Myocardial Infarction: New Meaning, Same Name

The Third Universal Definition of Myocardial Infarction (MI), presented at the European Society of Cardiology (ESC) 2012 Congress and published in 5 international journals^a simultaneously, is the latest in a series of definitions that were first published in 2000.² This revision, an update to the 2007 definition,³ incorporates use of the new ultrasensitive troponin assays and refined imaging techniques, which can now detect ever-smaller ischemic myocardial injury.

The document also contains a new section that describes situations in which troponin levels can be elevated in myocardial injury and cell death without overt myocardial ischemia.   

•  How do we distinguish between these two situations?

•  How are novel imaging techniques improving our diagnostic accuracy?

•  And, what are the implications of this new definition for clinical care and research?

To help put the new definition into clinical context for primary care physicians, we turn to the host of CardiologyNow, Payal Kohli, MD and her guest for this podcast, Dr Yerem Yeghiazarians. Dr Yeghiazarians is Associate Professor of Medicine and Leone-Perkins Family Endowed Chair in Cardiology at the University of California, San Francisco. He is also Co-Director, Adult Cardiac Catheterization Laboratory; Director, Peripheral Interventional Cardiology Program; Director, Translational Cardiac Stem Cell Program, Cardiovascular Research Institute, Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, also in San Francisco.

^a Circulation, the Journal of the American College of Cardiology, the European Heart Journal, Global Heart, and Nature Reviews Cardiology.

To review the tables mentioned in this podcast, please see the original paper in the September 25th issue of the journal Circulation.

Table 1. Elevations of Cardiac Troponin Levels Because of Myocardial Injury

Table 2. Universal Classification of Myocardial Infarction (5 different types)

Take-home Overview

In 2000, MI was defined as any necrosis in the setting of myocardial ischemia. The 2007 update to this definition recognized that different conditions can lead to myocardial necrosis and 5  types of myocardial infarctions were defined:

      Type I: spontaneous MI

      Type II: demand event or supply/demand mismatch

      Type III: sudden death, no biomarker data available

      Type IV: peri-percutaneous coronary intervention (PCI) MI

      Type V: coronary artery bypass graft (CABG)-related MI

1. The 2012 update incorporates the more sensitive troponin assays as well as imaging studies to help distinguish myocardial infarction from myocyte injury:

      a.  Biomarkers: Because current biomarker assays are so sensitive, not every biomarker elevation is interpreted as evidence of an acute MI and may instead reflect myocardial injury or renal dysfunction.  Therefore, in general, a rise and/or fall pattern in biomarkers is needed to meet the criteria for MI. However, if a patient presents late in his/her clinical course, the biomarker levels may already be falling and therefore, non-diagnostic. In these circumstances, imaging can be used to diagnose MI (see below).

      b.  Imaging: Technological advances in imaging technologies, including echocardiogram, radionuclide, MRI and CT scans have improved the ability to apply these modalities to patients who may be presenting late with falling troponins or those who are already biomarker-negative. New loss of myocyte viability (as evidenced by myocardial contraction, the presence of fibrosis, etc.) on these modalities can now be used to diagnose MI.  Furthermore, the negative predictive value of these tests is high and can be used to rule out MI in patients who are biomarker negative.

2. This new definition is valuable because it provides improved clinical diagnostic accuracy and a standardized tool for research studies.

References

1. Thygesen K, Alpert JS, Jaffe AS, Simoons ML, Chaitman BR, White HD; Writing Group on behalf of the Joint ESC/ACCF/AHA/WHF Task Force for the Universal Definition of Myocardial Infarction. [Published online ahead of print August 24, 2012.] Circulation. http://circ.ahajournals.org/content/early/2012/08/23/CIR.0b013e31826e1058.full.pdf

2. Alpert JS, Thygesen K, Antman E, Bassand JP. Myocardial infarction redefined—a consensus document of The Joint European Society of Cardiology/American College of Cardiology Committee for the redefinition of myocardial infarction. J Am Coll Cardiol. 2000 Sep;36(3):959-69. Abstract available at: http://www.ncbi.nlm.nih.gov/pubmed/10987628

3. Thygesen K, Alpert JS, White HD; Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial Infarction.  Universal definition of myocardial infarction. Circulation. 2007;116:2634-2653. Full text PDF available at: http://circ.ahajournals.org/content/116/22/2634.full.pdf