What Actually Causes MINOCA and Why the Workup Matters

MINOCA is not a diagnosis. It is a question the angiogram could not answer and the workup can.

The term stands for Myocardial Infarction with Non-Obstructive Coronary Arteries. What it actually describes is a heart attack confirmed by troponin elevation and ischemic evidence, in a patient whose coronary angiogram showed no stenosis above 50%. The clean angiogram does not explain what happened. It rules out one mechanism. Five or six others remain on the table, and they are not interchangeable.

The Mechanism

To understand why MINOCA requires investigation rather than reassurance, the physiology of each possible cause matters. The coronary angiogram images the lumen of the major epicardial arteries: it tells you whether blood flow is mechanically obstructed above 50% in vessels visible at angiographic resolution. What it cannot see is the artery wall, where plaque lives below the surface. It cannot capture dynamic events like vasospasm, which occur and resolve before the catheterization begins. It cannot resolve SCAD when the dissection flap is subtle. It cannot image the microvasculature, which regulates most coronary flow. It cannot see a thrombus that has already dissolved. A “clean” angiogram excludes obstructive disease. It does not reconstruct the event.

This matters especially for women. In the MINOCA population, women are over-represented relative to their proportion of obstructive MI cases. The VIRGO study (Dreyer and colleagues, published in Circulation, 2015) found that MINOCA accounted for approximately 10% of MI cases overall but a higher proportion among younger women. The Swedish MINOCA registry, analyzed by Lindahl and colleagues (published in JAMA Internal Medicine, 2017), documented a one-year mortality of approximately 2.5% and a rate of major adverse events at four years that was comparable to obstructive MI. Being told “your arteries are clean” at discharge does not correspond to a low-risk prognosis when the mechanism is unidentified.

The AHA’s 2019 Scientific Statement on MINOCA, authored by Tamis-Holland and colleagues and published in Circulation, formalized the definition and called for systematic investigation of etiology in every MINOCA case. The position is explicit: MINOCA is a working diagnosis that should initiate investigation, not terminate it.

The Six Mechanisms Under the Umbrella

Plaque disruption without occlusion. The coronary artery wall contains atherosclerotic plaque, but neither rupture nor erosion creates a stenosis large enough to show as significant on angiography. In younger women, plaque erosion, in which the intact fibrous cap overlies an eroded endothelial surface with clot forming above it, is more common than plaque rupture. The PROSPECT II substudy data, combined with OCT-based evidence from Jia and colleagues (JACC, 2017), have clarified that erosion-related events are more prevalent in premenopausal women and in those with fewer conventional risk factors. The clot that triggered the event often dissolves before the catheterization begins. The artery looks clean. The event was real.

Coronary vasospasm. Focal, intense, transient constriction of an epicardial artery can reduce flow to the point of ischemia or infarction. Because spasm is reversible and typically lasts minutes to under an hour, the artery returns to near-normal caliber before the angiogram is performed. The test sees resting anatomy, not the anatomy during the event. Provocation testing with intracoronary acetylcholine or ergonovine is required to diagnose vasospasm definitively. Vasospasm occurs at rest, often nocturnally or in cold conditions, which differentiates it clinically from exertional ischemia. The Prinzmetal variant angina literature, dating from the 1970s and extended by Japanese investigators in the COSMO-Japan registry and Italian groups at University of Catanzaro, has documented that vasospasm can produce ST-elevation MI with clean arteries and that it recurs without appropriate therapy.

SCAD (Spontaneous Coronary Artery Dissection). The inner wall of the coronary artery tears, creating a false lumen that compresses the true lumen. The standard angiogram may show subtle haziness or mild irregularity easily dismissed as artifact. OCT identifies the intramural hematoma or dissection flap with the resolution needed to make this diagnosis. SCAD accounts for approximately 35% of MIs in women under 50 and is 80 to 95% female in published registries (Saw et al., JACC, 2016; Hayes et al., JACC Cardiovascular Imaging, 2018). Triggers include extreme physical exertion, emotional stress, and the peripartum period; it is the leading cause of pregnancy-associated MI. Missing SCAD has treatment consequences: aggressive anticoagulation used routinely in ACS may worsen the intramural hematoma and extend the dissection.

Coronary microvascular dysfunction. The small vessels that regulate most coronary blood flow fail to dilate on demand or actively constrict. The epicardial arteries on the angiogram look entirely normal. The ischemia is real and measurable but only with functional testing. Coronary flow reserve below 2.0 to 2.5, measured with a thermodilution or Doppler wire, confirms the diagnosis. In the context of an acute troponin elevation, CMD can cause genuine myocardial infarction via sustained underperfusion at the microvascular level without macrovascular obstruction.

