Acute Plaque Change

Slide 1 · Acute Plaque Change

Rupture · Erosion · Intraplaque hemorrhage

Plaque vulnerability

Acute thrombosis

Ischemic injury

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Acute plaque change: A mechanism of sudden ischemia

A long-standing atheroma can become clinically dangerous over a short interval.

Surface disruption exposes thrombogenic material and recruits thrombus.

A coronary or cerebral artery may become critically obstructed without preceding severe fixed stenosis.

Pre-existing plaque

Abrupt plaque change

Thrombus formation

Acute ischemia / infarction

Slide 3 · Learning objectives

Distinguish plaque rupture, erosion, and intraplaque hemorrhage.

Relate fibrous-cap architecture to mechanical vulnerability.

Explain intrinsic and extrinsic triggers of plaque disruption.

Trace thrombosis, embolization, and healing to clinical outcomes.

Forms of injury

Structural vulnerability

Triggers

Tissue consequences

Slide 4 · What constitutes an acute plaque change?

A sudden structural alteration of an established intimal atheroma.

Acute change is distinct from gradual plaque enlargement and fixed stenosis.

Thrombosis is the major immediate determinant of many catastrophic events.

Lumen

Rupture / clot — schematic

Slide 5 · Chronic stenosis and acute complications are different pathways

Stable fibroatheromas may progressively reduce perfusion under increased demand.

Abrupt surface changes create an immediate thrombogenic interface.

Both mechanisms arise from atherosclerosis but need not coincide in the same lesion.

PATHWAY 1

PATHWAY 2

Gradual luminal narrowing

Abrupt disruption + thrombus

Fixed flow limitation

Sudden loss of perfusion

Slide 6 · Anatomic substrate: A plaque in the intima

Atheroma is an intimal lesion beneath the luminal endothelial surface.

The fibrous cap overlies a lipid-rich necrotic core.

Shoulder regions may be enriched in macrophages and lymphocytes.

Underlying medial structure can be compressed by a growing lesion.

Lumen

Fibrous cap — schematic

Slide 7 · Composition of the mature atheroma

Smooth muscle cells and collagen constitute much of the fibrous cap.

Macrophages, T lymphocytes, and foam cells contribute to cellular components.

Extracellular lipid, dead-cell debris, and variable calcifications populate the core.

Small new vessels may occur toward plaque periphery.

SMCs + collagen

Inflammatory cells

Necrotic / lipid core

Neovessels, calcification

Slide 8 · Slow progression can precede abrupt clinical conversion

Atheromas accumulate lipids, cells, and extracellular matrix over years.

Later cap erosion or rupture can trigger thrombosis in a brief interval.

A prior period without angina does not establish plaque stability.

Plaque formation

Cap/core remodeling

Acute surface change

Thrombotic event

Slide 9 · Fixed narrowing does not fully predict acute risk

Many culprit coronary plaques were noncritical before an acute event.

Mechanical fragility and blood thrombogenicity matter in addition to lumen diameter.

Angiographic appearance alone cannot reliably forecast plaque rupture.

PATHWAY 1

PATHWAY 2

Anatomic stenosis

Biologic vulnerability

Degree of lumen loss

Cap/core + inflammation + triggers

Slide 10 · Three principal forms of acute plaque change

Rupture or fissuring: Fibrous-cap disruption with exposure of highly thrombogenic plaque constituents.

Erosion or ulceration: Loss of protective luminal surface with exposure of subendothelial matrix.

Hemorrhage: Bleeding into the plaque, increasing lesion volume.

Rupture / fissure

Erosion / ulceration

Intraplaque hemorrhage

Slide 11 · Plaque rupture is a structural failure of the cap

Cap disruption establishes communication between flowing blood and plaque core.

Highly thrombogenic contents initiate coagulation and platelet deposition.

The resulting luminal thrombus can become completely obstructive.

Lumen

Rupture / clot — schematic

Slide 12 · Fissuring may be focal rather than extensive

Even localized cap breaks can expose thrombogenic material.

Rupture severity and thrombus extent are separate variables.

