic trafc. Lipolysis is increased and renal sodium reabsorptionis decreased. The overall effect of ANP is to counter increases in bloodpressure and volume caused by the RAA system. ANP and NT-ANPhave been shown to be increased in patients with AMI and heart failureand in those with adverse outcomes, although not particularly reinfarc-tion. However, although levels of ANP and BNP correlate, it is only BNPthat consistently provides additional prognostic information beyondleft ventricular function [159,181,182].

2.3.3. AdrenomedullinAdrenomedullin was originally isolated from human pheochro-

mocytoma tissue and subsequently found in the adrenal medulla,kidney, lung, peripheral vascular bed, and the cardiac ventricles. It isa cardiovascular regulatory peptide with vasodilatory, diuretic andnatriuretic functions and also inhibits aldosterone secretion, bro-blast proliferation and cardiomyocyte hypertrophy. Levels of adreno-medullin increase in parallel to the progression of cardiovasculardisease, including hypertension, renal failure, heart failure andpulmonary hypertension. It can also attenuate infarct developmentduring acute ischaemia-reperfusion injury. It is suggested that rapidup-regulation of adrenomedullin in the coronary circulation mayexert a cardio-protective effect via autocrine/paracrine mechanismsafter the onset of AMI [188,189]. Elevated adrenomedullin levels areindicative of cardiac remodelling. However, patients with a varietyof cardiomyopathies with elevated indices of left ventricular massand diastolic dysfunction also have higher adrenomedullin levelscompared with patients with non-remodelled hearts. Adrenomedullinhas the potential to inuence the pathological process in both theacute phase of AMI and the subsequent remodelling and haemody-namic features associated with chronic heart failure. Adrenomedullinmay also augment BNP-induced natriuresis [189].

2.3.4. Reninangiotensinaldosterone systemAfter AMI, the increasing preload (volume) and afterload (vaso-

constriction) stimulates the RAA system [190]. Renin catalyses theconversion of angiotensinogen to angiotensin l followed by conver-sion to angiotensin II by angiotensin converting enzyme. Angiotensinll stimulates the sympathetic nervous system and aldosterone pro-duction, acts as a vasoconstrictor, is involved in sodium retention,activates smooth muscle cell growth and migration, promotes cardiacbrosis, promotes oxidative stress, activates monocyte/macrophagemigration, activates release of adhesion and inammatory moleculesand is prothrombotic [191,192]. Aldosterone is responsible for sodiumand water retention. During AMI, aldosterone promotes a broad spec-trum of detrimental cardiovascular effects, including acute endothelialdysfunction, inhibition of nitric oxide activity, increased endothelialoxidative stress, increased vascular tone, rapid occurrence of vascularsmooth muscle cell and cardiac myocyte necrosis, collagen depositionin blood vessels, and myocardial hypertrophy and brosis. Aldosteronerises and decreases rapidly within hours of infarction [193].

Levels of these neuro-endocrine markers are often raised in AMIwhich may be due to pain (catecholamines), or due to the complica-tions of AMI including heart failure, shock and arrhythmias. Despitethe salutary contribution these analyte investigations have made toour understanding of the pathophysiology of ACS (and other formsof acute and chronic cardiac injury), with the exception of BNP, theyhave not entered clinical practice in the form of widely applied diag-nostic/prognostic tests. Nevertheless, treatment of patients with AMI(and heart failure) with inhibitors of the neuro-endocrine systemreduces morbidity and mortality. Large trials have demonstratedreduction in mortality, left ventricular dysfunction, reinfarction andstroke with the use of -blockers [194197], reduction in mortality,reinfarction and heart failure with the use of ACE inhibitors[198203], reduction in death and heart failure with the use of ARBs(or equivalence to ACE inhibitors) [204,205] and reduction in mortalityand heart failure in thosewith reduced left ventricular functionwith the

use of aldosterone inhibitors [206].

A summary of established biomarkers can be seen in Table 1.

