Lab Assessment of Cardiac Function Flashcards
Will an EKG always show that a heart attack has occurred?
no, you may need to rely on labs
What regulatory proteins in cardiac muscle are considered to be heart specific?
troponin
What is the ideal cardiac marker? does it exist?
100% specific, 100% sensitive, and no it does not exist.
What are the current cardiac markers that we have?
myoglobin, CK-MB, troponin T or I, BNP
How do you diagnose an MI?
- relies on clinical history, symptoms
- elevation of cardiac markers
- EKG findings
How long before there is irreversible myocardial necrosis?
4-6 hours
What is myoglobin?
a heme protein found in striated skeletal and cardiac muscle. myoglobin’s job is to trap oxygen so muscle cells can work properly. (not a good marker to rely on if someone has renal disease!!)
What is the pattern of changes for myoglobin?
rise within 1-3 hours, peak at 8-12, returns to normal at 18-30. For diagnosis of an MI, serial myoblogins must be ordered.
What change in myoglobin would be highly diagnostic for an MI?
if the myoglobin level DOUBLES within 1-2 hours post initial value. (the degree of elevation corresponds with the level of infarct).
What can myoglobin help a practioner determine?
If a patient is suitable for thrombolytics, and if there is success or failure of reperfusion.
What are the normal ranges for myoblogin?
males: 30-90
females: less than 50
What is CK?
it is an enzyme that is involved in the transfer of energy in muscle metabolism.
What are the three isoforms of CK?
CK-BB: brain (only found if barrier is breached)
CK-MB: heart
CK-MM: muscle (accounts for almost all CK activity)
How would you know if CK-MB is normal?
It should be less than 5% of total CK.
How must CK-MB always be evaluated?
As a relative percent of total CK
What is the pattern of changes for CK-MB?
begins to rise 4-6 hours after onset, peaks at 12-20 hours, and returns to normal at 24-28 hours unless new damage has occurred.
T/F: the rose and subsequent fall of both total CK and CK-MB is nearly always indicative of an AMI?
True
What are the +/- of relying on CK-MB?
advantages: acute marker for damage, can detect reinfarction. disadvantages: unable to detect AMI in patient who does not seek immediate attention.
What is Troponin?
It is a complex of 3 proteins (TnT, TnI, and TnC) that bind to the thin filaments of striated muscle (cardiac and skeletal) but are not present in smooth muscle. Together they function to regulate muscle contraction. TnT and TnI are specific for cardiac.
Do TnI and TnT normally circulate in the blood
no, which why they are very sensitive markers for cardiac damage.
What is the pattern of changes for troponin?
begins to rise 3-6 hours, peaks in 14-20 and stays elevated for 5-10 days!!! Serial measurements taken at x3 8hour intervals are needed over a 48 hour period to diagnose an MI (so 6 measurements in total)
How do you rule out an MI when myoglobin and troponin are measured?
myoglobin = pos, trop= neg
how do you determine the occurrence of an AMI or cardiac injury when myoglobin and CK-MB are normal?
troponin WILL be positive if an infarct has occurred.
What are the +/- of Troponin?
advantages: detect for several days
disad: unable to detect reinfarction soon after initial infarction.