The overlying blood clot may obscure a relatively small plaque defect.

Lumen

Rupture / clot — schematic

Slide 13 · The necrotic core is thrombogenic when exposed

Plaque core contains lipid, necrotic debris, and blood-derived proteins.

A torn cap allows these constituents to contact flowing blood.

Tissue factor–dependent coagulation, together with platelet activation, favors thrombus growth.

Loss of cap integrity

Core exposed to blood

Platelet + coagulation response

Luminal thrombosis

Slide 14 · Rupture: From mechanical tear to thrombus

A vulnerable cap fails when local stress exceeds its resistance.

Blood contacts underlying plaque contents at the site of failure.

Activated platelets and coagulation products form a growing thrombus.

Mechanical loading

Fibrous-cap tear

Thrombogenic exposure

Thrombus

Slide 15 · Why thrombus after rupture can be occlusive

Rupture directly exposes particularly thrombogenic plaque material.

Coagulation and platelet accumulation can rapidly narrow the available lumen.

Complete obstruction may cause acute downstream infarction.

Lumen

Rupture / clot — schematic

Slide 16 · Plaque erosion denotes surface loss with an intact cap

Erosion involves endothelial loss and exposure of the subendothelial matrix.

The fibrous cap need not rupture into the necrotic core.

The denuded luminal surface can nevertheless support platelet-rich thrombosis.

Lumen

Eroded surface — schematic

Slide 17 · The endothelium protects blood from matrix exposure

An intact endothelial lining separates circulating platelets from subendothelial structures.

Surface denudation removes this antithrombotic barrier.

Exposure of the basement membrane facilitates platelet adhesion and thrombosis.

PATHWAY 1

PATHWAY 2

Intact endothelial interface

Denuded luminal interface

Matrix separated from blood

Thrombogenic matrix accessible

Slide 18 · Erosion and rupture are not equivalent lesions

Rupture has a breach in the fibrous cap and access to the underlying core.

Erosion can create thrombus despite an intact cap.

Both can present clinically with abrupt ischemia, but their tissue-level mechanisms differ.

A

B

Lumen

Rupture / clot — schematic

Lumen

Eroded surface — schematic

Cap breach + thrombus

Endothelial erosion

Schematic cross-sections

Slide 19 · Erosion can produce nonocclusive thrombosis

Exposed subendothelial matrix can recruit thrombus on the plaque surface.

Fully occlusive thrombosis occurs less often than with rupture.

The magnitude of residual flow depends on thrombus burden and vasomotor tone.

Lumen

Eroded surface — schematic

Slide 20 · Ulceration describes destructive surface injury

Surface ulceration removes the normal luminal covering of the plaque.

Exposed thrombogenic surfaces promote clot formation.

In the acute-change classification, ulceration is discussed with erosion.

Lumen

Eroded surface — schematic

Slide 21 · Intraplaque hemorrhage adds blood within the atheroma

Hemorrhage enlarges the plaque core or its immediate surroundings.

The resulting volume expansion can increase luminal compromise.

A contained hemorrhage may also increase tension on the overlying cap.

Lumen

Hemorrhage — schematic

Slide 22 · How blood may enter an atherosclerotic plaque

A defect in the surface can permit bleeding into the lesion.

Thin-walled neovessels at the plaque periphery can also bleed.

Both routes contribute to increased plaque volume.

Cap or surface defect

Fragile plaque neovessels

Intraplaque bleeding

Plaque expansion

Slide 23 · Hemorrhage may acutely enlarge the stenosing mass

The same arterial lumen now faces a larger intimal protrusion.

Acute mass effect is distinct from thrombus deposited inside the lumen.

Greater plaque volume may precipitate additional cap stress.

A

B

Lumen

Fibrous cap — schematic

Lumen

Hemorrhage — schematic

Thick collagen cap

Core hemorrhage

Schematic cross-sections

Slide 24 · Hemorrhage and rupture can reinforce one another

Intraplaque hemorrhage can increase internal plaque pressure and deformation.

Cap disruption may itself be associated with hemorrhage into the lesion.

