Coronary Artery Disease
Diagnosis of Coronary Artery Disease
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These articles provide education to enhance your healthcare partnership. All treatment decisions should involve your healthcare team. Use this knowledge to have informed discussions, not replace medical care.
In Brief
Understanding cardiac testing becomes straightforward once a single insight is clear: different tests answer fundamentally different questions. Is heart muscle being injured right now? Is blood flow becoming inadequate during stress? Is plaque present in the arterial wall? Does anatomy suggest high risk? A result on any one test means “no evidence of the specific problem this test detects” — which is genuinely useful and precise information, with the understanding that each domain answers its own question independently. Results that seem contradictory — a high calcium score alongside a normal stress test, elevated troponin without a classic heart attack, severe symptoms alongside a normal angiogram — become coherent the moment the question each test was designed to answer is understood. This article explains which question each test asks, why clinical context shapes what any result means, and how diagnostic information guides decisions rather than producing certainty.
What Cardiac Tests Are Actually Trying to Figure Out
Coronary testing is not simply about finding plaque. Each test is designed to answer a specific clinical question — and recognising which question each test addresses is what allows results to be interpreted correctly and acted upon with confidence.
There are four core domains:
Is heart muscle being injured right now? This is the injury domain. The relevant tests are troponin and the ECG. The question is urgent and time-sensitive.
Is blood flow becoming inadequate when the heart works harder? This is the ischaemia domain. The relevant tests are stress tests of various kinds. The question applies to both acute presentations and stable symptoms.
Is plaque present in the arterial wall? This is the atherosclerosis domain. The relevant tests are coronary calcium scoring and CT angiography. The question applies primarily to risk stratification and prevention.
What does the anatomy look like, and does it suggest high risk? This is the anatomy domain. The relevant tests are CT angiography and cardiac catheterisation. The question guides revascularisation decisions.
These four domains require different tests, produce different kinds of information, and lead to different clinical decisions. CT angiography straddles the atherosclerosis and anatomy domains — it can show plaque presence and degree of narrowing — but it cannot determine by itself whether a particular narrowing is actually restricting blood flow. That requires physiological testing.
Keeping these four domains distinct is what transforms apparently contradictory results into coherent clinical information. A normal stress test confirms that blood flow was adequate during those testing conditions — precise and actionable information within the ischaemia domain, with plaque burden being a separate question addressed by different tests. A high calcium score confirms that plaque is present — equally precise and actionable within the atherosclerosis domain, with flow restriction being a separate question that requires physiological assessment.
Testing changes the probability that a condition is present or significant — it rarely produces certainty in either direction. A normal result means “no evidence of the specific problem this test detects under these conditions” — which is genuinely useful information, with the understanding that other questions may remain open.
| Clinical Question | Domain | Primary Tests |
|---|---|---|
| Is heart muscle being injured right now? | Injury | ECG, troponin |
| Is blood flow becoming inadequate during stress? | Ischaemia | Stress testing |
| Is plaque present? | Atherosclerosis | Calcium scoring, CT angiography |
| What does the anatomy look like? | Anatomy | CT angiography, catheterisation |
| Is a specific narrowing restricting flow? | Physiology | FFR, iFR |
| Is weak heart muscle recoverable? | Viability | Nuclear imaging, MRI, stress echo |
Why Context Determines What Any Result Means
Before any test is ordered, clinicians estimate how likely it is that the condition of interest is actually present. This is called pre-test probability — the starting point that fundamentally shapes whether testing is useful and how results should be interpreted.[1]
The principle is protective rather than restrictive. When the likelihood of disease is very low, a positive test result is more likely to represent a statistical false alarm than a true finding — and pursuing it can initiate further testing without meaningful benefit. When disease is highly likely — a 65-year-old with diabetes, hypertension, and exertional pressure — testing determines severity and guides strategy rather than establishing whether disease exists at all.
Testing provides the most value in the middle: patients with intermediate probability, where a result can genuinely shift clinical thinking and meaningfully change management.
Two doctors may recommend different tests for the same patient — and both may be clinically reasonable. Local expertise and technology availability differ. The same anatomy may be evaluated with stress imaging at one centre and CT angiography at another. One clinician may prioritise physiological significance; another may prioritise anatomical definition. Evolving evidence, patient preferences, and risk tolerance all influence the decision. Different testing recommendations do not necessarily reflect disagreement about the underlying diagnosis — they often reflect different valid approaches to the same clinical question.
No test performs equally well in every situation. The same test may be highly accurate in one population and unreliable in another. Results are always interpreted alongside clinical context, symptoms, risk factors, and the specific question being asked — not as standalone verdicts.
The Five Clinical Contexts
The appropriate testing strategy depends entirely on which clinical question is being asked. The same symptom — chest pressure — may lead to very different testing depending on whether it began an hour ago or has been predictable for three months.
Emergency: Is Acute Coronary Syndrome Occurring Right Now?
When someone presents with symptoms suggesting acute coronary syndrome — chest discomfort, breathlessness, sweating, nausea — the approach is time-sensitive and protocol-driven.[2] An ECG should be obtained within 10 minutes of arrival. This single test determines the immediate pathway.
