Sect 7.3 - Cardiac Biomarkers

Troponin

Myoglobin

CK (CK-MB/CK2)

LD (LD1, LD2)

AST

Electrolytes

When cardiac cells are damaged, chemicals leak into the bloodstream, which include (6):

Creatinine Kinase (CK)

enzyme composed of two polypeptide chains, B and M

CK-MM, CK-MB, CK-BB

3 isoenzyme forms of CK

CK-BB

associated with brain and nerve tissue

also embryotic form found in serum of newborn babies & malignancies in which tumor cells exhibit characteristics of embryonic cells

aka CK1

CK-MB

associated with cardiac muscle

aka CK2

CK-MM

associated with skeletal muscle tissue

aka CK3

released into circulation from necrotic heart muscle

What prompts the release of CK-MB from cardiac muslce tissue?

4-6 hours after AMI

When do CK-MB levels begin to increase after AMI?

12-24 hours after AMI

When do CK-MB levels begin to decrease after AMI?

enzymes: pyruvate kinase (PK) and LD

product measured: NADH (reduced form of NAD)

Forward reaction for CK measurement:

enzyme(s) used & product measured

Creatine → Creatine Phosphate

enzymes: Hexokinase (HK) and G6PD

product measured: NADPH (reduced form of NADP)

Reverse reaction for CK measurement:

enzyme(s) used & product measured

Creatine Phosphate → Creatine

reverse rxn

In the measurement of CK, which method is most commonly used: forward or reverse reaction?

Immunoinhibition Method (CK measurment)

involves inhibiting the M isotope of CK-MB

B isotope is the only one measured

the rate of NADH formation is measured & directly proportional to serum CK-B activity

RBCs contain adenylate kinase (catalyzes production of ADP to ATP) that increased ATP that participates in assay reaction leading to falsely increases CK activity

ATP is involved in the reaction for the measurement of CK-MB by immunoinhibition.

Why does hemolysis cause interference, and would we see false (+) or (-)?

Lactate Dehydrogenase (LD)

enzyme composed of two polypeptide chains, H and M

the least specific of the serum enzymes used for cardiovascular assessment → found in ALL tissue

5 isoenzymes

How many isoenzymes are there for LD?

LD1 (HHHH)

LD2 (HHHM)

LD3 (HHMM)

LD4 (HMMM)

LD5 (MMMM)

What are the 5 isoenzymes of LD & their H and M combinations?

concentration of LD2 is greater than LD1

Electrophoretic pattern of LD1 and LD2 in normal patients

concentration of LD1 is greater than LD2

Electrophoretic pattern of LD1 and LD2 in cardiac muscle damage

"Flipped pattern"

Concentration of LD1 is greater than LD2 is known as

RBC hemolysis

Megaloblastic anemias

Name 2 other conditions that can also cause an electrophoretic pattern similar to that seen with cardiac muscle damage: LD1 > LD2

3-4 days

The flipped pattern (LD1 > LD2) lasts up to how long after AMI?

12-24 hours after AMI

When do Total LD levels begin to increase after AMI?

48-72 hours after AMI

When do Total LD levels PEAK after AMI?

7-10 days

When do Total LD levels return to normal?

Enzymatic reaction

Immunological method

Electrophoresis

3 methods used to measure LD

enzyme: Lactate dehydrogenase (LD)

product measured: NADH

Enzymatic Reaction for LD measurement

enzyme(s) used & product measured

Lactate + NAD+ ←→ pyruvate and NADH

Immunological method

LD1 or LD2 isoenzymes can be isolated out using Ag-Ab reactions, with Ab for M subunit, enabling measurement of unbound H subunits

Electrophoresis

What is the third type of measurement method for LD besides the enzymatic and immunological methods?

Troponin

contractile proteins found within muscle fibers that help regulate contractions

Troponin C

Troponin I

Troponin T

3 troponins that work as a complex to exert an effect on actin to control muscle contraction

Troponin C

calcium-binding component of troponin complex

Troponin I

inhibitory component of troponin complex

myocardium (heart muscle)

Troponin I (TnI) is found only where in adults?

Troponin T

tropomyosin-binding component of troponin complex

uniquely specific to cardiac muscle & is released shortly after cardiac muscle damage

dying muscle fibers (specific for tissue death)

What prompts the release of Troponin I and T from cardiac muscle tissue?

heart muscle fiber damage and necrosis

Increases in the concentration of Troponin I and T indicate

1. very specific because it is only released during tissue death

2. stays elevated for 2 weeks

Why is Troponin is the preferred marker of detection of AMI?

within 6 hours of AMI

When do Troponin levels increase?

10-24 hours after AMI

When does Troponin levels PEAK?

1-14 days after AMI

Troponins that are released from damaged heart muscle remain in bloodstream for how long?

