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INOCA and special ischemic phenotypes

TL;DR — Ischemia with non-obstructive coronary arteries (INOCA) is an umbrella, not a negative angiogram. Endotypes include impaired coronary flow reserve, increased microvascular resistance, microvascular spasm, epicardial vasospasm, and non-coronary mimics; they can coexist (Kunadian 2020, PMID 32626906). Reduced coronary flow reserve predicts adverse outcomes across populations (Kelshiker 2022, PMID 34849697). CorMicA showed that invasive coronary-function testing linked to endotype-specific therapy improved angina and quality of life, establishing clinical utility for diagnosis even without a completed hard-outcome trial (Ford 2018, PMID 30266608). Vasospastic angina requires standardized nitrate-responsive symptom, ECG, and provocation criteria (Beltrame 2017, PMID 26245334). Women are disproportionately affected and have often been mislabeled as having non-cardiac symptoms; non-obstructive disease is not benign (Grant 2024, PMID 38548464).

Terminology

Term Definition What it does not mean
INOCA Ischemia with no obstructive epicardial CAD “No coronary disease”
ANOCA Angina with no obstructive CAD Objective ischemia already proven
Microvascular angina Symptoms/ischemia attributable to coronary microvascular dysfunction One uniform mechanism
Vasospastic angina Transient epicardial spasm causing ischemia Fixed stenosis
MINOCA MI criteria with no obstructive coronary lesion and no immediately obvious alternative Final diagnosis
Type 2 MI Ischemic injury from supply–demand imbalance Necessarily normal coronaries

MINOCA and INOCA overlap but are not synonyms: MINOCA begins with an acute MI syndrome and demands mechanism finding; INOCA usually describes chronic ischemic symptoms (Parwani 2023, PMID 37067753).

Coronary microvascular dysfunction

Coronary microvascular dysfunction (CMD) can result from structural remodeling, endothelial dysfunction, impaired vasodilation, increased resting flow, extravascular compression, or microvascular spasm. The same CFR value can therefore arise through different combinations of flow and resistance (Kei 2023, PMID 37511046).

Test Abnormality sought Main limitation
PET myocardial blood flow/CFR Global or regional flow reserve Radiation, access, thresholds vary
Stress CMR Perfusion reserve and scar Access, analysis, contraindications
Doppler echo CFR LAD flow reserve Operator and acoustic-window dependence
Invasive CFR Vasodilator reserve Influenced by resting flow and epicardial disease
IMR Hyperemic microvascular resistance Invasive; pressure/temperature assumptions
Acetylcholine testing Epicardial or microvascular spasm/endothelial response Requires protocol, expertise, rescue capability

Meta-analysis links lower CFR with mortality and cardiovascular events, but thresholds and measurement platforms differ (Kelshiker 2022, PMID 34849697). Earlier meta-analysis similarly found endothelial and microvascular dysfunction prognostic in normal/non-obstructive angiography (Brainin 2018, PMID 29407076).

Diagnostic endotypes

Endotype Typical invasive pattern Treatment logic
Structural CMD Reduced CFR, elevated IMR Risk-factor treatment; beta-blocker/ACEi/statin; symptom agents
Microvascular spasm Symptoms/ischemic ECG with acetylcholine, no epicardial ≥90% spasm Calcium-channel blocker; nitrate response variable
Epicardial vasospasm ≥90% constriction plus symptoms and ischemic ECG Calcium-channel blocker and nitrates; avoid triggers
Mixed CMD + spasm Both physiology and provocation abnormal Combined individualized therapy
Non-coronary chest pain Normal function testing and alternative evidence Avoid repeated coronary procedures; pursue cause

The COVADIS criteria standardize microvascular angina and vasospastic angina to reduce incompatible research populations (Ong 2018, PMID 29031990; Beltrame 2017, PMID 26245334).

