Flashcards in Biomarkers of Infarction Deck (16)
What are the diagnostic criteria for an acute myocardial infarction (heart attack)?
Typical rise and/or fall of a cardiac biomarker (preferably troponin) with at least one value above the 99th percentile, and at least one of the following:
1. Ischemic symptoms
2. Development of Q waves on ECG
3. New ECG changes of ischemia (ST elevation or depression)
4. Imaging evidence of new loss of viable myocardium
5. Identification of intracoronary thrombus by angiography or autopsy
Why is troponin used as the recommended biomarker for Myocardial Infarctions?
- Troponin is central to the definition of acute myocardial infarction – patients can have negative elevated CK-MB levels even if they have suffered an AMI (Acute myocardial infarction).
- Greater diagnostic window - Due to slow release of Troponin, it is detectable in the blood for several days. CK-MB is cleared rapidly.
- Greater specificity than CK-MB - Certain isoforms of Troponin I and T are only found in heart muscle
What causes elevation of cardiac troponin?
Most of the troponin within the myocyte is found in the structural elements of the cell, so when necrosis occurs there is a steady leaching of troponin into the circulation.
What are some examples of reasons for elevated troponin in the absence of MI?
- renal failure
- extreme exertion during exercise
- certain medications
- being stabbed
- many more
What were some of the previous biomarkers used?
- CK-MB – however many people suffer an AMI without elevated CK-MB levels. It also has a narrower diagnostic window than troponin.
- AST (aspartate transaminase) was the first used, however it is not specific for heart damage - use for liver function test instead
- LDH (lactate dehydrogenase) – low specificity
- Myoglobin – low specificity
What causes elevated CK?
- Exercise – very common. Usually improved in 3-5 days.
- Muscle injury – trauma, ischemia, shock, burns
- Renal failure
- alcohol – binge drinking or chronic overuse
- endocrine problems
- myopathies (disease of muscle tissue)
- electrolyte disorders
What are the liver function tests?
- total bilirubin
- alkaline phosphatase
- y glutamyl transferase
- alanine aminotransferase (‘transaminase’ or ALT)
- aspartate aminotransferase (AST)
- total protein
What are common causes of elevated transaminase levels?
- NAFLD (non-alcoholic fatty liver disease)
- viral hepatitis
- coeliac disease
What are the transaminase rules of thumb?
Transaminase = ALT
Aspartame aminotransferase = AST
ALT usually > AST
- If AST > 2x ALT – think alcohol or cirrhosis.
- Alcohol does not usually cause ALT >5x normal.
- NAFLD ~2-4x
- viral hepatitis can be >20x if acute, often 2-3x in chronic C, and 2-15x in Chronic B
- Ischemia – VERY elevated. If >ALT 1500 consider ischemia.
What are some of the patterns of liver dysfunction?
a) Cholestasis (Jaundice) – bile cannot flow from the liver to the duodenum, therefore expect high bilirubin.
b) Enzyme induction – increased production of y glutamyl transferase in the liver.
c) Hepatic – high alanine aminotransferase
What would you typically see for NAFLD?
high y glutamyle transferase and high alanine aminotransferase
What would you suspect if a patient has only mildly elevated bilirubin but nothing else suspicious?
Do most lipid accumulations remodel the artery outwards or inwards?
Outward remodeling of the artery.
Luminal stenosis (inwards) tends to occur late in the process, and there can be considerable atheroma without significant luminal narrowing.
For arterial lesions, what is the best predictor of rupture?
The fibrous cap thickness
What are most Acute Coronary Syndromes caused by?
NOTE: Acute coronary syndrome is a term used for any condition brought on by sudden, reduced blood flow to the heart.
Rupture of the fibrous cap. Thrombosis occludes the remaining artery.