Atherosclerosis: Pathogenesis from Fatty Streak to Plaque Rupture

Definition and pathophysiology

Atherosclerosis is a chronic, inflammatory disease of the arterial wall in which lipid accumulation, vascular-cell dysfunction, immune-cell recruitment, extracellular-matrix remodelling, and thrombosis interact to produce focal arterial lesions. Although epicardial coronary arteries are a major site of disease, atherosclerosis is systemic and may affect multiple arterial territories.

The arterial wall is biologically active. Endothelial and smooth-muscle cells normally regulate vascular tone, preserve an antithrombotic surface, and control the adhesion and migration of inflammatory cells. Dyslipidaemia, cigarette smoking, hypertension, diabetes mellitus and other adverse influences disturb these functions. The resulting endothelial dysfunction promotes inappropriate vasoconstriction, adhesion of circulating cells, inflammatory-cell entry into the intima, and thrombus formation.

Atherosclerosis is therefore not simply a disorder of lipid storage. Its biology includes:

• accumulation and modification of lipids within the intima;

• recruitment of innate and adaptive inflammatory leukocytes;

• oxidative stress and persistent local inflammation;

• smooth-muscle-cell migration and proliferation;

• extracellular-matrix synthesis and degradation;

• neovascularization and intraplaque haemorrhage;

• calcification and remodelling;

• episodic plaque disruption followed by thrombosis.

Atherosclerotic disease usually evolves over decades. Intimal thickening may be present during the second and third decades of life, while clinical manifestations commonly emerge much later. Despite this prolonged course, its major complications—including myocardial infarction, unstable angina and stroke—may occur abruptly and without preceding warning.

Initiation and progression of the fatty streak

The earliest visible lesion is the fatty streak, produced by the accumulation of lipid and inflammatory cells within the arterial intima. Monocytes enter the intima, differentiate into macrophages and participate in a sustained inflammatory response. Lipid accumulation, oxidative stress and immune activation progressively alter the local vascular environment.

The extracellular matrix is an active component of lesion development rather than merely a structural scaffold. Smooth-muscle cells and fibroblasts contribute to matrix production, while inflammatory-cell proteinases degrade matrix constituents. The balance between synthesis and degradation influences plaque architecture and mechanical stability.

Atherosclerotic lesions commonly arise at sites of disturbed flow, including branch points in the epicardial coronary arteries. Early lesions may undergo positive or compensatory remodelling, in which the vessel enlarges outward before a major reduction in the lumen becomes apparent. Consequently, a plaque may be biologically advanced despite producing relatively limited angiographic stenosis.

Lipid accumulation and plaque architecture

The major coronary risk factors—high LDL cholesterol, cigarette smoking, hypertension and diabetes mellitus—disturb endothelial function and favour the accumulation of fat, smooth-muscle cells, fibroblasts and extracellular matrix beneath the endothelium.

Plaques that are particularly prone to rupture characteristically contain:

• a large lipid-rich core;

• abundant foam cells and macrophages;

• a thin fibrous cap;

• positive remodelling;

• neovascularization;

• intraplaque haemorrhage;

• adventitial inflammation;

• spotty calcification.

Nevertheless, the presence of these features does not imply inevitable clinical disruption. Fewer than 5% of thin-capped fibroatheromas have been identified as the source of an acute myocardial infarction during long-term follow-up. Moreover, several potentially high-risk plaques may coexist within one coronary tree, and inflammatory activity may be widespread rather than confined to a single lesion.

Plaque composition is heterogeneous. Lipid-rich, macrophage-rich plaques are commonly associated with rupture, whereas lipid-poor plaques with fewer macrophages and abundant matrix are more prone to superficial erosion. Rupture tends to produce fibrin-rich red thrombi, while erosion is associated with platelet-rich white thrombi. The therapeutic significance of this distinction remains under investigation.

Plaque neovascularization and haemorrhage

As plaques enlarge, they may develop an intrinsic microcirculation through endothelial-cell migration and proliferation. Plaque neovessels are associated with angiogenic mediators including vascular endothelial growth factor, fibroblast growth-factor forms, placental growth factor and oncostatin M.

These microvessels may facilitate continued leukocyte trafficking and permit further plaque growth by improving oxygen and nutrient delivery. They are also fragile. Rupture of plaque neovessels may cause haemorrhage and local thrombosis, followed by additional smooth-muscle proliferation and matrix accumulation.

Calcification and remodelling

Calcification is one of the morphological features associated with atherosclerotic disease. Spotty calcification is particularly associated with lesions producing acute manifestations. Calcific nodules represent another possible substrate for acute coronary syndromes and are associated with recurrent acute coronary syndromes, major adverse cardiovascular events and target-lesion revascularization.