Thus intraplaque bleeding is both an acute plaque event and a possible contributor to further disruption.

Hemorrhage

Plaque expansion

Cap loading

Potential rupture

Slide 25 · Mechanism-level comparison of the three forms

Rupture exposes plaque-core constituents to blood.

Erosion removes luminal endothelial protection without necessarily breaking the cap.

Hemorrhage expands the plaque itself and may add to stenosis or instability.

Finding / insult

Process

Immediate effect

Rupture

Cap/core communication

Thrombosis

Erosion

Loss of luminal surface

Thrombosis

Hemorrhage

Bleeding into lesion

Plaque expansion

Slide 26 · Surface thrombosis is the critical acute interface

Both rupture and erosion can lead promptly to thrombus formation.

The thrombus—not simply the original plaque mass—often causes the abrupt flow deficit.

Acutely formed clot can be mural, subtotal, or occlusive.

Lumen

Rupture / clot — schematic

Slide 27 · Culprit plaques may have been clinically silent

Clinical silence does not imply absence of atherosclerosis.

Many plaques causing acute coronary occlusion had produced only mild or moderate prior narrowing.

Sudden disruption creates a risk that is not captured by symptoms alone.

PATHWAY 1

PATHWAY 2

Before event

After rupture

Mild/moderate stenosis

Thrombus occupies lumen

Slide 28 · A lumenogram cannot show every component of risk

Conventional angiography primarily depicts the vascular lumen.

Cap composition, inflammation, and necrotic-core properties affect rupture susceptibility.

Standard angiography is therefore inadequate to predict an individual future rupture.

PATHWAY 1

PATHWAY 2

Lumen-focused view

Wall pathology

Residual lumen appears acceptable

Thin cap + inflamed core

Slide 29 · A relatively stable fibrous plaque

A broad, collagen-rich cap resists mechanical loading.

Relatively little inflammation limits collagen breakdown.

Less lipid-rich necrotic material leaves fewer features favoring rupture.

Lumen

Fibrous cap — schematic

Slide 30 · Features associated with plaque vulnerability

Thin fibrous cap with diminished mechanical reserve.

Relatively large necrotic lipid core beneath the cap.

Inflammatory-cell infiltrates that promote matrix turnover.

Less effective replacement of collagen by resident smooth muscle cells.

Lumen

Thin cap — schematic

Slide 31 · Plaque burden and plaque vulnerability are distinct

Severely stenotic lesions may remain relatively fibrotic and stable.

Less stenosing lesions may harbor thin caps and inflammatory activity.

A pre-event degree of narrowing is not a sufficient surrogate for rupture probability.

A

B

Lumen

Fibrous cap — schematic

Lumen

Thin cap — schematic

Thick collagen cap

Thin cap + large core

Schematic cross-sections

Slide 32 · The fibrous cap is the load-bearing structure

Collagen-rich extracellular matrix supplies tensile strength.

Smooth muscle cells contribute to maintenance of this cap.

Thin or poorly maintained cap tissue fails more readily under local forces.

Lumen

Fibrous cap — schematic

Slide 33 · Collagen is the principal cap-strength determinant

Collagen provides tensile support for the plaque surface.

Loss of cap collagen weakens tissue resistance to shear and mechanical strain.

Strength depends on the balance of collagen production and degradation.

Collagen synthesis

Collagen degradation

↔

Fibrous-cap integrity

Slide 34 · Smooth muscle cells synthesize protective collagen

Plaque smooth muscle cells elaborate cap extracellular matrix.

Their presence contributes to repair and stability.

Loss or functional suppression of these cells reduces the capacity to replace collagen.

Plaque SMCs

Collagen synthesis

Cap reinforcement

Relative stability

Slide 35 · Loss of cap smooth muscle cells increases fragility

Fewer matrix-producing cells leave a weaker repair response.

A cap rich in inflammatory cells but poor in SMCs may be under-repaired.

Reduced synthesis acts together with proteolytic degradation.

SMC depletion

Reduced collagen synthesis

Thinner / weaker cap

Higher rupture susceptibility

Slide 36 · Cap remodeling is continuous, not static

Fibrous cap collagen is constantly synthesized and degraded.

