CARDIAC

BIOMARKERS IN

ACS

DR MAHENDRA

CARDIOLOGY,JIPMER

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Biomarker- definition

“A characteristic that is objectively measured and evaluated as an indicator

of normal biological processes or pharmacologic responses to a

therapeutic intervention”

Specificity- 1. Analytical specificity 2. Diagnostic specificity1

Analytical specificity of a biochemical marker depends not only on avoiding

any methodological cross reactivity with other biologically related

molecules, but also on biological characteristics of the marker as well,

showing no other tissue sources, even in trace amounts or under

pathological conditions, in addition to the anatomic or histologic target

1.Saah AJ et al, Ann Intern Med 126:91-94; 1997

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Ahmad MI et al, Biomarkers in Acute Myocardial Infarction. J Clin Exp Cardiolog 3:222 ;2012

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Timeline of development of cardiac

biomarkers for ACS

Pankaj G, et al. Intern Emerg Med 12:147–155; 2017

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TROPONINS

Proteins that regulate interaction between actin and myosin in cardiac and

skeletal muscle

Troponin C – synthesized in both cardiac and skeletal muscle

Troponin I and Troponin T isoforms- highly specific and sensitive to cardiac

myocytes, so known as cardiac troponins(cTn)

Plasma half life of cTn- 2 hours

92-95% troponin attached to actin thin filament of sarcomere and only 5-

8% remain unbound in cytoplasm

Unbound cTn- Early releasable Troponin Pool (ERTP)- immediately

released following myocyte injury

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cTn subunits are detectable in the peripheral circulation when damage to

the cardiac myocyte first leads to the release of cytoplasmic cTn, which

accounts for 3% to 5% of cTnI and 7% of cTnT levels

Latency period for necrosis and troponin release is 2 hours, so needs to be

repeated at 6-9 hours interval

Reaches peak concentration in 12-24 hours

cTn remains detectable for days (4–7 days for cTnI and 10–14 days for

cTnT)

Cleared by reticuloendothelial system

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Measurement of troponin in blood has a dual role:

1. abnormally high concentrations are indicative of AMI

2. mildly abnormal concentrations suggest increased short-term risk

for a future cardiac event

Independent predictor of early postoperative cardiovascular complications

following non-cardiac surgery and early predictor of short-term mortality in

vascular surgery patients as well as a predictor of MI and death after

CABG

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Antman EM, et al. Cardiac-specific troponin I levels to predict the risk of mortality in patients with acute coronary

syndromes. N Engl J Med 1996;335:1342-9

Falahati A et al, Implementation of serum cardiac troponin I as marker for detection of acute

myocardial infarction. Am Heart J 137(2):332-7; 1999

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Highly sensitive troponin

The definition of high-sensitivity cTn is not clearly established, but last generation assays can detect cTn in approximately 95% of normal individuals

New 5th generation hs-cTn T and I assays which can detect troponin at concentrations 10- to 100-fold lower than conventional assays

Increases the sensitivity of cTn in the first few hours after coronary occlusion

The negative predictive value(NPV)of hs-cTn assays is 95% for AMI exclusion when patients are tested on arrival at the ED

These hs-cTn assays have allowed the diagnostic cutoff to be lowered to the level of the 99th percentile or lower while maintaining precision at a CV of <10%

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Pankaj G, et al. Intern Emerg Med 12:147–155; 2017

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Pankaj G, et al. Intern Emerg Med 12:147–155; 2017

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D. del Val Martin et al. / IJC Metabolic & Endocrine 8 (2015) 20–23

