Cardiac Enzymes-Diagnostics Flashcards
Ischemia
- Temporary diminished supply of blood (oxygen and nutrients) to the myocardium resulting in reversible effects
- Due to obstruction or constriction of the coronary vessels supplying the myocardium
Myocardial Ischemia
-Ischemia may develop slowly as arteries become obstructed over time or it can occur quickly when an artery becomes suddenly obstructive
Causes of an MI
- Coronary artery disease
- Blood clot
- Coronary artery spasm
CAD
- Most common cause of ischemia
- Plaques comprised mostly of cholesterol which build up in arterial wall
- Blood flow restricted by build up of plaques and/or rupture of plaques which can result in blood clot
Blood clot
- Plaque build up ruptures which results information of localized clot
- Blood clot may travel to the coronary arteries from another area of the body= rare
Coronary artery spasm
-Arterial wall spam resulting in in temporary interruption of blood flow
Acute MI
-Myocardial cell death due to prolonged ischemia
Histological cell death
-Takes about 20 minutes
Complete necrosis of myocardial cells
=2-4 hrs
ST depression greater than or equal to 1 mm
-More specific and coveys worse prognosis
ST depression greater than or equal to 2 mm in greater than or equal to 3 leads
- Associated with a high probability of NSTEMI and predicts significant mortality
- ->35% mortality @ 30 days
ST elevation
-ST elevation @ the J point in 2 contiguous leads or more of 0.2 mV or more in males or 0.15 mV ore more in females in leads V2-V3
Tall T waves
- earliest changes seen in acute MI
- Most often seen in the anterior chest leads
Isolated tall T waves
- In leads V1-V3 may be due to ischemia of posterior wall of the left ventricle
- ->the mirror image of T wave inversion
Creatine Kinase
-An enzyme released with muscle or brain tissue injury
Total CK
Ck-MB in heart
CK-MM in muscle
CK-BB in brain
CK-MB
- Begins to increase 4-6 hrs after myocardial injury
- Peaks in 18-24 hrs
- Normalizes in 48-71 hrs
Troponin I
Inhibits the interaction of myosin with actin
Troponin T
Binds the troponin components to Tropomyosin
Troponin C
Contains the binding sites for the Ca2+ that helps initiate contraction
Troponin-I
-Greatest sensitivity for myocardial injury
Troponin-I onset
-Begin to increase 4-8 hrs after an MI
Troponin-I Peak
@ 18-24 hrs
How long does a Troponin-I stay elevated?
5-14 days
Myoglobin (MB)
Protein found in skeletal and cardiac muscle
When does MB increase?
2-4 hrs after myocardial injury
=Peaks the earliest!
–>diminished utility due to lower sensitivity
When is the CK-MB the most sensitive and specific for myocardial injury?
when measured w/in 24-36 hrs of the onset of chest pain
Pathological Q Waves
> 1 mm wide
2 mm deep
Seen in leads V1-V3
