Definition and Pathophysiology
ST-segment elevation myocardial infarction (STEMI) is an acute myocardial infarction associated with a working diagnosis of persistent ST-segment elevation or an accepted equivalent in the setting of ischaemic symptoms. The immediate pathophysiological objective is restoration of blood flow to the infarct-related myocardial territory and limitation of infarct size.
The extent of myocardial injury is strongly influenced by total ischaemic time. This interval includes:
The time from symptom onset to recognition and seeking medical assistance.
Prehospital assessment, treatment and transport.
Diagnostic assessment and initiation of reperfusion therapy.
The interval from treatment initiation to restoration of coronary flow.
Early reperfusion, reduction of myocardial energy requirements and mitigation of reperfusion injury are complementary objectives of initial STEMI management. The principal acute complications fall into two broad categories:
Electrical complications, particularly ventricular arrhythmias.
Mechanical or pump-failure complications, including heart failure and cardiogenic shock.
Most out-of-hospital deaths occur early and are commonly related to ventricular fibrillation. More than half of deaths attributable to ventricular fibrillation occur during the first hour, making rapid recognition, defibrillation capability and expedited reperfusion central to survival.
Clinical Presentation and Symptoms
The characteristic symptom prompting activation of the STEMI pathway is ischaemic-type chest discomfort, although dyspnoea may also be a presenting feature. The source material emphasizes that patients and families should be educated to recognize chest discomfort or dyspnoea as potentially indicating myocardial infarction, particularly in individuals with hypertension, diabetes or previous angina.
Patients should be advised to seek emergency medical assistance rather than self-presenting to an emergency department or contacting primary care first. If ischaemic discomfort persists, emergency medical services should be called. Patients who have been prescribed sublingual nitroglycerin should be instructed in its appropriate use, although specific dosing instructions are not provided in the source material.
Delayed help-seeking is associated with older age, female sex, Black race, lower socioeconomic or uninsured status, a history of angina or diabetes, and consultation with relatives or physicians before contacting emergency services. These factors support the need for targeted public education, particularly among underserved groups and ethnic minority communities.
Late presentation is clinically important:
Within 12 hours of symptom onset: reperfusion therapy is recommended for all patients with a working diagnosis of STEMI.
More than 12 hours after onset: primary PCI remains indicated when there are ongoing ischaemic symptoms, haemodynamic instability or life-threatening arrhythmias.
Twelve to 48 hours after onset: routine primary PCI should be considered in otherwise stable patients.
More than 48 hours after onset: routine PCI of an occluded infarct-related artery is not recommended in stable, asymptomatic patients without severe ischaemia.
Evaluation and Physical Examination
The initial evaluation should be structured to establish a working diagnosis of STEMI rapidly, identify haemodynamic or electrical instability and determine the appropriate reperfusion pathway.
Important early clinical priorities include:
Recognition of symptoms suggestive of myocardial infarction.
Rapid acquisition and interpretation of a 12-lead ECG.
Assessment for haemodynamic instability, acute severe heart failure and cardiogenic shock.
Identification of life-threatening arrhythmias.
Assessment for high-risk mechanical complications.
Determination of symptom onset time and anticipated time to primary PCI.
Patients with STEMI should be monitored in a setting capable of continuous rhythm surveillance and immediate resuscitation. Emergency medical teams should be able to perform resuscitative manoeuvres, including defibrillation, and transport patients promptly to facilities with continuous medical and nursing expertise in arrhythmia management and advanced cardiac life support.
The physical examination should specifically seek evidence of:
Hypotension or other haemodynamic instability.
Acute heart failure.
Cardiogenic shock and end-organ hypoperfusion.
Right ventricular infarction.
Mechanical complications, including ventricular septal rupture, papillary muscle rupture and free-wall rupture.
Electrical instability or ongoing ischaemia.
The source material does not provide a detailed examination sequence or specific physical signs for each complication.
Diagnostics
Electrocardiography
The 12-lead ECG is central to the early diagnosis and triage of STEMI. In systems of care, arrival-to-ECG time at a referring hospital should be no more than 10 minutes. In selected prehospital systems, ECG transmission may allow diagnosis before hospital arrival and facilitate early activation of the catheterization laboratory team.
A working diagnosis of STEMI should trigger immediate triage for reperfusion therapy. ECG findings also guide assessment after fibrinolysis. Failure of fibrinolysis is defined by less than 50% ST-segment resolution within 60–90 minutes of administration.
