Enzymes and cardiac markers Flashcards
What is the Michaelis Menten constant (Km)?
Substrate conc at which the reaction velocity is 50% of the maximum rate of reaction
In which order are cystolic and sub-cellular enzymes released?
Release of cytosolic enzymes happens first, followed by release of sub-cellular enzymes (as they leak out of cells after necrosis)
Where can enzymes be measured?
Enzymes can be measured in the SERUM (i.e. in injury) or the TISSUE (abnormalities)
Name 2 physiological causes of raised ALP
Normal bone growth!
- 3rd trimester of pregnancy (from placenta)
- Childhood growth spurts
Name 2 pathological causes of raised ALP <5x the upper limit
Bone – tumours, fractures, osteomyelitis
Liver – infiltrative disease, hepatitis (doesn’t go up nearly as much as AST/ALT)
Name 2 pathological causes of raised ALP >5x the upper limit
- Bone – Paget’s disease, osteomalacia
- Liver – cholestasis, cirrhosis
Which enzyme is elevated in acute pancreatitis?
Amylase
Which enzyme is low in chronic pancreatitis?
Faecal elastase
What biomarker is used in IBD?
Faecal calprotectin- indicates inflammation
What are the 3 forms of creatine kinase?
Three forms (they are dimers containing either M (muscle) and B (brain) subunits):
- CK-MM = skeletal muscles (responsible for almost the entire normal plasma activity)
- CK-MB = cardiac muscle
- CK-BB = brain (activity is minimal even in severe brain damage)
What is creatine kinase a marker of?
Muscle damage
What condition is caused by statins and causes a raised CK-MM?
Statin-related myopathy
Causes of a raised CK
- Muscle damage due to any cause
- Myopathy (e.g. Duchennes) >x10 Upper Limit
- Myocardial infarction >x10 UL
- Severe exercise 5x UL
- Physiological (Afro-Caribbean <5x UL
Give two other uses of measuring enzymes
- Markers of therapeutic response or drug toxicity
E.G. measurement of TPMT activity before starting patients on thiopurine drugs such as azathioprine - As reagents for measurement of other substances
E.G. glucose oxidase is used to measure glucose in plasma
Which enzyme is the best to measure following MI?
Troponins
Which enzymes are the cytosolic and sub-cellular enzymes in the myocardium?
Myoglobin = cytosolic enzyme (rise quickly)
CK-MB = sub-cellular (mitochondria and nuclei)
When do troponins…
a) rise
b) peak
…post MI?
a) 4-6 hours
b) 12-24 hours
How long do troponins remain elevated following MI?
3-10 days
When should troponins be measured in someone with chest pain?
At 6 hours and again at 12 hours after onset of chest pain
If after 12-24 hours if there is no rise in troponin, has someone had an MI?
Almost certainly NOT
What are the diagnostic criteria for MI?
Diagnostic Criteria for Acute MI = either of the following:
Typical rise and gradual fall in troponin or more rapid rise and fall in CK-MB with at least one of the following:
- Ischaemic symptoms
- Pathological Q waves on ECG
- ECG changes of ischaemia
- Coronary artery intervention
Pathological findings of an acute MI
Are cardiac biomarkers enough to diagnose MI when deciding about thrombolysis? Why?
No.
None of the current cardiac biomarkers rise quickly enough to aid decisions regarding thrombolysis (therefore it is decided based on clinical findings and ECG findings)
What are the markers of cardiac failure?
Natriuretic peptides (NP):
- Atrial NP (secreted by atria)
- Brain NP (secreted by ventricles) used for:
Assess ventricular function
To exclude heart failure in a clinical setting (highly sensitive)