2.4. Novel cardiac biomarkers

2.4.1. CholineCholine is an enzymatic product of phospholipase D. Phospholi-

pase D, is involved in endothelial dysfunction, and is considered amarker of plaque instability, as well as a marker of severe myocardialischaemia, and has been associated with elements of the metabolicsyndrome. Isomers of choline are emerging as important componentsin the cellular signal transduction pathways also involved in coronaryplaque inammation and destabilization [207,208]. Studies haveshown that choline offers no obvious improvement of an earlybiochemical diagnosis of AMI. However it has been found to predictadverse events including cardiac death, non-fatal cardiac arrest,non-fatal myocardial infarction, development of heart failure, revas-cularization, life-threatening arrhythmias and heart failure eitheralone or within a composite end-point [207,208].

2.4.2. F2 isoprostanesF2 isoprostanes are a biologically active product of arachidonic

acid metabolism. The biosynthesis of F2 isoprostanes is thought tooccur in many different cells involved in the formation of atheroscle-rosis, including monocytes. This has been supported by studies show-ing elevated F2-isoprostane levels in those who smoke and havedyslipidaemia and in the urine of those with unstable angina [207].Studies have shown increased levels of free F2 isoprostane in thosewith ACS compared to those without. Increased free F2 isoprostanehas also been shown to be predictive of a composite end-point of

needed for development, differentiation, and tissue repair in variousorgans. Under normal physiologic conditions, the placenta is theonly tissue that expresses signicant amounts of GDF-15 but hasbeen shown to up-regulate in a wide range of cancers and in manytissues following injury, ischaemia, and other forms of stress. Animalmodels show that GDF-15 is induced in the heart in response toischaemia-reperfusion injury, pressure overload, and heart failure,possibly via pro-inammatory cytokine and oxidative stress depen-dent signalling pathways [143,209211]. Studies have found thatcirculating levels of GDF-15 are elevated in patients with AMI/ACSbut not statistically signicantly different from thosewith other cardiacdiagnoses or different chest pain aetiologies [209,210] and higher thanhealthy controls [211].

GDF-15 has been shown to independently predict mortality or acomposite of death and non-fatal AMI and that risk is graded. Theassociation with non-fatal AMI alone is less strong. cTnT and NT-proBNP appear to be prognostically superior than GDF-15 but riskstratication can be improved by measuring both cTnT/NT-proBNPand GDP-15 [210]. In a sub-study of the FRISC II trial randomizingpatients with non ST elevation ACS to an invasive compared with aconservative strategy, patients with an elevated cTn but normalGDF-15 did not have a detectable benet from the invasive strategywhilst patients with elevated cTn and elevated GDF-15 levels, did[212].

2.4.4. CopeptinPreprovasopressin is the precursor peptide for anti-diuretic hormone,

copeptin and neurophysin ll. Anti-diuretic hormone is involved in the

osis Performance in prognosis

pecurrcritkernger

r foras s

onge

fter

fter

n an

c fo

c fo

c fo

287S.J. Aldous / International Journal of Cardiology 164 (2013) 282294non-fatal myocardial infarction, development of heart failure, revas-cularization, and death [207].

2.4.3. Growth-differentiation factor-15Growth-differentiation factor-15 (GDF-15) is a stress-responsive

member of the transforming growth factor-b cytokine superfamilyand is involved in regulating inammatory and apoptotic pathways

Table 1Summary of current cardiac biomarkers.

Biomarker Performance in diagn

NecrosisCardiac troponin Highly sensitive and s

myocardial necrosis. Cstandard biochemical

AST First biochemical marlacks specicity. No lopurpose.

CK/CKMB Second line biomarkediagnosis of AMI, notspecic as cTn

LDH Lacks specicity. No lthis purpose.

Myoglobin Marker of AMI early aonset, lacks specicity

hFABP Marker of AMI early aonset, lacks specicity

Ischaemia modied albumin Less sensitive than cTspecicity

InammationInammatory markers(CRP, TNF, IL6, cell adhesion molecules, myeloperoxidase,PAPPA, matrix metalloproteinases, CD40L, PDGF, PGF)

Not sensitive or speci

NeurohormonalBNP/NT-proBNP Not sensitive or speci

Other(ANP, adrenomedullin, RAA hormones)

