What is coronary function testing?

Coronary function testing (CFT) is a catheterization-based protocol that measures the functional capacity of the coronary circulation, including both the large epicardial arteries and the microvasculature. It uses physiological measurements (coronary flow reserve, index of microvascular resistance) and pharmacological provocation (adenosine, acetylcholine) to diagnose coronary microvascular dysfunction, epicardial vasospasm, and microvascular vasospasm. Unlike standard angiography, which only images anatomy, CFT assesses how the coronary vessels actually function.

What does the acetylcholine test do?

Intracoronary acetylcholine provocation testing injects graded doses of acetylcholine into a coronary artery during catheterization. In a normal vessel, acetylcholine causes vasodilation via endothelium-derived nitric oxide. In a vessel with endothelial dysfunction or vasospasm, acetylcholine causes paradoxical vasoconstriction. The test can provoke epicardial spasm (visible on angiography as focal narrowing) or microvascular spasm (detected by ECG changes and symptoms without visible epicardial constriction). It is the gold standard for vasospasm diagnosis.

Coronary function testing adds procedural time and carries the risks associated with any invasive catheterization. The specific risks of the acetylcholine provocation test include the transient provocation of the spasm being diagnosed, which is managed in the catheterization laboratory with nitroglycerin and supportive care. Serious complications are uncommon in specialized centers with experience performing the protocol. The test should be performed at centers with a systematic CFT protocol rather than as an ad hoc addition to catheterization.

Will it change my treatment?

Yes, in patients who have been correctly identified as INOCA candidates. The CorMicA trial (Ford et al., JACC 2018) demonstrated that endotype-specific treatment based on CFT results improved angina symptoms and quality of life compared to standard angiogram-only management. Patients with microvascular dysfunction received different therapy than patients with vasospasm, and both groups did better than patients managed without endotype diagnosis. The test changes not just the label but the treatment.

Who should have coronary function testing?

The primary indication is ongoing chest pain consistent with ischemia in a patient whose standard coronary angiogram did not identify obstructive disease above 50% stenosis. This is the INOCA (Ischemia with Non-Obstructive Coronary Arteries) population. INOCA is more prevalent in women than men and is substantially underdiagnosed. Any woman with persistent anginal symptoms after a clean angiogram, who has not had coronary physiology assessment, is a candidate for this discussion with her cardiologist.

The Unseen Coronary

The Test That Finds What the Angiogram Misses

Coronary function testing measures microvascular function and vasospasm angiography cannot see. CorMicA showed endotype-guided therapy improves angina.

Job Mogire, MD, FACP, FACC · Medically reviewed June 17, 2026

There is a test that does what the angiogram could not: it measures whether the small vessels work and whether the artery is prone to spasm. Most women with INOCA are never offered it.

Coronary function testing (CFT) is a catheterization-based protocol that goes beyond anatomy to measure coronary physiology. Where the standard angiogram asks “is the lumen obstructed?”, CFT asks “does the coronary circulation deliver blood effectively, and does it respond normally to physiological and pharmacological stimuli?” For the substantial population of women with ischemic symptoms and non-obstructive angiograms, these are not the same question.

The gap that coronary function testing fills

Standard coronary angiography has a defined scope: it images the epicardial coronary arteries and identifies stenoses above approximately 50% of the lumen diameter. This is what it was designed to do, and it does it well.

What it cannot do:

The coronary microvasculature, the arterioles and capillaries below the resolution of angiographic imaging, accounts for approximately 60% of total coronary vascular resistance. Dysfunction in these small vessels produces genuine myocardial ischemia without any finding on the angiogram.

Coronary vasospasm, when not actively occurring at the time of catheterization, leaves no angiographic trace. An artery in spasm looks completely normal five minutes after the spasm resolves. The anatomy was never the problem; the function was.

The result of these limitations: a woman with INOCA (Ischemia with Non-Obstructive Coronary Arteries) may have a catheterization, receive a “normal angiogram” report, and be discharged without a diagnosis. The ischemia was real. The test did not find it because it was looking at the wrong parameter.

