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INOCA & Coronary Microvascular Disease
Microvascular
Angina
Chest pain despite a normal coronary angiogram. Microvascular angina is a genuine, diagnosable, treatable condition — and one that is frequently missed. Specialist invasive assessment is required to identify it accurately.
Overview
What Is Microvascular Angina?
Microvascular angina refers to chest pain or tightness caused by abnormalities in the small coronary vessels — the microvasculature — deep within the heart muscle wall. These vessels are too small to be visible on standard coronary angiography, which explains why patients can have a completely normal-appearing angiogram and yet still experience genuine cardiac chest pain.
The modern clinical framework for this condition is INOCA — Ischaemia with Non-Obstructive Coronary Arteries. It encompasses two principal endotypes: coronary microvascular dysfunction (CMD), in which the small vessels fail to dilate adequately in response to increased demand; and coronary vasospasm, in which the arteries intermittently contract and restrict blood flow. Both can coexist in the same patient, and both can cause symptoms indistinguishable from conventional obstructive coronary disease.
The condition is not benign. Patients with established microvascular dysfunction have a meaningful increase in cardiovascular risk compared with the background population, and the quality of life impact of repeated, unexplained chest pain — often accompanied by repeated hospital admissions that yield no diagnosis — is substantial.
A normal coronary angiogram does not mean the pain is not cardiac. In patients with INOCA, the angiogram is normal precisely because the abnormality lies in vessels too small to be seen.
The Diagnostic Gap
Why Microvascular Angina
Goes Undiagnosed
The majority of patients with microvascular angina go through the same sequence of events: symptoms, GP referral, ECG and echocardiogram (both often normal), and ultimately a coronary angiogram. When the angiogram returns normal, they are told their heart is fine and that the pain is unlikely to be cardiac in origin.
This conclusion is not entirely wrong — a normal angiogram does confirm the absence of significant obstructive coronary disease. But it does not exclude microvascular dysfunction. Identifying CMD requires additional invasive testing — intracoronary pressure wire assessment, measurement of the Index of Microcirculatory Resistance (IMR) and Coronary Flow Reserve (CFR), and in some patients a provocation test with intracoronary acetylcholine to identify vasospasm. Most catheter laboratories do not routinely perform these tests at the time of a standard diagnostic angiogram.
The result is that patients are discharged, their symptoms persist, they return to their GP, are re-referred, and the cycle repeats. Some are labelled with anxiety or functional symptoms. The psychological burden of this diagnostic odyssey — often lasting years — compounds the physical symptoms significantly.
The WISE-CVD and CorMicA trials have confirmed that invasive coronary function testing in patients with INOCA changes diagnosis and management in the majority of cases — and improves outcomes. This testing requires a specialist who performs it routinely.
Dr Nijjer performs comprehensive invasive coronary function testing — including IMR, CFR, and acetylcholine provocation — as part of his diagnostic assessment for patients with unexplained chest pain and non-obstructive coronary arteries. This is the same physiological testing framework he contributed to developing during his PhD research at Imperial College London.
About Coronary Physiology (iFR) →Patient Population
Who Is Affected?
Microvascular angina affects both men and women, but women — particularly in the peri- and post-menopausal period — are disproportionately represented. Oestrogen has a protective effect on coronary microvascular function; as levels decline, the risk of CMD increases.
This demographic pattern contributes to the diagnostic problem. Women with chest pain are statistically less likely to be referred for invasive testing than men with equivalent symptoms, and when they are investigated, the finding of a normal angiogram is more likely to be interpreted as reassuring rather than as a trigger for further functional assessment. The result is a group of patients — predominantly women — who have genuine cardiac disease that is systematically under-investigated.
The condition is not limited to women or to older patients, however. Younger patients of either sex can develop microvascular dysfunction in the context of diabetes, hypertension, inflammatory conditions, or as a consequence of previous cardiac events. A history of prior myocardial infarction, in particular, can lead to permanent microvascular damage affecting the region supplied by the infarct-related artery.