An ST-elevation pattern consistent with acute myocardial infarction (STEMI) means the artery is assumed to be completely or near-completely occluded until proven otherwise. Clinicians assume acute occlusion because delays in reperfusion increase irreversible myocardial injury. The catheterisation laboratory is activated immediately. Absent this pattern, the presentation may represent a non-ST-elevation MI (NSTEMI), unstable angina, or a non-cardiac cause — additional evaluation continues in parallel.
STEMI, NSTEMI, and unstable angina are not fundamentally different diseases. They represent different patterns of coronary obstruction and myocardial injury, classified by what the ECG shows and whether troponin is elevated. STEMI typically reflects complete or near-complete occlusion. NSTEMI reflects partial obstruction with detectable myocardial injury. Unstable angina reflects an unstable plaque producing ischaemia without yet causing measurable cell death. All represent acute coronary syndrome — the distinction affects urgency and approach, not the underlying biological process.
For patients with STEMI and multivessel disease, treating only the artery causing the acute event was historically standard practice. The COMPLETE trial demonstrated that in haemodynamically stable patients, addressing significant non-culprit lesions — either during the index procedure or shortly afterward — reduces subsequent cardiovascular events compared to treating the culprit alone.[3] This does not mean every lesion gets stented: lesion significance, patient stability, and procedural risk all factor into the decision.
For patients without ST-elevation, serial troponin measurement distinguishes myocardial infarction from other causes of chest symptoms. High-sensitivity assays allow rapid rule-out protocols — in appropriate clinical contexts, undetectable troponin at baseline and on repeat testing makes acute MI very unlikely.[4,5] But troponin results are never interpreted in isolation. The pattern of rise and fall, the ECG findings, symptom timing, and overall clinical picture all matter.
Troponin measures damage to heart muscle cells — identifying that injury has occurred is exactly what it is designed to do. Elevated troponin indicates myocardial injury, which can result from coronary occlusion (Type 1 MI), but also from conditions that create a supply-demand mismatch without plaque rupture: severe anaemia, prolonged low blood pressure, rapid heart rhythms, respiratory failure, heart failure, sepsis, pulmonary embolism, myocarditis, or severe kidney disease (Type 2 MI or non-ischaemic injury).[4] Identifying the specific cause is the essential next step, because treatment differs substantially depending on the mechanism.
The emergency department is designed to detect immediate danger — not to map lifetime plaque burden. A negative emergency workup means no acute injury was detected under those conditions: precisely the answer the evaluation was designed to provide, while other clinical questions may be addressed through different pathways.
Stable Symptoms: Is Blood Flow Limited Enough to Explain Symptoms?
When someone develops stable, predictable exertional symptoms — pressure with climbing stairs, breathlessness that reliably resolves with rest — the clinical question is different: Is coronary blood flow becoming inadequate when the heart works harder, and would the answer change management?[6]
Stable symptoms are evaluated deliberately rather than urgently. Evaluation begins with symptom pattern, physical examination, baseline ECG, and risk factor assessment. Not everyone with possible coronary symptoms needs extensive testing — the decision depends on pre-test probability and whether results would change what happens next.
Two fundamentally different testing approaches exist:
Functional testing (stress tests of various kinds) asks whether the heart develops evidence of ischaemia — inadequate blood flow — when demand increases. It detects physiological significance but cannot map anatomy.
Anatomic testing (CT angiography, catheterisation) asks what the coronary arteries look like. It can identify plaque and narrowing but may find lesions that are not physiologically significant.
Neither approach is universally superior. The appropriate choice depends on pre-test probability, the clinical question being asked, and what result would be actionable for that patient.
| Functional Testing | Anatomic Testing | |
|---|---|---|
| What it asks | Does blood flow become inadequate during stress? | What do the coronary arteries look like? |
| What it detects | Ischaemia — inadequate flow relative to demand | Plaque and narrowing |
| What it may miss | Non-obstructive plaque; microvascular disease | Lesions that narrow anatomy but don’t restrict flow |
| Best for | Determining physiological significance | Anatomical definition; plaque characterisation |
For decades, the clinical assumption was straightforward: find coronary blockages, fix them, outcomes improve. The ISCHEMIA trial fundamentally challenged this for stable disease.[10] More than 5,000 patients with stable CAD and moderate-to-severe ischaemia were randomised to either immediate catheterisation with revascularisation plus optimal medical therapy, or medical therapy alone with catheterisation reserved for treatment failure.
Over a median follow-up of 3.2 years, there was no significant difference in cardiovascular death, MI, hospitalisation for unstable angina, heart failure, or cardiac arrest. This trial changed how cardiologists think about stable coronary disease. It did not eliminate the role of revascularisation — the invasive strategy provided better symptom control for patients with frequent angina, and high-risk anatomy (particularly left main disease) remains an indication for revascularisation. Patients with severely reduced ejection fraction were excluded from ISCHEMIA, and the evidence base for revascularisation in that group comes from separate trials.[9,10] But it established that in stable patients with acceptable symptoms on medical therapy, finding ischaemia on a stress test does not automatically indicate a procedure is needed.
In stable disease, revascularisation is primarily for symptom relief or specific high-risk anatomy — not because a stress test was positive.