Coronary embolism. Clot, air, calcific material, or other particulate from a proximal source travels into the coronary tree. Atrial fibrillation with thrombus formation, patent foramen ovale allowing paradoxical embolism from venous sources, valvular disease, infective endocarditis with vegetation, and hypercoagulable states are all relevant mechanisms. Angiography may show an area of cutoff that has cleared by the time of catheterization. The echocardiogram looking for PFO and the echocardiographic or transesophageal assessment of valvular disease are part of the embolic workup.

Supply-demand mismatch (Type 2 MI). A process outside the coronary arteries reduces myocardial oxygen supply or increases demand beyond what the coronary system can deliver. Severe anemia, sustained tachyarrhythmia, sepsis with hemodynamic compromise, and perioperative hypotension are clinical examples. The arteries are not the primary problem. Troponin rises because the myocardium outstrips supply capacity; the mechanism is physiologic, not obstructive. Treating this category with antiplatelet therapy and statins designed for Type 1 atherosclerotic events is not merely ineffective; it may misallocate the clinical focus toward the coronary arteries when the underlying driver is systemic.

What the Evidence Shows

The CMR yield in MINOCA is the strongest evidentiary pillar for systematic workup. Lindsey and colleagues, and separately Dastidar and colleagues (Journal of the American College of Cardiology, 2017), documented that CMR performed within two weeks of a MINOCA event identified an etiology in 68 to 87% of cases. Without CMR, the same patients would have been discharged without a confirmed mechanism. The finding mix across these studies included myocarditis, ischemic infarction with subendocardial LGE, Takotsubo cardiomyopathy, and dilated cardiomyopathy.

The Reynolds et al. dataset, which focused specifically on women presenting to academic centers with chest pain and a discharge of MINOCA or unexplained troponin elevation, confirmed that CMR was the diagnostic pivot point. The difference between myocarditis and plaque erosion-related ischemic infarction, for example, is not detectable by angiography or standard ECG. CMR separates them by LGE pattern with specificity exceeding 90% for myocarditis by the updated Lake Louise Criteria (Ferreira et al., JACC Cardiovascular Imaging, 2018).

For SCAD specifically, the data on intracoronary imaging yield from Saw and colleagues at Vancouver General Hospital, representing one of the largest SCAD registries internationally, show that OCT identified dissection in cases where standard angiography was read as mildly irregular or near-normal. The angiographic miss rate for SCAD is not trivial; cross-sectional arterial imaging is the test that makes the diagnosis.

For vasospasm, the largest provocation testing datasets come from Japanese investigators, given that acetylcholine provocation is routine at catheterization in Japan. Studies from Yasue and colleagues and subsequent data from the COVADIS group confirm that vasospasm provocation is safe when performed with appropriate monitoring and that it identifies a diagnosis in 30 to 50% of patients with unexplained angina and clean coronaries.

The Workup, in Sequence

Cardiac MRI is the highest-yield next step for most MINOCA patients. CMR performed within days to weeks of the acute event identifies the etiology in 68 to 87% of cases across published series. It distinguishes ischemic infarction from myocarditis, identifies Takotsubo morphology, and can reveal LV thrombus requiring anticoagulation. Without CMR, the etiology in a substantial majority of MINOCA cases remains unknown at discharge. Current ESC and AHA guidelines both recommend CMR as part of the MINOCA workup.

Intracoronary imaging (OCT or IVUS) during cardiac catheterization adds resolution the angiogram cannot provide. When SCAD or plaque disruption is suspected, OCT cross-sections the artery wall and can identify dissection flaps, intramural hematoma, or eroded plaque beneath a non-stenotic surface. OCT is preferred over IVUS for SCAD because of its superior resolution in smaller vessels and its ability to characterize intramural hematoma thickness. The trade-off is that OCT requires contrast injection and may carry a small procedural risk that must be weighed against diagnostic benefit.

Vasospasm provocation testing with intracoronary acetylcholine is the reference standard for diagnosing coronary vasospasm. It is performed during catheterization and involves controlled delivery of a vasoconstrictor to identify exaggerated, focal, reversible response. It is underutilized in the United States but diagnostically essential in patients with rest-predominant symptoms, nocturnal onset, or cold-triggered events. The COVADIS criteria (Beltrame et al., European Heart Journal, 2017) provide standardized definitions for diagnosing vasospastic angina, and the diagnostic standard is provocation testing with angiographic confirmation.

Echocardiography with bubble study addresses the embolic workup. Transesophageal echocardiography or contrast-enhanced transthoracic imaging can identify PFO, left atrial thrombus, valvular vegetations, or other structural sources of embolism.

Hypercoagulable panel is relevant for patients where coronary embolism is on the differential: antiphospholipid antibodies, protein C, protein S, factor V Leiden, and prothrombin gene mutation testing. This is most relevant in younger patients without conventional risk factors, or those with prior thrombotic events or a family history of clotting disorders.

