Definition and conceptual framework
Acute coronary occlusion is the abrupt or progressive reduction of coronary blood flow sufficient to produce myocardial ischaemia and, when prolonged or severe, myocardial necrosis. It most commonly reflects atherothrombosis: disruption of an atherosclerotic plaque followed by platelet activation and coagulation, with formation of an intraluminal thrombus. The clinical spectrum includes unstable angina, non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI).
The traditional term “vulnerable plaque” describes an atherosclerotic lesion thought to be susceptible to disruption and thrombosis. Typical features include a lipid-rich core, a thin fibrous cap, macrophage and foam-cell accumulation, expansive or positive remodelling, neovascularization, plaque haemorrhage, adventitial inflammation, and spotty calcification. However, the concept has important limitations. Although thin-capped fibroatheromas may have imaging characteristics associated with rupture, fewer than 5% of such lesions caused a clinical event during 3.4 years of follow-up in a prospective study of patients with acute coronary syndrome. Thus, an individual plaque’s morphology does not reliably establish that it will cause an acute event.
A more clinically useful model considers both the plaque and the patient. Multiple potentially high-risk plaques may exist throughout the coronary tree, while inflammation and thrombotic susceptibility are often systemic rather than confined to a single lesion. Consequently, local revascularization must be accompanied by systemic treatment aimed at stabilizing the broader atherosclerotic disease.
Pathophysiology
Mechanisms of acute coronary syndrome
The major mechanisms producing acute coronary syndromes are:
Plaque rupture with exposure of thrombogenic material.
Superficial plaque erosion.
Thrombosis associated with a calcified nodule.
Epicardial or microvascular coronary spasm.
Spontaneous coronary artery dissection.
Coronary embolism of cardiac or non-cardiac origin.
Oxygen supply–demand mismatch, including demand-related events in the presence of fixed coronary disease.
More than one mechanism may operate simultaneously. Some acute coronary events occur without an identifiable culprit thrombus.
NSTE-ACS generally reflects an imbalance between myocardial oxygen supply and demand. In many cases, the initiating process is plaque disruption with thrombosis; other cases result from spasm, microvascular dysfunction, embolism, dissection, hypotension or shock, respiratory failure, severe anaemia, sustained bradyarrhythmia, tachyarrhythmia, or severe hypertension with or without left ventricular hypertrophy.
Among patients with NSTE-ACS undergoing angiography, approximately 10% have no critical epicardial stenosis. In some of these patients, microvascular obstruction or epicardial spasm may account for the ischaemia.
STEMI usually results from rapid thrombotic occlusion of a previously atherosclerotic coronary artery. Slowly progressive severe stenoses are less likely to cause STEMI because collateral vessels may develop over time. By contrast, an acute thrombus may form at a site that was previously only mildly or moderately stenosed.
Plaque rupture
Plaques prone to rupture characteristically contain a large lipid pool, numerous macrophages or foam cells, and a thin fibrous cap. Disruption of the cap exposes the lipid core and extracellular matrix to circulating blood. Tissue factor within the plaque and tissue-factor-bearing microparticles contribute to activation of coagulation.
Plaque rupture is typically associated with a fibrin-rich, red thrombus. The size and persistence of the thrombus depend not only on plaque composition but also on circulating thrombotic and fibrinolytic factors.
Plaque erosion
Plaque erosion is increasingly recognized and is present in at least one-third of acute coronary syndromes in the cited material. Eroded plaques tend to be lipid-poor, contain fewer macrophages, and have a relatively matrix-rich structure. The thrombus is more often white and platelet-rich than the fibrin-dominant thrombus associated with plaque rupture.
The mechanisms of erosion include endothelial injury, flow perturbation, Toll-like receptor 2-related pathways, hyaluronan-associated processes, and neutrophil recruitment. Inflammation remains relevant, but its cellular and molecular signature may differ from that of cap rupture. Whether the distinction between rupture and erosion should routinely alter treatment remains under investigation.
Calcified nodules
A calcified nodule can disrupt the luminal surface and precipitate thrombosis. Patients with ACS caused by calcific nodules have been described as having high rates of recurrent ACS, major adverse cardiovascular events, and target-lesion revascularization.
Platelet activation and coagulation
Thrombus formation involves coordinated platelet and coagulation responses:
Platelets adhere to the injured arterial surface.