Some patients — disproportionately women — have typical angina and objective ischaemia but no significant obstruction on angiography. This is called INOCA: ischaemia with non-obstructive coronary arteries.[9] A “normal angiogram” in this context is a finding that redirects the clinical question rather than ending it — the ischaemia is real, the symptoms are real, and the problem lies in a different domain: the smaller vessels within the heart muscle itself may be unable to increase blood flow normally (microvascular dysfunction), or the arteries may constrict episodically (vasospasm). Identifying this physiology opens the path to targeted treatment. The CorMicA trial demonstrated that stratifying treatment based on invasive coronary function testing significantly improved angina and quality of life compared to standard care.[24]
Asymptomatic with Risk Factors: How Intensive Should Prevention Be?
For people without symptoms who have cardiovascular risk factors — hypertension, diabetes, dyslipidaemia, family history of premature coronary disease — the testing question is about risk stratification rather than symptom diagnosis.[12]
Risk calculators estimate 10-year cardiovascular event probability based on traditional risk factors. For most people, this provides sufficient guidance for prevention decisions. When the calculator yields an intermediate result — not clearly high enough to warrant treatment, not clearly low enough to defer it — coronary calcium scoring can refine the decision.[13]
A calcium score of zero in an intermediate-risk patient is associated with lower near-term event rates on average in population studies and can support deferring statin therapy in genuinely uncertain cases — a genuinely useful finding that shifts the risk conversation. Clinical context still applies: in younger patients, smokers, and those with diabetes, non-calcified plaque may be present and cardiovascular risk remains relevant to ongoing prevention decisions. A high calcium score confirms substantial atherosclerosis is present and supports more intensive prevention, even when traditional risk factors alone suggested lower risk.
Calcium scoring is a plaque test, not a blockage test. It measures whether plaque has been present long enough to mineralise — it cannot determine whether any narrowing is restricting blood flow.
Routine stress testing of asymptomatic individuals is not recommended.[6] If finding ischaemia in stable symptomatic patients with documented disease (as in ISCHEMIA) does not reduce cardiovascular death or MI compared to medical therapy, finding it in asymptomatic individuals is even less likely to change meaningful outcomes.
Known Coronary Disease with Symptom Change: Has Something Become Unstable?
Patients with established coronary disease — prior myocardial infarction, prior stenting or bypass surgery, known stenoses — require a different framework when symptoms change. The question is no longer whether coronary disease exists: it does. The question is whether something has progressed, become unstable, or is explaining a new pattern of symptoms.[17]
Stenting one lesion does not prevent disease development in other segments. Grafts placed during bypass surgery can narrow or occlude over years — saphenous vein grafts have substantially higher attrition rates over the first decade than arterial grafts.[27] The stented segment can narrow again over time (in-stent restenosis), or a clot can form at the stent site if antiplatelet therapy is stopped prematurely (stent thrombosis).[26] New symptoms in these patients warrant prompt evaluation rather than extended observation.
Any change from a patient’s established stable pattern — symptoms at lower activity levels, at rest, with new associated features — may represent the disease transitioning from stable to unstable. The threshold for evaluation is lower than in patients without known disease.
Before Non-Cardiac Surgery: Would Findings Change the Surgical Plan?
Before major non-cardiac surgery, some patients undergo cardiac evaluation. The goal is not necessarily to find and fix coronary disease — it is to determine whether surgery can proceed safely and whether any cardiac optimisation is needed beforehand.[18]
The key principle: preoperative cardiac testing is only useful if the result would actually change management. Emergency surgery proceeds regardless of cardiac status. Patients with good exercise capacity — able to climb two flights of stairs or walk briskly without cardiac symptoms — demonstrate adequate cardiac reserve for most procedures, though the final decision is made with the surgical and anaesthetic team. Patients with known stable coronary disease on optimal medical therapy often have no additional testing ordered because it would not change the plan.
Testing is most valuable when surgery is intermediate or high risk, functional capacity is uncertain, and results might alter the timing, monitoring, or medical preparation for surgery.
Testing Pathways in Practice
Understanding the four domains and five clinical contexts is most useful when connected to what actually happens — the sequence of tests a person encounters depending on how their cardiac story begins. These are the three most common real-world pathways.[2,25]
Pathway 1: Acute Severe Symptoms — The Emergency Route
A patient arrives in the emergency department with chest pressure, sweating, and breathlessness. This is the most time-critical pathway. The sequence is:
ECG within 10 minutes — the single most important immediate test. If it shows ST-elevation consistent with STEMI, the artery is assumed acutely occluded. The patient goes directly to the catheterisation laboratory. There is no stress test, no CT scan, no waiting for biomarkers — the anatomy is addressed immediately because every minute matters.
If no ST-elevation — the presentation may be NSTEMI, unstable angina, or a non-cardiac cause. Serial high-sensitivity troponin measurements at 0 and 1–3 hours, combined with the ECG and clinical assessment (often structured using the HEART score — History, ECG, Age, Risk factors, Troponin), stratify risk.[23] High-risk patients — those with rising troponin, high-risk ECG changes, or a concerning clinical picture — proceed to early catheterisation, typically within 24 hours.[2] Lower-risk patients may be safely discharged with close follow-up or outpatient evaluation.
Key point: in this pathway, catheterisation is both the diagnostic and the therapeutic procedure — it identifies the anatomy and allows immediate treatment if intervention is warranted. A stress test is not part of the acute route.
Pathway 2: Stable Exertional Symptoms — The Outpatient Route
A patient reports predictable chest pressure when climbing stairs, reliably resolving with rest, present for several weeks. This pathway is deliberate rather than urgent. The sequence per the 2021 ACC/AHA Chest Pain Guideline:[25]
History, examination, baseline ECG, risk factor assessment — establishes pre-test probability before any imaging.