CorMicA: testing changes treatment

CorMicA randomized patients without obstructive disease to disclosure of invasive function-test results with stratified therapy versus blinded usual care. The intervention improved angina and quality of life at 6 months (Ford 2018, PMID 30266608).

CorMicA was not powered to show fewer MI or deaths. Its contribution is proof that a mechanistic diagnosis can improve symptoms and reduce diagnostic ambiguity.

CorMicA lesson Boundary
A normal angiogram does not complete the evaluation Not every patient requires invasive testing
Endotype-linked treatment improves symptoms Hard-outcome benefit is unproven
Spasm and CMD can coexist Single-label algorithms may fail
Diagnostic disclosure can validate illness Expectation effects remain possible in unblinded care

Vasospastic angina

International criteria require nitrate-responsive angina, transient ischemic ECG changes, and documented coronary spasm for a definitive diagnosis; suspected disease can be classified when components are incomplete (Beltrame 2017, PMID 26245334).

Episodes often occur at rest and can produce MI, syncope, ventricular arrhythmia, or sudden death. Calcium-channel blockers are central; long-acting nitrates are commonly added. Nonselective beta-blockade can worsen some spasm phenotypes, and smoking is an important modifiable trigger (Jenkins 2024, PMID 38343041).

Women and diagnostic inequity

Women are more likely than men to have angina/ischemia without obstructive lesions and are overrepresented in microvascular and vasomotor research (Grant 2024, PMID 38548464). Sex and gender affect referral, symptom interpretation, risk-factor exposure, and outcomes (Regitz-Zagrosek 2023, PMID 36316574).

The unsafe inference “non-obstructive = non-cardiac” can produce repeated emergency visits, inappropriate reassurance, and delayed risk-factor treatment. Conversely, labeling every symptom as CMD without objective testing can also cause overtreatment.

MINOCA: a working diagnosis

After angiography shows no obstructive culprit in a patient meeting MI criteria, evaluation may identify plaque disruption/erosion, spasm, embolism, spontaneous dissection, microvascular dysfunction, myocarditis, Takotsubo syndrome, or non-ischemic injury (Parwani 2023, PMID 37067753).

Test Candidate mechanism
CMR Infarction pattern, myocarditis, Takotsubo
OCT/IVUS Plaque disruption, thrombus, dissection
Provocation testing Epicardial/microvascular spasm
Echo/ventriculography Wall-motion and structural complications
Rhythm/embolic evaluation Coronary embolism source

Secondary prevention should be mechanism-specific where evidence permits; universal DAPT or statin conclusions cannot be assumed for myocarditis or Takotsubo.

Therapy by mechanism

Phenotype Common therapeutic direction Evidence gap
Reduced CFR/high IMR Statin/ACEi risk treatment, beta-blocker, ranolazine selectively Hard outcomes and comparative symptom efficacy
Epicardial spasm CCB, nitrates, smoking cessation Optimal refractory strategy
Microvascular spasm CCB; individualized nitrates/other antianginals Few adequately powered RCTs
Refractory microvascular angina Multidisciplinary symptom and risk management; trials Device and drug efficacy
MINOCA Treat identified mechanism Many mechanisms lack RCTs

Live ClinicalTrials.gov queries verified COSIMA for refractory microvascular angina (NCT04606459; recruiting, 144 estimated), a reducer study in INOCA/CMD (NCT05492110; active, 54 actual), and ExINOCA exercise training (NCT06529848; recruiting, 100 estimated).

Trial phenotype checklist

Required field Reason
Obstructive-disease exclusion method Angiography and CCTA thresholds differ
Objective ischemia Separates ANOCA from confirmed INOCA
CFR platform and cutoff PET, Doppler and invasive values are not identical
IMR or resistance measure Distinguishes low reserve from structural resistance
Acetylcholine protocol Defines epicardial versus microvascular spasm
Baseline antianginal washout/use Strongly affects symptom endpoint
Menopausal/sex variables Women are overrepresented but incompletely phenotyped
Patient-reported instrument Enables comparable symptom effect sizes
Hard outcomes and repeat care Measures prognosis and diagnostic utilization

Without these fields, a trial labeled “microvascular angina” can pool opposite vasomotor phenotypes and obscure a real treatment interaction (Kunadian 2020, PMID 32626906).