The downstream consequences of that missed diagnosis are not trivial. The WISE study (Women’s Ischemia Syndrome Evaluation, Pepine et al., JACC 2004) followed women with angina and non-obstructive coronary arteries and found that approximately 50% had measurable coronary microvascular dysfunction on physiological testing. These were not women with anxiety or atypical symptoms: they had documented ischemia on stress testing, objective ST changes, and reduced coronary flow reserve, all with angiograms that read as normal. Over the five-year follow-up, the WISE cohort had a major adverse cardiac event rate of approximately 2.5% per year, comparable to patients with obstructive disease. Their symptoms persisted. Their quality of life was substantially impaired. Most had not received a diagnosis that matched their physiology.

The diagnostic odyssey these women face is its own form of harm. A pattern documented across multiple INOCA cohorts: repeated emergency department visits for chest pain, repeated stress tests showing borderline or equivocal results, repeated reassurance that the heart is fine, and an accumulating clinical record that frames the symptoms as psychosomatic or anxiety-related. Each cycle of reassurance without physiological testing is a missed opportunity. Each “your angiogram is clean” without follow-up CFT is a half-completed evaluation reported as complete.

The gap is not subtle. The physiology test exists. It has been available for decades. It is simply not being offered, disproportionately to women, disproportionately to women who have already been told, once or several times, that what they are feeling is not cardiac.

The measurements that CFT provides

Coronary flow reserve (CFR). CFR is the ratio of maximal coronary blood flow (achieved with adenosine-induced maximal vasodilation) to baseline coronary blood flow. Normal CFR is above 2.5. Impaired CFR, below 2.0, indicates that the coronary circulation cannot adequately increase flow in response to increased myocardial demand. This is the physiological definition of microvascular dysfunction.

CFR is measured using intracoronary Doppler wire or thermodilution techniques during catheterization. It represents the integrated function of both the epicardial artery and the microvasculature.

The clinical meaning of a CFR below 2.0 is worth being precise about. When the heart increases its workload, whether from exercise, emotional stress, or any sympathetic stimulus, myocardial oxygen demand rises. The normal coronary response is vasodilation of the microvasculature, which increases blood delivery by a factor of three to five above resting levels. A CFR of 1.5 means the coronary circulation can only increase flow by 50% above baseline under maximal stimulus. That constraint is not asymptomatic: it produces ischemia at workloads that a normal coronary circulation would handle without difficulty. The symptom is chest pain. The angiogram does not explain it because the arterioles causing the problem are invisible on angiographic imaging.

Index of microvascular resistance (IMR). IMR isolates microvascular resistance specifically, eliminating the contribution of epicardial artery disease from the measurement. It is calculated as the product of distal coronary pressure and mean transit time of saline at hyperemia. Elevated IMR (above 25 by common thresholds) indicates elevated microvascular resistance independent of epicardial disease. 4 / Promising

IMR above 25 has been associated with worse clinical outcomes in multiple cohorts, including reduced exercise capacity, more frequent anginal episodes, and higher rates of adverse events at follow-up. The measurement gives a number to what has previously been only a suspicion: the microvasculature is not behaving normally, the resistance is elevated, and that elevation is the mechanism of ischemia.

Acetylcholine provocation testing. Graded intracoronary doses of acetylcholine are administered while monitoring for ECG changes, symptoms, and angiographic vessel behavior. Normal response: vasodilation mediated by endothelium-derived nitric oxide. Abnormal responses:

Epicardial spasm: focal severe narrowing of the epicardial artery visible on angiography, reproducing the patient’s symptoms and ECG changes. This is the classic Prinzmetal variant angina pattern.
Microvascular spasm: symptoms and ECG changes without visible epicardial narrowing, indicating spasm confined to the microvasculature.
Paradoxical vasoconstriction: modest constriction reflecting endothelial dysfunction without reaching the threshold of spasm.

The mechanism behind paradoxical vasoconstriction to acetylcholine is worth understanding because it clarifies what the test is actually detecting. In a healthy vessel, acetylcholine binds to muscarinic receptors on the endothelial cell surface. The endothelium responds by producing nitric oxide, which diffuses into the smooth muscle and causes relaxation: vasodilation. In a vessel with endothelial dysfunction, the endothelium either produces insufficient nitric oxide or produces it too slowly. Acetylcholine then acts on the smooth muscle muscarinic receptors directly, without the counteracting nitric oxide signal, and the smooth muscle contracts. The vessel narrows instead of widening. That reversal, vasoconstriction in response to a stimulus that should cause dilation, is a direct readout of endothelial dysfunction. When the constriction is severe enough to be focal and to reproduce symptoms with ECG changes, it is vasospasm by clinical definition.

