Coronary Anatomy and Segmental Classification for the Clinician

Introduction

Clinical assessment of coronary artery disease (CAD) requires integration of symptoms, cardiovascular risk, coronary anatomy, myocardial ischaemia, ventricular function and the anticipated benefit–risk balance of revascularization. Coronary angiography remains primarily an anatomical examination, whereas contemporary decision-making increasingly combines anatomical imaging with functional assessment.

A central practical principle is that the visual severity of a stenosis does not reliably establish its haemodynamic importance. A lesion that appears moderate may be functionally important, while an anatomically severe lesion may not identify the patient most likely to benefit from intervention. Conversely, apparently mild lesions may rupture and precipitate myocardial infarction or sudden death. Coronary anatomy must therefore be interpreted within the broader clinical and physiological context.

Definition and Pathophysiology

Coronary artery disease and obstructive stenosis

Anatomically significant epicardial CAD is conventionally defined as stenosis of at least 70%, while a left main coronary stenosis of at least 50% is considered significant. These thresholds describe luminal narrowing, not necessarily the physiological effect of the lesion.

The apparent percentage stenosis is calculated relative to an adjacent reference segment presumed to be relatively normal. This assumption may be incorrect when atherosclerosis is diffuse, leading to underestimation of the overall disease burden. Angiography also provides limited information about plaque composition, vulnerability and the risk of future plaque rupture.

Anatomical severity versus functional significance

The physiological effect of a coronary lesion depends on more than its visual diameter reduction. Relevant determinants include:

• Lesion eccentricity

• Vessel tortuosity

• Calcification

• Plaque rupture or asymmetric filling defects

• Serial lesions

• Vessel size

• The relationship of the lesion to side branches

• The extent and distribution of downstream myocardium

• Collateral circulation

• Diffuse distal disease

Thus, a visually “borderline” 50–70% lesion may be functionally significant, whereas a severe-appearing lesion may not produce demonstrable ischaemia. Functional assessment with pressure or flow measurements, intravascular imaging, or fractional flow reserve derived from computed tomography can refine interpretation.

Coronary plaque and future events

Angiographic stenosis severity is an imperfect predictor of future myocardial infarction or sudden death. Lesions causing only mild obstruction may rupture, thrombose and occlude. Many acute myocardial infarctions arise from lesions that previously obstructed less than 50% of the lumen. Assessment of total coronary disease burden, including non-obstructive plaque, therefore contributes prognostic information beyond identification of focal severe stenoses.

Coronary anomalies

Coronary artery anomalies are uncommon among the general population but account for a substantial proportion of sudden cardiac death in young athletes. Clinically, they may be categorized according to whether they are:

• Not associated with ischaemia

• Associated with episodic ischaemia

• Associated with obligatory ischaemia

Anomalies may involve the coronary ostium, origin, termination, congenital absence or hypoplasia. Anomalous aortic origin of a coronary artery from the opposite sinus of Valsalva is associated with increased sudden-death risk, particularly in individuals younger than 35 years during or after vigorous exercise. Anomalous origin of the left coronary artery is less frequent but is considered more malignant than anomalous origin of the right coronary artery.

High-risk anatomical features include:

• An interarterial course between the aorta and pulmonary artery

• A slit-like orifice

• A high origin

• Acute-angle take-off

• An intramural course, including its length

Coronary Arterial Segments and Clinical Classification

Epicardial coronary territories

Clinical interpretation commonly considers the major epicardial vessels and their myocardial territories:

• Left main coronary artery

• Left anterior descending artery

• Left circumflex artery

• Right coronary artery

The left main coronary artery is clinically important because disease compromises both the left anterior descending and left circumflex distributions. Proximal left anterior descending disease is particularly relevant because it threatens a large anterior and septal myocardial territory. Right and circumflex coronary disease must be interpreted in relation to dominance, branch involvement and the distribution of threatened myocardium.

The source material does not provide a formal numbered segmental nomenclature or a complete branch-by-branch anatomical classification. It does, however, identify clinically important proximal and mid-vessel segments, the left main stem, the proximal left anterior descending artery, major-vessel segments and lesions involving bifurcations or long and complex coronary segments.

