CHAPTER TWO

Current Applications of CardiacTroponin T for the Diagnosisof Myocardial DamageMartina Vasatova*,1, Radek Pudil†, Jan M. Horacek‡,}, Tomas Buchler}*Institute of Clinical Biochemistry and Diagnostics, University Hospital Hradec Kralove, Hradec Kralove,Czech Republic†1st Department of Medicine—Cardioangiology, University Hospital Hradec Kralove, Faculty of Medicinein Hradec Kralove, Charles University in Prague, Prague, Czech Republic‡Department of Internal Medicine, Faculty of Military Health Sciences in Hradec Kralove, University ofDefence, Hradec Kralove, Czech Republic}4th Department of Internal Medicine—Hematology, University Hospital Hradec Kralove, Faculty ofMedicine in Hradec Kralove, Charles University in Prague, Prague, Czech Republic}Department of Oncology, First Faculty of Medicine, Charles University and Thomayer Hospital, Prague,Czech Republic1Corresponding author: e-mail address: martina.vasatova@fnhk.cz

Contents

1.

AdvISShttp

Introduction

ances in Clinical Chemistry, Volume 61 # 2013 Elsevier Inc.N 0065-2423 All rights reserved.://dx.doi.org/10.1016/B978-0-12-407680-8.00002-6

34

2. Biology and Function 34

2.1

History 35 2.2 Cardiac myofibrillar apparatus 35 2.3 Troponin complex function 36 2.4 Troponin isoforms 36 2.5 Myocardial ischemia and necrosis 38

3.

Troponin Assays 38 3.1 History 38 3.2 Principle of test 39 3.3 Cutoffs and sensitivity 39 3.4 Preanalytic factors 41 3.5 Assay standardization 42

4.

TnT Clinical Applications 43 4.1 Myocardial necrosis 43 4.2 Pulmonary artery embolism 51 4.3 Pulmonary artery hypertension 52 4.4 Heart failure 53 4.5 Cardiomyopathies 53 4.6 Arrhythmias 54 4.7 Cardiotoxicity induced by anticancer therapy 55

5.

Biologic Variability 57

33

34 Martina Vasatova et al.

6.

Conclusion 59 Acknowledgments 59 References 59

Abstract

Biochemical markers of myocardial injury play an important role in the diagnosis of car-diovascular diseases. Measurement of cardiac biomarkers is one of the most importantdiagnostic tests in acute myocardial infarction (AMI), heart failure, and other cardiovas-cular disorders. Recently, the European Society of Cardiology, the American College ofCardiology Foundation, the American Heart Association, and the World Heart Federa-tion have published a consensus definition of AMI that includes a detailed guidelinefor the assessment of biochemical markers in suspected disease. The cardiac troponins(cTnI and cTnT) were recommended as preferred markers of myocardial necrosis inthis setting. Herein, we review cardiac troponin biochemistry, the performance charac-teristics of cTnT assays, and optimal utilization of troponin in patients with proven orpossible cardiovascular disease. We also discuss the use of troponin tests, with emphasison cTnT, in different clinical situations in which its levels may be elevated.

1. INTRODUCTION

Cardiovascular disease is the leading cause of death among adults in the

most developed countries and many developing countries. Cardiovascular

diseases cause considerable disability and loss of productivity that substan-

tially contribute to increased health care costs, especially in the aged.

Cardiovascular disease is a general term coveringmany diseases that affect

the heart or circulatory vessels, such as hypertension, angina pectoris, ath-

erosclerosis, ischemic heart disease, acute myocardial infarction (AMI), heart

failure (HF), cerebrovascular diseases and stroke, arrhythmias, valvular heart

disease, and peripheral vascular disease.

One of the most important biochemical tests for the assessment of car-

diovascular disease is the measurement of cardiac markers. Cardiac tropo-

nins, due to their sensitivity and specificity, have been recommended as

biomarkers of choice for diagnosis of myocardial necrosis [1,2].

2. BIOLOGY AND FUNCTION

Cardiac troponins are regulatory proteins that control the calcium-

mediated interaction of actin and myosin resulting in contraction and relax-

ation of striated muscle.

35Current Applications of Cardiac Troponin T

2.1. HistoryMolecular basis of excitation–contraction coupling in the heart has been an

area of intensive research since Ringer [3] recognized the influence of Ca2þ

on heart contraction in 1883. In 1940, Heilbrunn [4] suggested that Ca2þ

served as a trigger for intracellular contractility. In 1953, Huxley [5,6] pro-

posed the sliding filament model of sarcomere function on the basis of X-ray

diffraction patterns and electron microscopy. In the 1960s, Ca2þ was iden-

tified as the physiologic activator of contractile proteins, and the sarcoplas-

mic reticulum was shown to regulate intracellular calcium release and

reuptake in muscle [7–11].

The first report on troponin was published in 1969. Katz biochemically

purified and Ebashi identified troponin as a Ca2þ binding site on myofibrillar

thin filament [12,13]. In 1971–1973, Greaser et al. [14–16] demonstrated that

the troponin complex comprised three distinct proteins: troponin C (TnC),

for binding Ca2þ and regulating thin filament activation; troponin I (TnI), for

inhibiting actin-activated myosin ATPase activity; and troponin T (TnT), for

binding tropomyosin (Tm).

2.2. Cardiac myofibrillar apparatusThe anatomy and organization of the cardiac myofibrillar apparatus provides

the foundation for understanding the molecular basis of cardiac contractility.

The functional unit of the cardiac myocyte is the sarcomere. The sarcomere

is composed of a precise geometric arrangement of myosin-containing thick

filaments surrounded by a hexagonal array of thin filaments containing actin

and the Tm/troponin regulatory complex. Actin monomers polymerize

into a double-helical structure longitudinally oriented around myosin.

Tm is a double-stranded a-helical protein that moves on the surface of

the thin filament during activation to a position near the groove of the actin

double helix [17].

The troponin complex is immobilized on the thin filament of

the contractile apparatus. It is the regulatory complex of the myofibrillar

thin filament that plays a critical role in regulating excitation–contraction

coupling in the heart. Troponin is composed of three protein units:

TnC (18 kDa), TnI (23 kDa), and TnT (35 kDa) [18]. These three

proteins are arranged 1:1:1 stoichiometrically and are distributed along

the thin filament with one troponin complex bound to every seven actin

monomers [17].

36 Martina Vasatova et al.

2.3. Troponin complex functionThe best studied function of the troponin complex is the modulation of con-

tractile function of the sarcomere in response to cytosolic calcium (Ca2þ)and protein phosphorylation (regulatory proteins of the sarcomere).

