Myocardial infarctions can be classified into various types based on pathology, clinical presentation, prognostic and treatment strategies. One method of classifying MI’s is the “Third Universal Classification of Myocardial Infarction”:

• Type 1 – Spontaneous MI: (top left corner) related to atherosclerotic plaque rupture, ulceration, fissuring, erosion or dissection with resulting intraluminal thrombus in 1 or more coronary arteries leading to decreased myocardial blood flow or distal emboli resulting in myocyte necrosis.
• Type 2 – MI secondary to an ischemic imbalance: (top right corner) condition other than coronary artery disease causes an imbalance between myocardial oxygen supply and/or demand. Examples: coronary artery spasm, embolism, brady and tachy arrhythmias, respiratory failure, anemia, hypotension, hypertension…
• Type 3 – MI resulting in death when biomarkers unavailable: (broken heart near the bottom left with no escaping trops) cardiac death suggestive of MI but death occured before blood samples obtained or before cardiac biomarkers could rise
• Type 4 – There are two different Type 4s, a – MI related to PCI and b – MI related to stent thrombosis (represented by the stent with a thrombus inside on the bottom left)
• Type 5 – MI associated with coronary artery bypass graft: represented by the cabbage in the bottom right

Why it is called the “Third” universal classification of MI? I am not quite sure, but the article  “Third universal definition of myocardial infarction” [1] explains:

“In 2000, the First Global MI Task Force presented a new definition of MI, which implied that any necrosis in the setting of myocardial ischaemia should be labelled as MI.¹ These principles were further refined by the Second Global MI Task Force, leading to the Universal Definition of Myocardial Infarction Consensus Document in 2007, which emphasized the different conditions which might lead to an MI.² This document, endorsed by the European Society of Cardiology (ESC), the American College of Cardiology Foundation (ACCF), the American Heart Association (AHA), and the World Heart Federation (WHF), has been well accepted by the medical community and adopted by the WHO.³ However, the development of even more sensitive assays for markers of myocardial necrosis mandates further revision, particularly when such necrosis occurs in the setting of the critically ill, after percutaneous coronary procedures or after cardiac surgery. The Third Global MI Task Force has continued the Joint ESC/ACCF/AHA/WHF efforts by integrating these insights and new data into the current document, which now recognizes that very small amounts of myocardial injury or necrosis can be detected by biochemical markers and/or imaging.”

References:

1. Kristian Thygesen, Joseph S. Alpert, Allan S. Jaffe, Maarten L. Simoons, Bernard R. Chaitman and Harvey D. White.”Third universal definition of myocardial infarction”.  http://www.world-heart-federation.org/fileadmin/user_upload/documents/Publications/ThirdUniversalDefinitionMI2012.pdf