Anatomical patterns relevant to risk

The following patterns are identified as high-risk findings in chronic coronary disease:

The significance of these patterns is prognostic and therapeutic rather than purely descriptive. Decisions regarding revascularization should also incorporate ventricular function, symptom burden, ischaemia, comorbidity, surgical risk, anatomical complexity, patient preferences and expected quality-of-life benefit.

Coronary anatomy and revascularization complexity

Important anatomical considerations include:

• Left main involvement

• Proximal vessel disease

• The number of diseased vessels

• The SYNTAX score or other measures of anatomical complexity

• Vessel calibre

• Calcification

• Tortuosity

• Bifurcation anatomy

• Diffuse distal disease

• The availability of suitable targets for revascularization

Diffuse severe distal disease may make a patient unsuitable for either PCI or CABG. In complex cases, treatment selection should be made by a Heart Team involving interventional cardiology, cardiac surgery, non-interventional cardiology and other relevant specialties.

Clinical Presentation and Symptoms

Symptoms suggesting chronic coronary disease

A detailed history should define:

• Onset

• Duration

• Character

• Location

• Triggers

• Relieving factors

• Time of day

• Associated symptoms

Potential angina equivalents include:

• Chest pain precipitated by emotional stress

• Exertional dyspnoea

• Exertional dizziness

• Pain in the arm, jaw, neck or upper back

• Fatigue

Symptoms may result from obstructive epicardial CAD, coronary vasospasm, microvascular dysfunction or another cardiac or non-cardiac cause. In patients with persistent or refractory symptoms, assessment should not stop at the identification of obstructive lesions; ANOCA and INOCA endotypes may require coronary functional testing.

Acute coronary syndromes

Patients with non-ST-segment elevation acute coronary syndrome may present with refractory angina, haemodynamic instability or electrical instability. These features warrant urgent or immediate invasive assessment when there are no serious comorbidities or procedural contraindications.

ST-segment elevation myocardial infarction generally requires urgent invasive treatment. Primary PCI is recommended for patients with ischaemic symptoms of less than 12 hours’ duration and is reasonable between 12 and 24 hours when clinical or ECG evidence of ongoing ischaemia persists. Primary PCI is also recommended in STEMI complicated by cardiogenic shock or acute severe heart failure, irrespective of the time since symptom onset.

Evaluation and Physical Examination

Initial clinical assessment

Initial assessment combines symptoms, cardiovascular risk factors, previous cardiovascular disease, examination findings and resting ECG. The pre-test likelihood of obstructive epicardial CAD should be estimated with the Risk Factor-weighted Clinical Likelihood model and refined using additional clinical information.

Factors that may modify the likelihood estimate include:

• Peripheral arterial findings

• Resting ECG abnormalities

• Resting echocardiography

• Vascular calcification identified on previous imaging

• Diabetes

• Chronic kidney disease

• Left ventricular ejection fraction

• The anginal threshold

When the estimated pre-test likelihood is very low, below 5%, further diagnostic testing may be deferred. In patients with a low likelihood above 5% but no more than 15%, coronary artery calcium scoring may assist reclassification.

Physical examination

The source material does not provide a comprehensive physical-examination description for suspected chronic coronary disease. It specifically supports assessment of the peripheral arteries as a factor that can modify the likelihood of CAD. Examination should therefore be integrated with the symptom history and resting investigations rather than used in isolation.

Risk stratification

Risk of adverse events should begin with clinical assessment and be refined using non-invasive testing. High-risk findings include:

• Duke Treadmill Score below −10

• Ischaemia involving at least 10% of the left ventricular myocardium on stress SPECT or PET

• Stress-induced hypokinesia or akinesia in at least 3 of 16 segments on stress echocardiography

• Stress perfusion defects in at least 2 of 16 segments on stress CMR

• At least 3 dobutamine-induced dysfunctional segments on stress CMR

• High-risk CCTA patterns listed above

Diagnostics

Resting electrocardiography

Resting ECG is part of the initial assessment of individuals with suspected chronic coronary syndrome. It also contributes to refinement of the clinical likelihood estimate and is central to acute coronary syndrome classification.