In the heart, cardiac troponin I (cTnI) is a key regulatory protein in the pro-

cess of cardiac muscle contraction linking Ca2þ–cTnC binding with the

activation of crossbridge reaction between the thin and thick filaments

(i.e., actin and myosin). cTnI inhibits actomyosin Mg2þ–ATPase and leads

to muscle relaxation by interrupting the actin–myosin linkage. Cardiac tro-

ponin C (cTnC) binds Ca2þ inducing conformational changes that are trans-

mitted by cardiac troponin T (cTnT) and cTnI phosphorylation to modulate

cTnI inhibition. cTnT interacts with both cTnI and cTnC as well as with

Tm to attach the cTn complex to the myofibrillar thin filament. The binding

of cTnI with cTnC is tighter than the binding of cTnT with cTnC and

cTnI. With triggered release of Ca2þ from intracellular stores at the onset

of contraction, Ca2þ binds to the N-terminal Ca2þ binding site of cTnC,

initiating a conformational change. This facilitates the crossbridge cycling

and myocyte contraction, thus regulating the force and velocity of striated

muscle contraction [18].

In diastole, Ca2þ is not bound to the regulatory site of cTnC protein; Tm

is in a blocking position held by the action of the tail of cTnT and by cTnI,

which is tethered to the thin filament by an inhibitory peptide (Ip).

In systole, Ca2þ binding to the regulatory site of cTnC induces release of

the TnI Ip from actin and release of cTnT from Tm resulting in a movement

of Tm, which permits the crossbridges to react with the thick filament. The

crossbridges are held in register on the thick filament by a cytoskeletal pro-

tein called titin, which ultimately connects to the Z-disk. Titin and myosin

binding protein C act to regulate the movement of the crossbridges away

from the thick filament as do the myosin light chains (MLC1 and MLC2;

Fig. 2.1) [17].

2.4. Troponin isoformsThere are tissue-specific isoforms of TnI, TnT, and TnC. Because the car-

diac isoform of TnC is shared by slow-twitch skeletal muscles, it is not useful

for diagnosis of cardiac injury [19].

Both cTnI and cTnT contain N-terminal extensions not present in

fast skeletal protein isoforms, suggesting unique roles for cTnI and cTnT

in the heart. It is also noteworthy that physiologically important sites of

TnlTnC

Actin

Tm

TnT

MLC1

Ca

MLC2MyBP-C

Titin

Figure 2.1 Structural changes occurring in thin filament proteins during the activationof the crossbridge cycle. Adapted from [17].

37Current Applications of Cardiac Troponin T

phosphorylation have been identified in cTnI and cTnT that are not present

in their skeletal isoforms [17].

There is one cTnI isoform in the myocardial tissue. This isoform has an

N-terminal 32 amino acid posttranslational tail. This sequence and its dis-

similarity (42% and 45%) with other isoforms made possible the generation

of highly specific monoclonal antibodies.

Three genes control cTnT. These genes and alternative mRNA splicing

produce a series of isoforms with variable sequences near the N- and

C-termini. Although human cardiac muscle contains four cTnT isoforms,

only one is characteristic of normal adult heart. Highly specific antibodies

have been generated against the N-terminus sequence of cTnT [19].

During fetal development, heart skeletal isoforms are gradually re-

placed by cTnI and cTnT. sTnI is no longer present in the heart by

the ninth postnatal month but its expression continues in slow skeletal

muscles. At this point, cTnI is the only isoform expressed in the heart.

Although all cTnT isoforms are expressed in the fetal human heart, the

expression of cTnT1 and cTnT3 predominates. In the postnatal period,

cTnT3 and cTnT4 isoforms prevail; however, cTnT1 and cTnT2 are also

detectable [17].

38 Martina Vasatova et al.

2.5. Myocardial ischemia and necrosisThe majority of troponin is bound in the contractile apparatus of

cardiomyocytes [20]. A very small fraction of cTnT (6–8%) and cTnI

(3–6%) remains free in the cytosolic compartment. Proteolysis of cTnI

and cTnT occurs in the myocardium in response to ischemia. Posttransla-

tional changes include degradation, formation of covalent complexes, phos-

phorylation, oxidation, N-terminal acetylation. Cardiac troponins are

degraded by proteases (calpain I, caspases, matrix metalloproteinase 2) pre-

sent in the myocardium as well as proteases in blood [21,22]. Troponins can

be released from necrotic myocardium as intact molecules and degraded

proteins [22]. As such, troponins comprise a heterogeneous mixture of free

posttranslationally modified, degraded, and truncated forms in the circula-

tion. Although cTnT circulates predominantly in free form, fragments

and complexes thereof (cTnT–cTnI–cTnC) have been reported [18,23].

After myocyte damage, there is a biphasic serum cTnT increase due to

the rapid loss of free cytoplasmic troponin (�12 h) followed by the gradual

release of myofibril-bound troponin complexes (3–5 days). Serum levels,

however, can remain elevated for 10–14 days. In contrast, the release of cTnI

is monophasic due to its low cytosolic pool [20].

Although the exact mechanism of troponin elimination is unknown, it is

likely cleared via the reticuloendothelial system due to its relatively large

molecular size. However, recent evidence has suggested that TnT may be

fragmented into molecules small enough for urinary excretion which may

explain the prevalence of increased TnT in renal failure.

3. TROPONIN ASSAYS

3.1. History

In 1982, Katus investigated the specificity of polyclonal goat antihuman car-

diac myosin–light-chains and detected a cardiospecific antibody directed

against a putative contaminant. This contaminant was purified and used

to develop monoclonal antibodies that subsequently led to the generation

of an enzyme immunoassay (EIA) for TnT [24].

In 1989, Katus et al. [25] described the first TnT enzyme-linked im-

munosorbent assay. This assay was composed of a capture polyclonal

antibody from sheep and a peroxidase-labeled monoclonal antibody for

detection. The assay procedure was relatively rapid (90 min) with a 500-

ng/L limit of detection (LOD). In 1992, a much more sensitive EIA

39Current Applications of Cardiac Troponin T

was developed using two specific TnT monoclonal antibodies. This one-

step sandwich assay used solid-phase streptavidin-coated polystyrene

tubes, a biotin-labeled capture antibody, and a horseradish peroxidase-

labeled secondary antibody. The measuring range for this TnT assay was

100–15,000 ng/L [26].

It took more than 11 years to firmly establish cTnT as a cardiac marker in

the clinical community. The absolute cardiospecificity of troponin and

improved risk prediction of chest pain patients, shown in many prospective

multicenter trials, were instrumental to its success [24].

The development of improved immunoassays for cTnT continued. TnT

second-generation assays used cardiospecific monoclonal antibodies com-

bined with electrochemiluminescence detection. Time of analysis was short-

ened (45 min). To increase specificity, recombinant human cTnTwas used in

third-generation assays. Analysis time decreased (9–18 min). Sensitive fourth-

generation immunoassays had substantially improved LOD (10 ng/L). The

troponin concentration (30 ng/L) at a CV <10% was used as the cutoff [27].

Recently, several methods with even higher analytical sensitivity, that is,

ultra- or high-sensitivity assays, for cardiac troponins have been developed.

The high-sensitivity cTnT (hs-cTnT) assay was a modification of previously

developed methods [28]. Unfortunately, higher analytical sensitivity

resulted in issues related to clinical interpretation.

3.2. Principle of testThe homogenous assay was composed of sample incubated with bio-

tinylated capture antibody and ruthenium-labeled detection antibody.

