Lab Assessment of Cardiac Function

Question 1

Will an EKG always show that a heart attack has occurred?

Answer 1

no, you may need to rely on labs

Question 2

What regulatory proteins in cardiac muscle are considered to be heart specific?

Answer 2

troponin

Question 3

What is the ideal cardiac marker? does it exist?

Answer 3

100% specific, 100% sensitive, and no it does not exist.

Question 4

What are the current cardiac markers that we have?

Answer 4

myoglobin, CK-MB, troponin T or I, BNP

Question 5

How do you diagnose an MI?

Answer 5

1. relies on clinical history, symptoms
2. elevation of cardiac markers
3. EKG findings

Question 6

How long before there is irreversible myocardial necrosis?

Answer 6

4-6 hours

Question 7

What is myoglobin?

Answer 7

a heme protein found in striated skeletal and cardiac muscle. myoglobin’s job is to trap oxygen so muscle cells can work properly. (not a good marker to rely on if someone has renal disease!!)

Question 8

What is the pattern of changes for myoglobin?

Answer 8

rise within 1-3 hours, peak at 8-12, returns to normal at 18-30. For diagnosis of an MI, serial myoblogins must be ordered.

Question 9

What change in myoglobin would be highly diagnostic for an MI?

Answer 9

if the myoglobin level DOUBLES within 1-2 hours post initial value. (the degree of elevation corresponds with the level of infarct).

Question 10

What can myoglobin help a practioner determine?

Answer 10

If a patient is suitable for thrombolytics, and if there is success or failure of reperfusion.

Question 11

What are the normal ranges for myoblogin?

Answer 11

males: 30-90
females: less than 50

Question 12

What is CK?

Answer 12

it is an enzyme that is involved in the transfer of energy in muscle metabolism.

Question 13

What are the three isoforms of CK?

Answer 13

CK-BB: brain (only found if barrier is breached)
CK-MB: heart
CK-MM: muscle (accounts for almost all CK activity)

Question 14

How would you know if CK-MB is normal?

Answer 14

It should be less than 5% of total CK.

Question 15

How must CK-MB always be evaluated?

Answer 15

As a relative percent of total CK

Question 16

What is the pattern of changes for CK-MB?

Answer 16

begins to rise 4-6 hours after onset, peaks at 12-20 hours, and returns to normal at 24-28 hours unless new damage has occurred.

Question 17

T/F: the rose and subsequent fall of both total CK and CK-MB is nearly always indicative of an AMI?

Answer 17

True

Question 18

What are the +/- of relying on CK-MB?

Answer 18

advantages: acute marker for damage, can detect reinfarction. disadvantages: unable to detect AMI in patient who does not seek immediate attention.

Question 19

What is Troponin?

Answer 19

It is a complex of 3 proteins (TnT, TnI, and TnC) that bind to the thin filaments of striated muscle (cardiac and skeletal) but are not present in smooth muscle. Together they function to regulate muscle contraction. TnT and TnI are specific for cardiac.

Question 20

Do TnI and TnT normally circulate in the blood

Answer 20

no, which why they are very sensitive markers for cardiac damage.

Question 21

What is the pattern of changes for troponin?

Answer 21

begins to rise 3-6 hours, peaks in 14-20 and stays elevated for 5-10 days!!! Serial measurements taken at x3 8hour intervals are needed over a 48 hour period to diagnose an MI (so 6 measurements in total)

Question 22

How do you rule out an MI when myoglobin and troponin are measured?

Answer 22

myoglobin = pos, trop= neg

Question 23

how do you determine the occurrence of an AMI or cardiac injury when myoglobin and CK-MB are normal?

Answer 23

troponin WILL be positive if an infarct has occurred.

Question 24

What are the +/- of Troponin?

Answer 24

advantages: detect for several days
disad: unable to detect reinfarction soon after initial infarction.

Question 25

What is the first cardiac marker to rise?

Answer 25

myoglobin

Question 26

What is the cardiac marker that stays elevated the longest?

Answer 26

troponin

Question 27

What is the cardiac marker that falls the fastest?

Answer 27

myoglobin

Question 28

What is BNP?

Answer 28

It is one of 4 natriuretic hormones that regulate blood pressure, electrolyte balance, and fluid volume. Cardiac ventricles secrete BNP under conditions of volume expansion, hypertension, and stretching of the walls.

Question 29

What does BNP antagonize?

Answer 29

the hormones of the RAAS

Question 30

What are the reference ranges for BNP?

Answer 30

0-99: normal (but from 80-100 you should suspect CHF) Greater than 100 is suspect for CHF.

Question 31

What does it mean if a patient has an increased BNP value in regards to CHF? MI?

Answer 31

poorer prognosis, risk of cardiac death

Question 32

What is IMA?

Answer 32

It is ischemia modified albumin. A change occurs in the amino terminus of albumin that causes IMA to be formed. It is produced continually during ischemia.

Question 33

What is the pattern of changes for IMA?

Answer 33

Rise within minutes, stay elevated for 6-12 hours, return to normal in 24 hours.

Question 34

why use IMA?

Answer 34

It can measure ischemia better than other cardiac markers. It has the clinical potential to be used for eval of chest pain in the ER setting.

Question 35

What is CRP?

Answer 35

CRP is c-reactive protein and it is a nonspecific marker for inflammation.

Question 36

What is the pattern of changes for CRP?

Answer 36

rises within 4-6 hours after an event, peaks in 24-48 hours, and returns to normal within 10 days.

Question 37

Hs-CRP:

Answer 37

heart specific c reactive protein. low risk is less than 1, avg risk is 1-3, high risk is greater than 3

Question 38

How can Hs-CRP be used clinically?

Answer 38

as a prognostic value to determine risk of Cardiac events, levels can be used to support drug treatment and lifestyle modification, levels do NOT correlate with atherosclerosis risk.

Question 39

What is homocysteine?

Answer 39

It is an independent risk factor for CV disease. Increased levels correspond to increased risk of atherosclerosis and other forms of vascular disease.

Question 40

Is homocysteine a reliable marker on its own?

Answer 40

No!!!! it can be increased by diet, medications, chronic diseases, genetics, defiency of vitamins, alcohol and smoking, and ethnic groups.