Muscle and Cardiac Markers

Question 1

4 markers used to detect muscle damage? (not smooth m.)

Answer 1

Myoglobin
Muscle enzymes
Contractile proteins
Naturietic peptides

Question 2

What is myoglobin? (recognise)

Answer 2

Haem like: contains iron but EXTRACTS oxygen from RBC

Present in cytoplasm of muscle cells

Filtered by GLOMERULUS

Brown urine when excess myoglobin present

Question 3

How is myoglobin excretedd?

Answer 3

Filtered by glomerulus

Excess causes red brown urine

Question 4

Muscles enzymes used as markers of damage? (3)

Answer 4

Creatine kinase

Aspartate aminotransferase (AST)

Lactate dehydrogenase

Question 5

What is CK used for in physiology?

Answer 5

Muscle specific enzyme

Used to generate ATP

Question 6

Structure of creatine kinase enzyme? Which type is most associated with cardiac muscle damage?

Answer 6

Dimer of M (muscle) or B (brain subunits

CK in skeletal muscle is CK MM (high in normal health)

CK in cardiac muscle is 30% CK-MB

THEREFORE high levels of CK-MB indicates cardiac damage

Question 7

Where is AST found?

Answer 7

Highest conc. in liver cells but not specific

High conc. in skeletal and cardiac muscles

Question 8

Which cells contain LDH?

Answer 8

All of them

Question 9

What is LDH used for?

Answer 9

Used less frequently now, but is a marker of increased cell turnover

Can indicate tumour growth (used for leukaemia, lymphoma)

Question 10

What percentage of CK in heart muscle is CK-MB?

Answer 10

30%

Question 11

When does CK-MB rise after MI?

Answer 11

Rises 4-9 hrs after MI and back to baseline at 48-72 hrs

Advantage of it is that if you see there is a second peak then you know there has been a re-infarction

Question 12

What is myalgia?

Answer 12

Muscle pain with no CK rise or severe muscle tenderness

Question 13

What is myositis?

Answer 13

Mild increase in CK and increased muscle breakdown

Question 14

WHat is rhabdomyolysis

Answer 14

RAPID muscle breakdown, CK can be 5-10 times upper limit of normal

Urine will be red

Myoglobin can block renal tubules so consider AKI! (give fluid)

Question 15

Biochemical consequences of rhabdomyolysis (6) recognise

Answer 15

• Rapid increase in CK and myoglobin
• Which leads to AKI
• Increases in K and PO4
• Metabolic acidosis (due to AKI, muscle components, or ischaemia)
• Increase in uric acid due to lots of purines
• Calcium-Initial fall then rise in recover phase

Question 16

Causes of skeletal muscle disease? (8 types)

Answer 16

• Physical
• Inflammation
• Endocrine (thyroid, adrenal)
• Electrolyte (K, Mg, PO4, Ca)
• Toxins (alcohol, statins etc)
• Genetic non metabolic(muscular dystrophies)
• Genetic metabolic (fatty acid oxidation defects, mitochondrial disorders)
• Cancer

Question 17

Components of all troponin complexes?

Answer 17

Troponin I (inhibits)

Troponin C (binds to Ca)

Troponin T (anchors the complex)

Question 18

Which troponin complexes are specific to cardiac muscle?

Answer 18

Cardiac troponin I (cTNI)

Cardiac troponin T (cTNT)

Question 19

How long does it take for levels of Troponin I and T to fall after MI? Disadvantage of this?

Answer 19

high levels initially, can take up to 7 days to settle

Difficult to detect re infarction, therefore use CK-MB

Question 20

Main troponin used in clinical practice?

Answer 20

Depends on assay used

Mostly Trop T in NI

Question 21

Non cardiac causes of raised Troponin T levels? (7)

Answer 21

Acute illness
PE
Sub arach
Stroke
CKD
Sepsis
Severe exertion

Question 22

Cardiac causes of raised troponin T? (5)

Answer 22

MI
Acute myocarditis
Post cardiac surgery
Aortic dissection
Cardiomyopathy

Question 23

Uses for BNP in heart failure (5)

Answer 23

Diagnosis
Screening for LV dysfunction
Risk stratification
Monitoring treatment

Can rule out HF!