Streptavidin-coated beads are added to bind immune complexes. The reac-

tion mixture is then transferred to the measuring cell where the beads are

magnetically captured. The measuring cell is washed to remove unbound

label and filled with detection buffer containing Tris-propylamine. Voltage

is applied and the emitted chemiluminescence is detected [28].

3.3. Cutoffs and sensitivityIn 2007, in an effort to standardize AMI diagnosis and troponin measure-

ment, the clinical definition was expanded to include cardiac biomarkers

(i.e., troponins) as a gold diagnostic standard [1,29,30]. The analytical

parameters of troponin assays were also defined. According to the definition

of AMI [1], the cutoff value is defined as the 99th percentile of a healthy

40 Martina Vasatova et al.

population and requires tests with a CV<10% at this concentration. Unfor-

tunately, no clinically available assays were available at that time with this

level of precision. This requirement stimulated the development of high

analytical sensitivity assays.

In 2010,Apple [31] classified commercially available troponin assays as “not

acceptable” (CV >20%), “clinically usable” (CV¼10–20%), and “guideline

acceptable” (CV<10%). Subsequently, the International Federation of Clin-

ical Chemistry and Laboratory Medicine published a comparison of clinically

available troponin methods [32]. Of the 24 assays, 9 were “guideline accept-

able” and9were “clinically usable” [31–33]. In the same year, La’ulu andRob-

erts [34] evaluated the performance characteristics of five cTnI assays. None

achieved a 10% CV at less than the 99th percentile concentration.

With the advent of high-sensitivity assays, it was possible to accurately

measure TnT at the recommended precision. These improved assays had

�10-fold higher analytical sensitivity and resulted in continued decrease

in the 99th percentile concentration, that is, from 600 (first generation)

to 14 ng/L (fifth generation) using hs-cTnT [28,35].

The new hs-cTnT method was a modification of the fourth-generation

assay. Although the biotinylated capture antibody was unchanged, the

detection antibody was a genetically engineered mouse–human molecule.

In this chimeric antibody, the constant C1 region in the monoclonal mouse

FAB fragment was replaced with a human IgG C1 region. The rationale for

this change was to reduce interference by human antimouse antibodies.

Analytical sensitivity was improved by the use of increased sample

(15–50 mL), increased detection antibody ruthenium concentration, and

decreased background signal via buffer optimization [28].

In 2010, Giannitsis et al. [28] validated a fifth-generation hs-cTnT

method. This assay had an analytical range of 3–10,000 ng/L and a 5-ng/L

LOD. The cutoff value was 14 ng/L at the 99th percentile cutoff for a healthy

reference population (CV¼9.0%, n¼616). This method was suitable for

detecting myocardial necrosis according to the definition of myocardial

infarction with the limit of quantification of 13 ng/L (CV¼10%;

Fig. 2.2). In the same year, Body et al. [36] reported on the diagnostic sen-

sitivity, specificity, and receiver-operating characteristic (ROC) curves of a

hs-cTnT method. ROC analysis demonstrated better diagnostic accuracy

versus fourth-generation methods with areas under the curve (AUC) of

0.94 and 0.86, for hs-cTnT and cTnT, respectively. Similar data were also

reported by Aldous et al. [37].

Troponin T, Elecsys hs-cTnT (ng/L)

99th percentileat 13.5 ng/L

Tota

l CV

(%

)

10

10

20

30

10 100 1000 10,000

Figure 2.2 Limit of quantification of the hs-TnT method with CV¼10%. Adaptedfrom [28].

41Current Applications of Cardiac Troponin T

3.4. Preanalytic factorsPreanalytical factors require consideration for main laboratory and point-

of-care assays. These factors are method dependent and need to be defined

for each troponin assay prior to clinical introduction [18].

For the most rapid testing, whole blood and plasma are preferred spec-

imens. Although serum, EDTA–plasma, and heparin–plasma were validated

for the hs-cTnT assay, samples should not be used interchangeably. For

example, EDTA, due to its ability to bind calcium, influences the degree

of cTn complex formation. Heparin can bind cTn and mask specific epi-

topes thus falsely reducing analyte concentration. As such, the use of ther-

apeutic heparin needs to be carefully evaluated in AMI.

Long-term stability of cTnT is also important for archival use. The stability

of cTnT is 24 h (2–8 �C) and 12 months (�20 �C). The hs-cTnT assay is

unaffected by hemolysis (hemoglobin <1 g/L). Icteric and lipemia

are generally not problematic below 428 mmol/L bilirubin and 15 g/L

triglycerides, respectively. In patients receiving high biotin therapy, sampling

should deferred until 8 h postadministration (interference biotin>82 nmol/L)

[18,38].

42 Martina Vasatova et al.

3.5. Assay standardizationcTnT assays have the benefit of being produced by a single manufacturer that

provides better method standardization. The use of a single calibrationmate-

rial reduces result variation and provides improved diagnostic consistency

[39]. Lack of comparable values and an inability to define a common deci-

sion limit have led to confusion among clinicians with respect to different

cTnI methods. It is critically important that a clinically relevant cardiac

marker such as cardiac troponins be measured with standardized methods

to achieve comparable results. In fact, the cTnI standardization subcommit-

tee of the American Association for Clinical Chemistry in collaboration with

the National Institute of Standards and Technology has developed a purified

cTnICT complex reference material (SRMNo 2921) recommended to cal-

ibrate commercial cTnI assays [18,40].

Giannitsis et al. [28] compared traditional cTnT (fourth generation) with

hs-cTnT methods. Although detection of low cTnT (<100 ng/L) can be

useful in some clinical situations, these methods were not comparable at this

concentration. At the fourth-generation cutoff (30 ng/L), hs-cTnT was

substantially increased (�50–100%) versus cTnT (Fig. 2.3) [28,41].

Average of Elecsys Tropo T hs STAT and Elecsys Tropo T STAT (ng/L)

(Ele

csys

trop

o T

hs

STA

T–E

lecs

ys tr

opo

T S

TAT

) / A

vera

ge %

15

-20

0

20

40

60

80

100

120

20 25 30 35 40 45 50 55 60

-1.96 SD

Mean

+1.96 SD

107.7

55.4

3.0

Figure 2.3 Bland–Altman analysis—comparison of Elecsys Tropo T hs STAT (Elecsys2010) and Elecsys Tropo T STAT (Elecsys 2010) [41].

Average of E170 Tropo T hs and Elecsys Tropo T hs STAT (ng/L)

0

-150

-100

-50

0

50

100 +1.96 SD

87.8

Mean

-0.2

-1.96 SD

-88.1

10 20 30 40 50 60 70 80 90 100 110

(E17

0 Tr

opo

T h

s -

Ele

csys

Tro

po T

hs

STA

T)

/ Ave

rage

%

Figure 2.4 Bland–Altman analysis—comparison of Elecsys Tropo T hs STAT (Elecsys2010) and Elecsys Tropo T hs (E170 Modular) [41].