Agonists such as collagen, ADP, epinephrine, and serotonin activate platelets.
Platelets degranulate and recruit additional platelets.
Thromboxane A2 promotes further platelet activation and local vasoconstriction.
The glycoprotein IIb/IIIa receptor undergoes a conformational change that permits fibrinogen-mediated platelet cross-linking.
Tissue factor exposure activates the coagulation cascade.
Factors VII and X contribute to thrombin generation.
Thrombin converts fibrinogen to fibrin and amplifies coagulation.
The resulting thrombus contains platelet aggregates and fibrin strands. Coronary occlusion may be complete, partial, transient, or persistent.
Solid-state and fluid-phase determinants
The consequences of plaque disruption depend on an interaction between:
Solid-state determinants: plaque tissue factor, tissue-factor-bearing macrophages and microparticles, lipid-core composition, and the extent of apoptosis.
Fluid-phase determinants: fibrinogen concentration, plasminogen activator inhibitor 1 (PAI-1), and endogenous fibrinolytic activity.
Inflammation influences both compartments. Fibrinogen and PAI-1 are acute-phase reactants, while inflammatory mediators can increase tissue-factor expression. A given plaque disruption may therefore produce only a small mural thrombus, transient obstruction, unstable angina, or a persistent occlusive thrombus causing myocardial infarction.
Coronary vasospasm and microvascular dysfunction
Dynamic reduction in coronary flow may arise from epicardial spasm or constriction of small intramural coronary arteries. Potential vasoconstrictor influences include platelet-derived mediators, endothelial dysfunction, adrenergic stimulation, cold exposure, cocaine, and amphetamines. Microvascular dysfunction may produce ischaemia without visible epicardial thrombosis.
Spontaneous coronary artery dissection and embolism
Spontaneous coronary artery dissection and coronary embolism are less common causes of acute coronary occlusion. Coronary emboli may originate from cardiac thrombi or masses, or from non-cardiac sources. Optical coherence tomography can identify spontaneous coronary artery dissection and may help avoid unnecessary stent implantation.
Clinical presentation and symptoms
Acute coronary occlusion may present with ischaemic discomfort, with or without ST-segment elevation. The supplied material does not provide a detailed symptom inventory, but it emphasizes that acute coronary syndromes can manifest through:
Ischaemic chest discomfort.
Resting dyspnoea, particularly when acute heart failure complicates ACS.
Clinical features of fluid overload in patients with ACS-associated acute heart failure.
Symptoms of recurrent ischaemia after PCI, including chest pain.
The absence of classic symptoms does not exclude significant disease. Silent coronary occlusion may occur when collateral flow prevents necrosis or when thrombosis is incomplete. In heart-transplant recipients, denervation may eliminate typical anginal symptoms, while diffuse graft arteriosclerosis may be underestimated by conventional angiography.
Right ventricular infarction
Right ventricular infarction usually accompanies a substantial inferior and septal left ventricular infarction. The classic clinical pattern is:
Hypotension.
Clear lung fields.
Elevated jugular venous pressure.
Isolated right ventricular infarction is much less common than right ventricular involvement associated with inferior infarction.
Acute heart failure and cardiogenic shock
Acute heart failure complicating ACS is associated with increased risks of renal deterioration, respiratory failure, pneumonia, and death. Patients are more likely to present with dyspnoea at rest and signs of volume overload. Cardiogenic shock may result from extensive ischaemia, multivessel disease, acute severe mitral regurgitation, or other mechanical complications.
Evaluation and physical examination
Initial evaluation centres on rapid clinical assessment, a 12-lead ECG, and measurement of cardiac biomarkers. The ECG remains central to the first management decision because it distinguishes patients with persistent ST elevation, who require immediate reperfusion consideration, from those without ST elevation.
Physical examination should assess for:
Hypotension and evidence of haemodynamic instability.
Jugular venous elevation with clear lungs, suggesting right ventricular infarction.
Pulmonary congestion and other signs of fluid overload.
Findings of acute heart failure.
Features of cardiogenic shock.
Possible mechanical complications, particularly when the clinical course deteriorates.
In patients with suspected ACS and acute heart failure, emergency echocardiography and chest ultrasonography are recommended to evaluate ventricular function, regional wall motion, valvular function, and mechanical complications.
Diagnostics
Electrocardiography
The ECG is the primary initial diagnostic and triage test in suspected ACS. Ischaemic ST-segment changes may precede elevation of cardiac biomarkers.