In suspected vasospastic angina, ambulatory ECG monitoring should be considered. In coronary anomalies, ECG may demonstrate rhythm or conduction disturbances, although the source material does not provide a specific ECG pattern for each anomaly.

Coronary computed tomography angiography

CCTA is recommended for patients with suspected chronic coronary syndrome and a low or moderate pre-test likelihood, defined in the source material as greater than 5% to 50%. It can diagnose obstructive CAD and estimate the risk of major adverse cardiovascular events.

CCTA is also recommended when functional imaging is non-diagnostic in patients with low or moderate likelihood. It is preferred for excluding obstructive CAD in this group and may be considered for patients with an intermediate coronary stenosis in a proximal or mid-vessel segment, using CT-derived FFR where appropriate.

CCTA provides particularly important information in coronary anomalies. It is the preferred modality for high-risk anatomy, including:

• Intramural courses

• Slit-like orifices

• Acute-angle take-off

• High or abnormal ostial origin

The limitations of CCTA and other CT approaches are not detailed comprehensively in the source material. Earlier guidance identifies circumstances in which image quality may be poor, including extensive coronary calcification, irregular heart rate, significant obesity and inability to cooperate with breath-holding.

Functional non-invasive imaging

Stress echocardiography is recommended for patients with a moderate or high pre-test likelihood of obstructive CAD, defined as greater than 15% to 85%. It is used to diagnose myocardial ischaemia and estimate major adverse cardiovascular event risk.

If two or more contiguous myocardial segments are not adequately visualized, intravenous ultrasound contrast microbubbles should be used to improve diagnostic accuracy. Contrast-enhanced myocardial perfusion assessment can provide information beyond wall motion and improve risk stratification. Doppler assessment of left anterior descending coronary flow reserve may be considered to improve risk stratification and assess microvascular function.

SPECT or, preferably, PET myocardial perfusion imaging is recommended in patients with moderate or high pre-test likelihood to:

• Diagnose and quantify ischaemia

• Identify scar

• Estimate major adverse cardiovascular event risk

• Quantify myocardial blood flow with PET

When SPECT or PET is performed using an unenhanced chest CT for attenuation correction, coronary artery calcium scoring should be measured to improve detection of non-obstructive and obstructive CAD.

Stress CMR is recommended in patients with moderate or high pre-test likelihood to diagnose and quantify ischaemia or scar and estimate major adverse cardiovascular event risk.

Coronary artery calcium scoring

Coronary artery calcium scoring may be considered around treatment decision thresholds and can improve risk classification. In persons with a low pre-test likelihood above 5% but no more than 15%, CACS may identify individuals whose calcium-weighted likelihood becomes very low.

Previously obtained chest CT scans should be reviewed for coronary calcification when available, since these findings may improve risk stratification and help guide treatment of modifiable risk factors.

Invasive coronary angiography

Invasive coronary angiography is indicated in selected clinical settings:

• Chronic coronary disease with previous sudden cardiac death or potentially life-threatening ventricular arrhythmia

• Chronic coronary disease with symptoms or signs of heart failure requiring assessment

• A high likelihood of severe ischaemic heart disease when revascularization is feasible

• Unacceptable ischaemic symptoms despite optimal medical therapy in a patient suitable for revascularization

• Uncertain diagnosis after non-invasive testing

• Suspected ANOCA or INOCA when invasive functional assessment is needed

• Acute coronary syndromes with high risk, refractory symptoms or instability

• STEMI requiring urgent reperfusion

When invasive angiography is undertaken, radial artery access is recommended as the preferred access site. Coronary pressure assessment should be available, particularly for intermediate non-left-main stenoses before revascularization.

Routine angiography is not recommended solely for risk assessment in asymptomatic patients without evidence of ischaemia on non-invasive testing. It is also not recommended in patients who decline revascularization or are not candidates because of comorbidity or personal preference.

