Non-obstructive coronary arteries

Article written and reviewed by Dr Luca Moretti

Non-obstructive coronary syndromes include conditions in which angina, ischemic equivalents, or myocardial ischemia are not explained by a hemodynamically significant epicardial stenosis. The anatomical finding alone does not identify the mechanism: the lumen may appear wide while the microcirculation and vasomotion are abnormal. Coronary angiography without obstruction is therefore not equivalent to a heart free of coronary disease. Modern assessment moves beyond simply excluding stenoses to identifying a treatable functional endotype.
The terminology distinguishes ANOCA, defined by angina or equivalents in the absence of obstruction, from INOCA, in which myocardial ischemia is documented. The two sets overlap but are not synonymous: a negative or inconclusive noninvasive test does not automatically eliminate a vasomotor mechanism, while an ischemic finding requires verification of its reliability. Classification describes the diagnostic state and may change with new data. It must not be used as a definitive label before alternative causes and functionally significant epicardial disease have been excluded.

The principal mechanisms include microvascular angina, microvascular dysfunction, vasospastic angina, and endothelial dysfunction. The first and third are clinical phenotypes; the second and fourth describe physiological abnormalities that may be symptomatic, asymptomatic, or secondary to other heart disease. Spasm and microvascular dysfunction may coexist in the same patient; this distinction prevents a single laboratory result from being turned into a complete clinical diagnosis.
Recognition is important because failure to characterize the condition leads to repeated consultations, urgent visits and angiograms, impaired quality of life, and untargeted treatments. Women are highly represented, but the condition affects all sexes and must not automatically be attributed to anxiety; prognosis is heterogeneous and cannot be inferred from the percentage of stenosis alone. Ventricular function, atherosclerosis, coronary reserve, spasm, and comorbidities contribute to individual risk.

Etiology, risk factors, pathogenesis, and pathophysiology

Coronary flow must increase rapidly as heart rate, contractility, and wall tension rise; this ability depends on coordinated dilation of conductance arteries, prearterioles, and arterioles. When the response is inadequate, flow reserve falls and the myocardium may become ischemic even without focal stenosis. CFR is a ratio of hyperemic to resting flow and is affected by both terms. Low CFR alone does not identify whether the problem is epicardial, microvascular, or due to high resting flow.
Structural microvascular dysfunction includes arteriolar remodeling, medial thickening, perivascular fibrosis, and rarefaction; these abnormalities increase the minimal resistance achievable during hyperemia and limit flow distribution to the subendocardium. Hypertension, diabetes, kidney disease, and hypertrophic heart disease promote the structural phenotype. Its presence does not imply that every episode of chest pain in the patient is ischemic.

In the functional phenotype, resting resistance and resting flow may be abnormally high, leaving reduced reserve despite relatively preserved hyperemic resistance. Sympathetic activation, abnormal metabolism, and endothelial dysfunction may contribute; the distinction between structural and functional CMD is physiologically useful, but the clinical boundaries are not absolute. Invasive indices and quantitative flow measurements must be interpreted together with blood pressure, heart rate, and current therapy.
Epicardial spasm results from smooth-muscle hyperreactivity and may produce marked focal or diffuse constriction, transient ischemia, and electrocardiographic changes. Microvascular spasm reproduces symptoms and ischemic signs without epicardial constriction above the diagnostic threshold; the endothelium, autonomic nervous system, inflammation, and Rho-kinase pathway participate to varying degrees. Smoking is the modifiable factor most strongly associated with epicardial vasospasm.

The endothelium regulates tone, thrombosis, inflammation, and permeability through nitric oxide and numerous mediators. In endothelial dysfunction, acetylcholine may provoke vasoconstriction instead of dilation; clinical spasm, however, is not explained exclusively by loss of endothelial function. Smooth-muscle hypercontractility may predominate even with nonuniform endothelial responses; endothelial dysfunction and vasospastic angina must therefore not be used as synonyms.
Diffuse non-obstructive atherosclerosis may reduce dilatory capacity, alter the pressure-flow relationship, and be associated with vulnerable plaques despite the absence of severe stenoses. CCTA and intracoronary imaging show vessel-wall disease that luminography may underestimate; atherothrombotic risk depends on plaque burden and systemic factors, not merely residual diameter. Prevention is therefore calibrated to documented disease and global risk.

