Cardiac Biochemistry- Cardiac Biomarkers

Question 1

What tests would you do on 45 year old man is admitted to the admissions ward with increasing chest pain on exertion for 2 weeks, He has had chest pain at rest for 2 hours, He has no relevant past medical history, He smokes 20 a year, Ambulance crew concerned he may be having a myocardial infarction, Need to take family history, Family history- father MT aged 35, brother MI aged 40

Answer 1

full blood count (haemoglobin), random glucose, lipids, urea and electrolytes (assesses kidney function), troponin T on admission and at 12 hours, ECG and chest x-ray. Important to take a good history. With all the information it is possible to determine if he is having a heart attack

Question 2

What can plaque rupture result in

Answer 2

Complete or sub occlusion of a vessel which results in blood being unable to flow and hypoxia damage to heart muscle

Question 3

What is released in plaque rupture

Answer 3

Tn (troponin)

Question 4

Why may troponin be important

Answer 4

A normal ECG on admission does not exclude myocardial infarction

Question 5

What would the perfect cardiac biomarker show

Answer 5

Increase early on in the acute presentation, pick up 100% of cases (sensitive) would be ‘negative’ in 100% of cases where the diagnosis was not MI (specific) would be easy and cheap

Question 6

Describe the use of myoglobin as a cardiac biomarker

Answer 6

It goes up with lots of things meaning that it is not specific

Question 7

Describe the use of creatine kinase as a cardiac biomarker

Answer 7

Enzyme released from muscle meaning that it is not specific for heart muscle but can be used to monitor patterns (patients have to be kept in and have their creatine kinase levels monitored for 3 days)

Question 8

Describe the use of CK-MB as a cardiac biomarker

Answer 8

It the fraction predominantly from the heart but is not a perfect measure

Question 9

Describe the use of LDH as a cardiac biomarker

Answer 9

Non-specific and takes a long time to go up

Question 10

Describe the use of troponin as a cardiac biomarker

Answer 10

Doesn’t go up as quickly as the ‘perfect’ cardiac biomarker might and may be elevated for a while post MI

Question 11

Describe creatine kinase increases

Answer 11

It increases following fairly intensive exercise and also after a fall (levels are high after high levels of muscular activity)

Question 12

What is the issue with using creatine kinase as a cardiac biomarker

Answer 12

It can be hard to tell the root cause of CK especially as people can tend to fall during an MI

Question 13

What are the 3 types of troponin

Answer 13

Troponin C, Troponin T and Troponin I

Question 14

Describe troponin C

Answer 14

Calmodulin-like protein

Question 15

What does troponin T bind to

Answer 15

Tropomyosin (TnT)

Question 16

What is the role of troponin I

Answer 16

TnI is actinomyosin ATPase inhibitor

Question 17

When does the release of the troponin complex occur

Answer 17

When cardiac muscle is damaged

Question 18

What is the troponin complex in cardiac muscle biologically different from

Answer 18

The troponin complex in skeletal muscle

Question 19

Why is there generally a release of troponin following MI

Answer 19

Heart muscle death occurs in MI

Question 20

Describe the features of troponin that make it a good cardiac biomarker

Answer 20

It is cardiospecific, is released in myocardial injury and is undetectable in health

Question 21

How is troponin measured

Answer 21

By immunoassay

Question 22

When are troponin samples taken

Answer 22

On admission and then 12 hours later

Question 23

Which types of troponin do you measure

Answer 23

TnT or TnI (fairly equal in detecting effectiveness)

Question 24

What does immunoassay require

Answer 24

The development of an antibody to detect specific epitopes (part of an antigen to which an antibody binds) on TnT/ TnI

Question 25

Which two antibodies are present in immunoassay

Answer 25

Both capture and detection antibodies

Question 26

What does the detection of antibody tell you

Answer 26

How much TnT is in the test tube

Question 27

What process tells you how much antibody is in the test tube

Answer 27

Electrochemiluminescence

Question 28

What is electrochemiluminescence

Answer 28

When you pass electricity across the test tube and the detection marker bound to TnT/ TnI glows

Question 29

How can you measure levels of TnT/ TnI using electrochemiluminescence

Answer 29

The amount of light produced is measurable, the more light generated the higher the levels of TnT/ TnI

Question 30

What do these results indicate:

TnT at 3 hours

Answer 30

Myocardial infarction

Question 31

Describe the new chemiluminescent immunoassay

Answer 31

Still immunoglobulins which bind to the antigen and emit light units which are proportional to amount of TnI in the sample. Has high sensitivity- measures in micrograms so able to detect troponin in 50% of people who are normal. Patients can be discharged after 3 hours

Question 32

Why is diagnosing MI quickly and accurately important

Answer 32

To ensure patients get the best treatment