43Current Applications of Cardiac Troponin T

These data indicate that significant calibration differences exist between

the fourth- and fifth-generation cTnT methods. As such, the assay-to-

reference material relationship needs to be more precisely defined. hs-cTnT

performed on the Elecsys 2010 and Modular Analytics SWA (E-170)

platforms (Roche Diagnostics) yielded comparable results (Fig. 2.4) [41].

4. TnT CLINICAL APPLICATIONS

4.1. Myocardial necrosis

Myocardial infarction is defined as cell death (necrosis of myocardial tissue)

due to prolonged ischemia, that is, a result of perfusion imbalance between

oxygen supply and demand. Necrosis usually evolves through oncosis,

defined as a primary increase in plasma membrane permeability [42].

In contrast, necrosis occurs as a result of secondary plasma membrane disin-

tegration associated with apoptosis.

The development of the complete necrosis takes at least 2–4 h or longer,

depending on the presence of collateral circulation, duration of coronary

44 Martina Vasatova et al.

artery occlusion, myocyte sensitivity to ischemia, preconditioning, and indi-

vidual demands for oxygen and nutrients. The area of necrosis is character-

ized by the presence of polymorphonuclear leukocytes. The presence of

mononuclear cells and fibroblasts and absence of polymorphonuclear leuko-

cytes is associated with healing. A healed infarction is manifested as scar tissue

without cellular infiltration.

Cardiac troponins play a crucial role in the diagnosis of myocardial

necrosis. According to the universally accepted definition, myocardial

infarction is diagnosed when blood levels of sensitive and specific biomarkers

such as cTn or CK-MB are increased in the clinical setting of acute myo-

cardial ischemia [1].

Although cTnT and cTnI increase in blood reflect injury leading to

necrosis of myocardial cells, they do not provide any clues with respect

to the underlying disease mechanism. Various possibilities have been

suggested for the release of structural proteins from the myocardium,

including normal turnover of myocardial cells, apoptosis, cellular release

of troponin degradation products, increased cellular wall permeability, for-

mation, and release of membranous blebs and myocyte necrosis. According

to the third universal definition [2], the term myocardial infarction should

be used when there is evidence of myocardial necrosis in a clinical setting

consistent with ischemia. Under these conditions, any one of a number of

criteria is required for the diagnosis of myocardial infarction. Detection of

increased and/or decreased cardiac biomarkers (preferably troponin) with

one value above the 99th percentile of normal reference population

together with the evidence of myocardial ischemia is required. Evidence

may be supported by symptoms of ischemia, electrocardiogram (ECG)

changes indicative of new ischemia (new ST-T changes or new left bundle

branch block, LBBB), development of pathological Q waves in the ECG,

imaging evidence of new loss of viable myocardium, or new regional wall

motion abnormality and identification of an intracoronary thrombus by

angiography or autopsy.

According to the third universal definition [2], percutaneous coronary

intervention (PCI)-related myocardial infarction is arbitrarily defined by a

greater than fivefold increase in cTn (relative to the 99th percentile) in

patients with normal baseline values or a rise in cTn values>20% if the base-

line values are increased and stable or decreased. Symptoms suggestive of

myocardial ischemia, new ischemic ECG changes, angiographic findings

consistent with procedural complications, imaging of new loss of viable

myocardium, or new regional wall motion abnormality are also required.

45Current Applications of Cardiac Troponin T

As such, serial cTn measurement is recommended (before or immediately

after the procedure and again at post 6–9 and 12–24 h).

Stent thrombosis associated with myocardial infarction is defined by cor-

onary angiography or autopsy findings in the setting of myocardial ischemia

in conjunction with increased and/or decreased cardiac biomarkers with at

least one value above the 99th percentile.

Coronary artery bypass grafting-related myocardial injury is defined by a

>10-fold increase in cardiac biomarkers (relative to the 99th percentile) in

patients with normal baseline cTn values. In addition, either new patholog-

ical Q waves or new LBBB, or angiographically documented new graft or

new native coronary artery occlusion or imaging evidence of new loss of

viable myocardium or new regional wall motion abnormality should be

present.

Troponin assessment should be performed at admission (a few hours fol-

lowing chest pain onset) and 3–6 h later. If early measurements do not show

increased cTn and clinical suspicion is high, an additional sample should be

obtained at 12–24 h. For diagnosis of myocardial necrosis, at least one cTn

value must be increased. Troponin remains increased 7–14 days following

the onset of symptoms.

In myocardial infarction, cTn have a typical rise and fall pattern. This

characteristic change helps one to exclude nonischemic causes. Other etiol-

ogies should be considered in the presence of increased cTn without myo-

cardial ischemia (Table 2.1).

Troponin assessment can be very useful for diagnosis of reinfarction.

If recurrent myocardial necrosis is suspected, immediate and second mea-

surements (3–6 h post) are recommended. A 20% increase in the second

measurement is diagnostic for recurrent myocardial infarction.

4.1.1 AMI with ST-segment elevationAMI with ST-segment elevation (STEMI) is defined by the presence of

ischemic symptoms and persistent STEMI on the ECG. The majority of

these patients will show a typical rise and fall of cTn and progress to

Q-wave myocardial infarction. The majority of STEMI is caused by an

occlusion of a major coronary artery as a result of disruption of an athero-

sclerotic plaque with subsequent formation of an occluding thrombus.

A minor role is played by local vasospasm (vasoconstriction) and micro-

embolization. In a few cases, thrombus may result from superficial erosion

of the endothelial surface.

Table 2.1 Causes of increased troponin level

Injury related to primary myocardial ischemia

Plaque rupture

Intraluminal coronary artery thrombus formation

Injury related to supply/demand imbalance of myocardial ischemia

Tachy/brady-arrhythmias

Aortic dissection or severe aortic valve disease

Hypertrophic cardiomyopathy

Cardiogenic, hypovolaemic, or septic shock

Severe respiratory failure

Severe anemia

Hypertension with or without LVH

Coronary spasm

Coronary embolism or vasculitis

Coronary endothelial dysfunction without significant CAD

Injury not related to myocardial ischemia

Cardiac contusion, surgery, ablation, pacing, or defibrillator shocks

Rhabdomyolysis with cardiac involvement

Myocarditis

Cardiotoxic agents, for example, anthracyclines, herceptin

Multifactorial or indeterminate myocardial injury

Heart failure

Stress (takotsubo) cardiomyopathy

Severe pulmonary embolism or pulmonary hypertension

Sepsis and critically ill patients

Renal failure

Severe acute neurological diseases, for example, stroke, subarachnoid hemorrhage

Infiltrative diseases, for example, amyloidosis, sarcoidosis

Strenuous exercise

Adapted from [2].

46 Martina Vasatova et al.

47Current Applications of Cardiac Troponin T

Occlusion of a coronary artery leads to rapid development of myocardial

necrosis (15–30 min). Because the necrotic process from the subendocardium

to the subepicardium is time dependent, early reperfusion is essential for effec-

tive treatment.