Patients with risk factors for coronary disease — elevated blood pressure, impaired glucose tolerance, hyperlipidaemia, smoking history — should be assessed for CMD rather than simply reassured by a negative angiogram.
Clinical Presentation
Symptoms of Microvascular Angina
The symptoms of microvascular angina overlap substantially with those of obstructive coronary disease — which is precisely why it is difficult to distinguish clinically without invasive testing. There are, however, some patterns that are characteristic.
Chest discomfort is the cardinal symptom — typically a pressure, tightness, or aching sensation felt centrally or across the front of the chest, sometimes with radiation into the left arm, jaw, or back. In contrast to classical angina, which predictably occurs on exertion and resolves with rest, microvascular angina may also occur at rest, is often more prolonged, and may not respond as promptly to sublingual nitrates.
Associated symptoms include breathlessness, fatigue, and a sense of exercise intolerance that is disproportionate to the patient's cardiac function as measured by standard tests. Symptoms may be precipitated by emotional stress, temperature change, or caffeine — reflecting the sensitivity of microvascular tone to sympathetic stimulation.
Many patients describe a high burden of repeated presentations to emergency departments, where troponins and ECGs return normal and they are discharged without a clear diagnosis. The pattern of recurrent presentations with normal investigations, in a patient with a credible cardiac symptom history, should itself raise suspicion of microvascular disease.
Specialist Assessment
How Dr Nijjer Diagnoses It
Definitive diagnosis requires invasive coronary function testing — a catheter procedure performed in the cardiac catheter laboratory. Dr Nijjer performs this as a comprehensive physiological assessment, going well beyond the anatomical angiogram that most patients have already had.
Pressure Wire Assessment
iFR / Coronary Physiology
A fine pressure-sensing wire is passed into the coronary artery to measure blood flow at rest and during hyperaemia. This confirms the absence of functionally significant epicardial disease and establishes the baseline for microvascular assessment. Dr Nijjer developed the iFR technique at Imperial College London.
Microvascular Resistance
IMR — Index of Microcirculatory Resistance
The IMR quantifies resistance within the coronary microvasculature using thermodilution. An elevated IMR confirms that the small vessels are not dilating appropriately in response to maximal demand — the hallmark of coronary microvascular dysfunction. IMR >25 is diagnostic of significant CMD.
Microvascular Capacity
CFR — Coronary Flow Reserve
CFR measures the ability of the coronary circulation to increase blood flow in response to physiological demand. A reduced CFR (below 2.0) indicates that the microvasculature cannot adequately augment flow — consistent with CMD. CFR and IMR together distinguish between microvascular and epicardial causes of reduced flow.
Vasospasm Testing
Intracoronary Acetylcholine Provocation
If vasospasm is suspected — either epicardial or microvascular — a provocation test with intracoronary acetylcholine is performed. This challenges the coronary tone and identifies whether abnormal vasomotion is contributing to symptoms. It is the only reliable way to diagnose vasospastic angina and requires specific expertise to perform safely.
The combination of IMR, CFR, and acetylcholine provocation provides a complete endotype characterisation — distinguishing microvascular dysfunction, epicardial vasospasm, microvascular vasospasm, and mixed mechanisms. This determines not just whether INOCA is present, but precisely which treatment pathway is appropriate.
Management
Treating Microvascular Angina
Treatment for microvascular angina is tailored to the specific physiological endotype identified at assessment. There is no single approach; the right treatment depends on whether the predominant abnormality is impaired vasodilation, microvascular vasospasm, or a combination of both.
Lifestyle optimisation — smoking cessation, blood pressure control, cholesterol reduction, regular aerobic exercise, and weight management — forms the foundation of treatment and reduces the downstream cardiovascular risk associated with CMD.
- StatinsReduce cardiovascular risk and have direct anti-inflammatory effects on the coronary microvasculature, improving endothelial function over time.