Hemodynamic factors may cause or amplify ischemia: anemia, tachycardia, severe hypertension, hypotension, and elevated filling pressures modify demand and perfusion. These factors do not define ANOCA or INOCA, but may unmask limited reserve; obstructive sleep apnea, obesity, and deconditioning may coexist and affect symptoms. Correcting them is part of management even when a coronary endotype has been demonstrated.
Women more often have angina without obstruction among people referred for coronary angiography, but this finding depends on selection and the prevalence of obstructive disease. Hormones, vessel size, inflammation, and the risk-factor profile may contribute without constituting a single explanation; the menopausal transition coincides with vascular and metabolic changes but is not a diagnostic criterion. Suspicion must not be reduced in men because the condition is less represented in some cohorts.

Autoimmune, inflammatory, and infiltrative diseases and cardiomyopathies may impair the microcirculation; in these cases, CMD is secondary to the substrate and treatment must include the underlying disease. Myocardial bridging may alter flow and vasoreactivity, while previous stents may be associated with segmental vasomotor dysfunction. Etiological classification distinguishes primary CMD from secondary CMD without assuming biological independence. The same physiological measurement may have different prognostic meaning in different contexts.

Pathological anatomy, classification, and progression

Epicardial arteries account for a small proportion of total resistance under normal conditions; prearterioles and arterioles regulate most of the gradient. Coronary angiography resolves the large vessels but does not directly visualize the microcirculation, which consists of segments below its resolution; a normal luminographic profile therefore does not demonstrate normal function. PET, CMR, Doppler, and invasive tests interrogate different aspects without producing direct histological images of the arterioles.
The term non-obstructive is generally applied in the absence of stenosis of 50% or greater by diameter, but anatomical percentage does not replace physiology. In intermediate lesions, FFR above 0.80 or iFR above 0.89 makes significant epicardial flow limitation in the assessed vessel unlikely; values at or below the respective thresholds instead identify ischemic physiology. Diffuse disease and a longitudinal gradient may produce ischemia without a single severe stenosis. Assessment must clarify whether the patient has purely non-obstructive disease or a mixed phenotype.

ANOCA classifies the clinical presentation, while INOCA adds objective evidence of ischemia. Definitive microvascular angina according to COVADIS requires symptoms, absence of obstruction, documented ischemia, and microvascular dysfunction; definitive vasospastic angina requires nitrate-responsive angina and spontaneous ischemic ECG changes or documented coronary spasm according to test criteria. A definitive diagnosis does not coincide with a single abnormal index. In incomplete cases, which components are present and which have not been demonstrated are stated explicitly.

Mechanistic assessment of non-obstructive coronary arteries

• Exclusion of obstructive or functionally significant epicardial stenosis.
• Documentation and characterization of symptoms compatible with ischemia.
• Investigation for objective ischemia when needed to define INOCA.
• Assessment of flow reserve and microvascular resistance.
• Vasomotor testing for epicardial or microvascular spasm in appropriate patients.
• Identification of non-obstructive atherosclerosis, myocardial bridging, and associated cardiac or systemic conditions.

Functional endotypes include reduced CFR with elevated resistance, reduced CFR with preserved resistance, epicardial spasm, microvascular spasm, and combined forms. The 2024 ESC guidelines consider CFR below 2.5 abnormal with either Doppler guidewire or thermodilution in the non-obstructive setting; the 2020 EAPCI consensus instead used the threshold below 2.0. The measurement method is decisive: the value must be interpreted as a continuous variable together with resting flow, hyperemia, medications, and signal quality. IMR of 25 or greater and HMR above 2.5 mmHg/(cm/s) indicate elevated resistance according to ESC 2024, while MRR below 2.7 is a newer and less established criterion.
Anatomical progression may include worsening non-obstructive atherosclerosis, but symptoms do not necessarily follow the same trajectory as plaque. Vasomotion and the microcirculation may improve, persist, or worsen independently of visible stenosis; clinical-anatomical discordance does not prove that pain is noncardiac. It instead calls for reassessment of the mechanism, comorbidities, and quality of previous measurements.

Repeated ischemia may contribute to diastolic dysfunction and reduced contractile reserve, but the relationship with heart failure with preserved ejection fraction is complex and bidirectional. Elevated filling pressures may in turn reduce the subendocardial perfusion gradient; low CFR is a prognostic marker in several populations without, on its own, demonstrating causality in every patient. Ventricular function and the systemic phenotype must be assessed separately.
A diagnosis of spasm may change over time with smoking, medications, autonomic activity, and control of triggers. Attacks do not necessarily leave permanent lesions, but prolonged episodes may cause myocardial infarction, arrhythmias, or sudden death; symptomatic remission does not always justify abrupt withdrawal of vasodilators. Decisions depend on initial severity, recurrences, arrhythmias, and prolonged stability.

