cardiac lab eval

Question 1

What are the cardiac biomarkers?

Answer 1

• troponin (main one)
• CK-MB
• myoglobin

Question 2

Lab tests for CV risk assessment?

Answer 2

• hs-CRP

- homocystine

Question 3

When do you use BNP?

Answer 3

• in HF management

Question 4

When are cardiac biomarkers used?

Answer 4

• in dx and risk stratification of pts with cardiac sxs
• not necessary for dx of pts who present with ischemic chest pain and EKGs with ST elevation
• follow the trend to peak
• useful to assess myocardial injury
• proteins that leak from myocardium secondary to ischemia
• differences b/t various biomarkers: time from ischemic injury to elevation of the lab values, and variable degrees of specificity for myocardial injury

Question 5

What is troponin a high specific marker for?

Answer 5

• cardiac muscle cell death
• it is a protein that is integral to muscle contraction
• found in skeletal and cardiac muscle
• Troponin I and T are isolated proteins specific for cardiac muscle
• released into systemic circulation when there is myocyte necrosis that leads to cell membrane disruption

Question 6

Troponin can ID pts at increased risk for what?

Answer 6

• adverse cardiac events
• several trials have demonstrated direct correlation b/t level of troponin in regards to mortality rate and adverse cardiac event rate in ACS
• higher the troponin the worse the outcome - large MI will have very high elevation of troponin -

Question 7

Different troponins?

Answer 7

• check either I or T (depends on facility)
• mult different assays so reference ranges may vary
• POC troponin used in the ER for rapid dx may be useful

Question 8

When do troponin levels rise and when do they peak?

Answer 8

• rises within 2-3 hours after cardiac insult and may stay elevated for 10 days to 2 weeks after event
• peak at 12-16 hrs
• wash out after thrombolytics will cause sig rise in troponins (won’t be true elevated marker)

Question 9

Troponin and CK-MB levels with and without reperfusion?

Answer 9

• with reperfusion - very elevated over 100, peaks and falls off quickly
• without: up to 75, not as high as with reperfusion but peaks longer
• CK-MB: with reperfusion preaks quickly, higher than with no reperfusion
• CK-MB: with reperfusion peaks longer, not as elevated

Question 10

What cardiac causes other than ACS will result in elevated plasma cardiac troponin?

Answer 10

• cardiac contusion
• cardiac surgery
• cardioversion
• endomyocardial biopsy
• CHF
• aortic dissection
• post PCI
• rhabdomyolysis
• myocarditis
• aortic valve disease
• hypertrophic cardiomyopathy
• tachyarrhythmia
• bradyarrhythmia, heart block
• apical ballooing syndrome
• pericarditis
• endocarditis

Question 11

What are noncardiac causes of elevated plasma troponin?

Answer 11

• PE
• severe pulm HTN
• renal failure
• stroke
• subarachnoid hemorrhage
• infilt disease: ex - amyloidosis
• cardiotoxic drugs
• sepsis
• critical illness
• extensive burns
• extreme exertion

Question 12

How is troponin used to dx MI?

Answer 12

• measure at presentation to ED
• repeat in 3-6 hrs post sx onset, may take up to 6 hrs post sxs/MI for lab test to rise
• highly sensitive assays have high negative predictive value for NSTEMI in setting of CP 2 hrs post onset of sxs (if neg after 2 hours, most likely they don’t have MI)
• may repeat beyond 6 hrs if:
  initial troponin normal, EKG changes present, pt has many high risk features
  (if pt has renal failure - troponin will stay stable, won’t increase like it would in an MI)

Question 13

What biomarker should you use for dx MI?

Answer 13

• troponin

- other cardiac biomarkers are not as sensitive or specific

Question 14

What is creatine kinase?

Answer 14

• enzyme found in muscle cells
• elevations suggest muscle damage and can be indicative of injury, rhabdomyolysis, MI, myositis, and myocarditis
• elevated in 1% of pts on statins
• may increase in hypothyroidism: when T3 is low, CK becomes elevated

Question 15

What are the 3 isoenzymes of creatine kinase?

