Hughes & Jefferson Ch9. Markers of Cardiac and Muscle Injury and Disease

Question 1

Cytosolic enzyme that facilitates the mitochondrial transfer of high-energy phosphates from the cytoplasm.

Answer 1

Creatine kinase (CK)

Question 2

Creatine kinase (CK) is a _______ that _______ the ________________ from the cytoplasm.

Answer 2

cytosolic enzyme, facilitates, mitochondrial transfer of high energy phosphates

Question 3

Three potential isoenzymes of CK

Answer 3

MM, MB, BB

Question 4

True or False: CK is widely distributed but found predominantly in brain tissue.

Answer 4

False. CK is found predominantly in muscle.

Question 5

Skeletal muscle contains approximately 99% _______ and 1% _______.

Answer 5

CK-MM, CK-MB

Question 6

The amount of CK-MB in skeletal muscle increases during injury due to __________.

Answer 6

muscle fiber regeneration

Question 7

Cardiac monocytes contain 20-30% _______, with the remainder being _______.

Answer 7

CK-MB, CK-MM

Question 8

The CK-BB isoform is found in other organs such as the ________, and is not routinely measured.

Answer 8

brain

Question 9

Normally, ________ accounts for more than 95% of circulating CK.

Answer 9

CK-MM

Question 10

The normal level of total CK is _______ in males, and _______ in females.

Answer 10

~55-170 U/L, ~30-135 U/L

Question 11

Individuals with larger muscles typically have (higher/lower) levels of total CK.

Answer 11

higher

Question 12

True or False: Relative specificity of CK-MB for myocardial tissue is useful in the investigation of suspected cardiac disease.

Answer 12

True

Question 13

In order to confirm a diagnosis of acute MI, a ________ increase is required with an increase in CK-MB fraction.

So, if normal CK-MB level is roughly 0-5 ng/mL, CK-MB level in acute MI is ________.

Answer 13

2-fold, >9 ng/mL

Question 14

The ratio of CK-MB to total CK can also be measured to determine cardiac disease.

What ratio of CK-MB to total CK suggests a cardiac source?

Answer 14

> 2.5

Question 15

CK levels usually increase by _______ following MI, peak at ________, and fall to normal by ________.

Answer 15

4-6 hrs, 18-24 hrs, 36-48 hrs

Question 16

Common markers of MI (4)

Answer 16

Creatine Kinase (total and CK-MB)
Troponins (cTnI, cTnT)
Lactate Dehydrogenase (LDH)
Myoglobin

Question 17

True or False: CK alone is enough to diagnose a small MI or a microinfarct. Moreover, CK levels increase during an episode of angina or pericarditis.

Answer 17

False. CK is not as sensitive as troponins and may not detect a small MI with limited myocardial injury or microinfarct.

CK levels also do not increase during episodes of angina or pericarditis.

Question 18

True or False: increased CK-MB levels can be observed in muscle injury with regenerating fibers, and the typical acute rise and fall of CK-MB levels occur as it does in MI.

Answer 18

False. While it is correct that CK-MB levels increase in muscle injury with regenerating fibers, as in marathon runners and rhabdomyolysis patients, the acute rise and fall of CK-MB levels DOES NOT occur.

Question 19

A cardiac cause for a raised CK level is suggested by: (4)

Answer 19

Clinical history of chest pain
Typical time course (rise and fall of CK levels)
Raised CK-MB level (>9 ng/mL)
Increased ratio of CK-MB : total CK (>2.5)

Question 20

Does total quantity of CK released have a relationship with the infarct size?

Answer 20

Yes. Total CK released correlates with infarct size. The higher the amount of CK released, the larger the infarct size.

Question 21

[Assessment of coronary artery reperfusion]
True or False: The peak CK level reflects how quickly the enzyme is cleared from the injured myocardium and is less closely linked to infarct size.

Answer 21

True.
Successful reperfusion, such as after angioplasty or thrombolysis, causes an early rise in CK-MB with a shorter duration because the enzyme is quickly “washed out” from the damaged heart area.

