Troponin T - contemporary approach towards diagnosing acute myocardial ischemia

T. A. Dezhinova

Leningrad Regional Bureau of Forensic Medical Examination

Saint Petersburg, Russia

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Introduction. The urgency of the problem to diagnose the acute ischemic disease including the acute myocardial infarction is obvious to every general practitioner. It is intensified with the fact that until very recently not a single known method has guaranteed any reliable diagnostics. For example, up to 25% of all the acute myocardial infarctions do not cause any changes in ECG and from 20 to 30% of them do not display any aching attack, especially with older people as well as those suffering from diabetes and hypertension.

It is necessary to search for new forensic medical criteria proceeding from the practical experience of forensic medical examination when it is sometimes quite difficult to establish that death occurred as the result of the acute myocardial ischemia and to make a differential diagnostics. Histological methods alone cannot always supply convincing diagnostic criteria in case of death 12 hours after the onset of a heart attack as micro morphological characters develop 12 to 24 hours after the onset of the attack.

Materials and methods. We have researched a possibility to apply the Enzyme Multiplied Immunoassay Technique (EMIT-test) for Troponin T to diagnose death resulting from the acute myocardial ischemia in the biological laboratory of the Leningrad Regional Bureau of Forensic Medical Examination.

The EMIT-test for Troponin T - a protein of the myocardial troponin complex - is nowadays of the great diagnostic value. The test was developed in 1991. It has a unique amino acid structure differing from that of the troponin in cross-striated muscles. It is peculiar of Troponin T that it is present in cardiomyocites in two fractions: free in cytozole and in the composition of the contractile fibres. Therefore, when myocardium is damaged, the cytozolic fraction is the first to disengage making the first peak of the Troponin T concentration increase in blood; then the second, the slower fraction starts disengaging itself. It means that Troponin T lends itself most widely for a diagnosis uniting the advantages of the quick and slow markers with the acute myocardial ischemia. Troponin T appears in blood a little earlier that CK-MB, two and a half hours after the onset of the heart attack, reaches its maximum in 8-10 hours (the first peak) and in 3-4 days (the second peak), and its level becomes standard in 10-14 days. Compare: CK-MB appears in blood three hours after the onset of the heart attack, reaching its maximum in twelve hours. The level of the ferment activity usually becomes standard in 72 hours.

Studies of the test undertaken in American and European hospitals have testified that Troponin T is diagnostically the most efficient one at present. This method is much more sensitive than CK-MB-mass method: about 60 per cent in three hours after the onset of the heart attack and up to 100 per cent in ten hours. The greatest advantage of Troponin T is its unique specificity that is close to 100 per cent.

The standard level of Troponin T must be close to zero because it should not get into the blood flow with healthy people.

Since 1995, Boehringer Mannheim has suggested the express diagnostics to define the quality of Troponin T. The result is obtained in 20 minutes, and the method does not require any special equipment. Bilirubin and lipemia do not prevent testing. Hemoglobin of up to 200 mg/dl does not affect the testing either.

Boehringer Mannheim diagnostic test systems have been used in the course of our work, following the instructions of the manufacturer.

We have examined eight cases (a control group) of instant death resulting from traffic accidents. Troponin T was absent in all the cases. Besides, there have been tested 24 cases where a differential diagnostics was required.

Cadaver blood was extracted from femoral veins during the first 24 hours after death.

The results of the biochemical analyses and the conclusions based on the biochemical tests have been compared with the final forensic medical diagnosis and histological data. The provisional biochemical diagnosis and the forensic medical diagnosis entirely coincided in 16 cases. The histological data have confirmed the conclusions of the analyses for Troponin T. The presence of Troponin T has been revealed in cadaver blood in all these cases.

Case histories. Example 1: Ms. G., born in 1976, fell down from a horse and instantly died. Troponin T revealed a sharply positive reaction. Histological data: dilatory myocardiopathy - dilation of the heart cavities, flabby and dull heart muscles. Conclusion: death resulted from dilatory myocardiopathy complicated with acute cardiovascular insufficiency. The trauma had nothing to do with the death cause.

Example 2: Mr. B., born in 1997, was found lying at his working place. Troponin T was revealed in blood. Histological data: multiple contractures of the heart muscular fibers of the second and third rate, marked cytoplasm fuchsinophilia and arteriole spasm; coronaritis, medium and small coronary artery branch sclerosis; moderate vascular myocardiosclerosis; focal myocardiocyte hypertrophy; plastic (contractile) myocardial insufficiency. Conclusion: death resulted from the disease - chronic coronaritis of the coronary arteries complicated with acute contractile myocardial insufficiency.

Example 3: Mr. P., born in 1948, came to otolaryngologist where he fell down and died. There was a sharply positive reaction of Troponin T. Histological data: some intramural artery sclerosis, small focal cardiosclerosis, focal hypertrophy of cardiomyocytes, myocardial stroma edema, leuco-lymphocytic cells close to vascular walls in one part of the myocardium, focal myocardial fragmentation, contractured changes in cardiomyocytes, parenchymal dystrophy of the myocardium, and uneven vascular blood flow. Conclusion: chronic myocardial ischemia, myocardial infarction.

Example 4: Ms. A., born in 1979, died at home before the arrival of an ambulance. The circumstances are not known. She was not registered at her local policlinics as having a special disease. The etiology of the coma is not clear. Histological data: brain plethora with tiny perivascular hemorrhages of the lungs, lever, kidneys, adrenal glands, and pancreas. Slightly marked pulmonary and brain edema. The beginning stage of bronchopneumonia with leukocytic exudates; spasms and anemia of cardiac vessels. Forensic biochemical examination: Troponin T - negative reaction. Urea in blood - 13.7 m mole/l (2.5-8.3 m mole/l standard); creatinine in blood - 212 micro mole/l (up to 133 micro mole/l standard); glucose in blood - 17.3 m mole/l (3.3-5.5 m mole/l standard); glycosylised hemoglobin - 12.2 p.c. (4.5-6.5 p.c. standard). The increase of the glucose and glucosylised hemoglobin can be connected with the discrete or beginning diabetes mellitus. Conclusion: death resulted from the disease - diabetes mellitus followed by the development of hyperglycemic coma.

The last example is of a particular interest not only because the diagnosis of the ischemic disease was excluded (no Troponin T was found in blood), but also because the biochemical blood test (both glucose and glucosylised concentrations were revealed) made it possible to diagnose correctly diabetes mellitus followed by the hyperglycemic coma.

Forensic medical experts have made a different diagnosis as the final one in five cases following the microscopic data despite the fact that the biological tests indicated myocardium damages. However, the histological analyses have confirmed the competence of the conclusions from the biological tests: in each of the cases, there were marked cardiac muscle damages (myocardium dystrophy and cardiosclerosis).

The results of the biochemical examination were doubtful in two out of three cases, where the biochemical data differed from the morphological characters of myocardial ischemic disease (no Troponin T was found), because it was carried out long after the death had occurred. And in one case, the death was caused by a congenital heart disease, which did not contradict the negative biochemical results.

Conclusions. It is for the first time that a biochemical examination of cadaver blood, used with the aim of diagnosing myocardium ischemic damages by means of the EMIT-test for Troponin T, enables one to draw authentic conclusions about the death cause. The diagnostic efficiency of the method for the cadaver blood has turned out to be 87.5 per cent. It is quite a good ground to recommend the biochemical analyses as a provisional springing express-test that facilitates the choice of the best possible ways for any further histological examinations.

References