Risk estimation — determines the testing approach. For intermediate-to-high pre-test probability, the guideline gives a Class I recommendation for either CCTA or stress imaging as the first-line test. Class I is the highest guideline recommendation level — evidence and expert consensus indicate that benefit substantially outweighs risk, and the intervention is recommended.[25]
- CCTA is generally preferred when the patient can cooperate with breath-holding, heart rate is controllable, and coronary calcification is not excessive. It provides anatomical information and, if an intermediate stenosis is found, CT-FFR can assess physiological significance from the same scan.[25]
- Stress imaging (stress echocardiography, nuclear stress, or stress MRI) is preferred when the baseline ECG is abnormal, when the patient cannot exercise adequately, or when functional information is the primary clinical need.
If CCTA finds intermediate stenosis (40–70%) → CT-FFR if available, or proceed to invasive catheterisation with FFR/iFR assessment.
If stress imaging is positive or high-risk features are present → invasive catheterisation.
If both are normal or low-risk → medical therapy and lifestyle optimisation; no catheterisation.
Key point: in this pathway, catheterisation is reserved for patients in whom non-invasive testing identifies high-risk features or where the anatomy remains unclear. Most patients with stable symptoms are evaluated and managed without ever reaching the catheterisation laboratory.
| Symptom Presentation | First Test | Typical Next Step |
|---|---|---|
| Acute severe symptoms, ST-elevation | ECG (10 min) | Direct to cath lab — no stress test |
| Acute symptoms, no ST-elevation | ECG + serial troponin | Risk-stratified: early cath if high-risk; outpatient if low-risk |
| Stable exertional symptoms, intermediate–high probability | CCTA or stress imaging | Cath if positive/high-risk; medical therapy if negative |
| Stable exertional symptoms, low probability | CAC scoring or exercise ECG | Reassurance or intensify prevention if positive |
| Asymptomatic with risk factors | Risk calculator | CAC if intermediate risk; intensify prevention if high CAC |
Pathway 3: Asymptomatic with Risk Factors — The Prevention Route
A patient has hypertension, mildly elevated cholesterol, and a family history of early heart disease, but no symptoms. The question is not diagnosis but risk stratification to guide prevention intensity.
Risk calculator (PREVENT-ASCVD equations) estimates 10-year cardiovascular event probability.[7] Most patients in the borderline-to-intermediate range (3–<10% 10-year risk) where the statin decision is uncertain benefit most from additional information.
Coronary calcium scoring — if the 10-year risk is in this intermediate range, a CAC scan can shift the decision meaningfully. A score of zero supports deferring statin therapy and reassessing in several years. A score ≥100 or ≥75th percentile for age and sex supports initiating therapy.[11,15,25]
There is no stress test in this pathway under guideline recommendations — finding ischaemia in asymptomatic individuals does not change cardiovascular outcomes compared to risk-factor-guided prevention alone.[6]
The Tests: What Each One Reveals
ECG (Electrocardiogram)
The ECG records the heart’s electrical activity. It can detect patterns consistent with acute ischaemia or prior myocardial injury, and identify rhythm abnormalities. In the injury domain, it is the fastest and most immediately actionable test — and obtaining one within 10 minutes of presentation is a guideline standard for any suspected ACS.[2]
Its domain is electrical: acute ischaemia patterns, prior injury, and rhythm. Coronary anatomy, plaque burden, and stable disease are answered by different tools — and a normal ECG is a genuinely reassuring finding within its own domain, confirming no acute electrical abnormality at that moment.
Troponin
Troponin is a protein released into the bloodstream when heart muscle cells are damaged. It is the injury-domain test. High-sensitivity assays can detect very small quantities, enabling rapid and reliable identification — or exclusion — of acute MI in appropriate clinical contexts.[4,5]
Troponin elevation means heart muscle has been injured. It does not identify the cause. In addition to coronary occlusion, troponin rises from heart failure, myocarditis, pulmonary embolism, sepsis, severe arrhythmias, kidney disease, and any condition that stresses or damages the myocardium. Seeing an elevated troponin is the beginning of a diagnostic process — not its conclusion.
The pattern matters as much as the number. A troponin level that rises progressively over several hours suggests ongoing injury. One that is mildly elevated and stable may reflect chronic cardiac strain or prior damage. One that peaks and then falls suggests acute injury that has peaked. Serial measurements — typically at 0 and 1–3 hours — provide the pattern, not any single value.
Echocardiography
Echocardiography uses ultrasound to image the heart in real time. It shows how each region of the heart muscle contracts, the size and function of the heart chambers, and valve anatomy and function. Regions with inadequate blood supply — from a prior heart attack or from ongoing ischaemia — may contract weakly, show no movement at all, or even bulge outward during contraction rather than squeezing inward. These wall motion abnormalities help localise prior or ongoing ischaemia.
Echocardiography cannot directly visualise coronary arteries or plaque. A normal resting echocardiogram provides valuable information about cardiac structure and function at rest — and when ischaemia may only appear during increased demand, stress echocardiography adds a provocative component to capture that additional information.
