Can Myocardial Infarction Occur in Non-Stenotic Coronary Artery Segments?
Yes, myocardial infarction absolutely can and does occur in non-stenotic coronary artery segments—this entity is formally recognized as MINOCA (Myocardial Infarction with Non-Obstructive Coronary Arteries) and accounts for 1-14% of all MI cases. 1
Definition and Diagnostic Criteria
MINOCA is defined by the presence of:
- Evidence of acute myocardial infarction with cardiac troponin elevation (≥99th percentile upper reference limit) 1
- Non-obstructive coronary arteries on angiography (defined as <50% stenosis in all epicardial vessels) 1, 2
- No clinically overt alternative diagnosis for the acute presentation 2
The demonstration of non-obstructive CAD does not preclude an atherothrombotic etiology, as coronary thrombosis is highly dynamic and the underlying atherosclerotic plaque can be non-obstructive. 1
Underlying Mechanisms
MINOCA encompasses multiple distinct pathophysiological mechanisms, which can be categorized as:
Epicardial Coronary Artery Disorders (Type 1 MI)
- Atherosclerotic plaque rupture, ulceration, fissuring, or erosion with non-obstructive or no visible CAD 1
- The plaque may appear non-obstructive on angiography but still cause thrombosis 1
- Spontaneous coronary artery dissection (SCAD), particularly common in younger women 1, 2
Supply-Demand Mismatch (Type 2 MI)
- Coronary artery spasm (vasospastic angina/Prinzmetal's angina), which can cause transient complete occlusion 1
- Spasm most commonly occurs focally and can happen even in angiographically normal segments, though these often have mural atherosclerosis on intravascular ultrasound 1
- Coronary embolism from cardiac or non-cardiac sources 1
- Coronary microvascular dysfunction (CMD), affecting small intramural resistance vessels 1, 3
Non-Coronary Causes (Myocardial Injury, Not True MI)
Clinical Significance and Prognosis
MINOCA is not a benign condition—the 1-year mortality is approximately 3.5%, with high rates of rehospitalization and significant socioeconomic burden. 1, 4, 3 The prognosis strongly depends on identifying and treating the underlying mechanism. 1
Diagnostic Approach
When coronary angiography reveals non-obstructive disease in a patient presenting with MI:
Immediately perform left ventricular angiography or echocardiography in the acute setting to assess wall motion abnormalities and exclude pericardial effusion 1, 2
Cardiac MRI should be performed within 2 weeks of symptom onset (Class I recommendation) to increase diagnostic accuracy 1, 2
Consider intracoronary imaging (IVUS or OCT) to detect overlooked plaque rupture or erosion 1, 4
Perform provocative testing for coronary vasospasm when clinically appropriate, though this is contraindicated in patients with high-grade obstructive stenosis 1, 4
Assess for coronary microvascular dysfunction through invasive or non-invasive coronary function testing 2, 3
Treatment Strategy
Treatment must be tailored to the specific underlying mechanism identified (Class I recommendation): 1, 2
- For vasospastic angina: Calcium channel blockers and nitrates are the mainstay 2
- For plaque disruption/thromboembolism: Aspirin plus consideration of dual antiplatelet therapy, though evidence is limited 2
- For coronary microvascular dysfunction: Patient-centered, mechanism-based approach targeting the specific pathophysiology 2, 3
Common Pitfalls
- Do not dismiss chest pain with non-obstructive coronaries as non-cardiac—this represents a major diagnostic error 4
- Recognize that Type 1 MI can occur with non-obstructive disease due to plaque rupture/erosion with subsequent thrombus resolution or embolization 1
- Women are disproportionately affected by MINOCA and coronary microvascular dysfunction, yet are often underdiagnosed 2
- A normal coronary angiogram does not exclude significant coronary pathology—intravascular imaging often reveals mural atherosclerosis even in "normal" segments 1