Community studies performed in the 1950s and 1960s demonstrated

high fatality 1-month rates (40–50%) for patients with presumed myocardial

infarction or acute coronary syndrome with half occurring in the first 2 h

[43–45]. Hospital mortality rates were substantially better (25–30%).

By themid-1980s, hospital mortality improved to 16% [46]. Improved treat-

ment, that is, coronary intervention, fibrinolytics, antithrombotics, and sec-

ondary prevention further reduced 1-month mortality to 4–6% [47,48].

In-hospital mortality of unselected STEMI patients in the European Society

of Cardiology (ESC) countries was 6–14% [49,50]. Mortality in registry

studies was higher, suggesting that the patients included in the randomized

studies were at lower risk [51]. Unfortunately, mortality remains substantial

(�12% in 6 months) [52].

Treatment strategy is based on the achievement of reperfusion as rapidly as

possible. Both randomized and registry studies have shown that delay in pri-

mary PCI was associated with poor outcome and increased mortality. Rapid

diagnosis and early risk stratification of acute chest pain patients are essential to

identify patients in whom immediate intervention would be beneficial.

Initial evaluation is based on the presence of chest pain lasting at least

20 min with no response to nitrates and the presence of STEMIs or new

LBBB. Blood sampling for myocardial markers of necrosis is recommended

in the acute phase. Although treatment may be initiated immediately, cTn

assessment can be helpful in the use of coronary angiography in LBBB

patients of unknown duration.

4.1.2 Acute coronary syndromes without persistent STEMIs(unstable angina and non-ST-segment myocardial infarction)

Acute coronary syndromes (ACS) have a common pathophysiological sub-

strate: atherosclerotic plaque rupture or surface erosion leads to thrombus

formation and distal embolization and results in myocardial hypoperfusion.

According to clinical symptoms, there are two categories of patients with

cardiac chest pain:

1. Patients with acute chest pain and persistent STEMI. This finding usually

reflects acute total coronary occlusion. The majority of these patients

will develop ST-elevation AMI. The primary objective of treatment

48 Martina Vasatova et al.

is to achieve rapid and complete reperfusion using primary angioplasty or

fibrinolytic therapy.

2. Patients with acute chest pain without persistent STEMI. At presentation,

these patients have frequently ST-segment depression, T-wave inversion,

flat T-wave, pseudonormalization of T waves or, less often, no ECG

changes. These so-called non-ST-elevation ACS (NSTE-ACS) require

cTn determination for further diagnostic assessment. cTn-positive patients

are classified as non-ST-elevation myocardial infarction (NSTEMI),

whereas cTn-negativepatients are classifiedashavingunstable angina (UA).

Hospital mortality rates in STEMI patients are similar or higher to NSTE-

ACS at 6 months [50]. Mortality in NSTE-ACS increases with long-term

follow-up, with a twofold difference at 4 years [50]. This difference may

be due to patient profile, that is, NSTE-ACS patients tend to be older with

more comorbidities, as well as less frequent use of invasive reperfusion strat-

egies in this setting.

The assessment of cTn plays a central role in the diagnosis and risk strat-

ification of patients with ACS not presenting with STEMI. Positive cTn is

indicative of non-STEMI myocardial infarction. Negative cTn identifies

patients with UA. cTn is more specific and sensitive versus traditional

markers such as creatine kinase (CK), CK-MB isoenzyme (CK-MB), and

myoglobin.

In non-STEMI ACS, myocardial cellular damage may result from distal

embolization of platelet-rich thrombi arising at the site of unstable (ruptured

or eroded) atherosclerotic plaques or occlusion of a small coronary artery.

The myocardial cellular damage (necrosis) is associated with cTn release into

the circulation. Therefore, in the clinical setting of myocardial ischemia

(chest pain, ECG changes, wall abnormalities), increased cTn indicates myo-

cardial necrosis (myocardial infarction).

According to current ESC guidelines for the management of acute coro-

nary syndromes in patients presentingwithout persistent STEMI, an initial rise

in cTn occurs within 4 h after the onset of symptoms. cTn may remain ele-

vated up to 2weeks (due to continued proteolysis of the contractile apparatus).

There is no substantial difference between cTnT and cTnI. According to

guidelines, the diagnostic cutoff for myocardial infarction is defined as a car-

diac troponin measurement exceeding the 99th percentile of a normal refer-

ence population using an assay with a CV �10%.

As noted earlier, many early cTn assays did not meet these precision

requirements. These criteria are now fulfilled by high- or ultra-sensitive

assays having a 10- to 100-fold lower LOD.

49Current Applications of Cardiac Troponin T

According to guidelines, blood should be drawn promptly and results are

available in 60 min. The test should be repeated 6–9 h after the initial assess-

ment if the first measurement is inconclusive. Repeat testing at 12–24 h is

advised if the clinical condition is still suggestive of acute coronary syndrome

(class of recommendation I, level of evidence A).

The superiority of new high- and ultra-sensitive assays is very clear in the

early phase of acute chest pain. The negative predictive value for myocardial

infarction with a single test on admission is high (95%). Only very early pre-

senters escape detection. Diagnostic sensitivity approaches 100%when a sec-

ond cTn measurement is performed within 3 h of presentation. Therefore, a

rapid rule out protocol (0 and 3 h) is recommended when hs-cTn is available

(class of recommendation I, level of evidence B) [53].

Improved sensitivity and the ability to measure very low cTn increased

diagnostic sensitivity but decreased assay specificity. This problem arises in

thecontextofvery lowcTn.Therearemanydiseasesaccompaniedby increased

troponin from nonischemic origin including aortic dissection, severe trauma,

pulmonary embolism, pulmonary hypertension, etc (Table 2.1). Underlying

mechanisms of troponin release in nonischemic conditions are not fully under-

stood, but increased troponin is associated with poor prognosis.

Increased troponin is frequently found in end-stage renal disease and

severe skeletal myopathies in the absence of ACS. In these patients, increased

troponin is also associated with poor outcome. In end-stage renal disease, it is

recommended to retest troponin 6–9 h with a change�20% considered sig-

nificant. Therefore, careful evaluation of clinical status and differentiation

between acute and chronic troponin increases are necessary to maintain

specificity.

4.1.3 Differential diagnosis of increased troponinThe ESC/AHA guidelines for the universal definition of myocardial infarc-

tion postulated criteria for myocardial infarction as detection of rise and/or

fall of cardiac biomarkers (preferably troponin) with at least one value above

the 99th percentile of reference population (URL) together with the evi-

dence of myocardial ischemia with at least one of the following: symptoms

of ischemia, ECG changes indicative new ischemia (new ST-T changes or

new LBBB), development of pathological Q waves in the ECG, and imag-

ing evidence of new loss of viable myocardium or new regional wall motion

abnormality.

The Joint ESC/ACCF/AHA/WHFTask Force has promoted the use of

the 99th percentile and declared that cTn precision �10% at this percentile

50 Martina Vasatova et al.

was desirable. These high- and ultra-sensitive assays can detect small myo-

cardial tissue damage. As such, any myocardial damage will increase the

number of analytically true-positive findings not detected by early cTn assays

[54]. These assays are able to detect any increase in troponin, but they cannot

answer the main question: is this troponin increase of ischemic or non-

ischemic origin?