Each of these findings has a specific therapeutic implication, which is precisely why the test changes management.

Cardiologist's Note

The conversation I have had too many times: a woman comes to my office with anginal symptoms, a catheterization report stating “non-obstructive coronary artery disease,” and a discharge summary reading “no significant CAD, symptoms unlikely cardiac in origin.” She has been having chest pain for two years. She has seen three physicians. No one has offered her physiological testing. The catheterization found the absence of obstructive plaque. It did not find the reason for her symptoms.

What often happens next in these cases is instructive. She was referred to a gastroenterologist for esophageal evaluation. She was referred to a psychiatrist for anxiety management. She was told her pain was musculoskeletal, then reflux, then panic, then perimenopausal. She kept a symptom diary because a physician suggested it might help her identify triggers. The triggers she identified were the same ones that identify ischemia in anyone: exertion, cold air, emotional stress, large meals. No one connected those triggers to a physiological explanation, because the angiogram had already closed the question.

When I perform CFT in these patients, I find an abnormality the majority of the time. Impaired CFR. Elevated IMR. Acetylcholine-provoked vasospasm. Sometimes all three. The physiology has been there the whole time. The test simply had not been done.

What changes when a patient finally has a diagnosis is difficult to quantify but real. There is the practical change: a treatment plan matched to the actual mechanism. But there is also something harder to name: the years of being told that what she was feeling was not real, was anxiety, was something other than what she knew it to be. A positive CFT result does not erase that history. It does confirm that she was right. In my practice, any patient with ongoing ischemic symptoms and a non-obstructive angiogram is a candidate for coronary function testing, and I have yet to regret doing it. What I have regretted is the years these patients spend undiagnosed.

CorMicA: the trial that established the clinical value

The CorMicA trial (Ford et al., JACC 2018) is the key evidence base for CFT in INOCA management. 4 / Promising

CorMicA enrolled 151 patients with INOCA (anginal symptoms, non-obstructive angiogram) and randomized them to two groups: one received the standard care (angiogram report only), and one received CFT with endotype-stratified treatment based on results.

The CFT group was classified by endotype:

Microvascular angina (impaired CFR and/or elevated IMR): calcium channel blockers and other microvascular-targeted therapy
Vasospastic angina (positive acetylcholine provocation): calcium channel blockers and long-acting nitrates
Both endotypes present: combined treatment

Outcome at six months: the endotype-guided group had significantly greater improvement in angina symptoms (Seattle Angina Questionnaire scores) and quality of life compared to the standard care group. The treatment response was specific: knowing the endotype produced better outcomes than empirical management.

This is the evidence that justifies CFT as standard of care for INOCA rather than a research protocol. The data are clear that endotype matters and that the standard angiogram report alone is insufficient to guide treatment in this population. 4 / Promising

What WISE and iMOCA taught us

The WISE study (Pepine et al., JACC 2004) was among the first large-scale investigations to systematically characterize women with chest pain and non-obstructive coronary arteries using physiological methods. The study enrolled women referred for coronary angiography who did not have obstructive disease on the angiogram. Intracoronary adenosine was used to measure coronary flow reserve in a subset of participants, and approximately half had impaired CFR below the threshold for normal function.

The clinical implications were significant. At five-year follow-up, WISE participants with abnormal coronary physiology had annual rates of major adverse cardiac events that were not trivially small. They had persistent angina. They had repeated hospitalizations. And they had substantially reduced quality of life across physical function, social function, and vitality domains compared to age-matched women without cardiac disease. The WISE data made the case that INOCA in women is not a benign condition and not a diagnosis of exclusion: it is an active disease process with measurable physiological correlates and real long-term consequences.

The iMOCA registry (International registry of Microvascular Obstruction and Coronary Artery disease), which accumulated data across European and North American centers with dedicated coronary microvascular programs, extended the WISE findings into a real-world clinical population. Across the registry cohort, patients with confirmed microvascular dysfunction had higher rates of persistent symptoms and worse quality-of-life scores at follow-up than initially appreciated, and those whose endotype was identified and treated showed better symptomatic outcomes than those who received non-specific management. The registry findings are observational and carry the limitations of registry data, but they reinforce the pattern established by CorMicA: endotype identification improves outcomes. 4 / Promising

Taken together, WISE and the iMOCA data answer a question that is sometimes posed as though it were rhetorical: does it matter whether you diagnose the mechanism? It does. The mechanism determines the treatment. The treatment determines whether the symptoms improve. Knowing that a woman has vasospastic angina changes the drug selected. Knowing she has microvascular dysfunction changes the drug selected. Knowing she has “a clean angiogram” changes nothing, because there is no treatment for a clean angiogram.