Immunoassay (Troponin measurement)

most common method for analysis of troponin I or troponin T

Ag-Tn in pts sample binds to ant-Troponin monoclonal Ab (anchor) and chemiluminescent/fluorescent label binds to Ag-Tn creating a sandwich with pts sample

the chemiluminescent signal is then detected (related to concentration of Tn present)

chemiluminescence

What is the most sensitive marker for TnT?

C-Reactive Protein (CRP)

sensitive positive acute phase protein, which appears in the blood following infection or inflammation due to tissue damage

important aspect of the immune response

any type of inflammation in the body

What conditions other than a heart attack may elevate CRP?

more sensitive and can detect very low amounts of CRP

What is the advantage of performing a hs-CRP vs. a standard CRP assay?

6-12 hours after AMI

When do levels of CRP begin to increase?

when inflammation subsides

When do levels of CRP begin to decrease?

Immunoassay (CRP and HS-CRP measurement)

1. link Ag-CRP in pts sample with CRP Ab to form Ag-Ab complex

2. CRP Ab is anchored using latex particles and joining of Ag and Ab allows to measure light scatter of latex particles using nephelometry

atherosclerotic inflammation

The HS-CRP assay can be used to monitor the risk of

CRP very non-specific; measure CRP twice, 2 weeks apart, to make sure the increased level is not due to an active infection or an inflammatory stimulus

Why do we run repeat CRP levels at 2-week intervals?

sample is invalid for heart related atherosclerotic inflammation; likely due to infection/inflammation

If HS-CRP is >10 mg/dl, what does that mean?

B-Natriuretic Peptide (BNP)/NT-ProBNP

Used to diagnose Heart Failure

Prompted to release into circulation due to fluid accumulation in the heart

Produced by left ventricle of heart

BNP

active form of B-Natriuretic peptide

NT-ProBNP

inactive form of B-Natriuretic peptide

acts on the kidney to increase excretion of fluid, helping to decrease cellular edema and the load on the left ventricle of the heart

Normal function of BNP/NT-ProBNP

edema due to heart failure

BNP and NT-ProBNP are specific markers for

Immunoassay

measurement of BNP and NT-ProBNP are performed by

BNP < 100 pg/ml

indicates no heart failure

BNP normal range

BNP 100-300 pg/mL

indeterminate of heart failure

repeat test

BNP >450 pg/ml

consistent with heart failure in adults under age 50

BNP >900 pg/ml

consistent with heart failure in adults over age of 50

NT-ProBNP

no heart failure

NT-ProBNP >125 pg/ml

heart failure

renal disease

exercise and diet

inflammation

What factors do physicians need to take into consideration when assessing the presence of heart failure and associated BNP/NT-ProBNP levels?

NT-ProBNP stays in circulation longer than BNP

Advantage of measuring NT-ProBNP vs BNP

ST2

Used to determine treatment for heart failure

do we need to start and how intense?

Interleukin-1

origin of ST2 in body receptor family responsible for inducing immune system

directly implicated in the progression of cardiac disease

sST2 and ST2L

2 isoforms of ST2

sST2

soluble ST2 (circulating form)

form of ST2 that is measured in the lab

ST2L

ST2 Ligand (membrane bound form)

cardiac muscle cells under conditions of mechanical stress

What prompts the release of sST2?

18 ng/ml

median normal sST2 value

35 ng/ml

standard cut-point sST2 value

indicates increase prognosis risk

pts condition is improving

When sST2 levels are low,

pt is at significant risk for worsening condition or death

When sST2 levels are high

true

T or F:

Homocysteine is NOT considered an "official" risk factor

Homocysteine

intermediate step between conversion of methionine and cysteine

folic acid and B vitamins

substances needed for conversion of methionine and cysteine with intermediate step of homocysteine

homocysteine will not convert to cysteine and will accumulate

If there is a deficiency in folic acid and B vitamins, what will happen?

atherosclerosis, CAD, CVA

conditions associated with elevated levels of Homocysteine

well balanced diet with folic acid and B vitamins

treatment for accumulation of Homocysteine

Immunoassay (Homocysteine)

most common method for analysis of homocysteine

must reduce all forms of homocysteine to free/unbound homocysteine first, which will bind with fluorescent labeled Ab

serum + reducing agent → free serum homocysteine

free serum homocysteine + free homocysteine Ab (labeled) → Ag-Ab complex

Myoglobin

a heme protein found in skeletal and cardiac muscle

can reversibly bind O2 similar to hemoglobin molec, and acts as an O2 carrier in the cytoplasm of muscle cells

damage to muscles

What prompts the release of Myoglobin into circulation?

first cardiac marker to rise (as early as 30 min) and an early indicator of AMI

Why is myoglobin important when it comes to AMI?

first few hours of AMI

When do Myoglobin levels begin to increase?

2-3 hours

When do Myoglobin levels peak?

Injury to skeletal muscle

diseases associated with increased breakdown of muscle tissue (muscular dystrophy, rhabdomylosis)

other conditions that elevated levels of Myoglobin may be associated with

Troponin (I and T)

Which cardiac biomarker is considered the preferred marker for detection of an acute MI?