Myocardial infarction, lactate

The skeletal muscle relaxants are contraindicated in patients with known hypersensitivity. Baclofen is contraindicated in skeletal muscle spasms caused by rheumatic disorders. Carisoprodol is contraindicated in patients with a known hypersensitivity to meprobamate. Cyclobenzaprine is contraindicated in patients with a recent myocardial infarction, cardiac conduction disorders, and hyperthyroidism, hi addition, cyclobenzaprine is contraindicated within 14 days of the administration of a monoamine oxidase inhibitor. Oral dantrolene is contraindicated in patients with active hepatic disease and muscle spasm caused by rheumatic disorders and during lactation. See Chapter 30 for information on diazepam. 

The nitrates are used cautiously in patients witii severe hepatic or renal disease, severe head trauma, acute myocardial infarction (MI), hypotiiyroidism, and during pregnancy (Pregnancy Category C, except for amyl nitrate) or lactation. 

Isozymes of Lactate Dehydrogenase Are Used to Detect Myocardial Infarctions... 

Figure 7-11. Normal and pathologic patterns of lactate dehydrogenase (LDH) isozymes in human serum. LDH isozymes of serum were separated by electrophoresis and visualized using the coupled reaction scheme shown on the left. (NBT, nitroblue tetrazolium PMS, phenazine methylsulfate). At right is shown the stained electropherogram. Pattern A is serum from a patient with a myocardial infarct B is normal serum and C is serum from a patient with liver disease. Arabic numerals denote specific LDH isozymes.

Assay of plasma enzymes aids diagnosis and prognosis. For example, a myocardial infarction elevates serum levels of lactate dehydrogenase isozyme I,. 

Appearance of creatine kinase (CK) and lactate dehydrogenase (LDH) inplasma after a myocardial infarction. 

Isoenzymes Isoenzymes are different forms of an enzyme which catalyze the same reaction, but which exhibit different physical or kinetic properties. The isoenzymes of lactate dehydrogenase (LDH) can be separated electrophoretically and can be used clinically to diagnose a myocardial infarction. 

An example of an enzyme which has different isoenzyme forms is lactate dehydrogenase (LDH) which catalyzes the reversible conversion of pyruvate into lactate in the presence of the coenzyme NADH (see above). LDH is a tetramer of two different types of subunits, called H and M, which have small differences in amino acid sequence. The two subunits can combine randomly with each other, forming five isoenzymes that have the compositions H4, H3M, H2M2, HM3 and M4. The five isoenzymes can be resolved electrophoretically (see Topic B8). M subunits predominate in skeletal muscle and liver, whereas H subunits predominate in the heart. H4 and H3M isoenzymes are found predominantly in the heart and red blood cells H2M2 is found predominantly in the brain and kidney while HM3 and M4 are found predominantly in the liver and skeletal muscle. Thus, the isoenzyme pattern is characteristic of a particular tissue, a factor which is of immense diagnostic importance in medicine. Myocardial infarction, infectious hepatitis and muscle diseases involve cell death of the affected tissue, with release of the cell contents into the blood. As LDH is a soluble, cytosolic protein it is readily released in these conditions. Under normal circumstances there is little LDH in the blood. Therefore the pattern of LDH isoenzymes in the blood is indicative of the tissue that released the isoenzymes and so can be used to diagnose a condition, such as a myocardial infarction, and to monitor the progress of treatment. 

Jaffe AS, Landt Y, Parvin CA,et al. Comparative sensitivity of cardiac troponin I and lactate dehydrogenase isoenzymes for diagnosing acute myocardial infarction. Clin Chem 42 1770-1776,1996. 

D-7) Serum LDH (lactate dehydrogenase) eleva- tion. LDH is a widespread intracellular enzyme that acts at this step. Detection of high serum levels is rather nonspecific for localizing the site of damage, but its measurement is helpful in confirming myocardial infarction or injury to the liver, skeletal muscle, or certain other tissues. The presence of 5 different isozymes of LDH helps to further localize the injury, as they are fairly tissue specific. For instance, LDj and LD2 are elevated in myocardial infarction, LD2 and LD3 elevation occur in acute leukemia LDs elevation follows liver or skeletal muscle injury. 

A 29-year-old woman took bromocriptine 5 mg/day postpartum to suppress lactation (1). Four days later she developed an acute anterior myocardial infarction. Angiography showed dissection of the left main and anterior descending arteries, with occlusion of the latter. She recovered after emergency arterial grafting. 

Dutt S, Wong F, Spurway JH. Fatal myocardial infarction associated with bromocriptine for postpartum lactation suppression. Aust NZ J Obstet Gynaecol 1998 38(1) 116-17. 

There were no differences in the activities of serum transaminases, lactate dehydrogenase, or creatine kinase in patients with myocardial infarction who received an 18-hour infusion of urokinase compared with patients who received glucose alone (38), but subacute alterations of liver function tests have been described with streptokinase and anistreplase (39). Unexplained increases in transaminase activities have been reported in almost 25% of patients treated with streptokinase (40). In view of the greater prominence of liver dysfunction with streptokinase than with alteplase it could be wiser to choose alteplase rather than streptokinase in patients with previous impaired hepatic function (41). 

E632 Jensen, A.E., Reikvam, A., NordgSrd, Pedersen, K.G. and Asberg, A. (1990). Diagnostic accuracy of Kodak creatinine kinase MB, Stratus creatine kinase MB, and lactate dehyrogenase isoenzyme 1 in serum after acute myocardial infarction. Clin. Chem. 36, 1847-1848. 

I 43. A 65-year-old obese male presents with severe indigestion and chest pain after a spicy meal. A lactate dehydrogenase (LDH) level obtained to evaluate possible myocardial infarction is normal, but the laboratory recommends that LDH isozymes be performed. The managing physician knows that lactate dehydrogenase is composed of two different polypeptide chains arranged in the form of a tetramer. Assuming that all possible combinations of the different polypeptide chains occur, how many isozyme forms of lactate dehydrogenase must be measured ... 

At present the determination of lactate does not belong to the most frequently performed analyses in clinical chemistry yet its popularity in the diagnosis of shock and myocardial infarction and in neonatology and sports medicine is increasing. Strong efforts are therefore being made to develop sensor-based lactate analyzers which may be readily used at the bedside. 

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