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Lab Medicine > Cardiac Enzymes > Flashcards

Cardiac Enzymes Flashcards

1
Q

When is myoglobin used and what is the normal range?

A

Used in early evaluation of patient with suspected MI, as well as to assist in diagnosis of disease or injury to skeletal muscle

Normal < 90 mcg/L

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2
Q

How does myoglobin exit the body?

A

Excreted in urine and is nephrotoxic

Can be measured in the urine

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3
Q

What reading is positive for myoglobin when using a urine dipstick for hemoglobin?

A

will get a positive dipstick for blood but no RBCs on the microscopic exam

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4
Q

What is the function of myolgobin in the body?

A

Myoglobin is an oxygen binding protein found in cardiac and skeletal muscle

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5
Q

Which cardiac enzyme provides an early indication of myocardial damage?

A

Myoglobin. Increased levels indicate cardiac muscle injury or death occur in about 3 hours

Disease or trauma to skeletal muscle causes elevations that can reach very high levels

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6
Q

How does Myoglobin compare to CPK test?

A

More sensitive than CPK isoenzymes but not as specific – may elevate with trauma, inflammation, or ischemic changes to noncardiac skeletal muscles

Main benefit over CPK-MB is that it may elevate earlier in some patients

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7
Q

Interfering factors of myoglobin

A

Recent administration of radioactive substances

Intramuscular injections can increase myoglobin levels due to localized muscle injury

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8
Q

Causes of increased levels of myoglobin.

A

MI – cardiac muscle injury causes cells to lyse and release myoglobin

Skeletal muscle inflammation (myositis)

Malignant hyperthermia, muscular dystrophy, skeletal muscle ischemia, skeletal muscle trauma, rhabdomyolysis – affect skeletal muscle

Seizures – persistent seizure injures skeletal muscle

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9
Q

Causes of decreased levels of myoglobin

A

Polymyositis – antimyoglobin antibodies exist and decrease myoglobin in blood

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10
Q

What do Troponin enzymes indicate and what are the normal ranges?

A

Used to determine if chest pain is caused by cardiac ischemia.

Specific indicator of cardiac muscle injury and is also helpful in predicting future cardiac events

Normal values:
Troponin I: < 0.03 ng/ml
Troponin T: < 0.2 ng/ml

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11
Q

These enzymes are biomarkers for cardiac disease

A

Cardiac troponins

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12
Q

What are the two types of cardiac Troponins?

A

Cardiac troponins can be separated from skeletal muscle troponins

The two cardiac specific troponins are cardiac troponin T (cTnT) and cardiac troponin I (cTnI)

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13
Q

What is the function of Troponins in the body?

A

Troponins are proteins in skeletal and cardiac muscle that regulate calcium dependent interaction of myosin with actin for the muscle contractile apparatus

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14
Q

How does the Troponin measurement compare to CPK-MB?

A

Used similarly to CPK-MB except troponins are more specific for cardiac muscle injury while CPK-MB can be elevated with severe skeletal muscle injury, brain or lung injury, or in renal failure.

Cardiac troponins are almost always normal in noncardiac muscle diseases and become elevated sooner and remain elevated longer than CPK-MB to expand the time window for diagnosis and treatment of myocardial injury

Cardiac troponins are more sensitive to cardiac muscle injury than CPK-MB

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15
Q

Describe the timeline of the rise and fall of Troponins after a myocardial injury

A

Become elevated as early as 3 hours after myocardial injury and remain elevated for 7-10 days for cTnI and 10-14 days for cTnT

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16
Q

When may Troponin measurements not be as helpful?

A

If reinfarction is considered, troponins may not be helpful because they could be elevated just from the first ischemic event. However, results can be compared to previous results.

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17
Q

How quickly can Troponins be determined and how does this affect treatment?

A

Troponins can be run in 20 minutes.

The earlier myocardial injury is detected, the more rapidly treatment can begin

The earlier revascularization occurs, the less myocardial muscle is injured – Time is muscle!

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18
Q

In unstable Agina what does an elevated Troponin level indicate?

A

muscle injury has occurred

if troponin levels are normal, no injury has occurred and there won’t be any lasting cardiac dysfunction

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19
Q

With detection of reperfusion associated with coronary recanalization, what indicates reperfusion?

A

a second peak or washout

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20
Q

How are Troponins used as an estimate of MI size?

A

late (4 weeks) troponin levels are inversely related to LV ejection fraction – late elevations are related to degradation of contractile apparatus

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21
Q

What do persistent elevations of Troponins indicate with CHF?

A

continued ventricular strain

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22
Q

How are troponins useful in detection of perioperative MI?

A

CPK-MB may elevate due to skeletal muscle injury during surgery, while cardiac troponins are not affected by skeletal muscle injury

23
Q

In the evaluation of severity of pulmonary emboli the disease may be more severe if troponins are elevated or lowered?

A

Elevated

24
Q

Interfering factors for Troponins

A

Troponin T levels can be falsely elevated in dialysis patients

25
Q

Causes of increased levels of Troponins?

A

Myocardial injury or infarction – this intracellular protein enters the bloodstream after myocardial cell death because of ischemia. Normally, no troponins can be detected in the blood

26
Q

What are Creatine Kinase (CK) and isoenzymes used for? What are the normal ranges?

A

Used to support the diagnosis of MI and also indicates neurologic or skeletal muscle diseases
Normal ranges:

Total CK:

Male 55-170 units/L

Female 30-135 units/L

Isoenzymes:

CK-MM: 100%, CK-MB: 0%, CK-BB: 0%

27
Q

Where is CK found?

A

CK is found in the heart muscle, skeletal muscle, and brain and is elevated when these cells are injured.