Atherosclerosis may produce either luminal narrowing or arterial dilatation. Positive remodelling can precede stenotic disease, whereas extensive matrix degradation and loss of structural integrity contribute to aneurysmal dilation in other vascular beds.

From plaque disruption to atherothrombosis

Most acute coronary syndromes result from fissuring, rupture or superficial erosion of an atherosclerotic plaque. These events expose plaque material and tissue-factor activity to circulating blood, initiating platelet activation and coagulation.

The process includes:

• platelet adhesion to the injured arterial surface;

• platelet activation and degranulation;

• recruitment and activation of additional platelets;

• parallel activation of the tissue-factor-dependent coagulation cascade;

• fibrin formation and incorporation of blood cells into the thrombus.

After initial platelet adhesion, agonists such as collagen, ADP, epinephrine and serotonin amplify platelet activation. Thromboxane A2 is released, producing local vasoconstriction, further platelet activation and potential resistance to fibrinolysis.

Activation also changes the conformation of platelet glycoprotein IIb/IIIa receptors. These receptors bind soluble adhesive proteins, particularly fibrinogen. Because fibrinogen can bind two platelets simultaneously, it cross-links platelets and promotes aggregation.

At the same time, tissue factor exposed by damaged endothelial cells activates coagulation factors VII and X. The cascade generates thrombin, which converts fibrinogen to fibrin. Both circulating and clot-bound thrombin amplify coagulation. The resulting coronary thrombus contains platelet aggregates and fibrin strands and may trap red blood cells.

The clinical consequence depends on the interaction between the plaque and the circulating blood. Plaque tissue factor, circulating fibrinogen and inhibitors of fibrinolysis such as plasminogen activator inhibitor 1 jointly determine whether disruption produces a small, transient or clinically silent thrombus, unstable angina, or a persistent occlusive thrombus causing myocardial infarction. Inflammation influences both components by regulating tissue factor, fibrinogen and plasminogen activator inhibitor 1.

Clinical presentation and symptoms

The source material focuses principally on the biological progression from atherosclerotic lesion to acute coronary thrombosis. It does not provide a comprehensive account of the symptom profile, differential diagnosis or physical findings of stable or acute coronary syndromes.

Acute manifestations may occur suddenly, even after a prolonged period of clinically silent disease. Plaque disruption with a reduction in coronary flow can produce myocardial ischaemia and acute coronary syndromes. Depending on the degree and duration of obstruction, the clinical spectrum includes unstable angina, non-ST-segment elevation myocardial infarction and ST-segment elevation myocardial infarction.

Clinical severity is influenced by:

• the myocardial territory supplied by the affected artery;

• whether obstruction is partial or complete;

• the duration of occlusion;

• the extent of collateral blood flow;

• myocardial oxygen demand;

• the possibility of early spontaneous thrombus lysis;

• the adequacy of tissue perfusion after restoration of epicardial flow.

Obstruction of the left main or proximal left anterior descending coronary artery is particularly hazardous because of the large myocardial territory at risk.

Evaluation and physical examination

The source material does not describe a complete physical-examination framework for atherosclerosis or acute coronary syndromes. Assessment is directed toward identifying myocardial ischaemia, defining the mechanism of arterial obstruction, evaluating the extent of atherosclerotic disease and recognizing conditions associated with premature or accelerated disease.

Clinical assessment should take account of conventional and disease-associated risk contexts, including:

• dyslipidaemia;

• cigarette smoking;

• hypertension;

• diabetes mellitus;

• obesity;

• systemic inflammatory disease;

• systemic lupus erythematosus;

• antiphospholipid syndrome;

• collagen vascular disease;

• hypercoagulability;

• cocaine or amphetamine exposure;

• prior percutaneous coronary intervention;

• cardiac or non-cardiac sources of embolism;

• cardiac transplantation.

Young patients with otherwise unexplained angina, myocardial infarction or stroke warrant consideration of an underlying inflammatory disease. Patients with systemic lupus erythematosus have at least twice the risk of myocardial infarction and stroke compared with the general population, and coronary events may occur at a young age. Antiphospholipid antibodies further increase thrombotic risk.

Diagnostics

Electrocardiography

Electrocardiography helps classify the acute coronary syndrome according to the presence or absence of ST-segment elevation. Biomarkers then distinguish myocardial infarction from unstable angina when ST-segment elevation is absent.

The diagnostic framework is:

Patients with ST-segment elevation may subsequently develop Q waves or may not. The source material does not provide detailed criteria for ST-segment elevation, Q-wave formation, infarct localization or serial ECG interpretation.