ST-segment elevation
Acute transmural or near-transmural ischaemia generally produces ST-segment elevation over the affected region, sometimes accompanied by hyperacute T waves. Reciprocal ST-segment depression may appear in leads representing the opposite cardiac surface and may occasionally be more conspicuous than the primary elevation.
Persistent ST-segment elevation identifies patients who are candidates for reperfusion therapy, either catheter-based or pharmacological when catheter-based treatment is unavailable.
Subendocardial ischaemia
Predominantly subendocardial ischaemia typically produces ST-segment depression in overlying leads, with ST-segment elevation in lead aVR. This pattern is common during spontaneous or provoked subendocardial ischaemia but does not exclude severe disease.
Evolution of the ECG
ST elevation may resolve as ischaemia evolves, with subsequent T-wave inversion. This evolution can lead to misclassification of an evolving STEMI as a non-ST-elevation event. Severe ischaemia or infarction may occur with minimal or absent ST-T abnormalities. Hyperacute T waves may precede or accompany ST elevation. A paradoxical pattern of precordial ST depression with prominent T waves, described in association with left anterior descending coronary occlusion, may also occur.
Infarction alters depolarization and may produce:
Q waves in leads corresponding to the infarct zone.
Reduced R-wave amplitude.
QRS notching or splintering.
Most patients with ST elevation who develop an infarction eventually develop Q waves, although a minority do not.
ECG after PCI
New chest pain after PCI requires an immediate 12-lead ECG. Recurrent ischaemia may reflect acute or subacute stent thrombosis, residual dissection, plaque prolapse, side-branch occlusion, thrombus at the treatment site, or untreated residual disease.
Coronary angiography
Coronary angiography identifies the infarct-related artery, the degree and distribution of epicardial disease, and the presence of an occlusive or subtotally occlusive lesion. Approximately 90% of STEMI cases have total occlusion of the infarct-related vessel on the initial angiogram, although spontaneous fibrinolysis can occur before angiography.
Angiography may underestimate diffuse or concentric disease, particularly in cardiac allograft vasculopathy, which involves proximal epicardial arteries and smaller intramyocardial branches. Angiography is also limited in defining plaque composition and the precise mechanism of thrombosis.
In suspected recurrent ischaemia after PCI, coronary angiography is the most expeditious method of identifying the cause.
Optical coherence tomography and intravascular ultrasound
Optical coherence tomography (OCT) has high sensitivity for intraluminal thrombus and can distinguish red from white thrombus. It is more sensitive than intravascular ultrasound (IVUS) for detecting fibrous-cap rupture and plaque erosion. OCT may also identify vulnerable plaques in non-culprit lesions and detect spontaneous coronary artery dissection.
Because OCT can help define the underlying mechanism of ACS, it has potential implications for treatment selection. However, the use of mechanism-specific therapy based on plaque rupture versus erosion remains an evolving area.
Coronary computed tomographic angiography and positron emission tomography
Coronary computed tomographic angiography can contribute to the assessment of plaque morphology and, in cardiac allograft vasculopathy, provides a non-invasive alternative to invasive contrast angiography for surveillance. Positron emission tomography may provide information about microvascular function in this setting.
Echocardiography
Emergency echocardiography is particularly important when ACS is complicated by acute heart failure or shock. It assesses:
Left and right ventricular function.
Regional wall-motion abnormalities.
Valvular function.
Mechanical complications.
The supplied material does not detail echocardiographic criteria for plaque vulnerability or acute occlusion.
Biomarkers and laboratory findings
Cardiac troponin is the principal biomarker used to distinguish unstable angina from NSTEMI in patients without ST elevation. Ischaemic symptoms without ST elevation and without detectable myocardial injury biomarkers are classified as unstable angina; with elevated cardiac troponin, the diagnosis is NSTEMI.
Cardiac biomarkers may be elevated before or after the ECG evolves, but repolarization abnormalities often precede biomarker elevation. Troponin elevation must be interpreted in clinical context. In acute heart failure, increased troponin may reflect myocardial injury related to heart failure rather than myocardial necrosis caused by acute coronary ischaemia.
After PCI, small rises in creatine phosphokinase or troponin are common and may reflect procedural myocardial injury. Only marked enzyme elevations, greater than 10 times the upper limit of normal, were associated in the supplied material with a less favourable long-term outcome.
