Cardiac Enzymes Flashcards
When is myoglobin used and what is the normal range?
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
How does myoglobin exit the body?
Excreted in urine and is nephrotoxic
Can be measured in the urine
What reading is positive for myoglobin when using a urine dipstick for hemoglobin?
will get a positive dipstick for blood but no RBCs on the microscopic exam
What is the function of myolgobin in the body?
Myoglobin is an oxygen binding protein found in cardiac and skeletal muscle
Which cardiac enzyme provides an early indication of myocardial damage?
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
How does Myoglobin compare to CPK test?
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
Interfering factors of myoglobin
Recent administration of radioactive substances
Intramuscular injections can increase myoglobin levels due to localized muscle injury
Causes of increased levels of myoglobin.
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
Causes of decreased levels of myoglobin
Polymyositis – antimyoglobin antibodies exist and decrease myoglobin in blood
What do Troponin enzymes indicate and what are the normal ranges?
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
These enzymes are biomarkers for cardiac disease
Cardiac troponins
What are the two types of cardiac Troponins?
Cardiac troponins can be separated from skeletal muscle troponins
The two cardiac specific troponins are cardiac troponin T (cTnT) and cardiac troponin I (cTnI)
What is the function of Troponins in the body?
Troponins are proteins in skeletal and cardiac muscle that regulate calcium dependent interaction of myosin with actin for the muscle contractile apparatus
How does the Troponin measurement compare to CPK-MB?
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
Describe the timeline of the rise and fall of Troponins after a myocardial injury
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
When may Troponin measurements not be as helpful?
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.
How quickly can Troponins be determined and how does this affect treatment?
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!
In unstable Agina what does an elevated Troponin level indicate?
muscle injury has occurred
if troponin levels are normal, no injury has occurred and there won’t be any lasting cardiac dysfunction
With detection of reperfusion associated with coronary recanalization, what indicates reperfusion?
a second peak or washout
How are Troponins used as an estimate of MI size?
late (4 weeks) troponin levels are inversely related to LV ejection fraction – late elevations are related to degradation of contractile apparatus
What do persistent elevations of Troponins indicate with CHF?
continued ventricular strain
How are troponins useful in detection of perioperative MI?
CPK-MB may elevate due to skeletal muscle injury during surgery, while cardiac troponins are not affected by skeletal muscle injury
In the evaluation of severity of pulmonary emboli the disease may be more severe if troponins are elevated or lowered?
Elevated
Interfering factors for Troponins
Troponin T levels can be falsely elevated in dialysis patients
Causes of increased levels of Troponins?
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
What are Creatine Kinase (CK) and isoenzymes used for? What are the normal ranges?
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%
Where is CK found?
CK is found in the heart muscle, skeletal muscle, and brain and is elevated when these cells are injured.
Describe the timeline of the rise and fall of CK after damage
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
Name the three types of CK isoenzymes
CK-BB
CK-MB
CK-MM
What is CK-MB specific for?
myocardial cells
Describe the timeline of the rise and fall of CK-MB after an infarction
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.
With what chest pain related conditions will CK-MB generally not go up
chest pain from angina
pulmonary embolism
or CHF
Causes of increased CK-MB levels
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
What does a high CK-MB suggest?
High CK-MB suggests that infarction has already occurred, precluding the benefit of thrombolytic therapy
This isoenzyme is helpful in quantifying degree of MI and timing the onset of infarction
CK-MB
What causes an elevation of CK-BB?
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)
Do large muscular peple have a higher or lower CK value?
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
What is indicated If CK is elevated from CK-MM?
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
Which isoenzyme makes up almost all of the CK in circulation in healthy people
CK-MM
Interfering factors for CK and isoenzymes?
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
Causes of increased levels of Total CK?
Diseases or injury affecting heart muscle, skeletal muscle, and brain
What causes increased levels of CK-MM
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
What is B-Type Natriuretic Peptide (BNP) used to identify? What are the normal and critical ranges?
Used to identify and stratify patients with congestive heart failure
Normal < 100 pg/mL
Critical > 100 pg/mL
What is the function of B-Type natriuretic peptides in the body?
Natriuretic peptides are neuroendocrine peptides that oppose the activity of the renin-angiotensin system.
What is the main source of BNPs?
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.
BNP is released in response to?
ventricular stretch
What are the effects of released BNP?
Cause vasorelaxation, inhibition of aldosterone secretion from the adrenal gland and renin from the kidneys to increase natriuresis and reduction of blood volume
BNP is a good marker for CHF. What does a high value indicate?
the higher the BNP the more severe the CHF
This is used to aid in the differential diagnosis of dyspnea?
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
What is the indication for patients with CHF whose BNP does not rapidly return to normal with treatment?
higher mortality rate in next several months than those whose BNP normalizes with treatment
Some labs measure BNP as?
Some labs measure BNP as an N-terminal fragment of pro-brain (B-type) natriuretic peptide (NT-pro-BNP)
Interfering factors of BNP
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
Causes of increased levels of BNP
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