Mixed forms often have a greater symptom burden and may require treatment combinations. A beta-blocker useful for demand and tachycardia may be unsuitable in uncontrolled epicardial vasospasm; nitrates effective on the large vessel may have a variable response in MVA. Classification helps prevent therapies that oppose the mechanism. It does not replace individual assessment of efficacy, tolerability, and adherence.
Nomenclature continues to evolve, and some studies include different populations under the same acronyms. ANOCA may include people without demonstrated ischemia, INOCA depends on the sensitivity of the test used, and CMD may also be present with obstructive coronary artery disease; every epidemiological finding must be read through the operational definition adopted. Unharmonized comparisons may overestimate differences and make percentages presented as universal inappropriate.

Clinical manifestations

The most common symptom is oppressive, constricting, or burning chest discomfort provoked by exertion, stress, or cold, but the threshold may vary. In microvascular dysfunction, recovery may be slow and pain may continue after exertion stops; the temporal profile guides assessment without identifying the endotype on its own. An atypical description does not exclude ischemia, and a typical description does not demonstrate it.
Dyspnea, fatigue, reduced exercise capacity, nausea, or epigastric discomfort may be equivalents. Symptoms are linked to concrete activities and quantified by frequency, duration, nitrate use, and limitation; the Seattle Angina Questionnaire provides a repeatable measure of health status. The CCS class describes limitation from angina but does not capture every microvascular or rest manifestation.

Vasospastic angina often occurs at rest, at night, or in the early morning, with a rapid response to nitrates and circadian variation in exercise tolerance. It may be associated with palpitations, syncope, and transient ST-segment changes; the circadian pattern is suggestive but insufficient for a definitive diagnosis. Exertional episodes may also occur with spasm, and mixed forms modify the presentation.
Migraine and Raynaud phenomenon are reported more frequently in some vasomotor populations, but are not diagnostic criteria. Gastrointestinal and musculoskeletal disorders and anxiety may coexist with a coronary cause; coexistence is more common than a dichotomy between organic and psychogenic pain. Each component is treated without invalidating symptoms or automatically attributing every episode to the heart.

Symptoms may persist after PCI because the procedure treats a stenosis but not the microcirculation, spasm, or endothelial dysfunction. Restenosis, residual lesions, and vessel physiology are assessed before further revascularization is considered. Post-PCI angina may therefore be structural, functional, or noncardiac. Repeated stents without a concordant target expose patients to complications without guaranteeing relief.
The history must identify drugs and substances capable of provoking vasoconstriction, including cocaine, amphetamines, some decongestants, triptans, and ergot derivatives. Fluoropyrimidines and other oncological treatments may induce vasomotor ischemia in specific settings; the temporal relationship with exposure is essential. Discontinuation is coordinated with the prescriber when the drug has an important indication.

New, prolonged, or rapidly worsening pain associated with severe dyspnea, diaphoresis, syncope, or instability is managed as a possible acute syndrome. A previous diagnosis of ANOCA or INOCA does not protect against thrombosis, dissection, embolism, or atherosclerotic progression; troponin distinguishes myocardial injury but does not establish its mechanism on its own. An acute event requires renewed assessment, not mere application of the chronic diagnosis.
Many patients unconsciously reduce activities and report less angina despite substantial limitation. Asking about walking distance, stairs, work, sleep, and avoided activities reveals the true burden; deconditioning further lowers the threshold and may amplify tachycardia and dyspnea. Rehabilitation must begin at a safe level, not with generic advice to exercise.

Anxiety and depression are common in chronic pain syndromes and affect quality of life, perception, and adherence. They do not automatically explain ischemia or vasomotor disorders and must not halt the pathway when suspicion is justified; mental health is assessed as a clinical comorbidity. Integrated treatment may reduce disability without replacing targeted coronary therapy.

Investigations and diagnosis

The initial assessment excludes acute coronary syndrome and urgent causes and obtains an ECG, complete blood count, kidney function, glucose, lipids, and selected parameters. Echocardiography assesses function, valves, hypertrophy, and pressures, while clinical risk guides the choice between anatomical and functional imaging; pretest probability is not nullified by sex or young age. Each examination is selected according to the diagnostic question it can answer.
CCTA reliably excludes significant stenoses when image quality is adequate and describes non-obstructive plaques, calcium, and alternative anatomy. Calcification, a high heart rate, and artifacts may make segments nonevaluable; a nonevaluable segment is not a negative result. Plaque burden contributes to prevention but does not demonstrate that pain arises from the microcirculation or spasm.

