Cardiac enzymes Flashcards
MI
- Temporary diminished supply of blood to myocardium –> reversible effects
- 1 cause of chest pain
MI cause
Obstruction or constriction of coronary vessels
Myocardial ischemia
May develop:
- Slowly as aa become obstructed over time
- Quickly when artery becomes suddenly obstructed
Myocardial ischemia causes
- Coronary artery disease = most common
- Blood clot
- Coronary artery spasm
CAD
- Plaques comprised of cholesterol which builds up in arterial wall
- Blood flow restricted &/or rupture of plaques –> blood clot
Blood clot
- Plaque builds up, ruptures –> localized clot
- May travel to coronary aa from another area of body (rare)
Coronary artery spasm
Arterial wall spasm –> temporary interruption of blood flow
MI sx
- Chest pain
- Dyspnea
- Nausea
- Pain radiating to neck, arms, back
- Epigastric pain
- Fatigue/ weakness
- Dizziness
- Impeding sense of doom
What type of patients present atypically w/ an MI?
- Elderly
- Females
- Diabetics
Acute MI
Myocardial cell death due to prolonged ischemia
Tall T waves
- Earliest change seen in acute MI
- Most often seen in anterior chest leads
Flattened T waves
Often seen in pts w/ myocardial ischemia, but often non-specific
Q waves
Typically seen in left-sided leads
Pathological Q waves
- > 40 ms wide
- > 2 mm
- 25% of depth of QRS
- Seen in leads V1-3
Pathological Q wave differential
- MI
- Cardiomyopathies
- Rotation of heart
- Lead placement errors
Intracellular enzymes & proteins
- Creatine kinase (CK or total CK)
- Creatine kinase myoglobin (CK-MB)
- Myoglobin (MB)
- Troponin **
CK
Released w/ brain or muscle injury
What are the 3 isoenzymes of CK?
Total CK:
- CK-MB in heart
- CK-MM in muscle
- CK-BB in brain
CK-MB may also present where?
- Small intestine
- Tongue
- Diaphragm
- Uterus
- Prostate
When does CK-MB increase?
4-6 hrs after myocardial injury
When does CK-MB peak?
18-24 hrs
When does CK-MB normalize?
48-72 hrs
What is the normal range of CK-MB?
5-25
When is CK-MB most sensitive/specific to MI?
Within 24-36 hrs of onset of chest pain
MB
- Protein found in skeletal & cardiac muscle
- Lower sensitivity
- Considered unnecessary w/ troponin testing
When does MB increase?
2-4 hrs after myocardial injury
When does MB peak?
6-12 hrs
When does MB normalize
24-36 hrs
What is the normal range for MB?
0-85
Troponin categories
- Troponin I (TnI)
- Troponin T (TnT)
- Troponin C (TnC)
- All regulatory proteins part of skeletal & cardiac muscle
- Each has unique fxn
Which troponin inhibits the interaction of myosin w/ actin?
Troponin I
Which troponin binds troponin components to tropomyosin?
Troponin T
Which troponin contains the binding sites for Ca2+?
Troponin C
- Initiates contraction
Which troponins are immunologically distinct enzymes?
I & C
Which troponin has the greatest sensitivity for MI?
Troponin I
- Detects small infarcts, myocardial injury
- May be elevated for other reasons other than MI
When does troponin I increase?
4-8 hrs
When does troponin I peak?
18-24 hrs
When does troponin I normalize?
5-14 days
What is normal troponin I?
<0.1
What range of troponin I is considered indeterminate?
.1-.9
What range of troponin I is myocardial injury likely?
1.0-1.4
W/ troponin I, what level is definitive for myocardial injury?
> or = to 1.5
Which cardiac enzymes are more accurate & sensitive? Serial markers or single initial?
Serial markers
- 4 to 6 hr intervals X 3
- Utilized less in unstable angina