The net direction of remodeling determines cap thickness and mechanical behavior.

Stabilization and destabilization are dynamic, potentially reversible processes.

Repair and synthesis

Proteolysis / depletion

↔

Dynamic cap remodeling

Slide 37 · Matrix metalloproteinases degrade cap matrix

MMPs participate in collagen breakdown inside plaques.

Macrophages and smooth muscle cells are prominent sources of MMPs.

Excess net proteolytic activity erodes the structural reserve of the fibrous cap.

Macrophages / SMCs

MMP production

Matrix degradation

Cap weakening

Slide 38 · TIMPs temper metalloproteinase activity

Tissue inhibitors of metalloproteinases (TIMPs) restrain MMP activity.

Endothelial cells, smooth muscle cells, and macrophages can make TIMPs.

Cap stability therefore depends on regulated proteolysis rather than MMP abundance alone.

MMP action

TIMP restraint

↔

Net matrix turnover

Slide 39 · Inflammation alters both sides of collagen balance

Inflammatory plaques exhibit increased matrix degradation.

Collagen production may simultaneously decrease.

The combined effect weakens the protective surface without requiring an increase in total plaque size.

Plaque inflammation

More collagen degradation

Less collagen synthesis

Fragile cap

Slide 40 · Cholesterol accumulation can amplify inflammation

Cholesterol-rich deposits stimulate inflammatory responses in the plaque.

Activated macrophages produce mediators that intensify local tissue injury.

This inflammatory milieu can favor protease activity and cap destabilization.

Lipid / cholesterol deposition

Plaque inflammation

Matrix-remodeling imbalance

Structural vulnerability

Slide 41 · The thin-cap, large-core combination matters

A larger core provides little load-bearing support beneath the cap.

A thin cap separates circulating blood from thrombogenic debris.

Inflammatory infiltrates further reduce resistance to mechanical injury.

Lumen

Thin cap — schematic

Slide 42 · Inflammatory activity near the plaque shoulder

The shoulder lies where the cap approaches adjacent relatively normal arterial wall.

Macrophages and T lymphocytes can be concentrated in these cellular regions.

Local proteolysis and mechanical stress make the cap–wall junction a potential failure site.

Lumen

Thin cap — schematic

Slide 43 · Rupture reflects stress exceeding cap strength

External mechanical forces impose load on plaque tissue.

Intrinsic cap architecture determines how much loading is tolerated.

Failure becomes likely when the applied stress surpasses local mechanical resistance.

PATHWAY 1

PATHWAY 2

Stress imposed

Cap resistance

Pressure, shear, constriction

Collagen + cap thickness

Slide 44 · Intrinsic and extrinsic determinants interact

Intrinsic: Fibrous-cap thickness, necrotic core, inflammation, cellular composition.

Extrinsic: Blood pressure, platelet reactivity, and local vasospasm.

Neither anatomy nor systemic triggers alone fully explains every acute event.

Cap architecture

Plaque inflammation

Hemodynamic load

Platelet / vasomotor state

Slide 45 · Pressure and vascular forces load the plaque

Arterial pressure generates circumferential wall stress.

Local flow and vessel geometry influence mechanical loading.

A structurally fragile cap may fail under forces tolerated by a stronger plaque.

Lumen

Fibrous cap — schematic

Slide 46 · Adrenergic stimulation can increase plaque stress

Sympathetic activation can raise systemic blood pressure.

Adrenergic signaling can also increase local vasoconstriction.

Both changes can raise mechanical forces at vulnerable sites.

Adrenergic activation

BP rise / vasoconstriction

Increased plaque loading

Potential disruption

Slide 47 · Vasoconstriction has two adverse effects

A narrowed functional lumen restricts residual blood flow.

Contraction of the arterial wall may magnify local mechanical loading.

At atheromatous sites, spasm can augment the effects of plaque change and thrombus.

PATHWAY 1

PATHWAY 2

Vasoconstriction

Atherothrombosis

Less available lumen

More obstruction + cap stress

Slide 48 · Endothelial dysfunction changes vasomotor balance

Healthy endothelium produces nitric oxide, a vasodilator.