Prehospital ECG and Catheterization Laboratory Activation
When EMS establishes a working diagnosis of STEMI, immediate activation of the catheterization laboratory team reduces treatment delay and may improve survival. Patients selected for emergency invasive management should bypass the emergency department and proceed directly to the catheterization laboratory.
Prehospital fibrinolysis requires:
The ability to transmit a 12-lead ECG for diagnostic confirmation.
Personnel trained in ECG interpretation and STEMI management.
Online medical command capable of authorizing field treatment.
Coronary Angiography and PCI
Primary PCI consists of immediate coronary angiography with PCI when indicated, usually with stent implantation and without preceding fibrinolysis. The procedural endpoint relevant to system timing is wire crossing of the infarct-related artery.
Radial access is recommended for PCI in acute coronary syndromes because it reduces bleeding and vascular complications compared with femoral access and is associated with lower mortality.
Routine aspiration thrombectomy before primary PCI is not useful.
Assessment of Nonculprit Coronary Arteries
In haemodynamically stable patients with multivessel disease, a significant nonculprit stenosis should generally be treated by staged PCI after successful treatment of the infarct-related artery. Staged intervention may occur during the same hospitalization or after discharge, up to 45 days after myocardial infarction.
PCI of a low-complexity nonculprit lesion during the primary procedure may be considered in selected stable patients with uncomplicated culprit-vessel revascularization, normal renal function and low procedural complexity. Routine treatment of a nonculprit artery during the index procedure is harmful in cardiogenic shock because of increased risks of death or renal failure.
Complex multivessel disease may require Heart Team assessment, with consideration of elective CABG where appropriate.
Biomarkers and Laboratory Findings
The source material does not describe cardiac biomarkers, laboratory diagnostic criteria or specific laboratory abnormalities. It emphasizes clinical assessment, ECG diagnosis, haemodynamic status and angiographic evaluation for rapid treatment selection.
Reperfusion Strategy
Primary PCI as the Preferred Strategy
Primary PCI is the preferred reperfusion strategy when it can be delivered within the relevant time target by an experienced team. It is superior to fibrinolysis when treatment delay is similar, reducing mortality, non-fatal reinfarction and stroke.
A primary PCI strategy is recommended when the anticipated interval from STEMI diagnosis to PCI-mediated reperfusion is less than 120 minutes. Primary PCI is also particularly favoured when:
Fibrinolysis is contraindicated.
The diagnosis is uncertain.
Cardiogenic shock is present.
Bleeding risk is high.
Symptoms have been present for more than 2–3 hours, when thrombus may be less readily lysed.
Primary PCI should be performed in patients presenting within 12 hours of symptom onset. It remains indicated in later presenters with ongoing ischaemia, acute severe heart failure, haemodynamic instability or life-threatening arrhythmias.
Fibrinolysis When Timely PCI Is Unavailable
If primary PCI cannot be performed within 120 minutes, fibrinolytic therapy is recommended within 12 hours of symptom onset in the absence of contraindications. Fibrinolysis should be initiated rapidly, with a treatment goal of administration within 10 minutes of first medical contact when it is selected as the initial strategy.
A pharmaco-invasive strategy requires immediate transfer to a PCI-capable centre after fibrinolysis, without waiting for evidence of reperfusion.
Rescue PCI
Rescue PCI is indicated when fibrinolysis fails, defined by less than 50% ST-segment resolution within 60–90 minutes. It is also indicated for:
Haemodynamic instability.
Electrical instability.
Worsening ischaemia.
Persistent chest pain.
Angiography After Successful Fibrinolysis
Patients with successful fibrinolysis should undergo angiography, with PCI of the infarct-related artery if indicated, within 2–24 hours of the fibrinolytic bolus. Patients developing new or persistent heart failure or shock after fibrinolysis require emergency angiography and PCI when indicated.
Emergency CABG
Emergency or urgent CABG may be effective when PCI is not feasible or unsuccessful and a large area of myocardium remains at risk. CABG should also be considered in patients with a patent infarct-related artery but unsuitable anatomy for PCI when a large myocardial territory is jeopardized or cardiogenic shock is present.
Emergency CABG is generally not appropriate after failed primary PCI when there is no ongoing ischaemia or large area of myocardium at risk, or when surgical revascularization is not feasible because of no-reflow or poor distal targets.