Not sensitive or speciic forent golderion for AMI

Highly predictive of adverse cardiac events including deathfurther ischaemia and need for revascularization. Treatmentsinstigated in response to cTn results improves outcomes

of AMI butused for this

No data

theensitive or

Not consistently predictive of future events

r used for No data

symptom Predictive of mortality. No data to suggestmyoglobin guided treatment inuences outcomes

symptom Predictive of mortality. No data to suggest hFABP guidedtreatment inuences outcomes

d lacks No convincing data

r AMI CRP in particular and some of the other markers are predictiveof mortality (and heart failure) but not recurrent ischaemia.Inammatory marker guided treatment does not inuence outcomes

r AMI Highly predictive of mortality and heart failure. BNP/NT-proBNPcan guide need for neurohormonal medical therapies (ACEinhibitors etc) but not invasive therapies

r AMI Possibly predictive of adverse events in univariate analyses.Cannot be used to guide treatmentregulation of the endogenous stress response via the hypothalamo-pituitary-adrenal axis and promotes renal water conservation andhence inuences osmoregulation and cardiovascular homeostasis.Copeptin, the C-terminal portion of provasopressin, is a 39-amino acidglycopeptide of unknown function in the circulation. Anti-diuretichormone has been shown to be elevated in heart failure and in differentstates of shock but is unstable with a short half life of only 5 to 15 min,

the ligands of the endothelium-specic receptor tyrosine kinase.

288 S.J. Aldous / International Journal of Cardiology 164 (2013) 282294but copeptin ismore stable and thereforemore readily amenable tomea-surement [143,213216].

Copeptin levels have been found to be signicantly higher inpatients with AMI as compared with patients having other diagnosesbut only in those presenting early [213]. Studies have shown that thediagnostic accuracy of cTn on presentation for the diagnosis of AMIwas improved by combination with copeptin [213216], howeverthis benet was less striking when hs-cTn assays were used. Inpatients with AMI, copeptin was also shown to predict left ventriculardysfunction and remodelling as well as clinical heart failure distantfrom the infarct period [215]. In addition, copeptin has been shownto be a marker of death and improves risk stratication when usedin conjunctionwith NT-proBNP. It has not been shown to be a predictorof recurrent ischaemia. [209].

2.4.5. AdiponectinAdiponectin is an adipocytokine, a regulator secreted by mature

adipocytes. It belongs to the collagen super family and shares homolo-gieswith collagens, complement factors, and TNF-. Adiponectin has in-sulin sensitizing, anti-inammatory, lipid metabolism, anti-atherogenic,and antiangiogenic effects [217220]. It appears to be an endogenousmodulator ameliorating obesity linked complications and is inverselycorrelated with cardiovascular risk factors such as type 2 diabetes,hypertension and coronary artery disease. In particular, adiponectinhas been shown to accumulate in the vascular subendothelial spaceafter damage of the endothelial barrier, where it inhibits monocyteadhesion to endothelial cells and inhibits themigration andproliferationof vascular smooth muscle (i.e. it is directly anti-atherogenic).Adiponectin levels have been found to be lower in females, the obese,those with type 2 diabetes/insulin resistance, those with dyslipidaemiainvolving high triglyceride levels and low high density lipoproteinlevels and thus the development of vascular pathology [217220].

The Health Professionals Follow-up Study has shown a correlationbetween low baseline plasma adiponectin and increased risk of AMIover a 6-year follow-up in subjects with no prior cardiovasculardisease [217220]. Plasma adiponectin concentrations have beenshown to be low in patients with AMI and in men with subsequentadverse events (cardiac-related death, recurrent AMI, unstable angina,and heart failure) and to fall during admission in women with adverseevents [217,220,221]. This was independent of other traditional meta-bolic and cardiovascular risk factors [220].

However, in contradistinction to these reports, others have foundeither an increased risk of all-cause mortality but not non-fatal AMI[222] or a trend to the composite of the two [218] in patients withACS and increased adiponectin levels. It has been suggested thathigher baseline levels of adiponectin may in fact be benecial undernormal and non-inammatory conditions but in those with activevascular or myocardial remodelling (including ACS or heart failure),there may be a counter-regulatory or compensatory increase inadiponectin levels. Other hypotheses include the possibility of adipo-nectin resistance and that total adiponectin is a less useful measure-ment than the relative proportions of the biologically active or highmolecular weight adiponectin to inert forms, trimeric or hexamericadiponectin [219].