Dysfunctional endothelium may shift the balance toward endothelin-mediated constriction.

The resulting local vasomotor changes can intensify plaque-related obstruction.

Nitric oxide (NO)

Endothelin

↔

Coronary vasomotor tone

Slide 49 · Activated platelets can intensify constriction

Platelets adhere and activate at a disrupted surface.

Locally released platelet contents include vasoconstrictive mediators.

The combination of platelet accumulation and spasm promotes dynamic luminal compromise.

Plaque surface injury

Platelet activation

Vasoactive release

Additional constriction

Slide 50 · Perivascular inflammatory mediators can affect tone

Inflammatory cells outside or around the vessel release vasoactive signals.

These mediators can promote local vasoconstriction.

Vasomotor tone is therefore influenced by vascular wall and adjacent tissue biology.

Perivascular inflammation

Local mediator release

Vasoconstriction

Greater plaque stress / lower flow

Slide 51 · Morning sympathetic changes and event timing

A morning increase in acute myocardial infarction occurrence.

On awakening, blood pressure spikes can be followed by greater platelet reactivity.

This observation illustrates time-varying extrinsic triggers rather than a fixed daily certainty.

Awakening

Adrenergic surge

BP / platelet reactivity

Higher event susceptibility

Slide 52 · Intense emotional stress may precipitate events

Severe stress can stimulate adrenergic and hemodynamic responses.

The source notes increased sudden-death events during major disasters.

A triggering circumstance interacts with a pre-existing susceptible vascular lesion.

Acute severe stress

Physiologic activation

Mechanical / platelet changes

Possible acute event

Slide 53 · Rupture initiates a linked platelet–coagulation response

Exposed matrix and plaque contents support platelet adhesion and activation.

Coagulation adds fibrin to the developing thrombus.

Accumulation can rapidly reduce the perfused luminal area.

Plaque injury

Platelet response

Coagulation / fibrin

Growing thrombus

Slide 54 · Platelets and coagulation drive thrombus propagation

Platelet-derived ADP and thromboxane A₂ recruit and activate more platelets.

Tissue factor–associated coagulation amplifies fibrin generation.

These processes reinforce one another at a thrombogenic plaque site.

Platelet recruitment

ADP / TXA₂ signaling

Coagulation + fibrin

Thrombus propagation

Slide 55 · Thrombotic obstruction is a spectrum

A small mural thrombus may leave much of the lumen patent.

A subtotal thrombus can cause marked, sometimes fluctuating ischemia.

Complete occlusion can abruptly terminate downstream arterial perfusion.

Mural / nonocclusive

Subtotal obstruction

Complete occlusion

Slide 56 · Complete occlusion can produce acute infarction

A completely obstructed coronary artery can cause myocardial necrosis.

Analogous thrombosis in relevant cerebral arteries can cause brain infarction.

Tissue outcome depends on vascular territory, collateral flow, and duration of reduced perfusion.

Occlusive plaque thrombus

Loss of downstream flow

Sustained ischemia

Tissue infarction

Slide 57 · Incomplete obstruction may still be clinically serious

Mural or partially occlusive thrombi compromise flow without total closure.

Thrombus size may change as deposition and removal fluctuate.

Clinical consequences range from unstable ischemia to infarction, depending on the setting.

PATHWAY 1

PATHWAY 2

Partly patent lumen

Occluded lumen

Variable perfusion

Critical flow interruption

Slide 58 · A coronary thrombus can embolize distally

Part of a mural thrombus may detach and travel downstream.

Smaller arterial branches and intramyocardial vessels can trap fragments.

Distal obstruction adds focal injury beyond the original plaque location.

Mural thrombus

Embolic fragment

Distal small arteries

Focal ischemic injury

Slide 59 · Distal microemboli may produce microinfarcts

Autopsy studies cited by the textbook show small coronary thromboemboli in sudden-death cases.

Fragments may be found in the distal intramyocardial circulation.