Thyroid function and inflammatory markers are appropriate in suspected myocarditis or in cases where a systemic process contributing to supply-demand mismatch needs to be identified.

Mechanism-Specific Medical Therapy: Why the Treatment Depends on the Underlying Cause

The most consequential clinical implication of identifying MINOCA etiology is that treatment diverges substantially by mechanism. A generic post-MI protocol applied without knowing the cause risks delivering the wrong therapy to a meaningful proportion of patients.

For plaque disruption events, including erosion and rupture without complete occlusion, the physiological substrate resembles standard Type 1 MI. Dual antiplatelet therapy, high-intensity statin therapy, and ACE inhibitor or angiotensin receptor blocker therapy apply in principle, though the evidence base is derived primarily from obstructive MI populations. Swedish MINOCA Registry data reported by Lindahl and colleagues in the European Heart Journal (2017) found that statin therapy and ACE inhibitor therapy were each independently associated with better outcomes in MINOCA patients, providing supporting evidence that plaque-related therapies confer benefit when atherosclerosis underlies the event.

Vasospastic MINOCA follows a different pharmacological logic. Calcium channel blockers, particularly verapamil and diltiazem, are the cornerstone of vasospasm management; they reduce the frequency and severity of coronary spasm by blocking calcium-mediated constriction of vascular smooth muscle. Long-acting nitrates provide adjunctive symptomatic benefit. Beta-blocker monotherapy is typically avoided in vasospastic disease because beta-blockade can allow unopposed alpha-adrenergic activity at the coronary vasculature, potentially worsening spasm in susceptible patients. This is the reverse of what a standard ACS protocol prescribes for troponin elevation, and applying ACS-standard therapy without knowing the mechanism carries meaningful treatment consequences.

SCAD management has evolved substantially as SCAD-specific outcome data have accumulated. Current consensus, supported by the Canadian SCAD Registry (Saw et al., JACC, 2016) and multiple institutional SCAD outcome series, favors conservative management in hemodynamically stable patients. Aggressive anticoagulation, standard in ACS, can potentially propagate an intramural hematoma by increasing pressure within the false lumen and extending the dissection. Percutaneous coronary intervention carries a substantially higher technical complication rate in SCAD than in obstructive atherosclerotic disease, because the dissected vessel wall does not respond predictably to balloon inflation and stenting. Conservative management frequently allows the artery to remodel and the hematoma to resorb. Some data suggest beta-blockers may reduce recurrence risk in SCAD; the role of long-term antiplatelet therapy beyond the acute period remains under investigation.

Coronary microvascular dysfunction requires its own treatment approach. ACE inhibitors and statins have supporting data for improving microvascular function through their effects on endothelial nitric oxide availability and vascular inflammation. Ranolazine, which reduces ischemic symptoms through late sodium current inhibition, has been evaluated in microvascular disease with evidence of symptomatic benefit. Standard ACS protocols do not target the microvascular pathophysiology, and their application without diagnosis of the underlying mechanism misallocates therapy.

For embolic MINOCA, the treatment target is the source. Atrial fibrillation with intracardiac thrombus directs long-term management toward anticoagulation for AF, not antiplatelet therapy for coronary disease. A patent foramen ovale with paradoxical embolism raises the question of PFO closure depending on clinical context. A hypercoagulable state identified in workup directs anticoagulation at the thrombophilia rather than at the coronary anatomy. In each scenario, the lesion is systemic; the coronary arteries are the victim, not the cause.

What to Do This Week

1. If you were hospitalized for MINOCA and discharged without a workup plan, ask your cardiologist directly: “What is the working etiology of my MINOCA, and was cardiac MRI ordered?” If the answer is that no MRI was performed, ask when it can be scheduled. CMR within the first two to four weeks of an event has the highest diagnostic yield.

2. If SCAD is a possibility given your age, symptom pattern, or circumstances such as recent delivery or extreme physical exertion at onset, ask specifically whether OCT was performed during catheterization and whether it is available for review.

3. If vasospasm is being considered, ask whether provocation testing is available at your center or whether a referral to a center that performs it is appropriate. Centers with vasospasm provocation programs are typically academic or high-volume interventional programs.

4. Request copies of your catheterization report, your discharge summary, and your echocardiography report. The angiography images and any OCT data are yours to obtain and bring to future cardiology appointments.

5. Bring the Tamis-Holland 2019 AHA Scientific Statement on MINOCA to any appointment where you are told “your arteries were clean, so you are fine.” The statement is publicly available and establishes that these two facts are not equivalent.

The goal of the MINOCA workup is not more testing for its own sake. It is identifying which mechanism among six or more produced the event, so that treatment addresses the actual problem. Without the mechanism, the prescription is a guess. With it, each choice in your management, from which medications to take, to which activities to approach cautiously, to how frequently you need follow-up, follows a defined clinical logic rather than a generic post-MI protocol that may not apply to what actually happened to you.