2.4.6. ST2ST2 is a peptide with a structural sequence of the interleukin (IL)-1

receptor family and has 2 isoforms, a membrane bound form, ST2L, aswell as a truncated soluble form,which lacks transmembrane and intra-cellular domains [223229]. ST2L binds free IL-33. This interface wasoriginally described to play a role in the inammatory process via theinduction of T helper cells. Soluble ST2, secreted in response to inam-matory signals, inhibits the binding of IL-33 to ST2L by acting as a solu-ble decoy receptor and the local ratio of IL-33 and soluble ST2 could

regulate IL-33-mediated signalling. It binds to macrophages leading toAngiopoetin-2 destabilizes the vessel to make it responsive toVEGF (and others) and angiopoietin 1 promotes vascular stabili-zation and counteracts VEGF induced angiogenesis [233,234].

ii) Apelin: This is the endogenous ligand for angiotensin-like 1receptor, is inotropic, diuretic (nitric oxide-dependent), vaso-dilatory and antagonizes the effects of angiotensin II [235,236].

iii) Platelet glycoprotein VI: This is a platelet membrane glycopro-tein that plays a crucial role in the collagen-induced activationand aggregation of platelets [237].

iv) Procalcitonin: This is a 116 amino acid hormone involved incalcium metabolism but has also been shown to be inducedin inammatory conditions. It is the prohormone of calcitoninand is produced in the medullary C cells of the thyroid glandbut may be produced in other tissues [238,239].

v) Micro-ribonucleaic acid (RNA): These are 1925-nucleotidenon-coding RNAs that have been implicated in regulating cellproliferation, differentiation, development and apoptosis. Theexpression prole of micro RNAs is tissue/cell-specic. Somecardio-specic micro RNAs are thought to play importantroles in cardiac/vascular development, hypertrophy, arrhythmiaand ischaemia [240242].

vii) Asymmetric dimethylarginine (ADMA): The methylarginines in-cluding ADMA,N-monomethylarginine and symmetric dimethy-larginine, are generated by the post-translational methylation ofarginine residues in proteins. ADMA inhibits endothelial nitricoxide synthase which leads to endothelial dysfunction due toincreased vasoconstrictor responses, adhesion of platelets andmonocytes, and proliferation of vascular smooth muscle cellsdown-regulation of pro-inammatory cytokines and may serve toprevent uncontrolled inammatory reactions [223,226,227,229,230].

ST2L via its binding of IL33 also has been shown to be induced inconditions of myocardial overload such as myocardial infarction andacute heart failure and other causes of myocardial stretch (leftventricular pressure and volume overload). The resulting negativeconsequences of these conditions including myocardial hypertrophy,dilation of ventricular chambers, and reduction in ejection fraction(remodelling), are reduced by ST2 blocking angiotensin II andphenylephrine-induced hypertrophy, in a possible cardio-protectiverole [224,227,228,230232]. ST2 is associated with cardiac structuralabnormalities such as dilated and dysfunctional left and right ventri-cles, reduced left ventricular ejection fraction, elevated lling pres-sures and diastolic dysfunction, and volume and site of infarctedmyocardium [223,225227,230,231]. Previous studies have reportedelevated ST2 in patients with acute coronary syndromes (as well aspulmonary diseases, acute heart failure, acutely dyspnoeic patientswith and without decompensated acute heart failure and chronicheart failure) but would not be a reliable diagnostic marker. ST2 hasbeen shown to predict mortality and heart failure in such patients[225231].

2.4.7. OtherOther novel markers have been tested only in smaller targeted

studies comparing those with AMI with healthy controls or otherpatients groups rather than generalized Emergency Departmentpopulations undergoing evaluation for ACS. These include:

i) Angiogenic factors: Angiogenesis (the formation of new capil-laries) is essential for the repair of wounds and tissue damagedby ischaemia, and therefore angiogenic factors in the heart areup-regulated in myocardial ischaemia. Angiogenic factors includeVascular Endothelial Growth Factor (VEGF) and the angiopoietins.VEGF is a glycoprotein that induces early endothelial cell migra-tion, proliferation and blood vessel formation. Angiopoietins are[243,244].