28
Q

Describe the timeline of the rise and fall of CK after damage

A

CK can rise within 6 hours after damage, peaks at 18 hours, and returns to normal in 2-3 days if damage is not persistent

29
Q

Name the three types of CK isoenzymes

A

CK-BB

CK-MB

CK-MM

30
Q

What is CK-MB specific for?

A

myocardial cells

31
Q

Describe the timeline of the rise and fall of CK-MB after an infarction

A

It rises 3-6 hours after infarction occurs, peaks at 12-24 hours, and returns to normal in 12-48 hours if no further damage occurs.

32
Q

With what chest pain related conditions will CK-MB generally not go up

A

chest pain from angina

pulmonary embolism

or CHF

33
Q

Causes of increased CK-MB levels

A

Acute MI, cardiac aneurysm surgery, cardiac defibrillation, myocarditis, ventricular arrhythmias, cardiac ischemia – any disease or injury to the myocardium causes CK-MB to be released from damaged cells

CK-MB will rise with shock , malignant hyperthermia, myopathies, or myocarditis

CK-MB present in very small amounts in skeletal muscle, so severe injury to or disease of the skeletal muscle can raise the CK-MB

34
Q

What does a high CK-MB suggest?

A

High CK-MB suggests that infarction has already occurred, precluding the benefit of thrombolytic therapy

35
Q

This isoenzyme is helpful in quantifying degree of MI and timing the onset of infarction

A

CK-MB

36
Q

What causes an elevation of CK-BB?

A

CK-BB mainly in brain and lung, so stroke or pulmonary infarction will cause elevation

Diseases that affect the central nervous system (brain injury, brain cancer, stroke, subarachnoid hemorrhage, seizures, shock)

Electroconvulsive therapy

Adenocarcinoma (breast and lung)

37
Q

Do large muscular peple have a higher or lower CK value?

A

Normal value of total CK and CK-MM varies according to a person’s muscle mass – large muscular people may have a higher CK than smaller people with less muscle mass

38
Q

What is indicated If CK is elevated from CK-MM?

A

injury to or disease of skeletal muscle is present, typically due to myopathies, vigorous exercise, multiple IM injections, electroconvulsive therapy, cardioversion, chronic alcoholism, or surgery

39
Q

Which isoenzyme makes up almost all of the CK in circulation in healthy people

A

CK-MM

40
Q

Interfering factors for CK and isoenzymes?

A

IM injections may elevate CK

Strenuous exercise and recent surgery may elevate CK

Early pregnancy may decrease CK

Muscle mass is directly related to a patient’s normal CK level

41
Q

Causes of increased levels of Total CK?

A

Diseases or injury affecting heart muscle, skeletal muscle, and brain

42
Q

What causes increased levels of CK-MM

A

Rhabdomyolysis, muscular dystrophy, myositis – diseases affecting skeletal muscle cause CK-MM to be released from damaged cells

Recent surgery, electromyography, IM injections, trauma, crush injuries – injury to skeletal muscle causes CK-MM to be released

Delirium tremens, malignant hyperthermia, recent convulsions, electroconvulsive therapy, shock – anoxic injury to skeletal muscle causes CK-MM to be released

Hypokalemia, hypothyroidism – have metabolic effect on skeletal muscle leading to injury and release of CK-MM

43
Q

What is B-Type Natriuretic Peptide (BNP) used to identify? What are the normal and critical ranges?

A

Used to identify and stratify patients with congestive heart failure

Normal < 100 pg/mL
Critical > 100 pg/mL

44
Q

What is the function of B-Type natriuretic peptides in the body?

A

Natriuretic peptides are neuroendocrine peptides that oppose the activity of the renin-angiotensin system.

45
Q

What is the main source of BNPs?

A

Main source of BNP is the cardiac ventricle

BNP is continuously released by the heart muscle cells in low levels but can be increased by neuroendocrine and physiologic factors, including hemodynamic load, to regulate afterload and preload.

46
Q

BNP is released in response to?

A

ventricular stretch

47
Q

What are the effects of released BNP?

A

Cause vasorelaxation, inhibition of aldosterone secretion from the adrenal gland and renin from the kidneys to increase natriuresis and reduction of blood volume

48
Q

BNP is a good marker for CHF. What does a high value indicate?

A

the higher the BNP the more severe the CHF

49
Q

This is used to aid in the differential diagnosis of dyspnea?

A

BNP

if BNP is elevated then it most likely is CHF

If BNP is normal then the dyspnea is most likely due to a pulmonary cause and not cardiac

50
Q

What is the indication for patients with CHF whose BNP does not rapidly return to normal with treatment?

A

higher mortality rate in next several months than those whose BNP normalizes with treatment

51
Q

Some labs measure BNP as?

A

Some labs measure BNP as an N-terminal fragment of pro-brain (B-type) natriuretic peptide (NT-pro-BNP)

52
Q

Interfering factors of BNP

A

BNP levels higher in healthy women than healthy men

BNP levels higher in older patients

BNP levels elevated in patients who have had cardiac surgery for 1 month postoperatively – does not reflect presence of CHF

Natrecor (nesiritide) is a recombinant form of endogenous human peptide used to treat CHF – will increase BNP levels

53
Q

Causes of increased levels of BNP

A

CHF, MI, systemic hypertension, heart transplant rejection, cor pulmonale – all have increased ventricular and/or atrial cardiac pressure to cause release of cardiac natriuretic peptides to cause relaxation of blood vessels (vasodilation), an increase in excretion of sodium (natriuresis) and fluid (diuresis), and decrease in injurious neurohormones (aldosterone, angiotensin II). All these work on vessels, heart, and kidneys to decrease fluid load on the heart

Lab Medicine (17 decks)

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