Invasive functional assessment

For intermediate coronary stenoses, lesion selection for intervention should be guided by functional assessment:

Coronary flow reserve, hyperaemic stenosis resistance and coronary flow capacity may be used as complementary investigations. Resting Pd/Pa, diastolic pressure ratio, resting full-cycle ratio and angiography-derived FFR may be considered alternatives.

Systematic wire-based pressure assessment of every coronary vessel is not recommended. Rather, pressure or flow assessment should be selective and directed toward lesions for which the physiological significance is uncertain or the result is likely to influence revascularization.

Intravascular imaging

IVUS and OCT provide additional information when angiography is limited, particularly in anatomically complex lesions. Intracoronary imaging guidance is recommended for PCI involving:

• Left main lesions

• True bifurcations

• Long lesions

• Other anatomically complex disease

These modalities complement, rather than replace, clinical and physiological assessment.

Biomarkers and Laboratory Findings

Basic biochemistry forms part of the initial diagnostic management of suspected chronic coronary syndrome. High-sensitivity C-reactive protein and/or fibrinogen may also be considered.

The source material does not provide a complete laboratory panel, specific diagnostic thresholds for cardiac troponin, or detailed biomarker algorithms. In acute chest pain, normal or inconclusive ECG and cardiac troponin results identify a setting in which CCTA may be used to exclude acute coronary syndrome in patients with a low-to-intermediate likelihood.

Additional clinical markers relevant to risk assessment include diabetes, chronic kidney disease and left ventricular ejection fraction. In patients with heart failure and suspected chronic coronary disease, the choice of diagnostic testing depends partly on ventricular function.

Treatment and Management

General principles

Optimal medical therapy for stable ischaemic heart disease includes:

• Reduction of reversible risk factors

• Lifestyle modification

• Treatment of conditions that aggravate angina

• Pharmacological control of ischaemia

• Antithrombotic treatment where indicated

• Lipid lowering

• Management of diabetes and heart failure

• Revascularization when symptoms remain unacceptable or when anatomy and clinical circumstances indicate prognostic benefit

In chronic coronary disease, revascularization has not generally been shown to reduce death or myocardial infarction compared with medical therapy alone, except in selected anatomical settings, particularly CABG for significant left main disease. Revascularization decisions should therefore be driven by symptoms, functional impairment, ventricular function, coronary anatomy, anatomical complexity, procedural risk and patient preferences.

Lifestyle and rehabilitation

Patients should receive an individualized discussion of cardiovascular risk and the anticipated benefits of treatment. Multidisciplinary behavioural approaches should accompany pharmacological management.

Recommended activity consists of:

• Moderate-intensity aerobic activity for at least 150–300 minutes per week, or

• Vigorous-intensity activity for 75–150 minutes per week

Sedentary time should be reduced. Home-based cardiac rehabilitation and mobile-health interventions may improve adherence to healthy behaviours and reduce hospitalizations or cardiac events.

Antianginal therapy

Antianginal treatment should be selected according to:

• Symptoms and their mechanism

• Comorbidities

• Concomitant medications

• Tolerability

• Left ventricular function

• The presence or absence of heart failure

• Local availability and cost

Ivabradine may be added for inadequate symptom control in patients with left ventricular systolic dysfunction and LVEF below 40%, or used as part of initial treatment in appropriately selected patients. It is not recommended as add-on treatment in chronic coronary disease with LVEF above 40% and no clinical heart failure. Combining ivabradine with a non-dihydropyridine calcium-channel blocker or another strong CYP3A4 inhibitor is not recommended.

For coronary endotypes without obstructive disease:

• ACE inhibition may be considered for endothelial dysfunction.

• Beta-blockers may be considered for microvascular angina associated with reduced coronary or myocardial flow reserve.

• Calcium-channel blockers are recommended for isolated vasospastic angina.

• Nitrates should be considered to prevent recurrent vasospastic episodes.

• In overlapping endotypes, combination therapy with nitrates, calcium-channel blockers and other vasodilators may be considered.