Other relevant laboratory or biological determinants include:
Fibrinogen, which can influence thrombus formation.
PAI-1, which may impair fibrinolysis.
Tissue factor and tissue-factor-bearing microparticles.
Systemic inflammatory markers such as C-reactive protein, which increase in patients at risk for ACS.
Although inflammatory and thrombotic markers support the systemic nature of plaque instability, the material does not establish validated biomarker thresholds for distinguishing plaque rupture from erosion.
Treatment and management
Immediate management principles
Management is determined initially by the ECG, clinical stability, biomarker evidence of myocardial injury, and the suspected mechanism of coronary obstruction. Persistent ST-segment elevation requires urgent reperfusion, preferably catheter-based when available. The management of non-ST-elevation presentations depends on the overall clinical and diagnostic assessment.
Because multiple high-risk plaques may coexist, treatment must address both the culprit lesion and the systemic atherosclerotic environment. Local revascularization alone does not eliminate the risk posed by non-culprit plaques.
Reperfusion and revascularization
Patients with persistent ST elevation are candidates for reperfusion therapy:
Catheter-based reperfusion is preferred when available.
Pharmacological reperfusion is an alternative when catheter-based treatment is unavailable.
The benefits of restoring flow are time-dependent. Myocardial contractile function is lost rapidly after coronary occlusion, while viability begins to decline after approximately 20 minutes. Progressive loss of viability may be complete by 6–12 hours. Early restoration of flow can salvage myocardium, although reperfusion itself may cause injury and recovery of contractile function may be delayed because of myocardial stunning.
In ACS complicated by acute heart failure or cardiogenic shock, immediate invasive coronary angiography is required. Patients with cardiogenic shock should be transferred promptly to a PCI centre for angiography and PCI of the infarct-related artery when indicated. If the anatomy is unsuitable for PCI, emergency coronary artery bypass grafting is recommended.
Antiplatelet and anticoagulant treatment
Antiplatelet and anticoagulant therapy improve outcomes because platelet activation and coagulation are central to thrombus formation. The supplied material does not provide drug doses or a complete acute pharmacological regimen.
Following stent implantation, dual antiplatelet therapy consists of aspirin plus a platelet P2Y12 receptor blocker such as clopidogrel, prasugrel, or ticagrelor. Premature discontinuation, particularly during the first month, substantially increases the risk of stent thrombosis.
Treatment of right ventricular infarction
Acute right ventricular infarction with shock requires:
Judicious volume replacement.
Early revascularization.
Maintenance of atrioventricular synchrony.
Mechanical circulatory support in refractory cases.
The right ventricle may recover contractile function well after reperfusion despite prolonged ischaemia.
Acute heart failure and cardiogenic shock
Management requires coordinated treatment of both ACS and acute heart failure. Depending on the clinical state, treatment may include:
Diuretics.
Vasodilators.
Inotropic agents.
Vasopressors.
Mechanical circulatory support in selected patients.
Invasive respiratory support.
Renal replacement therapy when required.
Routine intra-aortic balloon pump use in ACS-associated cardiogenic shock did not reduce mortality at 30 days, 1 year, or 6 years in the cited material. The benefit of percutaneous mechanical circulatory support devices and venoarterial extracorporeal membrane oxygenation remains unclear. Observational data described higher mortality and bleeding with micro-axial mechanical support than with intra-aortic balloon pump, and caution is advised until further randomized evidence becomes available.
PCI-related complications and recurrent ischaemia
PCI complications include:
Acute occluding thrombus.
Severe coronary dissection.
Distal embolization.
Microvascular occlusion and no-reflow.
Side-branch closure.
Coronary perforation.
Stent thrombosis.
Restenosis.
Stent thrombosis may be acute, subacute, late, or very late. It is reduced by complete stent deployment and appropriate dual antiplatelet therapy. When recurrent ischaemia is suspected after PCI, immediate ECG assessment should be followed by coronary angiography when indicated.
Restenosis and stent thrombosis
The supplied material reports the following approximate first-year restenosis frequencies:
| Treatment | Approximate restenosis frequency |
|---|---|
| Balloon angioplasty alone | 20–50% |
| Bare-metal stent | 10–30% |
| Drug-eluting stent | 5–15% |
Clinical restenosis is usually recognized by recurrent angina or other symptoms within 12 months. Less commonly, it presents with NSTEMI or STEMI. Treatment generally involves repeat PCI with balloon dilation and implantation of another drug-eluting stent. Other options for symptomatic recurrent restenosis include brachytherapy, drug-coated balloons, and coronary bypass surgery.