Furthermore, there is no clear definition of the rise and fall of troponin in

patients with AMI. Therefore, considerable effort has been dedicated in

devising strategies to analyze the role of kinetic changes in troponin.

This concept was used for the first time by Fesmire in 2000 [55]. They

measured CK-MB and cTnI at 2 h intervals to improve diagnostic sensitivity

and specificity for AMI. Combining the two tests (delta MB �1.5 ng/mL

and/or delta cTnI �0.2 ng/mL) resulted in increased sensitivity to 89.5%

for AMI and 61.9% for angina pectoris (AP; p<0.005).

Reichlin et al. evaluated absolute and relative cTn changes for early diag-

nosis of myocardial infarction [56]. In this prospective study, hs-cTnT and

ultra-sensitive TnI were measured in 836 patients presenting to emergency

department with AMI symptoms. Blood samples were collected at presen-

tation, 1 h, and 2 h. This study found that an absolute change in cTn at 2 h

had significantly higher diagnostic accuracy versus relative change. The

hs-cTnT ROC-derived cutoff was 7 ng/L.

Mueller et al. evaluated the kinetic changes of hs-cTnT in 784 patients

with ACS or increased hs-cTnT not caused by ischemia to rule in or rule out

NSTEMI [57]. This study evaluated relative and absolute changes 3–6 h

after admission. An absolute change with the ROC-optimized value of

9.2 ng/L yielded an AUC of 0.898 and was superior to all relative changes

in these populations. The positive predictive value for the absolute change

was 48.7%, whereas the negative predictive value was 96.5%. In a specific

ACS population, absolute change with the ROC-optimized value of

6.9 ng/L yielded a 82.8% positive predictive value and a 93.0% negative pre-

dictive value.

These studies clearly indicate that serial testing of troponin may substan-

tially improve diagnostic sensitivity and specificity.

4.1.4 Practical recommendations for useThe Study Group on Biomarkers in Cardiology of the ESCWorking Group

on Acute Cardiac Care has prepared recommendations for troponin mea-

surement in acute cardiac care [18]. After the introduction of hs-cTnT,

the same group released recommendations on the use of hs-cTn in clinical

51Current Applications of Cardiac Troponin T

practice [58]. Presently, only hs-cTnT (Roche, Cobas E170) meets the pro-

posed criteria for a high-sensitivity assay suitable for routine use.

It is clear that high-sensitivity assays detect cTn release earlier than older

methods. As such, patients with stable coronary artery disease, HF, end-stage

renal disease, pulmonary embolism, and other conditions (Table 2.1) can

present with troponin levels above the 99th percentile. In fact, �2% of

the general population has cTnT above the 99th percentile. Therefore, lab-

oratory evidence of increased troponin must be interpreted in the context of

clinical status.

This study group has also suggested a general concept regarding the use

of high-sensitive assays [58].

• Use the 99th percentile concentration of the reference population as the

cTn URL.

• The diagnosis of acute myocardial necrosis requires a significant change

with serial testing. At low cTn baseline (�99th percentile), the change

should be substantial for clinical significance. For markedly increased

baseline, a minimum change of 20% is required. Testing other early

markers such as myoglobin or creatine kinase MB is no longer needed.

• Blood sampling in patients with suspicion of AMI should be performed

on admission and 3 h. Measurement of hs-cTn should be repeated 6 h

after admission if the 3-h value was unchanged, but clinical suspicion

of AMI is high.

• cTn is a marker of myocardial necrosis and not a specific marker of AMI.

The latter may be only diagnosed with a rise and/or fall of cTn together

with characteristic symptoms, and/or EKG changes indicative of ische-

mia and/or imaging evidence of acute myocardial ischemia. Consider

also other causes of myocardial necrosis (e.g., acute HF or myocarditis)

when an increased hs-cTn result is obtained.

• Stable or inconsistently variable cTn without significant dynamic

changes is likely markers of chronic structural heart disease.

4.2. Pulmonary artery embolismThe assessment of TnT (or TnI) is recommended for risk stratification of

patients with pulmonary embolism. Increased troponin is associated with

increased mortality [59]. According to histopathologic findings, transmural

right ventricular infarction despite patent coronary arteries has been found in

patients who died because of massive pulmonary embolism. Increased plasma

TnT was associated with poor prognosis in acute pulmonary embolism.

52 Martina Vasatova et al.

Becantini et al. performed a meta-analysis of 20 studies and evaluated the

prognostic value of troponin in acute pulmonary embolism [60]. This study

showed that increased troponin was significantly associated with short-term

mortality (odds ratio [OR], 5.24; 95% CI, 3.28–8.38), with death resulting

from pulmonary embolism (OR, 9.44; 95% CI, 4.14–21.49), and with

adverse outcome events (OR, 7.03; 95% CI, 2.42–20.43). Furthermore,

increased troponin was associated with high mortality in the subgroup of

hemodynamically stable patients (OR, 5.90; 95% CI, 2.68–12.95).

Lankeit evaluated the prognostic role of hs-cTnT in 156 normotensive

patients with acute pulmonary embolism [61]. This study showed that

64% of these patients had hs-cTnT �14 ng/L. Baseline hs-cTnT was higher

in patients with an adverse 30-day outcome compared to those with an

uncomplicated course. The cutoff value (14 ng/L) was associated with an

excellent prognostic sensitivity and negative predictive value (both 100%).

In comparison, 50% of the patients with adverse early outcome would have

been misclassified as low-risk by cTnT using a 30 ng/L cutoff. In summary,

increased hs-cTnT was associated with reduced long-term survival.

According to current guidelines [59], cTnT assessment is recommended

in patients with acute pulmonary embolism and can help risk stratification.

Furthermore, it can help identify patients who will benefit from more

aggressive treatment.

4.3. Pulmonary artery hypertensionIncreased cTn is an independent predictor of fatal outcome in patients with

pulmonary artery hypertension (PAH). The study of Torbicki et al [62] eval-

uated cTnT in 56 cases of PAH. cTnT was detected in 14% of patients.

Despite similar pulmonary hemodynamics, they had increased heart rate,

decreased mixed venous oxygen saturation, and increased N-terminal pro-

B-type natriuretic peptide (NT-proBNP). Cumulative survival estimated

by Kaplan–Meier curves was significantly worse at 24 months in cTnT-

positive patients.

Eggers et al. [63] studied high-sensitive cTnT and cTnI and their asso-

ciation with hemodynamic parameters in 56 patients with PAH undergoing

right heart catheterization. This study found that 37.5% of patients with

precapillary PAH had troponins above their respective 99th percentiles.

Both hs-troponins demonstrated weaker associations with hemodynamics in

patients with precapillary PAH but correlated significantly to NT-proBNP.

Mortality was only predicted by hs-cTnI.

53Current Applications of Cardiac Troponin T

In conclusion, cTn is a potentially useful marker for risk stratification in

PAH, but its value in everyday clinical practice needs to be established.