An important additional value of echocardiography: it identifies aortic valve stenosis — narrowing of the valve at the outflow of the left ventricle — which can produce exertional chest pressure, breathlessness, and reduced exercise tolerance that closely resembles coronary angina. Severe aortic stenosis requires valve intervention, and echocardiography is the key test for detecting it. Many patients have both conditions, and recognising aortic stenosis ensures that the right treatment pathway is pursued alongside coronary evaluation.
Ejection fraction (EF) measures the proportion of blood the left ventricle pumps out with each contraction. If the heart fills with 100 mL and ejects 60 mL, the EF is 60%. Normal EF is typically at or above the mid-50s. An EF below 40% indicates significantly reduced pumping function (HFrEF — heart failure with reduced ejection fraction), which carries important implications for prognosis and treatment.[20]
The 2022 AHA/ACC/HFSA Heart Failure Guideline defines the following EF categories, which are used consistently across clinical practice:[20]
| EF Range | Classification |
|---|---|
| ≥50% | DPreserved — normal or near-normal pumping |
| 41–49% | Mildly reduced |
| ≤40% | Reduced (HFrEF) |
| ≤35% | Severely reduced — viability assessment becomes relevant |
Natriuretic peptides (BNP and NT-proBNP) are blood tests measuring hormones released when the heart is under sustained pressure or volume stress. Elevated levels suggest heart failure or significant cardiac strain, and help distinguish cardiac from non-cardiac causes of breathlessness. They do not diagnose coronary disease directly, but elevated levels in a patient with chest symptoms support a cardiac rather than non-cardiac explanation for symptoms.[20]
Viability testing becomes relevant when EF is markedly reduced — typically at or below 35% — and clinicians are considering whether revascularisation might improve heart function.[20] The key question is whether weak heart muscle is permanently scarred or simply underperfused and potentially recoverable.
Hibernating myocardium describes viable muscle that is alive but not contracting well because its blood supply is chronically reduced. This muscle may recover meaningful function if adequate blood flow is restored. Scarred myocardium has died and been replaced by fibrous tissue — it cannot recover regardless of revascularisation. Viability testing distinguishes these by examining whether tissue retains metabolic activity (nuclear imaging with PET/FDG) or lacks scar (cardiac MRI with late gadolinium enhancement), or responds to a low-dose medication that stimulates temporarily improved contraction in viable cells (dobutamine stress echocardiography).
Stress Testing
Stress testing evaluates the ischaemia domain: does the heart develop evidence of inadequate blood flow when demand increases? It answers a specific physiological question — not a plaque question, and not an anatomical question. That precision is its strength.
The heart is stressed either by exercise (preferred when feasible, because exercise capacity itself provides prognostic information) or by medications that mimic the effects of exercise on the heart.[6] During or after stress, the study looks for ECG changes, wall motion abnormalities (stress echocardiography), or reduced perfusion to specific regions (nuclear stress imaging). Any of these patterns indicates that blood flow cannot keep pace with demand in the territory supplied by a narrowed artery.
A normal stress test is a meaningful result: it confirms that no flow-limiting ischaemia was detected under those testing conditions. Understanding its domain — ischaemia, not plaque burden — also clarifies why separate testing may be appropriate when the clinical question involves atherosclerosis or anatomical risk rather than current flow limitation. Plaques can accumulate and remodel over years before producing detectable ischaemia, which is why plaque-domain tests like calcium scoring address a genuinely different question.
| Modality | Best Used When | Important Limitations |
|---|---|---|
| Exercise ECG | Patient can exercise adequately; baseline ECG is interpretable | Lower sensitivity; cannot localise ischaemia; limited if baseline ECG abnormal |
| Stress echocardiography | Good cardiac windows expected | Operator-dependent; image quality limitations in some patients |
| Nuclear stress (SPECT/PET) | Poor echo windows; perfusion quantification needed | Radiation exposure; some false positives from attenuation artefact |
| Stress cardiac MRI | Comprehensive; no radiation | Limited availability; requires breath-holding; device contraindications |
Coronary Calcium Scoring
Coronary calcium scoring uses a CT scan to detect and quantify calcified plaque in the coronary arteries. Where calcium is found, atherosclerosis has been present long enough to mineralise — typically years. A detectable score is direct evidence that plaque exists, independent of whether any symptom is present or any risk calculator has flagged elevated risk.[11,12]
Calcium scoring is an atherosclerosis-domain test. It precisely measures calcified plaque presence and quantity. Physiological flow assessment and non-calcified plaque characterisation are addressed by different tests designed specifically for those questions — which is why calcium scoring pairs naturally with risk calculators and, in selected cases, with functional or anatomic evaluation.
Score ranges based on the Agatston method, interpreted per the MESA cohort framework:[11,12]
| CAC Score | Why It Matters |
|---|---|
| 0 | No calcified plaque detected; associated with lower near-term event rates on average |
| 1–99 | Mild atherosclerosis present |
| 100–299 | Moderate atherosclerosis |
| ≥300 | Extensive atherosclerosis |
A score of zero is associated with lower near-term event rates — a useful finding for guiding statin decisions in intermediate-risk patients, discussed further in the asymptomatic prevention pathway above. A high score confirms substantial atherosclerosis throughout the coronary tree, supporting more intensive preventive treatment rather than procedural evaluation.
