What Is a Myogram?

For myocardial enzyme examination, the inspection of myocardial enzymes is mainly to determine myocardial ischemic necrosis or cell membrane permeability.

Myocardial enzymes

Correct

1. Overview of serum enzymes: P232

Lactate dehydrogenase (LDH), aspartate aminotransferase (AST), creatine kinase (CK), creatine kinase isoenzyme (CK-MB), -HBD COOH COOH

1. Custom nomenclature: named according to the source of the enzyme, the nature of the catalytic reaction and the substrate.

Substrate: amylase, protease

Properties: dehydrogenase, transferase

Source: Pancreatic amylase,

(I) Excretion of serum enzymes: P234

1. Urinary tract: the main way of low molecular weight enzymes in serum

2. Bile is not a serum enzyme excretion pathway

(B) liver or

(One)

(A) Synthesis anomaly: P238

Reduction of synthesis

2. Increased synthesis

(B) Increased release of enzymes from damaged cells:

Is the main mechanism of most serum enzymes during disease

(3) Other mechanisms:

Renal failure oliguria

(1) Lai's colorimetric method: P115

Cardiac Enzyme Tester

1. Principle:

COOH COOH COOH COOH

(CH2) 2 + CH2 AST (CH2) 2 + CH2

C = O HC-NH2 37 HCNH2 C = 0

COOH COOH COOH COOH

Ketoglutarate aspartate glutamate oxaloacetate

COOH CH3

CH2 Aniline citrate C = 0 + CO2

C = 0 decarboxylated COOH

COOH

Pyruvate

CH3

C = 0 + pyruvate2.4 = + H2O

COOH

2.4-Dinitrophenylhydrazine acid, grass yellow, alkali added, brown red

Colorimetric comparison with standard concentration pyruvate (505nm)

2. Normal reference value: 8-28u

3. Notes

(1) Hemolytic specimens cannot be used for AST measurement, because AST in RBC is 10 times that of serum.

(2) The physical and chemical properties of M-AST and C-AST are different. The Ag properties are different and controlled by different genes, but they catalyze the same reaction and are the same I enzyme.

(3) The simpleness and relative accuracy of the Lye's colorimetric method is the reason for its popularity.

(4) It is difficult to ascertain that the product formation is directly proportional to time during the enzyme reaction period.

Oxaloacetate is an inhibitor of AST competition. As the reaction progresses, the product and enzyme reaction continue.

(5) Color reaction and substrate concentration problems.

Ketoglutarate can also react with 2.4-dinitrophenylhydrazine to produce another brown phenylhydrazone, which increases the false positive of the AST test.

In order to reduce its interference, the wavelength is selected at 490-530nm, at this time pyruvate is twice as much as ketoglutarate

2.4-Dinitrophenylhydrazine can also show color in alkaline solution, which makes the absorbance pseudo-increase.

(6) A. Coupling with transamination:

ALT

Pyruvate + glutamic alanine

Therefore, the liver disease AST and ALT consume pyruvate at the same time, and the AST measurement results are reduced.

B. Product bypass

Lactic acid

LDH NADH + H +

Pyruvate

-Ketoglutarate + asparag aa AST oxaloacetate + glutaa.

MDH + NADH + H +

Malic acid

Therefore, interference by LDH and MDH reduces the AST measurement result

(2) Some external continuous monitoring methods of enzyme coupling:

1. Principle: L-asparagus aa. + -ketoglutarate AST oxaloacetate + glutaa.

Oxaloacetic acid + NADH + H + MDH Lmalic acid + NAD +

340nm

Decrease in absorbance to calculate AST activity

2. Reference value: male <40u / L 37

Female <35u / L 37

3. Note:

(1) Separate serum immediately after blood collection to avoid hemolysis

Serum and blood clots cannot be set together for a long time

(2) Serum, room temperature for 4-8h, 2-6 , 7d, -20 for 8 months

(3) Anticoagulant plasma:

EDTA, 2Na, heparin have no inhibitory effect on AST

Do not use oxalate anticoagulants as they inhibit AST activity

(4) The AST concentration is too high. Dilute and redo.

(5) There are no coupling transamination and product bypass problems

(6) There is no ketoglutarate interference, the substrate concentration can be appropriately increased to complete the reaction

(7) Glutamate dehydrogenase (GLDH) is present in the substrate

-Ketoglutarate + NADH + H ++ NH3 GLDH Valley aa. + NAD ++ H2O

Consumption of NADH + H + makes the result false.

(8) LDH with pyruvate in sedan

Pyruvate + NADH + H + LDH Lactic acid + HAD +

Consume NDAH + H +, making the result high

(9) In the case of the indicated enzyme, oxaloacetate can automatically decarboxylate to generate pyruvate, which results in a low result. LDH should be added to make it more accurate

It does reflect AST vitality.

So MDH and LDH together serve as indicator enzymes

Clinical significance:

1. AST is the most abundant in the myocardium, so it peaks at 6-12h during the acute myocardial infarction, peaks at 48h, and returns to normal at 3-5d.

