What are the types of myocardial infarction (MI)?

Types of Myocardial Infarction

The American College of Cardiology defines five distinct types of myocardial infarction based on their underlying pathophysiology, each requiring different management approaches. 1

Type 1 MI: Spontaneous Atherothrombotic MI

• Type 1 MI results from atherosclerotic plaque rupture, ulceration, fissuring, erosion, or dissection with resulting intraluminal thrombus in one or more coronary arteries. 1
• This leads to decreased myocardial blood flow or distal platelet emboli with ensuing myocyte necrosis. 1
• Type 1 MI represents the majority of NSTEMI cases (65%-90%). 2
• This is the classic "heart attack" caused by coronary artery disease and requires immediate revascularization strategies. 3

Type 2 MI: Supply-Demand Mismatch MI

• Type 2 MI occurs when conditions other than coronary artery disease contribute to an imbalance between myocardial oxygen supply and demand. 1
• Common causes include coronary endothelial dysfunction, coronary artery spasm, coronary embolism, tachy/brady-arrhythmias, anemia, respiratory failure, hypotension, and hypertension with or without left ventricular hypertrophy. 1
• Additional causes include hypoxemia, spontaneous coronary artery dissection, and coronary microvascular dysfunction. 3
• Treatment focuses on correcting the underlying cause rather than emergent revascularization—oxygen supplementation for hypoxemia, rate control or cardioversion for tachyarrhythmias, blood transfusion for anemia. 4
• Patients with Type 2 MI have multiple comorbidities and causes of in-hospital mortality are not always cardiovascular-related. 2

Type 3 MI: MI Resulting in Death Without Biomarker Confirmation

• Type 3 MI occurs when patients suffer cardiac death with symptoms suggestive of myocardial ischemia but biomarker values are unavailable. 1, 3
• This classification is identified only after death and applies when the patient dies before blood samples can be obtained or before cardiac biomarkers rise. 1

Type 4 MI: PCI-Related MI

• Type 4a MI is associated with percutaneous coronary intervention and is defined by elevation of cardiac troponin values >5× the 99th percentile upper reference limit in patients with normal baseline values. 1
• Additional evidence is required: symptoms of ischemia, new ECG changes, angiographic complications, or imaging evidence of new loss of viable myocardium. 1
• This classification distinguishes procedural myocardial injury from clinically significant MI during PCI. 3

Type 5 MI: CABG-Related MI

• Type 5 MI is associated with coronary artery bypass grafting and is defined by elevation of cardiac biomarker values >10× the 99th percentile URL in patients with normal baseline values. 1
• Additional criteria include new pathological Q waves, new left bundle branch block, angiographic evidence of graft or native coronary artery occlusion, or imaging evidence of new loss of viable myocardium. 1
• The higher threshold (>10× vs >5× for PCI) reflects the greater expected myocardial injury from open-heart surgery. 3

Clinical Classification for Immediate Management

Beyond the pathophysiologic types, MI is also classified by ECG presentation to guide immediate treatment:

• STEMI (ST-Elevation MI) is characterized by chest discomfort and ST elevation in two contiguous leads, requiring immediate reperfusion therapy. 3
• NSTEMI (Non-ST-Elevation MI) is characterized by chest discomfort but no persistent ST-segment elevation, requiring risk stratification to determine timing of invasive management. 3
• Both Type 1 and Type 2 MI can present as either STEMI or NSTEMI, though most present as NSTEMI. 2

Critical Clinical Pitfall

It is crucial to distinguish between Type 1 and Type 2 NSTEMI early in the clinical course because they require fundamentally different treatments. 2 Type 1 requires antiplatelet therapy and revascularization, while Type 2 requires treatment of the underlying supply-demand imbalance. 4 Misclassification leads to inappropriate management—either unnecessary invasive procedures for Type 2 MI or delayed revascularization for Type 1 MI. 2

Additionally, MI may present with atypical symptoms or even without symptoms, especially in women, elderly patients, diabetics, and post-operative or critically ill patients. 1