Coronary angiography and computed tomography

Coronary angiography identifies luminal obstruction and can demonstrate focal stenoses, but it may underestimate diffuse disease. This limitation is particularly important in transplant-associated coronary arteriosclerosis, which is concentric, diffuse and may involve smaller intramyocardial branches.

Coronary computed tomographic angiography can demonstrate:

• calcified and non-calcified plaque;

• severe coronary stenoses;

• plaque ulceration;

• coronary aneurysms;

• diffuse coronary involvement;

• inflammatory features in selected settings.

In patients with inflammatory diseases, coronary CT may assist cardiovascular-risk assessment. Perivascular fat attenuation and pericoronary adipose-tissue density techniques can quantify vascular inflammation, although the source material does not establish their routine clinical role.

Optical coherence tomography

Optical coherence tomography can visualize plaque ulceration and contribute to identifying the mechanism of an acute coronary syndrome. It is particularly relevant when distinguishing plaque rupture or erosion and in the investigation of myocardial infarction with non-obstructive coronary arteries.

Positron emission tomography

Positron emission tomography has been used in surveillance of transplant-associated coronary arteriosclerosis and may provide information about microvascular function. The source material does not specify diagnostic thresholds or standardized protocols.

Collateral circulation and stenosis severity

When coronary narrowing develops gradually, collateral vessels may form. These vessels can maintain myocardial viability at rest but may not provide sufficient flow during increased demand.

A reduction of approximately 50% in coronary diameter limits the ability to increase flow when myocardial demand rises. At approximately 80% diameter reduction, resting flow may also decline, and small further reductions in the stenotic lumen can provoke ischaemia at rest or with minimal stress.

As epicardial resistance increases, distal resistance vessels dilate to preserve flow. Once maximal vasodilation has occurred, myocardial perfusion becomes dependent on distal coronary pressure. Physical activity, emotional stress and tachycardia can then increase oxygen demand sufficiently to produce ischaemia.

Biomarkers and laboratory findings

Myocardial injury biomarkers

Cardiac troponin is the principal biomarker identified in the source material for distinguishing myocardial infarction from unstable angina in patients without ST-segment elevation. A positive cardiac troponin indicates myocardial injury in the appropriate clinical setting; the source material does not provide assay-specific thresholds or serial-testing protocols.

Haemostatic markers

Acute coronary thrombosis may be accompanied by increased markers of platelet activation, thrombin generation and fibrin formation. Reported findings include:

• fibrinogen degradation products;

• platelet factor 4;

• P-selectin;

• fibrinopeptide A;

• thrombin–antithrombin complexes;

• prothrombin fragment 1.2.

Fibrinopeptide A reflects thrombin-mediated fibrin formation and rises during the early hours of ST-segment elevation myocardial infarction. Marked increases in fibrinopeptide A, thrombin–antithrombin complexes and prothrombin fragment 1.2 are associated with increased mortality risk in patients with ST-segment elevation myocardial infarction.

Inflammatory markers

Systemic inflammatory markers, including C-reactive protein, may be increased in individuals at risk of acute coronary syndromes. Inflammation may precede the acute event and reflects the systemic nature of atheroma instability. The material does not define diagnostic or prognostic cut-off values.

Lipid and metabolic findings

Atherosclerosis is associated with elevated LDL cholesterol and, in relevant clinical contexts, hyperglycaemia and abnormalities in other circulating prothrombotic factors. Obesity may be accompanied by increased triglycerides and LDL cholesterol and reduced HDL cholesterol. In systemic lupus erythematosus, lipid abnormalities may include increased very-low-density lipoprotein and triglycerides, elevated or normal LDL cholesterol, reduced HDL cholesterol and impaired cholesterol efflux.

The source material does not provide treatment targets or laboratory monitoring schedules for lipid parameters.

Treatment and management

Principles of management

Management of atherosclerotic disease must address both the local culprit lesion and the systemic substrate. Because multiple high-risk plaques may exist throughout the coronary tree and inflammatory activity may be diffuse, local revascularization should be accompanied by systemic measures aimed at stabilizing atherosclerotic lesions and reducing thrombotic risk.

The source material emphasizes the importance of an integrated “chain of survival” for ST-segment elevation myocardial infarction. This begins with prehospital care and continues through early hospital management, with the aim of implementing reperfusion promptly.

Antithrombotic treatment

Platelets are central to coronary thrombus formation and are therefore major therapeutic targets in the initial management of ST-segment elevation myocardial infarction. Antiplatelet and anticoagulant therapies improve clinical outcomes in acute coronary syndromes, supporting the central pathogenic role of thrombosis.

