Cardiac Biomarkers 2 Flashcards
What is the universal definition of an MI?
- rise and/or fall of cardiac biomarkers (pref. troponin) with at least 1 value above the 99th percentil reference limit with one of the following:
ischemic symptoms EKG changes pathological Q waves Imaging evidence for new loss of viable myocardium or wall abnormality IC thrombus on angiography or autophy
What is the pathopysiology of acute coronary syndrome?
unstable plaque plaque rupture intracoronary thrombus formation reduced blood floow myocardial ischemia myocardial necrosis
What are the three different proteins complexed together in cardiac troponin?
TnC (binds the Ca)
TnI (Actomyosin-ATP inhibition subunit)
TnT (tropomyosin binding subunit)
Which is better for MI diagnosis - troponin T or troponin I measurements?
doesn’t matter - they’re diagnostically equivalent.
What group of patients will have a increased prevalence of TnT elevations? Is this a false positive?
renal failure
this is not a false positive - they still have an MI, and they have a worse prognosis
What are the three cytosolic isoenzymes of creatine kinase?
MM
MB
BB
True or false: CK-MB is specific for myocardium?
false - it’s more prevalence in cardiac tissue, but there’s also some in brain and skeletal
Do we use CK-MB to diagnose ACS anymore?
nope - troponin is way better
but you can use it if a troponin assay isn’t available for whatever reason
What do we use CK-MB for them?
- can be used to estimate infarct size (but we don’t do this regularly either)
Which will identify more patients at risk: a sensitive troponin assay with slightly more imprecision or an insensitive assay with excellent precision?
sensitive with more imprecision
A troponin with
20%
What are some causes of (relatively) chronic troponin elevations (and thus, why we care more about the trend to diagnose an MI)?
cardiac procedures non-cardiac, but major procedures tachy/brady-arrythmias heart failure renal failure
What constitutes a significant change in troponin trend?
Frustrating, it’s not well-defined and will change depending on the assay
if the troponin level was close to the 99th percentile, suggest a change of at least 3 standard devisions, as determiend by the individual lab
or evidence for a serial increase or decrease of over 20% is required if the initial value is elevated
At what time points should you measure the delta?
in theory between 0 and 3 hours and between 0 and 6 hours
How does hemolysis affect troponin measurement?
can increase or decrease depending
What are the pros and cons of using POC troponin testing int he ED?
It increases turnaround time and decreases length of stay in the ED, but it has lower analytical precision, sensitivity. It’s not cheaper and it hasn’t improved patient outcomes (maybe has even worsened outcomes)
Troponin can also be elevated in heart failure, so what do you do when faced with an acute heart failure patient with a positive troponin in the ER?
carefully consider clinical context and talk with cardiology or PCP
How is BNP cleared
degraded by neutral endopeptidase, NP receptors and passive removal by multiple organs
How is NT-proBNP cleared?
renallly, so interpretation in CKD patients is problematic
Which is has the longer half-life - BNP or NT pro?
Nt-proBNP
Is there a diagnostic difference between BNP and NT-proBNP?
no, they generally correlate very well except NT-proBNP concentrations are higher due to the longer biological half-life
Which gender typically has a higher BNP?
females
How does BMI affect BNP levels?
more likely to have a false negative in obese individuals because adipocytes participate in the removal of NPs from circulation