Stent thrombosis occurs in approximately 1–3% of stents. It may cause death in 10–20% of affected patients and myocardial infarction in 30–70%. Second-generation drug-eluting stents have lower late and very late thrombosis rates than first-generation devices.
For stents, 6 months of dual antiplatelet therapy is recommended in the supplied material, with longer treatment considered according to atherothrombotic and bleeding risks. After PCI for ACS, treatment up to 1 year should also be considered. Elective surgery requiring antiplatelet interruption should, if possible, be postponed until at least 3 months and preferably 6 months after drug-eluting stent implantation.
Systemic plaque stabilization
Because plaque susceptibility and inflammation are diffuse, affected patients should receive systemic therapy directed at stabilizing multiple high-risk lesions. The supplied material emphasizes lipid-lowering therapy as capable of depleting intimal lipid collections, halting plaque progression, or producing regression. It does not provide specific lipid targets, drug doses, or a complete secondary-prevention regimen.
Guideline-based recommendations
The material supports the following principles:
Use the 12-lead ECG as the central initial triage test. Persistent ST elevation identifies patients requiring urgent reperfusion consideration.
Use cardiac troponin to distinguish unstable angina from NSTEMI when symptoms occur without ST elevation.
Perform immediate invasive coronary angiography in ACS complicated by acute heart failure or cardiogenic shock.
Perform emergency echocardiography or chest ultrasonography in these patients to assess ventricular function, regional wall motion, valves, and mechanical complications.
Transfer cardiogenic-shock patients promptly to a PCI centre for angiography and infarct-related artery treatment when appropriate.
Use emergency CABG when shock-associated coronary anatomy is unsuitable for PCI.
Recognize plaque rupture, erosion, calcified nodules, spasm, dissection, embolism, and oxygen supply–demand imbalance as distinct mechanisms rather than assuming all ACS results from the same lesion type.
Use OCT when defining thrombus type, cap rupture, erosion, or spontaneous coronary artery dissection may influence management.
Administer dual antiplatelet therapy after stent implantation, with duration individualized to the competing risks of thrombosis and bleeding.
Avoid premature discontinuation of dual antiplatelet therapy, especially during the first month after implantation.
Use systemic treatment to stabilize the broader coronary disease, because culprit and non-culprit high-risk plaques may coexist.
Prognosis and follow-up
Determinants of myocardial injury
The extent of myocardial damage depends on:
The territory supplied by the occluded artery.
Whether occlusion is complete or partial.
Duration of occlusion.
Collateral blood flow.
Myocardial oxygen demand.
The possibility of spontaneous thrombus lysis.
The adequacy of perfusion after reopening the epicardial artery.
The presence of multivessel or diffuse coronary disease.
A large area of myocardium at risk, severe baseline stenosis, multivessel disease, and diffuse coronary disease increase the risk of haemodynamic collapse when PCI fails or procedural complications occur.
Infarct size is prognostically important. Larger infarct size is associated with higher subsequent rates of heart failure and all-cause mortality or hospitalization.
Follow-up after PCI
Follow-up should include assessment for:
Recurrent angina or other ischaemic symptoms.
Recurrent ACS.
Stent thrombosis.
Restenosis.
Heart failure.
Ventricular dysfunction.
Consequences of procedural myocardial injury.
Adherence to dual antiplatelet therapy and systemic plaque-stabilizing treatment.
Recurrent symptoms within 12 months should raise concern for restenosis, although recurrent ischaemia may also result from stent thrombosis, residual dissection, side-branch occlusion, plaque prolapse, or untreated coronary disease.
Long-term risk
The risk of recurrent events is not confined to the treated culprit lesion. Multiple high-risk plaques and widespread inflammation may persist throughout the coronary circulation. Long-term management therefore requires continued systemic prevention in addition to technically successful revascularization.
The concept of plaque vulnerability remains biologically valuable but clinically imperfect. Future management may incorporate biomarkers and imaging capable of distinguishing plaque rupture from erosion and identifying the dominant mechanism of acute ischaemia. Such mechanism-guided treatment remains investigational in the supplied material.