Question 22

Why is CK-MB used in the diagnosis of an additional MI or extension of the original infarct instead of troponin?

Answer 22

Since CK-MB levels decrease shortly after acute MI, if the levels suddenly increase again, it can be an indicator of an additional MI or extension of the original MI. Troponin levels remain elevated for a prolonged period after MI, so while it permits late diagnosis, it cannot detect an additional MI or an extension of the original MI.

Question 23

Non-cardiac causes of raised CK levels:

Answer 23

Skeletal muscle injury (myopathies)
Brain injury (stroke)
Hypothyroidism

Question 24

Structural proteins present within cardiac myocytes involved in the interaction between contractile proteins actin and myosin.

Answer 24

Troponins

Question 25

2 types of troponins and where are they typically found.

Answer 25

Cardiac Troponin I (cTnI), specific to cardiac monocytes.
Cardiac Troponin T (cTnT), also in cardiac monocytes but expressed to a minor degree in skeletal muscle.

Question 26

Why is MI associated with an early rise of troponins?

Answer 26

Due to release of troponins from cytoplasmic pool.

Question 27

What causes a later sustained rise in troponin levels during MI?

Answer 27

Breakdown of structural actin and myosin filaments.

Question 28

True or False: Only Troponin I is used in the detection of cardiac injury.

Answer 28

False. Both troponins are considered to be relatively specific for myocardial injury, and can both be used for MI diagnosis.

Question 29

Cardiac troponin levels post-MI has a similar time course to CK-MB, rising 4-6hrs and peaking 18-24hrs after MI, however troponin levels remain raised for ___________ post-MI.

Answer 29

up to 10 days

Question 30

How do troponin levels help in the diagnosis of MI?

Answer 30

Troponin levels remain raised for a prolonged period post-Mi. So if a patient presents several days after chest pain when CK-MB levels are normal, troponin levels may be assessed for MI diagnosis.

Question 31

Cardiac troponins are not normally detected in blood. The normal level for cTnT is _______. Any significant increase represents myocardial injury.

Answer 31

<0.01 mcg/mL

Question 32

According to the European Society of Cardiology and American College of Cardiology, the cutoff troponin levels for acute MI is _______.

Answer 32

0.03 mcg/mL

Question 33

True or False. Cardiac troponin levels reflect infarct size and correlate with prognosis.

Answer 33

True.

Question 34

cTnI levels of _______ suggest significant myocardial injury.

Answer 34

> 1.5 ng/mL

Question 35

Although cardiac troponins are specific for myocardial injury, increased levels may occur in _______ and _______.

Answer 35

acute pulmonary embolism, myocarditis

Question 36

Increased cardiac troponin levels occur during acute pulmonary embolism due to _____________.

Answer 36

acute right ventricular strain

Question 37

A false-positive increase in cardiac troponin levels may occur in _________. 10-15% of patients with this condition exhibit mildly raised levels of cTnT, while 5% have increased levels of cTnI.

Answer 37

chronic renal failure (CRF)

Question 38

Why should troponin levels be measured from serum samples?

Answer 38

Heparin in plasma samples can bind to cTnT and reduce levels by 15-30%, causing an inaccurate diagnosis.

Question 39

Clinical uses of cardiac troponin levels (5)

Answer 39

Diagnosis of acute MI
Prognosis of acute MI
Late diagnosis of acute MI
Exclusion of acute MI in patients with chest pain
Diagnosis of microinfarction

Question 40

Why are troponin levels more sensitive markers of myocardial injury compared to CK-MB?

Answer 40

CK-MB levels may be raised due to injury in non-cardiac tissue. In cases like these, troponin levels may be assessed to effectively determine whether myocardial injury has occured.

Question 41

True or False: Increased troponin levels correlated with increased infarct size.

Answer 41

True

Question 42

How do troponin levels allow a late diagnosis of MI?

Answer 42

Troponin levels remain increased for up to 10 days post-MI.

Question 43

How do troponin levels allow exclusion of acute MI in patients with chest pain?

Answer 43

As cardiac troponins are very sensitive markers of myocardial injury, normal levels 12 hrs post chest pain may be used to rule out MI.