Antithrombotic therapy

For chronic coronary disease without another clear indication for oral anticoagulation:

Bleeding risk should be assessed with PRECISE-DAPT, the ARC-HBR tool or another validated method when relevant to antithrombotic decisions.

Lipid lowering

The recommended LDL-C target is:

• LDL-C below 1.4 mmol/L, or 55 mg/dL

• At least a 50% reduction from baseline

For statin-intolerant patients who remain above target on ezetimibe, combination with bempedoic acid is recommended. Bempedoic acid should also be considered when the target is not achieved with the maximum tolerated statin dose plus ezetimibe.

Diabetes, obesity and inflammation

SGLT2 inhibitors with proven cardiovascular benefit are recommended in patients with type 2 diabetes and chronic coronary disease to reduce cardiovascular events, independently of baseline or target HbA1c and irrespective of other glucose-lowering treatment.

Semaglutide should be considered in patients with chronic coronary disease who do not have diabetes but are overweight or obese, with BMI at least 27 kg/m2, to reduce cardiovascular mortality, myocardial infarction or stroke.

Low-dose colchicine, 0.5 mg once daily, should be considered in patients with atherosclerotic CAD to reduce myocardial infarction, stroke and the need for revascularization.

Heart failure and left ventricular dysfunction

Patients with chronic coronary disease and heart failure should be enrolled in a multidisciplinary heart-failure programme. Sacubitril/valsartan is recommended as a replacement for an ACE inhibitor or ARB in chronic coronary disease with heart failure and reduced ejection fraction, to reduce heart-failure hospitalization and death.

When LVEF is below 35% and obstructive CAD is suspected, invasive angiography is recommended with a view to assessing whether CABG may improve prognosis, while considering procedural risks and expected benefit. In patients with LVEF above 35% and a low or moderate likelihood of obstructive CAD, CCTA or functional imaging is recommended.

In HFpEF with angina or equivalent symptoms and normal or non-obstructive epicardial coronary arteries, PET, CMR perfusion or invasive functional coronary testing should be considered to detect or exclude coronary microvascular dysfunction.

Revascularization in chronic coronary disease

Revascularization should be considered when angina remains unacceptable despite optimal medical treatment, when anti-ischaemic medications cause troublesome adverse effects, or when the anatomy and clinical context indicate a prognostic advantage.

Selection between PCI and CABG requires:

• Assessment of symptom severity and functional limitation

• Coronary anatomical complexity

• Left ventricular function

• Comorbidities and operative risk

• Life expectancy

• Patient preferences

• Expected completeness of revascularization

• Anticipated effects on quality of life and future events

A Heart Team discussion is recommended for complex cases, particularly when PCI and CABG have similar guideline recommendations.

For LVEF ≤35%, the choice between revascularization and medical therapy alone should follow careful evaluation of the coronary anatomy, the relationship between CAD and ventricular dysfunction, comorbidities, life expectancy, procedural risk and patient perspectives.

Left main disease

In patients with significant left main disease and low surgical risk:

• CABG is recommended over medical therapy alone to improve survival.

• CABG is preferred overall to PCI because of lower risks of spontaneous myocardial infarction and repeat revascularization.

• PCI is an alternative when left main disease is of low anatomical complexity, with SYNTAX score ≤22, and PCI can achieve a completeness of revascularization equivalent to CABG.

PCI technique

Intracoronary IVUS or OCT guidance is recommended for anatomically complex PCI. FFR, iFR or QFR should guide lesion selection in multivessel disease. Pressure assessment at the end of PCI may identify patients at risk of persistent angina and later clinical events, while further pressure-guided treatment may identify lesions suitable for additional PCI.

Acute coronary syndromes

NSTE-ACS

An urgent or immediate invasive strategy is indicated for refractory angina or haemodynamic or electrical instability, provided there are no serious comorbidities or procedural contraindications.