4.4. Heart failureHF is frequently associated with increased cTn. In a patient cohort of the

Valsartan Heart Failure Trial, plasma cTnT and hs-cTnT were measured

in 4053 patients with chronic HF [64]. cTnT was detected in 10.4% of

the population (fourth-generation assay, LOD¼10 ng/L), and in 92.0%

with hs-cTnT (LOD¼5 ng/L). Median hs-cTnT concentration was

12 ng/L, close to the 99th percentile (14 ng/L). Patients with increased

median cTnT or hs-cTnT had more severe HF and poorer outcome.

hs-cTnT was positively associated with risk of death.

TnT was measured using an older cTnT and a hs-cTnT assay in 202

patients with acute decompensation of HF and without criteria of AMI

[65]. Patients were followed for 406 days (median). Using a primary out-

come of all-cause mortality, hs-cTnT was positive in 98% of patients versus

56% for cTnT. Approximately, 81% patients had hs-cTnT above the 99th

percentile.

The mechanism of TnT release into circulation in HF is unclear. Slow

continuous troponin release can be caused by ongoing myocyte death.

Another proposed mechanism is that myocyte stretch leads to transient loss

of cell membrane integrity thus resulting in leakage of cytosolic troponin.

These data suggest that TnT in acute or chronic HF is associated with

disease severity and could potentially be used as a prognostic marker.

4.5. CardiomyopathiesThe introduction of high-sensitivity assays into clinical practice opened the

possibility to analyze the role of troponin in the pathophysiology and risk

stratification of patients with cardiomyopathies.

4.5.1 Dilated cardiomyopathyKawahara et al. [66] evaluated cTn in dilated cardiomyopathy of non-

ischemic origin. This study, using a conventional cTnT and a hs-cTnT

assay in 85 patients, found increased cTnT (�30 ng/L) in 4 patients (5%)

and hs-cTnT (�10 ng/L) in 46 patients (54%). In nonsurvivors (n¼20),

cTnT was increased in 2 patients (2%) and hs-cTnT was increased in

17 patients (85%).

54 Martina Vasatova et al.

4.5.2 Hypertrophic cardiomyopathyBecause hypertrophic cardiomyopathy (HCM) is associated with structural

change and remodeling, it seems likely that these changes would be accom-

panied by cTn release into the circulation. In patients with the obstructive

form of HCM, some markers (including natriuretic peptides) were associ-

ated with obstruction severity while others were associated with

remodeling.

Moreno et al. [67] studied 95 hemodynamically stable HCM patients.

A complete history and clinical examination were performed including

12-lead EKG, echocardiography, 24-h ECG-Holter monitoring, symptom-

limited treadmill exercise test, and late gadolinium enhancement with cardiac

MRI.Risk factors for sudden deathwere evaluated. Serumhs-cTnTwasmea-

sured. A high proportion (42%) of these patients had increased hs-cTnT.

Increases were proportional to severity of clinical symptoms (dyspnea), the

New York Heart Association (NYHA) functional class, degree of outflow

obstruction, the presence of systolic dysfunction, and the presence of the gad-

olinium enhancement. Furthermore, hs-cTnT was positively correlated to

maximum left ventricular (LV) wall thickness, left atrial diameter, and outflow

gradient.

4.5.3 Other cardiomyopathiesIncreased TnT has been documented in a broad spectrum of cardiomyop-

athies. Increased TnT was found in LV hypertrabeculation/noncompaction

(LVHT) [68], a disease frequently associated with neuromuscular disorders.

This retrospective study analyzed TnT in 100 LVHT. TnT positivity (17%)

was associated with neuromuscular disorder and predicted poor outcome.

Plasma troponin is also increased in patients with abnormal myocardium

structure (amyloidosis, Fabry’s disease, etc). Buss et al. [69] demonstrated that

TnT was associated with survival of patients with systemic light-chain amy-

loidosis. Kumar et al. [70] found that TnT served as a prognostic marker for

1-year mortality.

Takotsubo cardiomyopathy is frequently associated with increased TnT

[71]. Twofold increased TnT was found in these patients presenting with

STEMI versus those with non-STEMI.

4.6. ArrhythmiasThe association of TnT and TnI with arrhythmias is well established.

Increased troponin was observed in prolonged supraventricular and ventric-

ular tachyarrhythmias even in presumed healthy individuals. The mechanism

is not fully understood, but the shortening of diastole with subsequent

55Current Applications of Cardiac Troponin T

subendocardial ischemia may play an important role. Myocardial stretch with

transient loss of cell membrane integrity may lead to release of cytosolic

troponin.

Underlying coronary artery disease is more frequent and facilitates tro-

ponin release in ventricular arrhythmia. Troponin release from patients

undergoing electric cardioversion and defibrillation can complicate diagno-

sis if myocardial infarction needs to be excluded.

Previously, we evaluated TnT in patients undergoing radiofrequency

catheter ablation for the treatment of various supraventricular tachyarrhyth-

mias [72]. We found significantly increased hs-cTnT which correlated to

number of applications and duration of procedure. As such, hs-cTnT

may serve as a useful monitor.

4.7. Cardiotoxicity induced by anticancer therapyCardiotoxicity is a well-known and potentially serious complication of anti-

cancer therapy. Anthracyclines and high-dose chemotherapy, especially

with cyclophosphamide, present the greatest risk [73–75].

4.7.1 Diagnostic methodsGiven the evolution of personalized medicine, identification of patients at risk

for cardiotoxicity is an important goal for cardiologists and oncologists [76].

Detection of subclinical myocardial damage is time-consuming and expensive

for chemotherapy patients [77,78]. Most approaches used in clinical practice

include evaluation of LV ejection fraction (LVEF) by echocardiography or

radionuclide ventriculography. Unfortunately, these strategies show low diag-

nostic sensitivity and predictive power for subclinical myocardial injury.

Other techniques such as endomyocardial biopsy are invasive and therefore

not suitable for routine clinical practice [79,80]. As such, there is considerable

interest in novel, noninvasive, and cost-effective diagnostic tools to identify

patients at risk for chemotherapy-induced cardiotoxicity [81]. Cardiac

markers have been evaluated in animal models and clinical studies [82–86].

Sensitive cardiac biomarkers to detect subclinical myocardial injury and

predict ventricular dysfunction represent an alternative diagnostic tool for

early detection of cardiotoxicity [74,87]. cTn and natriuretic peptides

may be useful, whereas CK-MB does not appear promising [88,89].

In 2011, a position statement from the Heart Failure Association of the

ESC on “Cardiovascular side effects of cancer therapies” was published

[90]. The document called for urgent identification and validation of reliable

biomarkers for the prediction and detection of cardiotoxicity of chemother-

apeutic agents. Simple biomarkers such as troponins and natriuretic peptides

56 Martina Vasatova et al.

should be considered but not a substitute for more conclusive studies includ-

ing echocardiography or similar modalities. In designing clinical trials, cur-

rently available biomarkers (i.e., troponins and natriuretic peptides) should

be incorporated when possible.