CK-MB

Cardiac muscle has higher CKMB levels (25–30%) compared with skeletal

muscle (1%), which is mostly CKMM

Measurement of CKMB, CKMB fraction or CKMB/CKMM ratio was a more

specifIc marker for AMI

The initial CK-MB rise occurs 4 to 9 hours after the onset of chest pain

induced by myocardial injury

The level peaks at 24 hours, and returns to baseline at 48 to 72 hours

One advantage of CK-MB over other markers is that it remains elevated

for longer periods and it is easier to detect reinfarction using serial CK-MB

measurements

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Myoglobin

Small cytoplasmic heme protein found in all muscles

Earliest marker to rise after AMI (2hrs from onset of chest pain)due to its

small size and high cytoplasmic content

Increases within 1 to 3 hrs in the setting of myocardial necrosis, peaks

within 6 to 9 hrs, and may become normal in 24 hrs

A single myoglobin measurement at presentation has been shown to have

a sensitivity of 70% and a NPV of 97.4% for predicting AMI among patients

with suspected ACS

Myoglobin has limited specificity for myocardial necrosis in patients who

have renal insufficiency and skeletal muscle trauma

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Chan and Ng BMC Medicine 2010, 8:34

H-FABP

Heart-type fatty acid-binding protein (H-FABP) is a cytosolic, low-molecular-weight protein involved in fatty acid transport and metabolism

Although it is expressed in high levels in the myocardium, small quantities also can be found in the brain, kidney, and skeletal muscle

H-FABP displays a very early raise after an AMI (i.e., increased concentrations can be detected as soon as 30 min after the onset of an ischemic episode)

Peaks in blood after ~6–8 hrs and returns to baseline values after 24–30 hrs

It is unsuitable as a test for patients presenting >6 hrs from onset of symptoms due to rapid renal clearance

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H-FABP has also been shown to independently predict mortality in patients

with ACS

When added to troponin for risk stratification, a negative troponin and H-

FABP level < 5.8 mcg/L was associated with zero mortality at six months1

A negative troponin but H-FABP level > 5.8 mcg/L was associated with a

4.93-fold increase in risk of death and 7.93-fold increase in risk if troponin

was positive and H-FABP > 5.8 mcg/L

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1.Kilcullen N et al, J Am Coll Cardiol 2007, 50:2061-2067

ISCHAEMIA MODIFIED ALBUMIN

On exposure to ischemic conditions, the N-terminus of albumin is

damaged, which makes it unable to bind metals

IMA levels in the blood increase within minutes of the onset of ischemia

and return to normal within 6–12 hrs

So, IMA has been implicated in the detection of acute ischemia prior to

necrosis

One study of patients with suspected ACS found that IMA had a better

NPV for ACS of 92% than the combination of CK-MB, myoglobin, and

cTnT (86%), and the use of all 4 biomarkers together resulted in an NPV of

95% 1

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1. Lee YW et al, Clin Chim Acta. 2007 Sep;384(1-2):24-7

CRP

Acute phase protein produced by the hepatocyted in response to

stimulation by IL-6

High CRP levels (10–15 mg/L) strong indicator of long-term future

cardiac events

In patients with MI treated with thrombolysis, high CRP levels (226 mg/L)

associated with an increased risk of death within the first 6 months of

the infarct event

In NSTEMI, increased CRP values are independent prognostic markers of

recurrent nonfatal myocardial infarction or cardiac death (GUSTO IV,

PROVE IT-TIMI 22)

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Pro-inflammatory markers

IL-6 and TNF-α

Ischemia and reperfusion of infarcted myocardium results in induction of

these cytokines

IL-6 negative inotropic effect mediated through myocardial nitric oxide

synthase

TNF-α cardio-inhibitory cytokine that depresses cardiac contractility

either directly or through induction of nitric oxide synthase.

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Markers of plaque destabilization

Metalloproteinases- Myeloperoxidase and PaPPA

In post-acute coronary syndrome MPO levels higher than median

predicted future death and MI at one year

After an AMI, MPO levels peak early, then decrease over time and do not

correlate with troponin or the neutrophil count

It is not affected by fibrinolytic therapy

PaPPA proatherosclerotic metalloproteinase which is highly expressed

in unstable plaques and their extracellular matrices

PaPPA > 2.9 mIU/L predicts a 4.6- fold increase in risk of cardiovascular

death, MI or revascularisation even without a raised troponin

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Markers of myocyte rupture

CD40L is a cytokine belonging to the TNF-α family and CD40 is its

receptor

CD40L is up-regulated on platelets within fresh thrombus

Platelet derived growth factor(PDGF)

