MINOCA (Myocardial Infarction in the Absence of Obstructive Coronary Artery Disease)

Definition

MINOCA is a working clinical diagnosis applied to patients who meet the criteria for acute myocardial infarction (AMI) but have no obstructive coronary artery disease (stenosis <50% in any major epicardial vessel) on angiography and no clinically overt alternate explanation for the presentation. It is an ischemic diagnosis — distinguishing it from myocardial injury (nonischemic troponin elevation) — and should prompt active investigation into the specific underlying mechanism.

Key Concepts

Diagnostic Criteria (AHA 2019)

Three criteria must all be met sources/minoca-aha-2019 (high):

1. AMI per 4th Universal Definition: rise/fall of cTn with ≥1 value >99th percentile + corroborative clinical evidence (symptoms, ischemic ECG changes, new wall motion abnormality, or coronary thrombus)
2. Nonobstructive coronaries: no stenosis ≥50% in any major epicardial vessel (includes normal arteries, <30% irregularities, 30–49% moderate stenosis); FFR >0.80 in borderline lesions retains MINOCA classification
3. No specific alternate diagnosis: excludes sepsis, PE, myocarditis, takotsubo (latter categorised separately per 4th Universal MI Definition)

Epidemiology

• Prevalence 5–6% of angiography-referred AMI patients; range 5–15% across populations sources/minoca-aha-2019 (high)
• Disproportionately affects women (~50% of MINOCA vs ~25% in AMI-CAD; women >2× more likely than men to have MINOCA)
• Younger age: mean 58 years vs 61 years in AMI-CAD
• Higher prevalence in Black, Maori, Pacific, and Hispanic populations
• Lower traditional CAD risk factor burden than AMI-CAD
• SCAD and MINOCA are prevalent causes of MI in pregnancy, accounting for the majority of ischemic events alongside atherosclerosis sources/cv-pregnancy-aha-2020 (high)

Traffic Light Diagnostic Algorithm

Three sequential decision steps sources/minoca-aha-2019 (high):

• Red — exclude overt mimics: clinically obvious nonischemic causes (sepsis, PE, myocarditis) → not MINOCA
• Yellow — exclude subtle mimics: (a) re-review angiogram for overlooked obstructive disease or SCAD; (b) CMRI to exclude myocarditis, takotsubo, cardiomyopathies; (c) intracoronary OCT/IVUS if any angiographic atherosclerosis present
• Green — MINOCA confirmed: working diagnosis established; mechanistic testing in specialized centres (provocative spasm testing, microvascular function testing, thrombophilia panel)
• CMRI strongly recommended but absence of necrosis does not exclude MINOCA (some MINOCA patients have no visible necrosis on CMR)

Six Mechanistic Causes

See concepts/Coronary-Vasospasm and concepts/Coronary-Microvascular-Dysfunction for detailed mechanistic pages.

Medical Management — SWEDEHEART Registry Data

Stratified propensity analysis, n=9,138, mean follow-up 4.1 years sources/minoca-aha-2019 (high):

• Statins: HR 0.77 (95% CI 0.68–0.87) — significant reduction in composite MACE
• ACE inhibitors/ARBs: HR 0.82 (95% CI 0.73–0.93) — significant reduction
• β-blockers: HR 0.86 (95% CI 0.74–1.01) — trend, not significant; contraindicated in coronary vasospasm
• Dual antiplatelet therapy: HR 0.90 (95% CI 0.74–1.08) — no significant benefit
• Secondary prevention medications should be individualised by underlying cause, not applied uniformly as in AMI-CAD
• MINOCA-BAT RCT (n≥3,500): prospective evaluation of ACEi/ARBs ± β-blockers — results awaited at time of 2019 statement

Prognosis

• Better than AMI-CAD but not benign sources/minoca-aha-2019 (high):
  • In-hospital mortality 0.9–1.1% (ACTION-GWTG, meta-analysis)
  • 12-month mortality 4.7% (meta-analysis)
  • 4-year mortality 13.4%; re-MI 7.1%; ischemic stroke 4.3%; HF hospitalization 6.4% (SWEDEHEART)
• ~25% develop angina within 12 months (similar frequency to AMI-CAD)
• VIRGO study: similar 1-month and 1-year mortality rates to AMI-CAD in young patients
• ST-elevation and shock/HF presentation are more strongly predictive of in-hospital death in MINOCA than in AMI-CAD

Contradictions / Open Questions

• Prognosis heterogeneity: VIRGO and Korean Infarct Registry show comparable outcomes to AMI-CAD; most registries suggest better outcomes — population differences (age, sex, cause mix) likely explain discrepancy sources/minoca-aha-2019 (high)
• DAPT uncertainty: SWEDEHEART showed no DAPT benefit in the overall MINOCA cohort, but this analysis did not isolate plaque disruption cases where DAPT is theoretically justified — evidence gap sources/minoca-aha-2019 (high)
• Microvascular dysfunction as cause vs consequence: inducible perfusion defects present in 2/3 of female MINOCA patients on stress CMR, but these occur with any cause of myocardial oedema (including myocarditis) — directionality unresolved sources/minoca-aha-2019 (high)
• FFR threshold: whether all 30–49% stenoses should undergo FFR measurement in MINOCA workup is unresolved; up to 25% of 30–50% stenoses have functionally significant FFR in stable patients sources/minoca-aha-2019 (high)

Connections

• Related to concepts/Coronary-Vasospasm — vasospasm is the most common single cause in provocative testing series
• Related to concepts/Coronary-Microvascular-Dysfunction — overlapping diagnosis; MINOCA is distinct from INOCA (stable ischemia without infarction)
• Related to concepts/Late-Gadolinium-Enhancement — CMR LGE used to confirm necrosis and exclude myocarditis/cardiomyopathy in MINOCA workup
• Related to concepts/Myocardial-Viability — wall motion abnormality pattern on imaging is part of MINOCA AMI diagnostic criteria
• Related to entities/SCAD — SCAD is a key nonatherosclerotic MINOCA cause; especially in women <50 and in pregnancy

Sources

• sources/cv-pregnancy-aha-2020
• sources/minoca-aha-2019