Non-Ischemic Causes of Angina
Angina without oxygen deprivation occurs primarily through four mechanisms: coronary artery spasm (vasospasm), coronary microvascular dysfunction, myocardial bridging, and diffuse atherosclerosis—all of which can cause chest pain despite normal or non-obstructive coronary arteries. 1
Primary Non-Ischemic Mechanisms
Coronary Artery Spasm (Vasospastic/Prinzmetal's Angina)
This represents focal or diffuse hypercontraction of epicardial coronary arteries causing transient, reversible occlusion 2, 3:
Clinical characteristics that distinguish vasospastic angina:
- Occurs spontaneously at rest without preceding increase in myocardial oxygen demand
- Characterized by transient ST-segment elevation that resolves spontaneously or with nitroglycerin
- Episodes cluster with prolonged asymptomatic periods (weeks to months)
- Circadian pattern with most attacks in early morning hours
- Exquisitely responsive to nitroglycerin 2, 3
Triggers include:
- Emotional stress
- Hyperventilation
- Exercise (paradoxically)
- Cold exposure 3
Associated conditions:
- Migraine headaches
- Raynaud's phenomenon
- Other vasospastic disorders 3
Important caveat: Even angiographically normal coronary segments often have mural atherosclerosis on intravascular ultrasound, causing localized endothelial dysfunction that predisposes to spasm 2, 3.
Coronary Microvascular Dysfunction (CMD)
Heightened sensitivity of the coronary microcirculation to vasoconstrictor stimuli combined with limited microvascular vasodilator capacity causes microvascular angina 1, 4. This involves:
- Dysfunction of endothelial cells in the microvascular network (likely from increased oxidative stress and inflammation)
- Mismatch between metabolic signaling and microvascular adaptation
- Enhanced smooth muscle reactivity in resistance vessels 4
Myocardial Bridging
Compression of epicardial coronary arteries during systole when they tunnel through myocardium, causing dynamic obstruction 1.
Diffuse Atherosclerosis
Non-focal disease that doesn't create discrete obstructive lesions but impairs coronary flow reserve 1.
Pathophysiological Mechanisms
The underlying defect in vasospasm involves dysfunctional endothelium that exposes medial smooth muscle to vasoconstrictors (catecholamines, thromboxane A2, serotonin, histamine, endothelin) 3. Additional mechanisms include:
- Impaired coronary flow-dependent vasodilation from decreased nitric oxide production
- Imbalance favoring vasoconstrictor factors (endothelin, angiotensin II) over vasodilators (prostacyclin, nitric oxide)
- Autonomic nervous system involvement with reduced parasympathetic tone and enhanced alpha-adrenergic receptor reactivity 3
Diagnostic Approach
For suspected vasospasm, diagnostic investigation must document transient myocardial ischemia and ST-segment elevation during chest pain (Class I recommendation) 2, 3.
Coronary angiography is recommended in patients with episodic chest pain accompanied by transient ST-elevation (Class I) 2, 3.
The 2024 ESC guidelines now emphasize invasive coronary function testing (CFT) should be available at initial coronary angiography when mechanisms of chest pain are uncertain after non-invasive testing 1. This represents a major shift toward mechanism-based diagnosis.
Provocative testing may be considered in patients with no significant angiographic CAD and no documented transient ST-elevation when symptoms possibly explained by coronary spasm are present (Class IIb) 2, 3. However, provocative testing is contraindicated in patients with high-grade obstructive stenosis (Class III) 2, 3.
Treatment Implications
Treatment with nitrates and calcium channel blockers is recommended for variant angina with non-obstructive coronary lesions (Class I) 2, 3. This contrasts sharply with typical exertional angina where beta-blockers are first-line.
Critical pitfall: Beta-blockers can worsen vasospastic angina by allowing unopposed alpha-adrenergic vasoconstriction and should be avoided 5, 6.
The 2024 ESC guidelines emphasize patient-centered, mechanism-based treatment guided by CFT results to improve symptoms and quality of life 1. This means identifying the specific endotype (epicardial spasm, microvascular spasm, or microvascular dysfunction) before selecting therapy.
Clinical Significance
Most attacks resolve spontaneously without MI, but prolonged vasospasm can cause MI, high-degree AV block, life-threatening ventricular tachycardia, or sudden death 3. Patients with atherosclerotic lesions are at higher risk and require aggressive risk factor modification 2, 3.
The key distinction from typical ischemic angina: these patients have normal exercise tolerance, negative stress testing, and angina at rest without precipitating causes—yet they have genuine myocardial ischemia requiring specific vasodilator therapy rather than anti-ischemic therapy aimed at reducing oxygen demand 3.