Coronary CT Angiography (CCTA)
CCTA uses CT scanning with intravenous contrast to create detailed images of the coronary arteries, showing both plaque presence and degree of narrowing. It straddles the atherosclerosis and anatomy domains and is increasingly valuable because it can detect plaque before narrowing becomes severe enough to produce symptoms or abnormal stress tests.[8] When the clinical question extends to physiological significance — whether a particular narrowing is actually restricting flow — CT-FFR adds a computational layer to the same dataset, estimating flow significance without requiring catheterisation. Where available and technically feasible, this combination answers both the anatomical and physiological questions from a single non-invasive study.[22,25]
A normal CCTA makes significant obstructive coronary disease unlikely. CCTA requires heart rate control, breath-holding, and minimal arrhythmia; heavy coronary calcification can create artefact that limits lumen assessment, in which case other imaging approaches are selected.
Invasive Coronary Angiography (Cardiac Catheterisation)
Catheterisation provides the most precise available anatomical map of the coronary arteries. A catheter is advanced from an artery in the wrist or groin to the coronary openings, contrast is injected, and X-ray imaging reveals the vessel lumen — the channel through which blood flows.[14]
Angiography shows the inside silhouette of the artery lumen — not the vessel wall itself. A plaque may extend deep into the wall without narrowing the lumen significantly, because arteries compensate by expanding outward as plaque accumulates (Glagov remodelling). This means angiography may underestimate plaque burden while accurately depicting the degree of narrowing.
The degree of narrowing on angiography does not determine functional significance alone. A 70% narrowing in a large artery may allow adequate flow; a 50% narrowing in a small artery or at a bifurcation may restrict it meaningfully. Percentage estimates from visual inspection of angiographic images have significant inter-observer variability — and the treatment threshold (stent versus medical therapy) depends critically on whether the lesion is actually 50% or 55%, or 68% or 72%. For intermediate lesions, additional physiological or imaging assessment is routinely required.
Understanding what a percentage means — and what else matters: When a patient is told “you have a 60% blockage,” the natural response is to focus on that number. In practice, percentage stenosis is one data point in a richer picture. The length of the lesion, the size of the vessel, whether it is the sole supply to a large territory, what happens to blood flow under stress, and whether the plaque is biologically stable or vulnerable all contribute to the clinical decision. This is why a person with a “40% blockage” can have a heart attack while someone with an “80% blockage” remains stable for years — plaque biology matters as much as plaque size, and both are part of what cardiologists assess.
Fractional Flow Reserve (FFR) and iFR
FFR and iFR answer a specific physiological question: does this particular narrowing restrict blood flow enough that fixing it would benefit the patient?[16] They fill the gap between anatomy (what the artery looks like) and physiology (whether flow is actually impaired).
A pressure-sensing wire is advanced past the narrowing. FFR measures the pressure gradient across the stenosis during maximal blood flow induced by a medication (adenosine). iFR makes a similar measurement at rest during a specific part of the cardiac cycle without requiring medication. Both generate a number — a ratio of pressure distal to the lesion compared to pressure proximal to it. A ratio at or below the threshold indicates the lesion is restricting flow and may benefit from intervention. A ratio above the threshold indicates the lesion is not restricting flow — and guidelines recommend against stenting such lesions.[21]
Guideline-recommended thresholds per the 2021 ACC/AHA/SCAI Revascularisation Guideline and the FAME trial:[15,21]
| Index | Threshold | Interpretation |
|---|---|---|
| FFR | ≤0.80 | Flow-limiting — revascularisation may benefit |
| FFR | >0.80 | Not flow-limiting — stenting not recommended |
| iFR | ≤0.89 | Flow-limiting |
| iFR | >0.89 | Not flow-limiting |
FFR tells you whether the narrowing is restricting flow — not whether the plaque is biologically stable. A normal FFR in a lipid-rich, thin-capped lesion does not indicate low future risk; it indicates that flow is currently adequate. Risk reduction requires medical therapy regardless of FFR result.
IVUS and OCT
Both IVUS (intravascular ultrasound) and OCT (optical coherence tomography) are catheter-based imaging tools that see inside the coronary artery wall rather than just its lumen silhouette.
Angiography shows only what is inside the artery — IVUS allows cardiologists to see the vessel wall itself, including plaque burden, composition, stent expansion, and the precise dimensions of the lumen and surrounding structures. It is particularly useful for left main assessment, optimising stent placement, and evaluating lesions where angiography is ambiguous.[21]
OCT uses light-based imaging rather than ultrasound, providing approximately ten times the resolution of IVUS but with less penetration depth into the vessel wall. It is exceptionally useful for examining stent placement detail, detecting subtle dissections, identifying thrombus, and characterising vulnerable plaque features — particularly thin fibrous caps over large lipid cores, which are structurally at risk for rupture.[21]
Neither IVUS nor OCT measures blood flow — that still requires FFR or iFR.
Plaque Biology Matters as Much as Plaque Size
Most heart attacks do not occur at the most severely narrowed segment of the coronary tree. They occur when a vulnerable plaque ruptures — triggering sudden clot formation that converts a moderate narrowing into a complete or near-complete obstruction within minutes.
Vulnerable plaques share certain biological features: a thin fibrous cap, a large lipid-rich core beneath it, active inflammation degrading the cap from within, and a tendency toward outward remodelling that preserves the lumen — making the plaque invisible to angiography until it ruptures. A heavily calcified plaque causing 80% narrowing may be structurally stable and remain so for years. A lipid-rich plaque causing 40% narrowing may rupture with no warning. The degree of narrowing visible on an angiogram reflects anatomy. It does not predict biological behaviour.