System-of-Care Time Targets
Total Ischaemic Time
System performance should be assessed continuously because system delay is modifiable and predicts mortality in patients undergoing primary PCI. Quality indicators should measure the intervals from first medical contact through reperfusion and identify operational barriers.
The major target intervals are summarized below.
| Process measure | Target or recommended approach |
|---|---|
| Arrival to 12-lead ECG at a referring hospital | ≤10 minutes |
| First medical contact to PCI when transport and system organization permit | Preferably <90 minutes in applicable EMS destination protocols |
| First medical contact to PCI when transport time is ≥45 minutes | <120 minutes |
| Diagnosis to PCI-mediated reperfusion | <120 minutes for primary PCI to remain the preferred strategy |
| Fibrinolytic administration when PCI cannot be delivered within 120 minutes | Within 10 minutes of first medical contact |
| Door-in to door-out at a non-PCI hospital | ≤30 minutes |
| Angiography after successful fibrinolysis | Within 2–24 hours |
| Assessment for failed fibrinolysis | ST-segment resolution at 60–90 minutes |
The 120-minute threshold is an absolute interval from STEMI diagnosis to PCI-mediated reperfusion, defined by wire crossing of the infarct-related artery. It is used to simplify selection between primary PCI and fibrinolysis.
EMS and Hospital Network Design
Optimal STEMI treatment requires regional networks linking:
EMS systems.
Non-PCI-capable referring hospitals.
PCI-capable receiving centres.
Intensive care and, where available, advanced haemodynamic support, cardiothoracic surgery and mechanical circulatory support.
Common written protocols should define diagnosis, destination, catheterization laboratory activation, transfer and backup arrangements. EMS should alert the PCI centre as soon as the reperfusion strategy has been selected. Patients should generally bypass the emergency department and be transported directly to a 24/7 PCI-capable centre.
For patients presenting to non-PCI centres, rapid transfer is required. A door-in to door-out interval of no more than 30 minutes is recommended. Automatic acceptance by the receiving centre, a one-call STEMI alert process and emergent interfacility transport can reduce avoidable delay.
Where geography prevents achievement of the primary PCI time target, networks should provide rapid fibrinolysis at the site of STEMI diagnosis, followed by immediate transfer to a PCI centre.
Quality improvement requires multidisciplinary review involving EMS, referring hospitals and PCI centres. Time intervals, clinical outcomes and operational problems should be measured, reported and used to refine the system.
Pharmacotherapy
Antiplatelet and Anticoagulant Therapy
All patients with acute STEMI should receive antiplatelet and anticoagulant therapy. The precise regimen and duration depend on:
The reperfusion strategy.
Ischaemic risk.
Bleeding risk.
Comorbidities.
The presence of another indication for ongoing anticoagulation, such as atrial fibrillation.
For patients undergoing PCI:
A loading dose of aspirin followed by daily aspirin is recommended.
A loading dose of a P2Y12 inhibitor followed by daily treatment is recommended.
Ticagrelor or prasugrel may be preferred to clopidogrel to reduce ischaemic events, including stent thrombosis.
Prasugrel should not be used in patients with a history of stroke or transient ischaemic attack.
Intravenous cangrelor may be considered in P2Y12 inhibitor-naive patients undergoing PCI to reduce periprocedural ischaemic events.
Intravenous unfractionated heparin is useful during PCI.
In patients with heparin-induced thrombocytopenia, bivalirudin or argatroban should replace unfractionated heparin.
No specific doses or treatment durations are provided in the source material.
Hospital Management
Monitoring Location
Patients with STEMI should initially receive continuous rhythm monitoring and access to immediate resuscitation. A coronary care unit is particularly important for patients with:
Refractory arrhythmias.
Cardiogenic shock.
Continuous intravenous vasoactive therapy.
Invasive haemodynamic monitoring.
Mechanical circulatory support.
Other major complications requiring intensive care.
Selected patients with low mortality risk who are stable after primary PCI may be managed in an intermediate-care telemetry unit equipped for continuous ECG monitoring and resuscitation.
Patients without heart failure, hypotension, heart block, haemodynamically compromising ventricular arrhythmias or persistent ischaemic discomfort may be transferred from the coronary care unit after approximately 24–36 hours. The duration of intensive care for complicated STEMI should be determined by ongoing requirements for haemodynamic monitoring, vasoactive medications, positive-pressure ventilation, mechanical circulatory support and close nursing supervision.