Associated microinfarcts support an embolic mechanism of myocardial injury.

Lumen

Fibrous cap — schematic

Slide 60 · Subclinical plaque disruption may recur

Not every ruptured plaque becomes completely occlusive.

Superficial platelet deposition and thrombosis may produce no recognizable symptoms.

Repeated episodes can change plaque composition over time.

Small plaque disruption

Nonocclusive thrombus

Organization / healing

Repeat injury

Slide 61 · Organized thrombus contributes to plaque enlargement

Healing converts superficial thrombus into incorporated tissue.

Successive silent disruptions can gradually increase lesion mass.

Thus thrombosis can promote both acute occlusion and chronic plaque progression.

Mural clot

Organization

Incorporation into plaque

Progressive stenosis

Slide 62 · Thrombin can stimulate intimal smooth muscle cells

Thrombin is a coagulation protease, not only a clot-forming factor.

Activation of protease-activated receptors on SMCs supports lesion growth responses.

The coagulation response can therefore remodel plaque biology after the acute episode.

Thrombus / thrombin

Protease-activated receptors

SMC activation

Lesion enlargement

Slide 63 · Flow restriction can result from several simultaneous forces

Fixed plaque volume reduces the resting luminal area.

Acute thrombus further occupies the lumen.

Superimposed vasospasm can transiently worsen the residual flow pathway.

Fixed atheroma

Superimposed thrombus

Vasoconstriction

Downstream ischemia

Slide 64 · Plaque stabilization modifies biology, not just size

Statins reduce circulating atherogenic cholesterol.

The textbook also notes reduced plaque inflammation as a stabilizing action.

Greater cap stability can lower vulnerability even when anatomic regression is modest.

Lipid lowering

Lower inflammation

↔

Relative plaque stabilization

Slide 65 · Classify an acute complication by its primary lesion

When the cap opens into the core, describe rupture or fissuring.

When the luminal endothelial covering is lost without cap rupture, describe erosion.

When blood accumulates within the lesion, describe intraplaque hemorrhage.

Finding / insult

Process

Immediate effect

Cap breach to core

Rupture

Thrombogenic contents exposed

Surface denudation

Erosion

Subendothelial interface exposed

Blood within lesion

Hemorrhage

Expanded plaque volume

Slide 66 · Case discussion: Infarction despite modest prior stenosis

A person without antecedent angina develops an acute coronary event.

Prior lumen imaging showed only mild-to-moderate fixed disease.

Mechanistic explanation: A susceptible plaque may have disrupted, followed by thrombosis.

Why can a noncritical stenosis become an acute culprit?

Surface change + superimposed thrombus

Slide 67 · Case discussion: Two plaques with similar lumen size

Plaque A has a thick collagen-rich cap and few inflammatory cells.

Plaque B has a thin cap, larger necrotic core, and abundant macrophages.

Plaque B has more structural features associated with acute rupture.

A

B

Lumen

Fibrous cap — schematic

Lumen

Thin cap — schematic

Thick collagen cap

Thin cap + large core

Schematic cross-sections

Slide 68 · Mechanistic synthesis: Injury, thrombus, outcome

Rupture and erosion can rapidly initiate luminal thrombosis.

Hemorrhage can expand and destabilize the plaque from within.

Resulting clinical consequences depend on thrombus extent, distal embolization, vasospasm, and tissue perfusion.

Plaque surface injury

Thrombus / embolus

Ischemia or infarction

Slide 69 · Five clinicopathologic conclusions

Culprit lesions need not be critically stenotic beforehand.

Cap thickness and collagen turnover are central determinants of rupture susceptibility.

Plaque inflammation can weaken matrix through altered synthesis and degradation.

Extrinsic pressure, platelet, and vasomotor changes can trigger events.

Silent thrombus organization is a mechanism of later plaque growth.

Slide 70 · Principal reading and image policy

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026. Chapter 11, “Blood Vessels,” pp. 455–458.

Related coronary pathophysiology: Chapter 12, “The Heart,” pp. 493–495.

Vascular illustrations in this lecture are original editable schematics, not diagnostic photomicrographs.