Quiz 3: Cardiac Flashcards
AMI
Acute Myocardial Infarction Common Symptoms: intense chest pressure, with impending sense of doom and pain to the left arm; other symptoms may include chest heaviness or burning, pain radiation to other areas, indigestion, vomiting, nausea and diaphoresis
Angina Pectoris
• Stable Angina: Myocardial ischemia, Chest discomfort upon exertion
• Unstable Angina: Can occur without exertion (more severe), Transient ischemia
- Platelet aggregation
- Coronary artery spasms
- Coronary thrombosis
ECG AMI Diagnosis
• ECG changes depend on the location and severity of myocardial necrosis
• 100% specificity, 50% sensitivity (myocardial infarctions that do not produce characteristic ECG changes)
Biochemical Markers of AMI
- AST - Aspartate aminotransferase
- LDH - (LD) Lactic dehydrogenase
- CK - Creatine kinase
Creatine kinase (CK)
- Takes at least 6 hours for there to be an “enzyme leak”.
- Enzymes should be re-assessed every 8 hours for the first 24 hours
- Enzyme is helpful in gauging the size of the AMI CK Isoenzymes found with Agarose gel electrophoresis with fluorescent detection.
CK3 skeletal muscle
CK2 heart muscle
CK1 brain
Measuring CK Levels
- Immunoinhibition/precipitation - Antibody to M subunit - Multiply results by 2 - Interference from CK-1 (BB)
- Most modern methods use two-site (“sandwich”) heterogeneous immunoassay - Measures CK-MB mass, rather than activity - Gives rise to a pseudo-percentage, often called the “CK- MB index”
AST
AST: Found in liver and heart – now more commonly measured as a liver enzyme
• Increased levels in AMI, but not specific
LDH Ratios (Normal and Disease State)
- Normal ratios: LD1 < LD2; LD5 < LD4
- LD1 > LD2 – Myocardial infarction, hemolytic anemia, pernicious anemia
- LD5 > LD4 –Liver disease
5 LDH Isoenzymes
LD1 – heart, rbc’s, kidney
LD2 – heart, rbc’s, kidney (Less than LD1) (LD2 makes up the largest fraction)
LD3 – lungs and other tissues
LD4 – wbc’s, lymph nodes, muscle, liver
LD5 - liver, skeletal muscle
Less Common Biomarkers for AMI
- C-reactive Protein
- Fibrinogen
- Lipoprotein (a)
- Homocysteine
C-Reactive Protein
- Evaluation of inflammatory processes, arthritis and autoimmune disease
- Also found in atherosclerotic plaque, may enhance expression of adhesion molecules, alter LDL cholesterol uptake by macrophages
- High sensitivity methods with detection limits of 0.2 mg/L allow differentiation of low level inflammation implication in coronary artery disease (CAD)
Fibrinogen
- Large glycoprotein - final step in the coagulation cascade
- Normal levels are 200-400 mg/dL
- Levels also correlate positively with other risk factors, increasing with LDL cholesterol and decreasing with increased HDL cholesterol levels
- Elevated fibrinogen associated with 1.5 fold increased risk of AMI or coronary death
Lipoprotein (a)
- LDL particle containing the apolipoprotein B-100 molecule and an apoprotein (a) molecule
- Plasma concentration is from 1-100 mg/dL, but most values are < 20mg/dL
- When chronically elevated, Lp (a) may be proatherogenic
- Recent studies show that asymptomatic individuals with high levels had a risk of CAD events 1.7 times those with lower levels
Homocysteine
- Amino acid byproduct of the metabolism of the essential amino acid methionine
- Assoc. with Vit. B6/12 and Folic Acid
- A link was established between moderate levels and atherosclerosis, and studies show homocysteine is associated with cardiovascular events
- Homocysteine lowering therapy has had conflicting results with respect to outcomes
- Measurement remains controversial
Myoglobin
- Intracellular heme protein that aids in the transport of oxygen
- Abundant in both cardiac/skeletal muscle
- Elevations detected within 1-4 hours (peak) after AMI symptoms; returns to normal after 12 hours
- Nonspecific (increases in MI and Renal damage) but sensitive marker–primarily used for negative predictive value.
- Usually measured by sandwich, nephelometric, turbidimetric, or fluorescence immunoassay
Relative Appearances of Markers
ECG Markers