These studies have shown that concentrations of VEGF [233,234],angiopoietin 2 [233,234], platelet glycoprotein VI [237], procalcitonin[245,246], Micro RNA-1 [240,242], micro RNA-133a, micro RNA-208a[240], micro RNA-499 [247], micro RNA-1291, micro RNA-663b [241]and ADMA [243,248] but not angiopoietin 1 [233,234] or tyrosinekinase [233,234] were signicantly higher and that concentrationsof apelin [235,236] were signicantly lower, in AMI cases comparedwith the other groups. Apelin [235,236], platelet glycoprotein V1[237] and procalcitonin [238,239] have also shown prognostic utilityfor death and/or other ischaemic events, however, where adjustmentfor clinical factors was made, prognostic utility was less robust.

A summary of novel markers is shown in Table 2.

3. Point of care cardiac markers

There aremany commercial point of care (POC) kits formeasurementof biomarkers including cTn, CKMB, myoglobin and BNP/NT-proBNPboth individually as well as in multi-marker panels. POC devices havebeen shown to reduce turn-around times compared with standard test-ing due to elimination of sample transfer time, no or minimal samplepreparation (analysers customarily use whole blood), and immediateavailability of results. It has been recommended that if standard labora-

laboratories and hospitals must be responsible for maintaining thatquality [250,251,255,257,258].

4. Multi-marker testing

A single cTn test can be insensitive for the diagnosis of AMI whenonly early results post-symptom onset are taken, even when high-sensitivity assays are used. Current AHA guidelines for cTn measure-ment, recommend testing on presentation and again at 812 h post-symptom onset [259] and National Academy of Clinical Biochemistryrecommends an early marker at 06 h and a denitive marker at69 h post-presentation [109]. With current international guidelinesrecommending disposition of 95% of Emergency Department patientsat 46 h, the requirement for follow-up cTn measurement at thesetime points means patient admission to in-patient hospital care orobservation units. Multiple markers analysed on presentation and/orrepeated within a shorter time interval to comply with EmergencyDepartment guidelines, may be sufcient for appropriate risk stratica-tion [252].

Studies have shown sensitivities for AMI of 80100% for CKMB/myoglobin up to 4 h post-presentation [252,260], 9496.7% for cTnI/myoglobin up to 1.5 h post-presentation [252,261], 92.6% for cTnI/

Pe

PrtrPrgu

GDF-15 Raised but not sensitive or specic for AMI PrfoPr

CotoPrinNPrtrPrVI guided treatment inuences outcomesPredictive of adverse events in univariate analyses. No data to suggest apelin guidedtrNN

289S.J. Aldous / International Journal of Cardiology 164 (2013) 282294Copeptin Marker of AMI early after symptom onset,may improve sensitivity of early cTn

Adiponectin Not sensitive or specic for AMI

ST2 Not sensitive or specic for AMI

Angiogenic factors Raised in AMI but insufcient dataApelin Lowered in AMI but insufcient data

Platelet glycoprotein VI Raised in AMI but insufcient data

Procalcitonin Raised in AMI but insufcient data

Micro-RNA Raised in AMI but insufcient dataADMA Raised in AMI but insufcient datatory testing exceeds amaximum60-minute turn-around time (the aver-age being 65128 min) or 25% of decision time, then a POC device (withan average turn-around time of 1526.5 min) should be implemented[249253]. POC testing has also been shown to reduce length of stay inthe Emergency Department [249,251,253]. Other potential advantagesinclude economic savings, assisting adherence to treatment, reductionin complications and patient satisfaction [249,253255]. Althoughmore expensive than laboratory tests, money is potentially saved byaccelerating management decisions in the Emergency Department andpreventing unnecessary admissions, however economic benets havenot been proven.

The major disadvantage of POC tests is their inferiority comparedwith standard testing. This is mainly due to reduced precision withmany not achieving recommended levels, and lack of standardization[249,250,256] leading to poor correlation and concordance betweenassays. Despite this, studies with POC biomarkers have shown diagnosticand prognostic utility akin to standard testing [249,250]. Neverthe-less, POC devices should remain compliant with quality require-ments in order to be employed in routine practice and the core

Table 2Summary of novel cardiac biomarkers.

