Cardiac Markers by N X Cardiac Markers 1
Cardiac Markers by. N. X.
Cardiac Markers 1. After the loss of integrity of cardiac myocyte membranes, intracellular macromolecules diffuse into the interstitium lymphatics, and microvasculature. 2. CK, CK isoforms, troponins, and myoglobin
Creatine Kinases 1. CK is formed by two subunits, B and M, and thus including isoforms CK-MB, CK-BB and CK-MM. 2. CK exists in various types of tissue. 3. CK-MB predominates in cardiac muscle. - up to ~45% of total CK in cardiac muscle - <1% of total CK in skeletal muscle
Creatine Kinases 4. Serum CK-MB levels rise within 2~8 hours after AMI. 5. CK-MB values return to normal 2~3 days after the event. 6. Reference range in NTUH (Abbott assay) CK 38~160 U/l CK-MB <16 U/l
Creatine Kinases A ratio of CK-MB mass: CK activity 2. 5 suggests MI. CK-MB from skeletal muscle produces a plateau pattern. CK-MB from MI peaks at approximately 12~24 hour.
Creatine Kinases
Troponins 1. Three subunits including troponin C, I, and T. The complex regulates the contraction of striated muscle. 2. Tn. C binds to calcium ions. Tn. I binds to actin and inhibits actin-myosin interaction. T binds to tropomyosin, attaching to thin filament. 3. Cardiac-specific isoforms
Troponins
Troponin I 1. Cardiac Troponin I (c. Tnl) is a cardiac muscle protein with a molecular weight of 24 kilo-Daltons. 2. The human c. Tnl has a additional amino acid residues on its N-terminal that are not exist on the skeletal form. 3. The half life of c. Tn. I is estimated to be 2~4 hours. 4. Serum increase is found between 2 -8 hours and returns to normal 7~10 days after AMI. 5. Cardiac Tn. I levels provide useful prognostic information. 6. Reference range in NTUH (Abbott assay) c. Tn. I <2 ng/ml
Troponin I NEJM 1996; 335: 1342 -9
Troponin T 1. Cardiac Troponin T (c. Tn. T) is present in fetal skeletal muscle. 2. In healthy adult skeletal muscle c. Tn. T is absent. 3. The gene of c. Tn. T may be re-expressed in skeletal muscle disease. (Clin Chem. 1999; 45: 2129 -2135) 4. Biological half life and early serum increases of c. Tn. T are similar to that of c. Tn. I. 5. Peak between 12~96 hours and return to normal 14 days after AMI.
Myoglobin 1. The major protein responsible for O 2 supply of striated muscle. 2. It is released into blood rapidly (as early as 1 hour) after damage to muscle cell. 3. Early detectable, more sensitive but non-cardiospecific. 4. High negative predictive value.
Comparison NEJM 2002; Vol. 346, No. 26: 2079 -82
Comparison
Comparison Cardiac markers in patients with CRF, n=159 (Circulation 1993; 88: 101 -106)
Comparison 1. CK and CK-MB may be elevated in renal and muscular disorders. 2. Elevated c. Tn. I level in uremic patients has been a source of great controversy. 3. Elevated c. Tn. T has been found in regenerating skeletal muscle and in patients with ESRD. (c. Tn. T is elevated in asymptomatic patients with CRF. Am J Clin Pathol 1996; 106: 118 -123) 4. Myoglobin is more suitable for the detection of reinfarction.
Utility After CABG or Vascular Surgery 1. Early ischemia or infarction after CABG is most likely to be due to problems with the grafts. 2. Due to the surgical trauma, the usual indicators of MI have uncertain diagnostic value. 3. It is important to establish new biochemical diagnostic limits for perioperative MI after CABG. 4. Cardiac markers are released rapidly into blood (washout) in cases of successful reperfusion after surgery. 5. Elevated c. Tn. I (Dade assay) is associated increased risk of 6 -month mortality and MI. (Circulation 2002; 106: 2366 -2371)
Utility After CABG Chest 2002; 121: 103 -111
Conclusion 1. Elevated serum c. Tn. I in patients with renal disorders, especially in lower ranges, should be interpreted with caution. 2. Cardiac Tn. I is useful for predicting short-term mortality in vascular surgery patients. 3. Normal values of cardiac markers after cardiac surgery are still not defined.
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