The Expert Working Group on Biomarkers of Drug-Induced Cardiac

Toxicity developed a list of “ideal biomarker” characteristics that includes

specificity, sensitivity, kinetics of appearance, and ability to bridge preclin-

ical and clinical applications [91]. As such, we evaluated the current literature

to define the clinical use of cTn for the detection of cardiotoxicity induced

by anticancer therapy.

4.7.2 Cardiac troponinsThe use of cTn as a cardiotoxicity marker was evaluated in seven clinical

studies [92–98]. Approximately, 1500 adult chemotherapy patients were

evaluated for cTnT and cTnI. Positive troponin patients varied (15–34%)

among these studies. It is likely that increased troponin reflected myocardial

cell injury in patients treated with potentially cardiotoxic chemotherapy.

A well-defined cutoff value for cTn in cardiotoxicity would lead to bet-

ter and more universal application of this marker. The cutoff would be opti-

mized to provide the highest level of sensitivity for myocardial injury at an

acceptable reliability (CV �10%).

Unfortunately, the sampling protocol used in these studies was inconsis-

tent [93]; troponin was measured at different intervals following chemother-

apy. Sampling at various time points would minimize this issue in order to

assess its potential biomarker utility [99].

Clinical evidence can be summarized:

1. Troponin predicts the occurrence of clinically significant LV dysfunc-

tion at least 3 months in advance [93,98].

2. Early increase troponin predicts future degree and severity of LV dys-

function [93,96].

3. In patients with positive troponin, persistent increase (one month after

the last chemotherapy) is related to 85% probability of a major cardiac

event within first year of follow-up [96,100].

4. Persistently negative troponin identifies patients with lowest cardiotoxicity

risk (99% negative predictive value) and who will not encounter cardiac

complications within at least the first year after chemotherapy.

The practical advantages of troponin as a biomarker of cardiotoxicity are:

1. Troponin detects cardiotoxicity much earlier than other diagnostic

methods for impaired cardiac function.

57Current Applications of Cardiac Troponin T

2. Troponin stratifies patients into low-risk and high-risk for cardiotoxicity,

the latter requiring more careful long-term cardiac monitoring by imaging

techniques.

The role of cTn in assessing risk of cardiotoxicity is supported by strong evi-

dence [101–104]. In fact, cTn has been incorporated into the National Can-

cer Institute classification of cardiotoxicity of anticancer therapy (Common

Terminology Criteria for Adverse Events).

We evaluated acute and chronic cardiotoxicity of anthracyclines using

fourth-generation cTnT (RocheDiagnostics) and cTnI (RandoxLaboratories

Ltd.) [105]. Results were correlated to echocardiography. Positivity of cTnI

during and after anthracycline treatment correlated with systolic and diastolic

LV dysfunction on echocardiography, while cTnT positivity after treatment

was only associatedwithLVdysfunction and cardiomyopathyonechocardiog-

raphy.Wedidnot find any significant correlation between the total cumulative

dose of anthracyclines and cTn after treatment. These results suggested that

cTnI measurement during treatment could predict future anthracycline-

induced cardiomyopathy risk. cTn in theperitransplant period (high-dose che-

motherapy followed by hematopoietic cell transplantation) was, however,

inconclusive [106–108].

5. BIOLOGIC VARIABILITY

Current guidelines advocate serial cTn testing for the diagnosis of

AMI so that a rising or falling pattern can be observed [1,2]. The National

Academy of Clinical Biochemistry has recommended a 20% change from

the baseline value to be suggestive of an AMI that is evolving (cTn increase)

or resolving (cTn decrease) [109].

Knowledge of biologic variation is important to assess data generated by

serial testing [110]. These studies, usually conducted in healthy individuals

without disease, were not possible for troponin until assays became available

that could reliably detect troponin in healthy individuals. It is hypothesized

that plasma troponin in healthy subjects was 0.1–0.2 ng/L due to normal

cardiomyocyte loss [35].

Wu et al. [111] used a Singulex cTnI assay to evaluate short- and long-term

biologic variation in healthy individuals (Table 2.2). The Erenna Immunoas-

say System, a single-molecule counting technology [112], has the lowest LOD

(0.2 ng/L) for all troponinmethods and a 10%CV at 1.8 ng/L [97]. Individual

(CVI) and group (CVG) CV were slightly lower for short-term results. This

findingwas expected because cardiac changes are unlikely on an hour-to-hour

basis but may change slightly week-to-week. Analytical precision (CVA) and

Table 2.2 Short- and long-term biological variation in cardiac troponins [111,113]

Troponin

Short term 0–4 h Long term 0–8 weeks

cTnT cTnI cTnT cTnI

Analytical variation CVA (%) 53.5 8.3 98.0 15.0

Biological variation CVI (%) 48.2 9.7 94.0 14.0

Biological variation CVG (%) 85.9 57.0 94.0 63.0

Index of individuality 0.84 0.21 1.40 0.39

RCV increase (%) 84.6 46.0 315.0 81.0

hs-cTnT (ng/L)

Female Male

hs-c

TnT

Freq

uenc

y

0 5 10 15 20 25 30

Figure 2.5 Distribution of cTnT values in the pooled reference populations measuredby the hs-cTnT method. Adapted from [28].

58 Martina Vasatova et al.

index of individuality were slightly higher hour-to-hour but not significantly

different from week-to-week. The low index of individuality indicates that

population-based reference intervals are less useful for interpreting cTnI versus

serial changes in individuals.

Vasile et al. [113] measured biologic variation using hs-cTnT (Table 2.2).

This study demonstrated relatively high RCV at 84.6% (short-term 0–4 h)

and 315% (long-term 0–8 weeks). The similar study reported biologic var-

iation using hs-cTNT on the Elecsys 2010 and E170 platforms (Roche

Diagnostics) [114]. RCV for the E170 and Elecsys 2010 assays were 64%

and 90% (hourly) and 138% and 135% (weekly), respectively. Because

RCV includes analytic and biologic variation, a higher value reflects higher

imprecision at low concentration rather than the biologic change. hs-cTnT

in most healthy blood donors (59%) was below the LOD (5 ng/L; Fig. 2.5)

59Current Applications of Cardiac Troponin T

and determination of biologic variability was affected by lower sensitivity of

the hs-cTnT method [72].

6. CONCLUSION

Troponin has become the biomarker of choice for myocardial necro-

sis. In this review, we have summarized its normal biochemical function and

evaluated data on clinical use, mainly that of TnT, in cardiovascular diseases

focusing on international guidelines. The need to standardize troponin mea-

surement across different test platforms is an area that requires additional

consideration. Despite early promising data, it is clear that additional

research is clearly warranted to further establish the usefulness of troponin

in a variety of disease states that impact normal cardiac function.

ACKNOWLEDGMENTSThe work was supported by MH CZ - DRO (UHHK, 00179906), research projects

PRVOUK P37/03, and MO 0FVZ0000503 (Ministry of Defence, Czech Republic), and

by long-term organization development plan 1011 (Faculty of Military Health Sciences in

Hradec Kralove).

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