Biomarker Performance in diagnosis

Choline Raised but not sensitive or specic for AMI

F2 isoprostanes Raised but not sensitive or specic for AMIeatment inuences outcomeso datao dataCKMB up to 8 h post-presentation [262] and 100% for cTnI/CKMB/myoglobin up to 2 h post-presentation [261,263] compared with sen-sitivities for cTn alone of 8692.3% [252,262,263]. These studies usedthe original WHO criteria/CKMB as the gold standard for the diagnosisof AMI which may over-estimate test performance. Subsequently, theCHECKMATE study has demonstrated that myoglobin/CKMB/cTnIpanel identied AMI patients earlier and provided better risk strati-cation for mortality compared with standard laboratory practice,myoglobin/cTnI panel and CKMB/cTnI panel [251,252]. Goodacre etal. showed that the use of a multi-marker panel in the EmergencyDepartment signicantly increased successful discharge, dened asdischarge within 4 h and no adverse events including death, non-fatal AMI, emergency revascularization, life-threatening arrhythmiaor hospitalization due to myocardial ischaemia within 3 months[254]. Other studies have shown that low risk patients identied bynegative early cTnI/CKMB/myoglobin had low (03%) death or AMI/ACS rates by 30 days to 6 months [261,264,265]. However, despitethese studies suggesting incremental benet of multiple biomarkers,these studies have been criticized for using, in particular, cTn assays

rformance in prognosis

edictive of mortality, ischaemia and heart failure. No data to suggest choline guidedeatment inuences outcomesedictive of mortality, ischaemia and heart failure. No data to suggest F2 isoprostaneided treatment inuences outcomesedictive of mortality and ischaemia. Single study suggests GDF-15 can guide needr invasive treatment to inuence outcomesedictive of mortality. No data to suggest copeptin guided treatment inuences outcomes

nicting results regarding whether low or high levels are predictive of events. No datasuggest adiponectin guided treatment inuences outcomesedictive of mortality and heart failure. No data to suggest ST2 guided treatmentuences outcomeso dataedictive of adverse events in univariate analyses. No data to suggest apelin guidedeatment inuences outcomesedictive of adverse events in univariate analyses. No data to suggest Platelet glycoprotein

290 S.J. Aldous / International Journal of Cardiology 164 (2013) 282294with low analytical sensitivity; negating the advantages that cTnalone may offer [100].

Other combinations using newer markers have also been pro-posed. Panels consisting of hFABP/cTn appear to have improvedearly diagnostic utility [266,267] compared with cTn alone butthis combination has not been compared with newer hs-cTn as-says. Panels consisting of cTnT/IL-10/myeloperoxidase/PGF [268],brinogen/NT-proBNP [269], hFABP/NT-proBNP [266], hFABP/NT-proBNP/cTnT [270] and cTn/copeptin [213,216] have been pro-posed as prognostic aids but require further prospective random-ized testing. Other have found no additional prognosticinformation beyond conventionally used stratication tools forcombinations of NT-proBNP, high-sensitivity CRP, matrixmetaloproteinase-9, PAPPA, myeloperoxidase, CD40L, IL 6/10/18,P- and E-selectin, cystatin C, glycogen phosphorylase-BB, d-dimer, brinogen [266,270272].

Conversely, multi-marker assessment has been shown to beassociated with higher Emergency Department, coronary care andcardiac intervention costs but lower general in-patient costs and hasnot been shown to reduce overall costs despite reducing admissions[273].

5. Summary

With the advent and development of cTn assays, cTn has beenshown to be a highly sensitive and specic marker for the diagnosisof AMI, ultimately resulting in a major change in the denition ofAMI. This was because studies demonstrated the relevance of cTnstatus in guiding the effective application of invasive therapies withbenet on outcomes. Newer hs-cTn assays identify more patients atrisk and earlier than standard assays which may accelerate currentdiagnostic protocols and improve outcomes, however, reduced spec-icity may lead to increased referrals and unnecessary investigations.

Other clinically valuable cardiac markers for the use in patients withAMI comprise BNP/NT-proBNP, and to a lesser extent, CRP, which are in-dependent predictors of adverse events including death, heart failureand possibly recurrent ischaemia. Despite this, their ability to inuenceoutcomes is much less established than that of cTn. Multiple markersmay accelerate the rule out of AMI and prevent unnecessary admissions.

Despite the multitude of cardiac biomarkers in production andunder investigation, none have convincingly demonstrated their incre-mental utility beyond that of cTn. Therefore, markers which (a) addspecicity or sensitivity to late generation troponin assays in detectionof AMI and (b) which provide objective evidence of unstable anginaor (c) provide prognostic utility with the ability to inuence outcomesremain unmet needs.

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