An early invasive strategy within 24 hours is reasonable for initially stabilized high-risk patients. A delayed invasive strategy within 25–72 hours is reasonable for patients who are not at high or intermediate risk. An ischaemia-guided strategy may be considered in selected stabilized patients after accounting for clinical risk and patient preference.

An early invasive approach is not recommended when extensive hepatic, renal or pulmonary failure, cancer or other major comorbidity makes the risks of revascularization outweigh the likely benefit. It is also not recommended in acute chest pain with low likelihood of ACS and negative troponin, particularly in women.

STEMI

Primary PCI should be performed in patients with STEMI and ischaemic symptoms of less than 12 hours’ duration. It should also be used when fibrinolysis is contraindicated, irrespective of the delay from first medical contact. Primary PCI is reasonable between 12 and 24 hours if ongoing ischaemia is supported clinically or by ECG.

Patients with STEMI complicated by cardiogenic shock or acute severe heart failure should undergo primary PCI irrespective of the delay from myocardial infarction onset. In a haemodynamically stable STEMI patient, PCI of a non-infarct artery should not be performed during the primary PCI procedure. Resuscitated out-of-hospital cardiac arrest patients whose initial ECG demonstrates STEMI should undergo immediate angiography and PCI when indicated.

Management of coronary anomalies

For anomalous coronary origins, management is based on:

• High-risk anatomical features demonstrated by CTA

• Evidence of exercise-induced ischaemia

• Symptoms

• The clinical circumstances, including prior aborted cardiac arrest

Stress-induced ischaemia assessed with advanced imaging is central to decision-making, including after surgical correction, especially in patients with a previous aborted cardiac arrest.

For coronary fistulae, symptoms, complications and a significant shunt are the principal indications for percutaneous or surgical closure.

Guideline-Based Diagnostic Pathway

A practical sequence supported by the recommendations is:

• Obtain a detailed history, assess cardiovascular risk factors and perform a resting ECG.

• Estimate the pre-test likelihood of obstructive CAD with the Risk Factor-weighted Clinical Likelihood model.

• Modify the estimate using examination of the peripheral arteries, ECG, echocardiography and prior imaging.

• Consider no further testing when the likelihood is below 5%.

• Consider CACS when the likelihood is above 5% but no more than 15%.

• Use CCTA as the preferred test when the likelihood is above 5% but no more than 50%.

• Use stress echocardiography, SPECT, PET or CMR when the likelihood is above 15% and functional information is required.

• Proceed to invasive angiography when non-invasive testing is inconclusive, when symptoms are unacceptable despite optimal medical therapy, when high-risk anatomy or ischaemia is present, or when an acute coronary syndrome requires an invasive strategy.

• Use FFR, iFR or QFR for intermediate lesions when the result will guide revascularization.

• Use IVUS or OCT for complex PCI, particularly left main, true bifurcation and long lesions.

Prognosis and Follow-Up

Prognosis depends on more than the severity of any individual angiographic stenosis. Relevant determinants include:

• Total plaque burden, including non-obstructive disease

• Presence and extent of inducible ischaemia

• Left ventricular ejection fraction

• Diabetes

• Chronic kidney disease

• Symptom threshold

• Number of diseased vessels

• Left main or proximal LAD involvement

• Coronary anatomical complexity

• Functional significance of intermediate lesions

• Heart failure

• Coronary anomaly anatomy and exercise-induced ischaemia

Follow-up should reassess symptoms, functional capacity, adherence, risk-factor control, lipid levels, tolerance of treatment and ventricular function when clinically indicated. Mobile-health interventions, behavioural strategies, simplified medication regimens, patient education and involvement of family and multidisciplinary teams are recommended to improve adherence.

Patients with recurrent or refractory angina and documented or suspected ANOCA or INOCA should undergo invasive coronary functional testing to define the underlying endotype and guide treatment. This is particularly relevant when symptoms persist despite apparently non-obstructive epicardial arteries or after revascularization.

In patients with coronary anomalies, follow-up should include assessment for exercise-induced ischaemia after intervention, especially when there has been an aborted cardiac arrest. The source material does not specify universal surveillance intervals or a standardized duration of follow-up.