Differential diagnosis boundary

INOCA is a positive ischemic framework, not a catch-all for every chest symptom after a normal angiogram. Myocarditis, pericardial disease, pulmonary disease, anemia, esophageal and musculoskeletal disorders, panic, and medication effects require proportionate evaluation; coexistence is possible. The goal is mechanism-directed care while avoiding both dismissal and unbounded coronary testing.

Evidence strength by endotype

Endotype/question Best current evidence Limitation
Does abnormal flow reserve matter? Meta-analysis links impaired coronary flow reserve with higher mortality and MACE across modalities and populations (Kelshiker 2022, PMID 34849697), consistent with earlier endothelial/CMD prognosis synthesis (Brainin 2018, PMID 29407076). Thresholds and methods are heterogeneous; prognostic association does not define treatment.
Does invasive testing improve symptoms? CorMicA randomized disclosed function-testing-linked therapy versus blinded results and improved angina/quality of life (Ford 2018, PMID 30266608). It was not powered for MI or death and tested a strategy bundle rather than one drug.
Does diltiazem correct vasomotor dysfunction? EDIT-CMD found no improvement in the overall invasive vasomotor endpoint, although some spasm-related measures may differ (Jansen 2022, PMID 35466050). A heterogeneous ANOCA population can dilute endotype-specific drug effects.
Can diagnostic labels be standardized? COVADIS criteria define vasospastic and microvascular angina (Beltrame 2017, PMID 26245334; Ong 2018, PMID 29031990). Consensus criteria improve comparability but are not themselves outcome validation.
Is MINOCA one disease? Contemporary reviews frame MINOCA as a working diagnosis requiring CMR, intracoronary imaging, and mechanism-directed testing (Parwani 2023, PMID 37067753); OCT frequently identifies otherwise occult substrates (Bryniarski 2021, PMID 34201727). Diagnostic yield depends on timing, expertise, and selection, and a detected abnormality may not be causal.
Are women uniquely affected? Sex/gender reviews show different phenotype mix and care pathways, with nonobstructive disease and CMD prominent among women (Regitz-Zagrosek 2023, PMID 36316574; Grant 2024, PMID 38548464). Referral bias and historical under-testing make prevalence estimates unstable.

Obstructive versus nonobstructive is the wrong binary

Epicardial stenosis, diffuse atherosclerosis, endothelial dysfunction, impaired vasodilator reserve, microvascular spasm, epicardial spasm, myocardial bridging, and noncoronary pain can coexist. CCTA or angiography that excludes a ≥50% stenosis answers only one question. ESC chronic-coronary guidance and the EAPCI consensus therefore support endotype-oriented testing in persistent symptoms, while acknowledging the thin hard-outcome evidence (Vrints 2024, PMID 39210710; Kunadian 2020, PMID 32626906).

This changes interpretation of placebo-controlled PCI. ORBITA and ORBITA-2 show that focal PCI can have variable symptom effects depending on background medication and phenotype, but neither tests microvascular or vasospastic therapy (Al-Lamee 2018, PMID 29103656; Rajkumar 2023, PMID 38015442). Persistent angina after technically successful PCI may therefore reflect residual diffuse disease, CMD, spasm, or noncardiac mechanisms rather than procedural failure alone (Joshi 2021, PMID 33944871; Simader 2024, PMID 38759906).

