Classification and Management of Myocardial Ischemia

1. Binary Framework (AMIS / NAMIS)

• The 2024 Circulation guideline introduces a binary system that classifies myocardial ischemia as Acute Myocardial Ischemic Syndromes (AMIS) or Non‑Acute Myocardial Ischemic Syndromes (NAMIS), encompassing both obstructive epicardial disease and non‑obstructive mechanisms such as microvascular dysfunction, vasospasm, and other non‑coronary causes【1】【2】【3】.
• The guideline recommends abandoning the terms “chronic” or “stable” coronary syndromes because they obscure the intermediate‑to‑high cardiac event risk observed in these patients【1】【2】.

2. Acute Myocardial Ischemic Syndromes (AMIS)

2.1 Plaque‑Related Acute Coronary Syndromes

• AMIS includes acute coronary syndromes (ACS) caused by plaque rupture or erosion, which cover STEMI, NSTEMI, and unstable angina and are characterized by intraluminal thrombus formation【3】【4】.

2.2 Non‑Obstructive Acute Ischemia

• AMIS also comprises acute ischemia from non‑obstructive mechanisms, specifically:

3. Non‑Acute Myocardial Ischemic Syndromes (NAMIS)

• NAMIS replaces “chronic”/“stable” terminology because patients classified under NAMIS experience intermediate‑to‑high long‑term cardiac event rates【1】【3】.

3.1 Ischemia from Epicardial Stenoses

• Patients with flow‑limiting obstructive coronary disease require functional (e.g., stress testing) or anatomic (e.g., coronary CT angiography) evaluation to guide revascularization decisions【3】.

3.2 Ischemia with Non‑Obstructive Coronary Arteries (INOCA)

• Approximately 40 % of individuals with suspected ischemia have ≤20 % stenosis in all vessels yet demonstrate objective evidence of coronary vasomotor dysfunction or microvascular abnormalities【1】.

3.3 Myocardial Infarction with Non‑Obstructive Coronary Arteries (MINOCA)

• MINOCA denotes myocardial necrosis occurring without obstructive epicardial disease【3】.

3.4 Additional Non‑Obstructive Mechanisms

• Other contributors to NAMIS include:

4. Universal Definition of Myocardial Infarction (ACC)

• Type 1 MI – Spontaneous infarction due to atherosclerotic plaque rupture, ulceration, fissuring, erosion, or dissection with resultant thrombus【4】.
• Type 2 MI – Infarction secondary to a supply‑demand mismatch caused by conditions such as coronary endothelial dysfunction, spasm, embolism, arrhythmias, anemia, respiratory failure, hypotension, or hypertension with/without LV hypertrophy【4】.
• Type 3 MI – Cardiac death with ischemic symptoms and presumed ECG changes when biomarkers cannot be obtained before death【4】.

5. ECG‑Based Clinical Presentation (ACC)

• ST‑Elevation MI (STEMI) – Persistent ST elevation in ≥2 contiguous leads with elevated troponin, indicating complete coronary occlusion that requires immediate reperfusion【4】.
• Non‑ST‑Elevation MI (NSTEMI) – Elevated troponin without persistent ST elevation, typically reflecting partially occluded arteries and subendocardial ischemia【4】.
• Unstable Angina – Transient ischemia with reduced coronary flow but normal troponin (no necrosis)【4】.

6. Critical Clinical Pitfalls (Circulation)

• Misconception: Absence of obstructive coronary disease does not equal absence of ischemia; 60–87 % of patients with typical angina lack obstructive stenoses yet many have genuine ischemia from microvascular dysfunction or vasospasm【5】. These patients are often incorrectly reassured and discharged without appropriate evaluation or therapy【5】.
• Prognostic Language: Using “chronic” or “stable” for non‑acute ischemia misleads clinicians and patients, as these individuals still face intermediate‑to‑high cardiac event rates during long‑term follow‑up【1】【3】.
• Management of Type 2 MI: Treatment should focus on correcting the underlying supply‑demand mismatch (e.g., treating anemia, optimizing heart rate and blood pressure) rather than pursuing urgent revascularization, which is the primary strategy for Type 1 MI【4】.

7. Pathophysiologic Mechanisms (Circulation & ACC)

• Supply‑Reduction Factors contributing to myocardial ischemia include: fixed atherosclerotic stenosis, dynamic obstruction from vasospasm, platelet‑driven thrombotic occlusion, microvascular dysfunction, and coronary embolism【2】【4】【5】.

All statements are derived from cited guideline or consensus documents; evidence grades were not explicitly provided in the source material.

Acute Coronary Syndrome and Myocardial Infarction

Definition and Classification

• Acute Coronary Syndrome (ACS) is a broader term that includes Myocardial Infarction (MI) as one of its subtypes, along with unstable angina, according to the American College of Cardiology 6, 7
• MI specifically refers to myocardial necrosis in a clinical setting consistent with acute myocardial ischemia, requiring elevated cardiac biomarkers, as defined by the European Heart Journal 8, 9
• Unstable angina is defined by myocardial ischemia without detectable myocardial necrosis, with normal troponin levels, as stated by the American College of Cardiology and European Heart Journal 10, 11

Pathophysiology

• ACS is typically caused by disruption of an unstable coronary artery atherosclerotic plaque with associated partial or complete coronary thrombosis, resulting in diminished blood flow to the myocardium, according to the American College of Cardiology 6, 7
• In MI, the ischemia is severe or prolonged enough to cause myocardial cell death, detectable by elevated cardiac biomarkers, as reported by the European Heart Journal 8, 9

Diagnostic Classification

• ACS is initially classified based on ECG findings into ST-elevation ACS and non-ST-elevation ACS, as stated by the European Heart Journal 8, 11
• Further classification into unstable angina or MI depends on cardiac biomarkers, such as troponin, according to the American College of Cardiology and European Heart Journal 6, 10

Clinical Presentation

• ACS presents with a broad spectrum of symptoms, from cardiac arrest and cardiogenic shock to patients who are pain-free at presentation, as reported by the European Heart Journal 8, 9
• The hallmark symptom of ACS is acute chest discomfort described as pain, pressure, tightness, or burning, according to the European Heart Journal 8, 9

Types of Myocardial Infarction

• Type 1 MI is characterized by atherosclerotic plaque rupture, ulceration, fissure, or erosion with resulting intraluminal thrombus, as defined by the European Heart Journal 8, 9
• Type 2 MI is myocardial necrosis caused by conditions other than coronary plaque instability, such as hypotension or severe anemia, according to the European Heart Journal 8, 9

Emerging Nomenclature

• Recent guidelines propose a new binary classification of "acute myocardial ischemic syndromes" (AMIS) and "non-acute myocardial ischemic syndromes" (NAMIS) to better encompass both obstructive and non-obstructive causes of angina and myocardial ischemia, as reported by Circulation 12, 13, 14