Current imaging can characterise plaque biology in important ways — OCT can identify thin-capped lesions, and CCTA can provide plaque composition information — and this is an active area of development. Medical therapy addresses the biology that imaging identifies: statins stabilise plaque, reduce lipid core size, and promote cap thickening across the entire coronary tree, not just at the site of a stent. Targeting plaque biology systemically is what makes medical therapy effective beyond anatomy.
Stable plaque still matters. Even plaque that is not immediately threatening to rupture reflects the cumulative vascular injury that predicts long-term cardiovascular risk. A high calcium score or diffuse non-obstructive disease on CCTA reflects years of atherosclerotic activity — and where extensive calcified plaque exists, non-calcified and potentially less stable plaque often coexists. Prevention targets the biology; procedures address the anatomy.
When Results Seem to Contradict
Results from different cardiac tests occasionally appear to point in different directions — and understanding why they do not actually conflict is one of the most useful insights in cardiac medicine. In nearly every case, the apparent contradiction resolves immediately when the four domains are applied: the tests were answering different questions, both accurately.
| Apparent Contradiction | What Is Actually Happening |
|---|---|
| High calcium score + normal stress test | DAtherosclerosis domain: plaque is present. Ischaemia domain: it has not progressed enough to restrict flow during exercise. Both results are accurate and compatible. |
| Severe symptoms + normal angiogram | Ischaemia is real; the problem is microvascular dysfunction or vasospasm — not a focal stenosis amenable to stenting. INOCA. Different physiology, not a diagnostic error. |
| Elevated troponin + no STEMI | Troponin indicates myocardial injury from any cause — not exclusively coronary occlusion. The injury may be from a Type 2 mechanism, heart failure, or another cardiac condition. |
| Normal ED evaluation + plaque on CT later | The ED test ruled out acute injury. The CT identified atherosclerosis — a different domain, a different question, both accurate. |
| 70% blockage on angiogram + normal FFR | Anatomically the narrowing appears significant; physiologically, blood flow across it is not restricted. Guidelines recommend against stenting a haemodynamically non-significant lesion. |
| Positive stress test + no stentable blockage on catheterisation | Stress testing detected ischaemia; catheterisation found no focal stenosis of typical interventional threshold. The ischaemia may be from microvascular dysfunction, diffuse non-obstructive disease, or vasospasm — all real, none amenable to stenting. |
Some tests are “today tests” — designed to detect immediate danger (acute injury, acute ischaemia). Others are “trajectory tests” — designed to assess long-term disease biology and risk. When a trajectory test is expected to predict a near-term event, contradictions appear. When each test is understood as answering its own specific domain question, they become complementary rather than conflicting.
Understanding What Each Test Actually Shows
Knowing what a test is and is not designed to detect helps set the right expectations — and makes it possible to ask the right follow-up questions with a clinician.
| How a Result Is Often Interpreted | What the Test Was Actually Designed to Show |
|---|---|
| “A normal stress test means my arteries are clear.” | Stress tests evaluate whether blood flow becomes inadequate during increased demand — an important finding. Plaque presence is a separate question that requires a different test. |
| “A high calcium score means I need a stent.” | Calcium scoring measures atherosclerotic burden and guides prevention intensity. It is a plaque test, not a blockage test — procedural decisions require additional physiological assessment. |
| “Elevated troponin always means a classic heart attack.” | Troponin indicates myocardial injury, which can arise from many conditions. Identifying the cause is the essential next step, and determines the appropriate treatment. |
| “A 70% blockage needs to be fixed.” | Percentage narrowing is one data point. Physiological significance (FFR/iFR), symptoms, overall anatomy, and clinical context all contribute to the decision — and often reveal that medical therapy is the right approach. |
| “A normal result means no future risk.” | Testing shifts probability and guides current decisions. Cardiovascular risk is a biological trajectory shaped by modifiable factors, not a fixed verdict from a single test. |
| “More testing means more safety.” | The right test for the right question is the goal. Each test involves real tradeoffs, and testing that does not change management carries risk without corresponding benefit. |
Why Cardiologists Sometimes Defer Stenting
Understanding why a cardiologist recommends medical therapy rather than a procedure — even when a visible narrowing is present — reflects one of the most important advances in cardiovascular medicine in the past decade.
As the ISCHEMIA trial established (discussed in the stable symptoms section above), in patients with stable coronary disease and acceptable symptoms, medical therapy produces equivalent outcomes to upfront revascularisation for the hard endpoints of death and myocardial infarction. Medical therapy is the appropriate first approach, not a second-best option. Revascularisation remains valuable for symptom relief in patients with frequent angina, and for specific high-risk anatomy — particularly left main disease.[9,10]
A physiologically non-significant lesion — one where FFR or iFR confirms that flow is not being restricted — should not be stented based on anatomy alone. The 2021 ACC/AHA/SCAI Revascularisation Guideline gives this a Class III recommendation — meaning the intervention should not be performed, as evidence indicates no benefit or potential harm from the procedure.[21]
Deferring intervention in these situations reflects the best available evidence about when procedures help and when they do not.
