Lecture 3 - Myoglobin and Troponin

Myoglobin

• oxygen binding protein of striated muscle (cardiac and skeletal)

• exists only as a monomer

• last resort oxygen reservoir, accessible only under extreme hypoxia

When can myoglobin release oxygen

at extremely low pO2 (extreme hypoxia)

What can cause elevated myoglobin

• striated muscle damage

• myocardial infarction — NOT cardiac specific

• muscular dystrophy

• renal failure ( is not excreted so myoglobin builds up in blood)

• Rhabdomyolysis

rhabdomyolysis

• breakdown of muscle fibers resulting in the release of muscle fiber contents (myoglobin) into the bloodstream

• causes myoglobinuria

Severe myoglobinuria may cause __

acute renal failure

Myoglobin can be used as an early marker of __

myocardial infarction (MI)

Describe myoglobin and its detection and uses in relation to MI

• detectable 1-3 hrs after onset of pain

• peaks 2-12 hrs post event

• used only to RULE OUT MI

• can NOT be used to rule in MI

Why is myoglobin not realistically useful as something to rule in MI

• it peaks 2-12 hrs post event

• most patients tend to wait before they see a doctor so the myoglobin level may have already decreased by the time they see the doctor

Troponin

central regulatory protein of striated muscle contraction

• regulates the interaction of actin and myosin thus regulates cardiac contraction

Troponin is localized in __

myofibrils (~96%) (specific for cardiac)

What components of Troponin are used as cardiac markers? Why?

Troponin I and Troponin T

• have different aa sequences that can be differentiated from skeletal muscle

• (TnC is not specific for cardiac)

What is the most useful test in assessing acute myocardial infarction

Troponin (I and T)

When can you begin detecting elevations in Troponin I or T

2-6 hrs after MI

Small elevation in TnI or TnT may indicate __

unstable angina

How long does Troponin stay elevated after an MI

4-14 days (helpful in detecting MI in late-presenting patient)

Troponin has eliminated the use of __

myoglobin for testing

testing troponin T and I

monoclonal aby immunoassay for serum (compare lab platforms/analyzer and POC to ensure correlation)