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Definition
1 - By the clinical exam achieved by the physician The BP is first high; it goes down thereafter to lower values than the subject’s normal values. A tachycardia is frequent in the beginning. But it is especially the pain in the chest that orients the physician; he will very quickly have an electrocardiogram achieved. 2 - The electrocardiogram a - Succession of the signs of the electrocardiogram Positive gigantic long T waves quickly replaced by an over-gap of the dome ST segment (Pardee’s waves).
Electrocardiogram of an infarct in way
of constitution. Occurrence between the 12th and the 36th hour, sometimes more precociously, of the Q wave, corresponding to a necrosis wave. Progressive reduction of the over-gap of the ST segment and negativisation of the T wave. In the scarstage, only the Q wave and the sub-epicardic ischemia persist (negative T waves). The slow or fast evolution of the electrocardiogram modifications has a prognosis indication: the fast apparition of the Q wave is a bad prognosis indicating the cardiac cells death; conversely, the fast reduction of the over-gap and the negativisation of the T wave is a good prognosis translating a precocious reperfusion of the heart muscle. b - Diagnosis of the localization of the infarct:
According to the localization of the heart artery that is blocked, 3 topographies of myocardial infarction roughly exist: the previous infarcts, the lower infarcts and the infarcts of the heart lateral wall. The association of a chest pain and of characteristic modifications of the electrocardiogram is sufficient to make the myocardial infarction diagnosis (90% reliability) and to transport the patient immediately toward a cardiology intensive care unit. 3 - The biologic exams The dosage of the enzymes of the heart muscle possesses both a diagnosis and prognosis value: CPK-MB (creatine-phospho-kinase, enzymes secreted by the cells of the heart muscle when they die) are very specific, including an elevation from the 3rd or 4th hour on with a normalization toward the 36th hour. This dosage is less and less often carried out for the benefit of the Troponin I dosage. Troponin I is a specific enzyme of the myocardium, and its rise is very precocious (the most precocious of the enzymes). Unfortunately, its specificity is not always very good, which means that when this enzyme is high, it does not always prove the existence of a myocardial infarction. Myoglobin is also an enzyme rising quickly during the myocardial infarction, but it is not specific of this affection. Transaminases (ASAT and ALAT, also secreted if a muscle dies) rise toward the 36th hour and become normal within 4 to 6 days. Finally, the rise of the LDH comes later but lasts more and sometimes permits a retrospective diagnosis. File last modified on july 24, 2006 |
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HOW
TO MAKE THE DIAGNOSIS OF A MYOCARDIAL INFARCTION?
Informations
on Heart & Vessels are only given by doctors who are specialized
in cardiology.