DR. ABDULRAHMAN AL-AJLAN MYOCARDIAL INFARCTION

Introduction The heart is a muscular organ whose function is pumping of blood around the body. It consists of four chambers separated by valves. Disorders of (myocardium). the heart may affect the heart muscle Pathology: MI occurs when the supply of blood to the coronary muscle is reduced below a critical value usually as a result of overlying thrombosis. Angina due to reduction of coronary perfusion caused by the narrowing of the arteries by atheromatous plaque. 2

Risk factors for coronary artery disease 1. age 2. gender 3. family history 4. Hyperlipidaemia 5. Smoking 6. Hypertension 7. Diet 8. Other disease such as diabetes mellitus, obesity 3

Myocardial Infarction Myocardial Infarction (MI), also Known as coronary thrombosis, is one of the commonest causes of mortality and morbidity in adults. Diagnosis: Biochemical testes complement the ECG findings. Three enzymes are commonly used in the diagnosis and follow up of MI. These are Creatine kinase (CK) Aspartate amino transferase (AST) Lactate dehydrogenase (LDH) 4

CK catalyzed the transfer of phosphate groups from creatine phosphate to ADP to form ATP serve as important energy source. CK is found primarily in muscle (skeletal heart) but also present in brain tissue. There are at least three isoenzymes of CK which can be separated by electrophoresis. CK from skeletal muscle produces a single band on electrophoresis. CK from brain tissue also yields a single isoenzyme but with a different mobility. 5

CK from heart muscle produces two bands, one of these seems to be identical with that of skeletal muscle, the other has a mobility intermediate between skeletal muscle CK and brain CK. Diagnosis: CK levels rapidly, peaking at 24 hours, with slower rises being shown by AST and LDH. CK is also released from damaged skeletal muscle. CK-MM in skeletal muscle. CK-MB (CPK 2 ) in heart cells, this isoenzyme is more specific indicators of cardiac muscle damage. Plasma enzyme activities are raised in about 95% of case of myocardial infarction and are some time very high. 6

The time sequence of changes in plasma enzymes after myocardial. Duration of rise (days) Start to rise (hours) Peak (hours) Enz CK AST LD 7

Lactate Dehydrogenasen (LD) LDH is the isoenzyme which catalyses the interconversion of lactic and pyruvic acids. LDH a good indicator of tissue damage, other additional information is needed to decide which tissue is injured. There are quantitive differences in the amount of LDH in various tissues. It is found in highest concentration in the liver, followed by heart and skeletal muscle. 8

RBCs contain about 200 times the normal plasma level. So care, should preventing hemolysis when collecting blood sample for the assay. LDH is used in the diagnosis of MI, LDH is not specific to cardiac muscle, because it is found in liver and red blood cells. 9

Five Isoenzyme of LDH have been separated by electrophoresis. LDH 1 (isoenzyme in heart) fastest moving enzyme. LDH 5 (isoenzyme in liver) slow moving enzyme. Red blood cells can release LDH 1, for this reason blood for LDH measurement must not be allowed to remain unseparated before analysis (haemolysis blood not used). 10

Other biochemical indicators: 1-Myoglobin: detectable 1-3 hrs after infarction (it is used as earliest indicator). 2-Troponin I and T Cardiac troponins I and T are highly sensitive and specific markers for acute MI. Like CK-MB, they are released from damaged cardiac muscle cells within 3-12 hrs of infarction but they remain elevated for much longer. Troponin T may take 2 weeks to return to normal levels, while increases in troponin I resolve within 5-10 days. 11