Invasive coronary angiography assesses the lumen and allows FFR or nonhyperemic indices to be measured in uncertain lesions. FFR above 0.80 and iFR above 0.89 make focal flow-limiting stenosis unlikely but do not exclude diffuse disease or microvascular abnormalities; a physiological pullback may distinguish a focal drop from a distributed gradient. The decision not to perform PCI should become the start of phenotyping, not the end of assessment.
CFR may be measured invasively with thermodilution or Doppler and noninvasively with PET, CMR, or transthoracic Doppler at experienced centers. ESC 2024 adopts CFR below 2.5 for invasive Doppler and thermodilution; the threshold below 2.0 in the 2020 EAPCI consensus remains a more restrictive and less sensitive historical reference, not a universal value applicable to every method. Global CFR integrates the epicardium and microcirculation. Blood pressure, heart rate, caffeine, medications, software, and adequacy of hyperemia may modify the result.

IMR combines distal pressure and transit time during hyperemia; a value of 25 or greater indicates elevated resistance in the 2024 ESC guidelines. HMR is derived from the ratio of distal pressure to hyperemic Doppler velocity: ESC uses a threshold above 2.5 mmHg/(cm/s), whereas the EAPCI document also reported 1.9 and emphasized the need for further validation. Normal resistance with reduced CFR may indicate high resting flow or a functional phenotype. Discordant values require physiological interpretation, not automatic binary classification.
Acetylcholine testing assesses endothelium-dependent vasoreactivity and propensity to spasm. ESC 2024 defines provoked epicardial spasm as positive when the usual pain and ischemic ECG changes accompany an angiographic reduction in lumen of at least 90%; the original COVADIS wording uses constriction greater than 90%. Symptoms and ECG changes with reduction below the threshold point toward microvascular spasm. The protocol must state doses, timing, withheld or continued medications, and control angiograms. Reproduction of pain alone without ischemic changes does not meet the spasm criterion.

Traditional stress tests may be negative when ischemia is diffuse and does not produce an evident regional gradient. Quantitative PET and perfusion CMR may detect global reductions in reserve; SPECT and stress echocardiography depend on extent, quality, and modality. A negative test reduces the probability of the phenomenon it measures, not of every functional coronary disorder. Discordance between symptoms and testing calls for reassessment of technique and alternative diagnoses.
Holter monitoring and ECG during pain are useful when vasospasm with transient changes or arrhythmias is suspected, but sensitivity is limited by the episodic nature. Negative monitoring does not exclude unrecorded attacks; documentation of transient ST-segment elevation or depression during symptoms increases the probability of ischemia. Syncope and palpitations may require more prolonged monitoring independently of angina.

The differential diagnosis includes reflux, esophageal disorders, chest-wall pain, pulmonary disease, anemia, thyroid disease, valvular heart disease, cardiomyopathies, and arrhythmias. Response to nitrates is not specific because the esophagus may also relax; an alternative diagnosis is demonstrated positively when possible. Its presence does not exclude a concomitant coronary endotype.

Treatment and prognosis

Treatment begins with a precise explanation: symptoms are recognized, obstructive stenoses have been excluded, and the mechanism remains to be identified. A written plan reduces repeat testing and defines warning signs; shared decision-making clarifies which therapies target symptoms and which target prevention. The absence of an indication for PCI does not mean absence of care.
Smoking, blood pressure, lipids, diabetes, weight, sleep, and activity are managed according to risk and documented disease. Statins and antiplatelet agents are not prescribed automatically for every case of ANOCA, but according to atherosclerosis, events, and bleeding profile; individualized prevention avoids both undertreatment and unjustified polypharmacy. ACE inhibitors or angiotensin receptor blockers may be indicated for blood pressure, kidney disease, ventricular function, and possible vascular effects.

In the phenotype with reduced CFR and elevated resistance, beta-blockers may reduce demand and prolong diastole if uncontrolled epicardial vasospasm does not coexist. Calcium channel blockers, ranolazine, and other antianginal drugs are selected according to heart rate, blood pressure, QT interval, and response; therapy for CMD has a less robust evidence base than therapy for obstructive coronary artery disease. A drug that is ineffective after an adequate trial is reassessed rather than accumulated indefinitely.
In vasospasm, calcium channel blockers are the cornerstone and may require high doses or selected combinations. Short-acting nitrates treat attacks; long-acting formulations may be added, considering tolerance and a nitrate-free interval. Nonselective beta-blockers may worsen vasoconstriction and are avoided in pure vasospasm. Smoking and vasoconstrictor substances must be eliminated through a concrete plan.