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GDF-15

GDF-15 is a stress-responsive member of the transforming growth factor-b

cytokine superfamily

High levels of GDF-15 have been found to be an independent predictor for

yearly mortality rate and the use of invasive strategy, and they add

prognostic value to current cardiac biomarkers, including BNP, cTnT, and

TIMI score

GDF-15 is not specific for cardiovascular disorders and has been found to

be elevated in a variety of malignancies (prostate, colon, glial)

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COPEPTIN

Copeptin is the more stable surrogate of arginine vasopressin (AVP)

Post AMI, vasopressin (1) increases peripheral vasoconstrictor activity

thus increasing afterload and ventricular stress

(2) increases protein synthesis in myocytes leading to hypertrophy

(3) vasoconstriction of coronary arteries

At presentation, copeptin level of < 14 pg/ml and a Trop T level of < 0.01

rules out a myocardial infarction with NPV of 99.7%

CHOPIN trial Adding copeptin to cTnI allowed safe rule out of AMI with a

NPV of99% in patients presenting early with a suspected ACS

Lack of specificity (elevated in sepsis)

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CYSTATIN-C

Cysteine protease inhibitor involved in the catabolism of proteins

This protein is synthesized in all nucleated cells at a constant rate, and is freely filtered by the glomerulus with no reabsorption into the blood

Cystatin C is less influenced by other factors like diet, muscle mass, or body constitution

Measurement of cystatin-C substantially improves the early risk stratification of a large population with suspected or confirmed non-ST elevation ACS

More recent studies confirm that cystatin-C concentration is independently correlated with cardiovascular risk, including myocardial infarction and cardiovascular death

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Jernberg T et al, Circulation. 2004;110:2342-2348

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Jernberg T et al, Circulation. 2004;110:2342-2348

Neutrophil gelatinase-associated

lipocalin (NGAL)

NGAL is a glycoprotein of 25 kDa

Serum NGAL level was significantly higher in the NSTE-ACS group compared to the control group (112.3±49.6 ng/mL vs. 58.1±24.3 ng/mL, p<0.001)

There was a significant positive correlation between serum NGAL levels and the GRACE (r=0.533 and p<0.001), SYNTAX (r=0.395 and p=0.006), and Gensini risk scores (r=0.575 and p<0.001)

The intermediate-high SYNTAX (>22) group had statistically significantly higher serum NGAL levels compared to the low SYNTAX (≤22) group (143±29.5 ng/mL vs. 98.7±43.2 ng/mL, p=0.001)

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Soylu et al. Serum NGAL level in NSTE-ACS, Anatol J Cardiol 2015; 15: 450-5

Micro RNAs

MicroRNAs (miRNAs) are non-coding RNA fragments of 22 nucleotides

with a key role in the regulation of mRNA coding for key proteins in the

maintenance of cell integrity

Levels of miR-1, -133a, -133b, and miR-499-5p increased in the hours

following infarction

miR-122 and miR-375 decreased in their plasma levels

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D'Alessandra et al .Eur Heart J (2010) 31 (22) 2765-2773

OTHER MARKERS

Choline enzymatic product of phospholipase D

Phospholipase D, is involved in endothelial dysfunction, and is considered

a marker of plaque instability, as well as a marker of severe myocardial

ischemia, and has been associated with elements of the metabolic

syndrome

F2 isoprostanes biologically active product of arachidonic acid

metabolism

Elevated levels found in smokers, dyslipidemia, unstable angina

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Point of care cardiac markers:

If standard laboratory testing exceeds a maximum 60-minute turn-

around time (the average being 65–128 min) or 25% of decision time, then a

POC device (with an average turn-around time of 15–26.5 min) should be

implemented

Current AHA guidelines for cTn measurement recommend testing on

presentation and again at 8–12 hrs post symptom onset

National Academy of Clinical Biochemistry recommends an early marker at

0–6 hrs and a definitive marker at 6–9 hrs post-presentation

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Roffi M, et al (2015) 2015 ESC Guidelines for the management of acute coronary syndromes in

patients presenting without persistent ST-segment elevation. Eur Heart J 37:ehv320

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