Types of Myocardial Ischemia
Myocardial ischemia should be classified using the new binary system of Acute Myocardial Ischemic Syndromes (AMIS) and Non-Acute Myocardial Ischemic Syndromes (NAMIS), which encompasses both obstructive epicardial coronary disease and non-obstructive mechanisms including microvascular dysfunction, vasospasm, and other non-coronary causes. 1
Primary Binary Classification
The 2024 Circulation guidelines propose abandoning outdated terminology like "chronic" or "stable" coronary syndromes in favor of a comprehensive framework that recognizes the full spectrum of ischemic mechanisms 1:
Acute Myocardial Ischemic Syndromes (AMIS)
AMIS encompasses all acute presentations of myocardial ischemia, subdivided into: 1
Acute Coronary Syndromes (ACS) from plaque rupture/erosion - This includes STEMI, NSTEMI, and unstable angina caused by atherosclerotic plaque disruption with intraluminal thrombus formation 1, 2, 3
Non-obstructive causes of acute ischemia including: 1
- Coronary dissection
- Epicardial coronary spasm
- Coronary embolism
- Microembolization
- Microvascular spasm
- Hypercoagulable states
Non-Acute Myocardial Ischemic Syndromes (NAMIS)
NAMIS replaces the misleading terms "chronic" or "stable" because these patients carry intermediate-to-high cardiac event rates and substantial residual prognostic risk 1. NAMIS includes: 1
Ischemia from epicardial coronary stenoses - Flow-limiting obstructive coronary disease requiring functional or anatomic testing to guide revascularization decisions 1
Ischemia with Non-Obstructive Coronary Arteries (INOCA) - Nearly 40% of patients with suspected ischemia have <20% stenosis in all vessels, yet demonstrate objective evidence of coronary vasomotor dysfunction or microvascular abnormalities 1
Myocardial Infarction with Non-Obstructive Coronary Arteries (MINOCA) - Myocardial necrosis occurring without obstructive epicardial disease 1
Additional non-obstructive mechanisms: 1
- Epicardial spasm
- Myocardial bridges
- Microvascular dysfunction (impaired dilation)
- Extramural microvascular compression
Traditional Classification by Myocardial Infarction Type
The Universal Definition of MI provides a mechanistic classification that complements the AMIS/NAMIS framework 2:
Type 1 MI - Spontaneous MI from atherosclerotic plaque rupture, ulceration, fissuring, erosion, or dissection with resulting intraluminal thrombus 2, 3
Type 2 MI - MI secondary to ischemic imbalance where conditions other than CAD contribute to supply-demand mismatch (coronary endothelial dysfunction, coronary spasm, coronary embolism, arrhythmias, anemia, respiratory failure, hypotension, hypertension with or without LVH) 2, 4
Type 3 MI - Cardiac death with ischemic symptoms and presumed new ECG changes but death occurring before biomarkers could be obtained 2
Clinical Presentation-Based Classification
For immediate triage and treatment decisions, maintain the ECG-based distinction 3, 5:
ST-Elevation MI (STEMI) - Persistent ST elevation in two contiguous leads with elevated troponin, indicating complete coronary occlusion requiring immediate reperfusion 2, 5
Non-ST-Elevation MI (NSTEMI) - Elevated troponin without persistent ST elevation, typically from partially occluded coronary artery causing subendocardial ischemia 2, 5
Unstable Angina - Transient myocardial ischemia with reduced coronary flow but without myocardial necrosis (normal troponin) 2, 5
Critical Clinical Pitfalls
The most dangerous misconception is equating "no obstructive coronary disease" with "no ischemia." Studies show that 60-87% of patients with typical angina do not have obstructive coronary stenoses, yet many have genuine myocardial ischemia from microvascular dysfunction or vasospasm 1. These patients are frequently falsely reassured and discharged without appropriate evaluation or treatment 1.
Avoid using terms like "chronic" or "stable" when discussing non-acute ischemia, as these convey a misleading sense of benign prognosis when patients actually face intermediate-to-high cardiac event rates during long-term follow-up 1.
Type 2 MI requires fundamentally different management than Type 1 MI - focus on correcting the underlying supply-demand mismatch (treating anemia, controlling heart rate, managing blood pressure) rather than pursuing urgent revascularization 2, 4.
Pathophysiologic Mechanisms
Myocardial ischemia results from an imbalance between oxygen supply and demand through multiple mechanisms 1, 2:
Supply reduction: Fixed atherosclerotic stenosis, dynamic coronary obstruction from vasospasm, platelet aggregation promoting thrombotic occlusion, microvascular dysfunction, coronary embolism 1, 6
Demand increase: Elevated heart rate, increased contractility, increased left ventricular wall stress 7
Mixed mechanisms: Most patients have superimposition of increased demand on decreased supply, particularly common in unstable presentations 8