- ACE inhibitors / ARBsReduce systemic vascular resistance and have beneficial effects on microvascular tone, particularly in patients with hypertension or reduced ejection fraction.
- Beta-blockersReduce heart rate and myocardial oxygen demand. Useful in the subset of patients with CMD driven by elevated heart rate or adrenergic tone.
- Calcium-channel blockersFirst-line for microvascular vasospasm. Amlodipine and diltiazem are most commonly used, selected on the basis of heart rate and symptom pattern.
- RanolazineA late sodium-channel inhibitor that reduces ischaemia without affecting heart rate or blood pressure. Particularly useful in patients who do not tolerate beta-blockers or in refractory cases.
- NicorandilA potassium-channel opener with additional nitrate action. Used in patients with persistent symptoms despite other agents, particularly those with elevated IMR.
Unlike obstructive coronary disease, microvascular angina is not treated by angioplasty or stenting — there is no visible lesion to treat. The response to endotype-directed medical therapy is the hallmark of good management.
Your Appointment
What to Expect at Consultation
Dr Nijjer's consultation for suspected microvascular angina is structured to establish a full clinical picture before recommending investigations. Bring all previous investigation results — including coronary angiogram reports, stress test results, echocardiograms, and any Holter monitor recordings.
The consultation will cover a detailed symptom history — including triggers, duration, frequency, and any associated symptoms. Dr Nijjer will review prior investigation results and explain what the angiogram does and does not tell us about microvascular function. If invasive physiological testing is indicated, the procedure, its purpose, and what the results might mean will be explained in full before any decision is made.
Not all patients with a normal angiogram require further invasive assessment. The clinical history, symptom pattern, and prior investigations will determine whether comprehensive coronary function testing adds meaningful diagnostic information in your specific case. Where it does, Dr Nijjer will perform the assessment as part of a day-case procedure and discuss the results with you before discharge.
Common Questions
Frequently Asked Questions
I've had a normal coronary angiogram. Can I still have microvascular angina?
Yes. A standard coronary angiogram shows the large epicardial coronary arteries but cannot visualise the coronary microvasculature — vessels typically 50–500 microns in diameter — where microvascular dysfunction occurs. A normal angiogram confirms the absence of obstructive coronary disease but does not exclude microvascular angina. Definitive diagnosis requires the additional invasive tests described above.
Is microvascular angina dangerous?
Microvascular angina is associated with an increased cardiovascular risk compared to the general population, though the absolute event rate is lower than in obstructive coronary disease. The quality of life impact of recurrent chest pain and repeated hospital admissions is substantial. Appropriate diagnosis and treatment reduces symptom burden and may reduce longer-term cardiovascular risk.
Can microvascular angina be cured?
There is no single curative treatment, but endotype-directed medical therapy significantly reduces symptoms in the majority of patients. The key is establishing which specific physiological abnormality is present — impaired vasodilation, microvascular vasospasm, or both — and selecting treatment accordingly. Many patients achieve substantial symptom control with appropriate medication and lifestyle modification.
What is the INOCA framework?
INOCA stands for Ischaemia with Non-Obstructive Coronary Arteries. It is the clinical framework used to categorise patients who have objective evidence of myocardial ischaemia but no significant obstructive disease on angiography. The INOCA framework encompasses coronary microvascular dysfunction, epicardial vasospasm, microvascular vasospasm, and mixed presentations — and directs appropriate endotype-specific treatment.
Further Reading
Additional Resources
The British Heart Foundation has published patient information on angina and chest pain. Dr Nijjer's published research on coronary physiology and INOCA is indexed on PubMed.
Related Conditions
Related Pages
Chest Pain with a
Normal Angiogram?
Dr Nijjer is one of the UK's foremost specialists in invasive coronary physiology and INOCA diagnosis. Same-week appointments at Harley Street. All major insurers recognised.