The source material does not specify individual antiplatelet or anticoagulant drugs, loading regimens, maintenance doses, duration of therapy or contraindications.

Reperfusion and revascularization

Acute ST-segment elevation myocardial infarction requires an expedited reperfusion strategy within an integrated prehospital and hospital system. The supplied material does not specify the preferred reperfusion modality, time targets, procedural techniques or adjunctive pharmacotherapy.

Revascularization is also relevant to patients with atherosclerotic disease in systemic inflammatory disorders and to selected patients with complex coronary lesions. However, treatment recommendations specific to these settings are not detailed.

Lipid lowering and systemic plaque stabilization

High-intensity lipid-lowering therapy can reduce intimal lipid accumulation and may halt plaque progression or promote regression. The source material supports systemic lipid lowering as part of the strategy to stabilize multiple high-risk lesions but does not provide drug names, doses, treatment targets or monitoring recommendations.

Management of risk-associated conditions

Risk-factor modification is central to limiting atherosclerotic progression. The source material identifies dyslipidaemia, smoking, hypertension and diabetes as major drivers of endothelial dysfunction and atherosclerosis. Obesity contributes through dyslipidaemia, chronic low-grade inflammation, impaired vasodilation and increased myocardial oxygen demand.

In systemic lupus erythematosus, cardiovascular risk is also influenced by hypertension, metabolic syndrome, renal impairment, glucocorticoid exposure and disease-associated lipid abnormalities. Prompt treatment of end-organ dysfunction has improved outcomes in lupus nephritis, while cardiovascular disease remains a leading cause of mortality in this population.

No specific lifestyle programme, blood-pressure target, glucose-lowering regimen or drug dose is provided.

Conditions with alternative mechanisms

Not all acute coronary occlusions are caused by conventional plaque rupture. Rare mechanisms include:

• coronary embolism;

• congenital coronary abnormalities;

• coronary spasm;

• spontaneous coronary artery dissection.

NSTE-ACS may additionally result from calcific nodules, plaque erosion, cardiac or non-cardiac embolism, vasospasm, spontaneous coronary artery dissection, restenosis after PCI or myocardial oxygen supply–demand mismatch. Management must therefore be adapted to the underlying mechanism, although the source material does not provide mechanism-specific treatment algorithms.

Guideline recommendations

The supplied guideline material supports the following principles:

• Atherosclerosis should be regarded as a systemic inflammatory and thrombotic disease rather than an isolated focal stenosis.

• Acute coronary syndromes are commonly initiated by plaque rupture or erosion, with platelet activation and coagulation occurring in parallel.

• In patients with suspected acute coronary syndrome, ECG and cardiac troponin are central to classification into ST-segment elevation myocardial infarction, non-ST-segment elevation myocardial infarction or unstable angina.

• ST-segment elevation myocardial infarction requires an integrated prehospital and hospital pathway to provide rapid reperfusion.

• Antiplatelet and anticoagulant therapies are supported by the thrombotic pathogenesis of acute coronary syndromes.

• Local revascularization should be accompanied by systemic therapy aimed at stabilizing multiple atherosclerotic lesions.

• Premature or disproportionate coronary disease should prompt consideration of systemic inflammatory disease, particularly systemic lupus erythematosus and other immune-mediated inflammatory diseases.

• Coronary CT may assist cardiovascular-risk assessment in inflammatory diseases, while advanced methods of assessing perivascular inflammation remain emerging tools.

• In transplant recipients, diffuse graft coronary disease may be underestimated by conventional angiography; CT angiography and PET may assist surveillance.

Specific drug doses, formal classes of recommendation and levels of evidence are not provided in the source material.

Prognosis and follow-up

Prognosis depends on the extent and biological activity of atherosclerotic disease, the location and completeness of coronary obstruction, the duration of ischaemia, collateral circulation, myocardial oxygen demand and the success of restoring perfusion.

Atherosclerotic disease is often diffuse. Multiple plaques may possess high-risk characteristics, and local inflammation may precede acute coronary events. These features explain why treatment directed only at an individual culprit lesion is insufficient and why long-term systemic plaque stabilization is important.

Patients with myocardial infarction in the setting of systemic inflammatory disease have worse outcomes than age-matched individuals without such disease, including higher risks of heart failure and mortality. Systemic lupus erythematosus is associated with accelerated arterial disease, premature myocardial infarction and stroke, while antiphospholipid syndrome further increases the risk of arterial, venous and small-vessel thrombosis.

Follow-up should therefore incorporate ongoing assessment and treatment of the systemic atherosclerotic substrate, together with surveillance for recurrent coronary events. The source material does not specify follow-up intervals, imaging schedules or biomarker-monitoring protocols.