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PubMed This is a summary of 20 peer-reviewed journal articles Updated
Cardiology

Getting the Right Diagnosis: Invasive Testing and Imaging

At a Glance

A normal or “clear” angiogram does not rule out nonobstructive coronary artery disease. Coronary function testing can assess small-vessel blood flow and artery spasms, while cardiac MRI helps identify infarction, myocarditis, or Takotsubo syndrome after MINOCA.

If you have been told your arteries are “clear” after a standard angiogram, you have only seen the “big pipes” of your heart. A standard angiogram is a visual test that looks for major blockages; it cannot easily see how the blood is actually flowing through the tiny vessels or how those vessels react to stress [1][2]. To find the true cause of your symptoms, doctors must move from looking at anatomy to testing function.

Current guidelines from major heart associations describe options to uncover the underlying “endotype” of your condition—whether it is a problem with the micro-vessels or a tendency for the arteries to spasm [3][4]. It is important to know that these tests are selected according to your symptoms, objective ischemia, suspected endotype, and local expertise.

Invasive Coronary Function Testing (CFT)

An Invasive Coronary Function Test (CFT) is a specialized procedure performed in a cardiac catheterization lab. While it starts like a regular angiogram, it goes much further by using tiny sensors and specific medications to “stress test” the arteries from the inside [3][5]. It carries procedural risks and is an option for selected patients with persistent or unexplained symptoms.

Measuring the “Micro-Plumbing” (Adenosine Testing)

During this part of the test, a doctor uses a medication called adenosine to dilate the blood vessels to their maximum capacity. They then measure two critical numbers:

  • Coronary Flow Reserve (CFR): This measures how much your blood flow can increase when your heart needs it most. A CFR less than 2.0 or 2.5 (depending on whether the lab uses Doppler or thermodilution protocol) is a sign of microvascular dysfunction [6][7].
  • Index of Microcirculatory Resistance (IMR): This measures how much “resistance” or “pressure” the blood faces as it tries to move through the tiny vessels. An IMR of 25 or higher is a commonly used threshold that suggests the micro-vessels are restricted or damaged [6][7].

Testing for Spasms (Acetylcholine Provocation)

Even if your flow reserve is normal, your arteries might be prone to sudden “cramping.” Doctors test for this using acetylcholine, a substance that normally causes healthy vessels to relax but causes dysfunctional ones to constrict [5][8].

  • Epicardial Spasm: If the large arteries visible on the screen constrict by 90% or more, accompanied by your typical chest pain and ischemic ECG changes, it generally confirms a large-vessel spasm [9].
  • Microvascular Spasm: Suggested when you experience typical chest pain and have ischemic ECG changes, but the large arteries do not show marked epicardial constriction [9][10].

The Crucial Role of Cardiac MRI (CMR) in MINOCA

If you have had a heart attack with “clear” arteries (MINOCA), a Cardiac MRI (CMR) is highly informative. It acts like a high-resolution “digital biopsy” that can see deep into the heart muscle [11][12].

Timing is important: a CMR is often most informative during the index admission or early after the event, but the exact timing depends on stability and access [13][14]. It can distinguish between several different causes:

  • True Infarction: Confirming a small heart attack caused by a tiny, dissolved clot or a vessel tear [15].
  • Myocarditis: Inflammation of the heart muscle, often caused by a virus, which can “mimic” a heart attack [12][16].
  • Takotsubo Syndrome: Also known as “broken heart syndrome,” where a part of the heart muscle temporarily weakens due to intense stress [12][17].

What to Look for in Your Test Report

When you receive your medical records, look for these specific measurements and terms. Note that missing CFR, IMR, acetylcholine, OCT, or IVUS values does not necessarily mean your testing was incomplete, as these tests are not routine for every angiogram.

Category Key Terms/Values to Find What It Indicates
Microvascular CFR, IMR Ability of tiny vessels to carry blood flow. Values depend on the lab method.
Spasm Acetylcholine, “Provocation,” “90% constriction” Tendency of vessels to “cramp” or constrict.
Structural FFR (Fractional Flow Reserve) Indicates if a specific intermediate epicardial lesion is flow-limiting. Not required if arteries are completely normal.
Imaging CMR, “Late Gadolinium Enhancement” (LGE) Presence of scarring, swelling, or inflammation.
Inside the Wall OCT or IVUS Tiny tears (SCAD) or plaque that regular X-rays miss [18][1].

Understanding these results allows you to move away from the “unexplained” label and toward a targeted treatment plan for your specific heart endotype [19][20]. You should also ask your doctor about non-invasive testing alternatives (like stress PET or stress CMR) to understand the full range of diagnostic options.

Common questions in this guide

Why can I have chest pain if my angiogram shows no blockage?
A standard angiogram mainly shows the large coronary arteries and may not reveal problems in the tiny vessels or arteries that spasm. Coronary function testing can assess blood flow through the small vessels and check whether the arteries constrict abnormally.
What does an invasive coronary function test measure?
An invasive coronary function test uses medications and pressure or flow measurements during cardiac catheterization. Adenosine testing evaluates how well the small vessels increase blood flow, while acetylcholine testing looks for artery spasms. Because the procedure has risks, it is used for selected patients with persistent or unexplained symptoms.
What do CFR and IMR mean on a heart test report?
Coronary flow reserve, or CFR, shows how much coronary blood flow can increase when the heart needs more oxygen. The index of microcirculatory resistance, or IMR, estimates resistance to flow through the small vessels. Commonly used thresholds are a CFR below 2.0 or 2.5, depending on the laboratory method, and an IMR of 25 or higher, but your laboratory's protocol matters.
What can an acetylcholine provocation test show?
Acetylcholine can reveal whether the coronary arteries tend to spasm. Marked narrowing of a large artery together with typical chest pain and ischemic ECG changes suggests epicardial spasm, while symptoms and ECG changes without major narrowing of the large arteries suggest microvascular spasm.
When is cardiac MRI used after MINOCA?
Cardiac MRI is often most informative during the initial hospital admission or soon after a heart attack with nonobstructive arteries, depending on your stability and access to testing. It can help distinguish a true infarction from myocarditis or Takotsubo syndrome, which can mimic a heart attack.
Which terms should I look for in my coronary test report?
Look for measurements such as CFR, IMR, FFR, acetylcholine provocation results, cardiac MRI findings, and terms such as late gadolinium enhancement. OCT and IVUS may show a small artery tear or plaque that a routine angiogram misses. Not seeing every term does not necessarily mean the evaluation was incomplete because these tests are not part of every angiogram.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Will you be performing a comprehensive Invasive Coronary Function Test (CFT) that includes both adenosine and acetylcholine testing?
  2. 2.What are the specific CFR and IMR thresholds used by your lab to diagnose microvascular dysfunction?
  3. 3.If I have had a heart attack (MINOCA), how quickly can we schedule a Cardiac MRI to look for inflammation or scarring?
  4. 4.Are you using 'bolus' or 'continuous' thermodilution to measure my coronary flow reserve?
  5. 5.If the acetylcholine test is negative for large-vessel spasm, will you still check for microvascular spasm (ST-segment changes on the ECG)?

Questions For You

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References

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This page is for informational purposes only and does not constitute medical advice. A cardiologist should interpret your coronary test results and advise which tests are appropriate for your situation.

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