The Testing Cascade and Choosing the Right Test
Each test involves real tradeoffs. Radiation exposure, iodinated contrast (with implications for kidney function), allergic reactions, procedural risks in invasive studies, and the clinical complexity of managing progressive uncertainty all accumulate across a testing sequence. When a test returns an equivocal or incidental finding, it initiates the next evaluation — which may return another intermediate result. At each step, particularly when the initial probability of meaningful disease was low, the proportion of actionable findings relative to incidental ones shifts.[19]
The goal is not fewer tests — it is the right test for the right question, in the right clinical context, for a patient whose pre-test probability makes the result meaningful. A well-chosen test that changes management provides genuine value. Testing is most useful when the information it generates — whether the result is normal, abnormal, or intermediate — would alter treatment, clarify prognosis, or meaningfully support decision-making.
A test result is interpreted together with the patient. Clinical context, symptoms, risk factors, prior test results, and the patient’s own values and goals all shape what any finding means and what should happen next. The person being tested is always part of the interpretation.
What This Means
Coronary testing is a process of progressively answering specific questions — each test designed to illuminate one domain of cardiac health, contributing to a picture that guides decisions with increasing precision. Understanding which question each test was designed to answer is what makes results interpretable, what makes apparently contradictory findings coherent, and what allows patients and clinicians to work together toward the best decisions.
Biology is continuous; lesions exist on spectra; imaging has inherent limits; physiology changes with demand, heart rate, and metabolic state. Medicine generates information that, in context, supports the best available decision — and that is genuinely powerful. The more clearly a patient understands what testing is measuring and why, the more meaningfully they can participate in conversations about their own cardiac health.
The goal of understanding cardiac testing is not to second-guess clinical decisions — it is to participate in them more meaningfully. Knowing which question a test was designed to answer, what a result specifically shows, and what question a clinician might address next transforms a patient from a passive recipient of testing into an informed partner in their own cardiac care.
Key Terms
Acute coronary syndrome (ACS): Umbrella term encompassing unstable angina, NSTEMI, and STEMI — conditions caused by sudden reduction in coronary blood flow, typically from plaque disruption and thrombus formation.
CT-FFR (CT-derived fractional flow reserve): Computational analysis of CT angiography data that simulates blood flow and estimates whether a narrowing is physiologically significant, without requiring catheterisation.
Ejection fraction (EF): The percentage of blood the left ventricle pumps out with each contraction. Normal is typically at or above the mid-50s; below 40% indicates significantly reduced pumping function.
Guideline recommendation class: A standardised grading system used by the ACC/AHA and other medical societies to indicate the strength of evidence behind a clinical recommendation. Class I means the intervention is recommended — benefit substantially outweighs risk. Class IIa means the intervention is reasonable — benefit likely outweighs risk. Class IIb means the intervention may be considered — benefit is uncertain or marginal. Class III means the intervention should not be performed — evidence indicates no benefit, or that harm may outweigh benefit.
FFR (Fractional flow reserve): A pressure-wire measurement across a coronary narrowing during cardiac catheterisation, determining whether the lesion restricts blood flow enough to benefit from intervention. Threshold: ≤0.80 indicates flow limitation.
Heart Team: Multidisciplinary approach to complex revascularisation decisions, involving cardiac surgeons and interventional cardiologists reviewing cases together to determine optimal treatment strategy.
Hibernating myocardium: Viable but poorly contracting heart muscle chronically underperfused at rest; may recover function if blood flow is restored before irreversible fibrosis occurs.
iFR (Instantaneous wave-free ratio): A pressure-wire measurement similar to FFR but performed without adenosine administration. Threshold: ≤0.89 indicates flow limitation.
INOCA (Ischaemia with Non-Obstructive Coronary Arteries): Angina and objective ischaemia in the absence of significant epicardial stenosis, typically due to microvascular dysfunction or vasospasm.
ISCHEMIA trial: Landmark 2020 trial demonstrating that in stable CAD with moderate-to-severe ischaemia, an initial invasive strategy did not reduce cardiovascular death or MI compared to optimal medical therapy alone.
IVUS (Intravascular ultrasound): Catheter-based ultrasound imaging of the coronary artery from inside, showing vessel wall and plaque rather than lumen silhouette alone.
NSTEMI: Non-ST-elevation myocardial infarction — MI confirmed by troponin elevation without ST-segment elevation on ECG.
OCT (Optical coherence tomography): Light-based catheter imaging of the coronary artery, providing very high resolution of near-surface structures including plaque morphology, stent apposition, and thrombus.
Pre-test probability: The estimated likelihood of a condition being present before any test is performed, based on clinical features, symptoms, and risk factors. Shapes how test results should be interpreted.
STEMI: ST-elevation myocardial infarction — MI with ST-segment elevation on ECG, indicating complete or near-complete coronary occlusion requiring immediate reperfusion.
SYNTAX score: An angiographic scoring system grading coronary disease complexity; higher scores indicate more complex anatomy where bypass surgery typically offers outcome advantages over stenting.
Type 1 MI: Myocardial infarction caused by plaque rupture or erosion leading to coronary thrombus formation and obstruction.
Type 2 MI: Myocardial infarction caused by supply-demand mismatch without plaque rupture — from conditions such as severe anaemia, hypotension, tachyarrhythmia, or respiratory failure.
Vulnerable plaque: A plaque with a thin fibrous cap, large lipid-rich core, and active inflammation — structurally prone to rupture regardless of the degree of luminal narrowing it produces.
References
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