Controversy: routine invasive function testing

Advocates emphasize diagnostic closure, fewer repeated nondiagnostic encounters, and CorMicA's symptom benefit. Skeptics emphasize limited outcome-scale randomized evidence, procedural burden, protocol variability, and uncertain availability. A definitive trial should randomize a care pathway, measure symptoms repeatedly, capture repeat emergency visits and tests, and remain powered long enough for MI/death while guarding against inappropriate antithrombotic treatment of non-atherothrombotic MINOCA (Ford 2018, PMID 30266608; White 2021, PMID 33372537).

Acute diagnostic safety intersects with the chronic phenotype. Women and men have overlapping ACS symptoms, but systematic review documents distributional differences that can affect triage (Ferry 2019, PMID 31431112; van Oosterhout 2020, PMID 32363989). High-sensitivity troponin identifies injury rather than its coronary mechanism (Park 2017, PMID 29016754), and chest-pain guidance therefore combines ECG, serial troponin, anatomy/functional testing, and clinical context (Gulati 2021, PMID 34709879). In persistent stable symptoms, US and ESC chronic-coronary guidance differ in how strongly they operationalize function testing, partly reflecting CorMicA's symptom evidence and the absence of outcome-scale trials (Virani 2023, PMID 37471501; Vrints 2024, PMID 39210710).

Patient-reported effects deserve co-primary status in this domain. Repeated invalidation, uncertainty, and activity restriction are not captured by death/MI composites; placebo-controlled symptom work in obstructive disease and post-MI distress research provide useful measurement methods even though the mechanisms differ (Rajkumar 2023, PMID 38015442; Chong 2025, PMID 40142595). A complete INOCA trial should report Seattle Angina Questionnaire domains, daily symptoms, medication burden, exercise/function, health-care use, diagnostic certainty, adverse effects, and hard events.

Mechanism-specific evidence remains uneven

WISE-CVD reproduced impaired coronary function in a lower-risk contemporary cohort of 235 women: mean CFR was 2.7±0.6 versus 2.6±0.8 in the original 181-woman WISE cohort, with similarly abnormal acetylcholine and nitrate responses (Anderson 2019, PMID 31772544). These cohort comparisons support persistence of the phenotype but do not provide a treatment effect.

MINOCA is especially vulnerable to etiologic misclassification. In a 38-patient prospective OCT/CMR study, plaque disruption occurred in 24%, thrombus in 18%, and ischemic late gadolinium enhancement in 23%; the infarct-related artery had more disruption (40% vs 6%) and thrombus (50% vs 4%) than non-infarct arteries (Opolski 2019, PMID 30343070). Conversely, a nonobstructive angiogram does not prove an atherothrombotic mechanism, so myocarditis, Takotsubo, spasm, embolism, and dissection still require active separation.

Treatment evidence should follow endotype. A 128-person, 96%-women crossover trial found no overall improvement in angina or perfusion with two weeks of ranolazine, although participants with CFR <2.5 improved perfusion and angina-frequency measures in subgroup analyses (Bairey Merz 2016, PMID 26614823). In 9,136 30-day MINOCA survivors from SWEDEHEART, statins (HR 0.77, 95% CI 0.68–0.87) and ACE inhibitor/ARB therapy (HR 0.82, 95% CI 0.73–0.93) were associated with fewer long-term major events, whereas DAPT was neutral (HR 0.90, 95% CI 0.74–1.08); residual confounding prevents converting these associations into universal mechanism-blind treatment (Lindahl 2017, PMID 28179398).

Open questions

  • Does routine coronary function testing improve hard outcomes or mainly symptoms and diagnostic certainty? (Ford 2018, PMID 30266608)
  • Which CFR/IMR thresholds generalize across PET, CMR, Doppler, and invasive platforms? (Kelshiker 2022, PMID 34849697)
  • Can sex-specific biology be separated from referral and ascertainment bias in INOCA? (Grant 2024, PMID 38548464)
  • Which therapies prevent arrhythmia and MI in vasospastic angina rather than only reducing symptoms? (Beltrame 2017, PMID 26245334)
  • Can rehabilitation improve physiology and outcomes in INOCA? (NCT06529848)

References

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