The concept and definition of myocardial infarction has long been accepted by consensus.
The World Health Organization defined acute myocardial infarction (AMI) from symptoms, ECG abnormalities and enzymes. More recently, however, the development of more sensitive and specific biomarkers and imaging techniques have allowed the detection of smaller or minor amounts of myocardial necrosis. The introduction of troponins into our current practice has also allowed a more precise definition of MI, even in patients with normal CPK, the traditional marker for the diagnosis.
In 1999 the ESC and ACC jointly re-examined the definition of AMI, taking in account the role of the new biomarkers and produced a consensus document which was published in 2000.
Given the considerable advances in the management of AMI since then, the ESC, ACC and American Heart Association joined the World Heart Federation in a Global Task Force - composed of experts in the fields of biomarkers, ECG, imaging, intervention and clinical investigation - to produce a new updated consensus document. This was published in 2007 - and reviewed in a Guidelines Symposium on Sunday.
The new definition they developed is now based on the evidence of myocardial cell death detected by different techniques and tools. A new classification was also introduced, incorporating our knowledge about myocardial revascularisation. Six types of AMI were classified:
- Type 1. Spontaneous AMI due to a primary coronary event
- Type 2. Secondary AMI due to an imbalance between supply and oxygen demand
- Type 3. Sudden unexpected cardiac death with accompanying signs of ischemia or fresh thrombus in a coronary artery
- Type 4a. AMI associated to PCI
- Type 4b. AMI associated to documented stent thrombosis
- Type 5. AMI associated to CABG
The new document extensively reviews the contribution of the different techniques for the diagnosis of AMI (ECG, biomarkers, and imaging), addressing some difficult issues such as the diagnosis in patients with previous AMI or reinfarction. 
One remarkable contribution covers the definition of AMI in the setting of revascularisation (CABG or PCI) with a particular emphasis on stent thrombosis. Despite pending further data and by arbitrary convention, the document established increases of biomarkers more than three times the 99th percentile URL for PCI and five times the 99th percentile URL for CABG as myocardial infarction.
These changes in the definition of myocardial infarction will have a substantial impact on clinical practice, clinical research and epidemiological data. The new document represents an important steep ahead in our knowledge in the field of coronary atherosclerosis.
Find the Guidelines here.