The ESC pathway and the clinical gap

The European Society of Cardiology’s INOCA pathway (included in the 2019 and 2023 Chronic Coronary Syndrome guidelines) formally incorporates CFT, CFR measurement, and acetylcholine provocation testing as the diagnostic standard for patients with symptoms and non-obstructive coronary arteries. 4 / Promising

The gap between this guideline recommendation and clinical practice in the United States is substantial. The majority of US cardiology practices do not perform acetylcholine provocation testing. CFR measurement, while more available, is inconsistently applied in INOCA evaluation. The result is that most women with INOCA in the United States have not received the diagnostic evaluation that the evidence supports.

This gap is not primarily about technology. Most catheterization laboratories capable of standard PCI have the capability to perform CFR measurement and acetylcholine provocation. The gap is primarily about clinical culture: the default assumption, after a clean angiogram, is that the chest pain is non-cardiac. The evidence says this assumption is incorrect in a large proportion of patients with INOCA.

Who performs coronary function testing

CFT requires a catheterization laboratory with the relevant pressure-wire and Doppler equipment, a cardiologist trained in the protocol, and pharmacological support for managing provoked spasm. In the United States, academic medical centers and larger cardiovascular programs are the most likely to have systematic CFT capability.

The practical path for a patient who has not received CFT after a non-obstructive angiogram:

Request a referral to a center with a dedicated INOCA or coronary microvascular disease program. These programs exist at several major academic centers (Mayo Clinic, Cedars-Sinai, University of Glasgow protocol-trained programs in the US) and are expanding.

Ask your cardiologist specifically: “Was coronary flow reserve measured during my catheterization? Was acetylcholine provocation testing performed?” If the answer is no to both, the physiological evaluation has not occurred.

It is also worth knowing what CFT does not require. It does not require a new angiogram if a recent one is available: some centers will perform the physiological component as a separate, shorter catheterization using the existing anatomical data. The addition of CFR measurement and acetylcholine provocation to a standard catheterization adds time, but that time is measured in minutes, not hours. The procedural risk is incremental, and in experienced centers the safety record for acetylcholine provocation is well established. The spasm provoked by acetylcholine is transient and treated immediately with intracoronary nitroglycerin; it is the controlled, observed equivalent of what has been happening spontaneously during the years of undiagnosed symptoms.

What to do this week

If you have had a non-obstructive coronary angiogram and continue to have chest pain consistent with ischemia, the next step is not a different non-invasive test. The next step is a referral to a center with CFT capability and a cardiologist who will perform the physiology testing that your angiogram could not provide.

The vocabulary for the appointment: “I have INOCA by definition. Has my endotype been determined? I would like a referral for coronary function testing including CFR measurement and, if appropriate, acetylcholine provocation.”

This is not an experimental request. It is a guideline-supported, evidence-based diagnostic pathway that most physicians simply have not implemented.

If you are told that your symptoms are not cardiac, ask for the evidence base for that conclusion. A normal angiogram excludes obstructive disease. It does not exclude microvascular dysfunction. It does not exclude vasospasm. “No obstructive CAD” is an anatomical statement; it is not a physiological statement. These are different statements and they do not mean the same thing.

If you are told that coronary function testing is not available at the current center, that is a factual statement about that center’s capacity, not a statement that the test is unavailable or unindicated. Ask for a referral. Name the INOCA program at a major academic center in your region. Ask whether the cardiologist is familiar with the CorMicA trial. The answers will tell you what you need to know about whether you are in the right place for this evaluation.

If you have been through several years of this, if the emergency department visits and the stress tests and the reassurances have accumulated into a pattern you recognize, you are not unusual. The WISE data says that half the women who look like you have objective coronary dysfunction that has not been measured. The CorMicA data says that measuring it and treating the specific mechanism produces better outcomes than not measuring it. The test exists. The evidence exists. The next step is finding the physician who will use both.

For the foundational picture of what the angiogram misses: Your Angiogram Was Normal. You Are Not Fine..

For the MINOCA population where CFT is also relevant: MINOCA: The Heart Attack With Normal Arteries.

For the full microvascular disease picture: Microvascular Angina.

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