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Universal definition of acute myocardial infarction - what needs reconsideration?

Acute Coronary Syndromes

The global MI task force for the universal definition representatives presented ongoing areas of controversy and confusion under the guidance of two of the co-chairs of the task force, Drs. Thygesen and Alpert. There were four presentations.

The classification of acute MI type 2: A knotty problem, by Professor Harvey White (also a co-chair of the task force) of Auckland, New Zealand. The current concept and definition of type 2 MI was reviewed. Dr. White pointed out a number of areas of widespread clinical uncertainty related to this specific entity. He emphasized the need for clinical judgment in determining which patients truly had elevated blood troponin as the result of atherosclerotic coronary arterial ischemic myocardial necrosis, and which patients had not had a true type 2 MI, but rather had elevated blood troponin levels secondary to myocardial necrosis caused by disease states other than coronary artery disease.

He made his case with two clear cut patient examples, one of whom was a young girl with a rapid supraventricular tachycardia and secondary elevation in blood troponin values. The second case involved a 70 year old man with a history of atherosclerotic coronary artery disease and respiratory failure complicated by hypotension, tachycardia, and hypoxemia. This patient also had elevated blood troponin values. Dr. White suggested on behalf of the task force that the first patient had not had a type 2 MI while the second patient did, indeed, manifest a type 2 MI. He then argued for careful clinical consideration combined with clinical judgment in the adjudication of patients who are less clear cut compared with the examples given and have an elevated blood troponin level truly representing a type 2 MI.

Ways acute MI can mimic other diseases – a plea for the use of imaging techniques, by Dr. Nina Ajmone Marsan, of Leiden, The Netherlands, who replaced Dr. Jeroen Bax. Dr. Ajmone presented three patient examples involving individuals in whom the clinical presentation was highly suggestive of acute MI but in whom subsequent multimodality non-invasive evaluation with echo, MR, and CT demonstrated the correct alternative diagnostic entity. One patient had suffered a type 1 aortic dissection, a second patient had acute myocarditis, and the third patient had suffered stress related myocardial necrosis, the apical ballooning syndrome. Dr. Ajmone emphasized the importance of distinguishing these entities from acute MI since the therapies involved would be quite different.

Are the Myocardial Infarction Criteria After Interventional Procedures Adequate? By Professor Allan Jaffe of the Mayo Clinic, Rochester, Minnesota. Professor Jaffe discussed the criteria for PCI-related acute MI. He pointed out the relative paucity of data related to the recommended criteria. These criteria require a normal baseline value for troponin. In most studies, the baseline troponin values were not normal as defined by the global task force; i.e., less than 99% of a normal upper reference limit. Indeed, it is when the baseline value for blood troponin is above this value that post-PCI values can be markedly elevated.

Dr. Jaffe presented data supporting the idea that when baseline troponin values are below the 99% upper reference limit that subsequent elevations in troponin or CK-MB are minimal and are not related to short or long-term prognosis. Thus, the diagnosis of acute MI can be made, but should not be used to infer an adverse prognosis or to modify therapy. Dr. Jaffe also suggested the need to re-evaluate prior studies based on the diagnosis of post-PCI myocardial necrosis.

The problem of being rational about the use of 99% and 10% variation coefficient for troponin determination for the cut-off limit for the diagnosis of acute MI, by Professor Bertil Lindahl. In this talk, Prof. Lindahl pointed out that the use of 99% of the reference value for blood troponin determination was a statistically defined cut off reference point, which varies from assay to assay because of inadequate quality control of the screening for normal subjects. He further emphasized the point that an elevated blood troponin level was not synonymous with the presence of an acute MI. Indeed, there are multiple entities that can result in myocardial necrosis in the absence of atherosclerotic coronary disease. He further supported the recent task force document from the biochemistry working group pointing out that modest increases in imprecision of blood troponin determinations do not cause false positive clinical results. However, they do increase the magnitude of change necessary to define a rising or falling pattern of blood troponin values.




Universal definition of acute myocardial infarction - what needs reconsideration?
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.