Answer 15

• CK-MM: skeletal muscle and heart: elev in muscle damage to heart or skeletal muscle, crush injury, seizures
• CK-MB: heart - elevated in MI, inflammation of heart muscle, RV and LV strain
• CK-BB: elevated in brain injury, meningitis, severe shock, stroke, hypothermia, restricted blood flow to bowel

Question 16

CK-MB peak levels?

Answer 16

• also found in skeletal muscle to lesser degree
• noted at 4-6 hrs after onset of sxs
• peaks at 24 hrs
• normalizes in 48-72 hrs

Question 17

Use of CK-MB in dx ACS?

Answer 17

• crusade registry: up to 28% of pts had discordant troponin and CK-MB results
• pts with neg troponin but CK-MB + their mortality = to pts who had neg troponin and CK-MB
  Grace registry (in hosp mortality): both troponin and CK-MB positive = high, troponin + and CK-MB neg = intermediate, and both markers negative = lowest
• shows that troponin is better inidcator for acute MI and mortality

Question 18

What is the CK-MB/CK relative index?

Answer 18

• helps to determine cardiac vs skeletal muscle injury
• clac by ratio of CK-MB to total CK
• ratio of less than 3 = skeletal muscle source, ratio is greater than 5 = cardiac source

Question 19

What is myoglobin?

Answer 19

• protein found in skeletal and cardiac muscle
• typically rises 2-4 hrs after onset of infarction
• peaks at 6-12 hrs
• normalizes in 24-36 hrs
• low sensitivity for AMI due to lack of cardioselectivity

Question 20

What is go to test for ruling out or in acute MI vs unstable angina?

Answer 20

• troponin is go to test
• some facilities still print out CK-Mb and myoglobin
• with sxs or an abnorm EKG a person may be having an MI with neg troponin if the lab is drawn prior to 2 hrs of onset of sxs, don’t tx the labs, tx your pt

Question 21

Lab tests of CV risk assessment?

Answer 21

• lipid profile
• hs-CRP
• homocystine

Question 22

What does CRP tell you?

Answer 22

• measure general levels of inflammation in the body, elevated in infections, chronic disease, and surgery
• nonspecific

Question 23

What is hs-CRP?

Answer 23

• high sensitivity
• an elevated hs-CRP: 2-3x the risk of MI, stroke, sudden cardiac death and PAD
• stronger predictor of heart disease and stroke than LDL
• major use is in primary prevention!!!!
• secondary prevention: may predict recurrent coronary events

Question 24

How can a pt lower the hs-CRP?

Answer 24

• cardiac diet
• exercise
• BP control
• smoking cessation
• statins
• do hs-CRP so pt will be motivated to lower it

Question 25

relation b/t CRP and LDL?

Answer 25

- if low CRP/low LDL very good chance of staying CV event free - if low CRP/high LDL increases chance of event - if high CRP and low LDL increases it even more - if both high CRP/High LDL: sig increase of vascular risk

Question 26

What is homocystine?

Answer 26

- amino acid - acquired mostly from meat protein - elevated levels of homocystine are related to genetics and low levels of B6, B12, and folate (veggie diet: naturally low homocystine) - green leafy veggies - low homocystine

Question 27

Link b/t elevated levels of homocystine and CVD?

Answer 27

- elevated levels of homocystine linked to CVD - decreasing homocystine levels with B vitamins may not improve outcomes - hyperhomocystinemia: prone to endothelial injury, blood clots, heart attack, stroke, miscarriage, pre-eclampsia - decreasing levels don't really improve CVD risk

Question 28

What is BNP?

Answer 28

- brain naturetic peptide - produced by ventricles and atria in response to an increase in volume and pressure - stim the release of ANP: body rids itself of Na in an attempt to decrease total body volume - may be helpful in diff b/t CHF and lung disease - don't use routinely to follow stable CHF

Question 29

Causes of elevated BNP other than CHF?

Answer 29

- elderly - women - renal failure - cirrhosis - ACS - myocarditis - PE - primary pulm HTN