2. Acute hepatitis, drug poisoning after surgery, AST is obvious

Liver Ca, chronic liver disease, myocarditis, AST moderate

Myositis, pleurisy, nephritis, AST mild

3. Acute hepatitis, AST, ALT at the same time , can reach 10-30 times the normal value, the early stage of jaundice has , which is helpful for early clinical diagnosis.

3.AST with I enzyme:

Significance of <yellow> diagnosis of myocardial infarction during serum enzyme measurement:

Myocardial C and liver C suffered substantial damage M-AST C-AST

M-AST has certain diagnostic significance for prognosis of liver disease

Myocardial infarction M-AST Therefore, the more M-AST , the higher the morbidity and mortality of myocardial infarction complicated with heart failure, especially the greater the significance of mortality.

4. Determination of serum lactate dehydrogenase: the effect of pH on it

LDH glycolytic enzyme, redox reaction

There are five isozymes LDH1-LDH5

1. Distribution and characteristics of LDH:

Widely distributed, mainly in the kidney, followed by the heart, skeletal muscle, other liver, spleen, pancreas, lung, the above-mentioned tissue lesions, and serum LDH. It mainly catalyzes the following reactions:

Llactic acid + NAD + pyruvic acid + NADH + H +

PH base positive reaction (L-P)

PH neutral reverse reaction (P-L)

Methodology

(I) Colorimetric method: P122

1. Principle: L-lactic acid + NAD + LDH pyruvate + NADH + H +

PH8.8

Pyruvate + 2.4-dinitrophenylhydrazine Pyruvate-2.4-dinitrophenylhydrazone

Sour grass yellow

Add NaOH brown red

The darker the color, the greater the enzyme activity

2. Reference value: 225-540u / dL

3. Note: the amount of product generated is not proportional to the reaction time

(1) Hemolysis is strictly forbidden because the LDH activity in RBC is 100 times that in serum.

(2) LDH is inhibited by heavy metal salts, EDTA, and oxalate. Serum specimens are best

(3) Serum samples 2-6 days, room temperature 48h

(4) The accuracy and reproducibility are the worst in the enzymological test, because the five isozymes have different ability to bind to the substrate, and the optimal reaction conditions are different.

LDH composition varies widely, so it is difficult to find the optimal reaction conditions for LDH. eg: myocardial infarction LDH1 , liver disease LDH5

(5) If the result is> 2500u / dL, dilute the specimen and redo.

(2) Continuous monitoring method (enzymatic method): P120

1. Principle: L-lactic acid + NAD + PH8.8-9.8 pyruvate + NADH + H +

The reverse reaction is 2-3 times faster than the positive reaction, so the reaction is biased to the left. Use P-L more.

LDH

Propionic acid + NADH + H + lactic acid + NAD +

PH7.4

Monitoring at 340nm, the decrease in absorbance is proportional to LDH.

2. Reference value: 240-460u / L 37

3. Note:

(1) Advantages of reverse reaction:

a. Less reagent, NAD + required, only 3% of NADH + H + used by L-P, less sample

b. The change in absorbance per unit time is large, the linear range of the reverse reaction is large, and the rate of the enzymatic reaction is 3 times faster than the positive reaction, which is conducive to determination. short time

c. Long linear relationship between enzyme activity over time

(2) Positive reaction advantages:

a.NADH + H + is more stable than NAD +, lower price, and easy to obtain pure products.

Substrate L-lactic acid is stable with the reverse reaction substrate pyruvate

bL-lactic acid inhibits LDH less than pyruvate inhibits LDH

(3) The continuous monitoring method can use the forward and reverse reactions, which is superior to the colorimetric method.

(4) The presence of metal ions can reduce NAD + stability

EDTA can be added to the reagent to make EDTA complex metal ions and increase NAD + stability.

(5) NAD + is unstable and produces substances that inhibit LDH. It is more stable in alkaline solution than in acid solution, and in Tris buffer solution than in phosphoric acid.

Stable in salt buffer.

(6) For certain batches of NADH + H + and LDH substances, check the quality of NADH + H + before use. NADH + H + is dissolved in Tris buffer.

The absorbance measured at 260nm and 340nm should be 2.3, indicating that it contains impurities such as NAD + and adenosine at 260nm.

(7) -ketobutyric acid, hydroxypyruvic acid and glyoxylic acid can be substituted for pyruvate as a substrate.

(8) Specimens cannot be hemolyzed

Clinical significance:

1.LDH : acute myocardial infarction, skeletal muscle injury, certain hepatitis, leukemia, cirrhosis, obstructive jaundice and malignant tumors.

2. Myocardial infarction: 12-24h, LDH , peak at 48-72h, and return to normal after 1-2W

3. Advanced LDH of malignant tumor, LDH of pleural and ascitic fluid caused by malignant tumor

4. In patients with chronic glomerulonephritis, SLE, and diabetic nephropathy, urine LDH can reach 3-6 times that of normal people, and urine contains a variety of LDH-inhibiting substances, such as urea

Small molecule peptides.

Low pH can also inhibit LDH activity.

5. LDH patients with normal uremia, LDH after dialysis because of higher urea in the body