Microvascular spasm may respond to calcium channel blockers and vasodilator strategies, but response is variable. Reduced CFR with spasm often requires a carefully titrated combination; stratified therapy guided by functional testing improved angina and quality of life in the CorMicA trial. That result has not yet demonstrated a definite reduction in myocardial infarction or mortality.
Progressive aerobic exercise, adapted resistance training, and rehabilitation improve capacity, risk factors, and confidence. Intensity is calibrated to symptoms, ischemia, blood pressure, and comorbidities; the individual pattern is considered in severe vasospasm. Cardiac rehabilitation is not merely lifestyle advice. It includes education, adherence, stress management, and monitoring of functional goals.

Management of menopause, anemia, thyroid disease, sleep apnea, inflammatory diseases, and noncardiac pain may reduce the overall burden. Hormone therapy is not initiated to treat ANOCA or prevent coronary events; sleep and mental health affect symptoms and recovery. Psychological interventions are complementary, not substitutes when an ischemic mechanism has been demonstrated.
Follow-up uses symptom frequency, SAQ scores, capacity, blood pressure, adverse effects, and personal goals. Repeat tests are not automatic: they are requested when a clinical change may modify diagnosis or therapy; the therapeutic response does not retrospectively validate an uncertain diagnosis. Spontaneous improvement, placebo effects, and changes in exposure must be considered without denying perceived benefit.

Average prognosis is less favorable than in populations without coronary disease but varies considerably. Atherosclerosis, reduced CFR, ventricular function, diabetes, and kidney disease increase risk; spasm with arrhythmias or prolonged episodes requires particular attention. Absence of obstruction does not permit absolute reassurance. Balanced communication avoids both alarmism and minimization.

Complications

The most common complication is persistent symptoms with limitation, absence from work, and reduced social participation. Failure to recognize the condition may lead to repeated consultations, exposure to radiation and contrast, and fragmented care; a defined diagnostic pathway reduces uncertainty without promising complete elimination of pain. A clinical coordinator facilitates titration and interpretation of new episodes.
Ischemia and non-obstructive atherosclerosis may be associated with myocardial infarction, stroke, heart failure, and cardiovascular death, with risk depending on the phenotype; these events are not inevitable, and percentages from a cohort must not be applied automatically to an individual. Prognostic stratification integrates function, plaque, physiology, and comorbidities. Prevention is intensified when expected benefit exceeds risk.

Vasospasm may cause myocardial infarction, atrioventricular block, ventricular tachyarrhythmias, syncope, and sudden death. Greater risk is associated with multivessel spasm, previous cardiac arrest, and persistent attacks despite therapy; arrhythmia monitoring is selected according to symptoms and documentation. A defibrillator does not replace control of spasm and is considered only in selected scenarios.
CMD is associated with reduced capacity, diastolic dysfunction, and risk of heart failure with preserved ejection fraction in some cohorts. Association does not mean that every case of CMD progresses to heart failure or that normalization of an index certainly prevents its onset; the appearance of progressive dyspnea requires appropriate echocardiographic and hemodynamic assessment. Congestion, blood pressure, and rhythm are treated according to dedicated guidelines.

Unguided treatments may cause bradycardia, hypotension, edema, headache, nitrate tolerance, and QT prolongation. Multiple combinations reduce adherence and may create symptoms incorrectly attributed to the disease; medication reconciliation verifies indication, benefit, and interactions at every visit. Maximum tolerated therapy is not the same as the maximum number of drugs.
Invasive tests carry risks of arrhythmia, prolonged spasm, dissection, bleeding, and kidney injury, generally low at experienced centers but not zero. Selection avoids procedures in patients whose result would not change management; procedural safety requires protocols, monitoring, and immediate availability of nitrates and resuscitation. Consent distinguishes catheterization risks from those specific to provocation.

An incomplete diagnosis may generate two opposite errors: attributing every symptom to ischemia or declaring it noncardiac because no obstruction exists. Both may delay appropriate care and increase anxiety; critical reassessment considers new data without erasing previous work. Language distinguishes certainty, probability, and hypotheses still to be tested.
The psychological burden may include fear of exertion, depression, and loss of confidence. Mental health screening and treatment improve overall care, but must not be used to delegitimize a documented vasomotor disorder; clinical communication is part of safety. Explaining the mechanism, limits of evidence, and recurrence plan reduces the risk of abandonment or inappropriate use of emergency services.

New symptoms or a marked change require reassessment for an acute syndrome, pulmonary embolism, aortic disease, and other emergencies. Previous coronary angiography does not protect against subsequent events or exclude progression; the patient receives instructions on warning signs and nitrate use. Continuity of care must make it possible to distinguish the usual pattern from a genuinely new presentation.