Cardiogenic Shock
Cardiogenic shock complicates approximately 5–10% of STEMI cases and has observed mortality rates of 30–50%. Management requires individualized assessment of treatment priorities and suitability for advanced therapies.
The preferred strategy in appropriate candidates is revascularization of the infarct-related artery by primary PCI. CABG is indicated when PCI is not feasible. If neither PCI nor CABG is suitable or accessible, fibrinolysis may be administered provided there is no contraindication.
Supportive measures include vasoactive agents and mechanical circulatory support to address end-organ hypoperfusion. Temporary mechanical circulatory support may be used in refractory shock that does not stabilize with other treatments, as a bridge to further decision-making or advanced heart-failure therapies.
Routine PCI of nonculprit arteries during the initial procedure should not be performed in cardiogenic shock.
Other High-Risk Complications
Important complications requiring prompt recognition include:
Cardiac arrest.
Ventricular fibrillation and other life-threatening arrhythmias.
Right ventricular infarction.
Acute mechanical complications, including ventricular septal rupture, papillary muscle rupture and free-wall rupture.
Acute severe heart failure.
The source material does not provide detailed protocols for the individual management of these complications.
Guideline-Based Recommendations
Reperfusion
| Recommendation | Class | Level |
|---|---|---|
| Reperfusion for STEMI with ischaemic symptoms lasting ≤12 hours | I | A |
| Primary PCI when anticipated diagnosis-to-PCI reperfusion time is <120 minutes | I | A |
| Fibrinolysis within 12 hours when timely primary PCI cannot be performed and there are no contraindications | I | A |
| Rescue PCI after failed fibrinolysis or with instability, worsening ischaemia or persistent chest pain | I | A |
| Immediate transfer to a PCI-capable centre after fibrinolysis | I | A |
| Angiography and PCI when indicated within 2–24 hours after successful fibrinolysis | I | A |
| Primary PCI for late presentation with ongoing ischaemia, instability or life-threatening arrhythmia | I | C |
| Routine primary PCI in stable patients presenting 12–48 hours after symptom onset | IIa | B |
| Routine PCI of an occluded infarct-related artery more than 48 hours after onset in stable patients without persistent symptoms | III | A |
Revascularization in Special Circumstances
| Clinical situation | Recommendation |
|---|---|
| Cardiogenic shock or haemodynamic instability | PCI, or CABG if PCI is not feasible, irrespective of time from symptom onset |
| Ongoing ischaemia, acute severe heart failure or life-threatening arrhythmia | PCI may be beneficial irrespective of symptom-to-treatment delay |
| Failed or infeasible PCI with a large myocardial territory at risk | Emergency or urgent CABG may be effective |
| Stable STEMI with multivessel disease after successful culprit-vessel PCI | Staged PCI of a significant nonculprit stenosis is recommended in selected patients |
| Low-complexity nonculprit disease in selected stable patients | PCI during the primary procedure may be considered |
| Cardiogenic shock with multivessel disease | Routine nonculprit PCI during the primary procedure should not be performed |
| Complex nonculprit disease | Heart Team evaluation and possible elective CABG may be appropriate |
Prognosis and Follow-Up
Prognosis is closely related to the speed and effectiveness of reperfusion and to the development of electrical or pump-failure complications. System delay is associated with mortality in patients treated with primary PCI. Rapid symptom recognition, early EMS activation, prehospital diagnosis, direct transfer to the catheterization laboratory and coordinated regional systems are therefore prognostically important.
The prognosis is particularly poor in STEMI complicated by cardiogenic shock, with mortality reported at approximately 30–50%. Ventricular fibrillation represents a major early risk, especially during the first hour and first 24 hours after symptom onset. Heart failure, right ventricular infarction and acute mechanical complications also increase mortality.
Follow-up planning should include:
Review of the reperfusion strategy and procedural outcome.
Assessment for residual significant nonculprit coronary disease.
Consideration of staged PCI during hospitalization or after discharge, up to 45 days after infarction, where indicated.
Continued evaluation for heart failure, arrhythmias and mechanical complications.
Coordination of post-discharge management with the broader chronic ischaemic heart disease and secondary-prevention pathway.
The source material does not specify a detailed outpatient medication regimen, cardiac rehabilitation programme, biomarker follow-up schedule or echocardiographic surveillance protocol.
