NSTEMI: Risk Stratification and Timing of the Invasive Strategy

Definition and pathophysiological context

Non-ST-segment elevation myocardial infarction (NSTEMI) is considered within the spectrum of non-ST-elevation acute coronary syndrome (NSTE-ACS). The clinical spectrum includes patients with a confirmed NSTEMI, patients with a working diagnosis of NSTE-ACS and a high probability of unstable angina (UA), and patients whose initial findings are less definitive.

The defining electrocardiographic feature is the absence of persistent ST-segment elevation. This does not imply low risk: patients with NSTE-ACS may have substantial myocardial ischaemia, dynamic ECG abnormalities, myocardial necrosis, haemodynamic deterioration, heart failure, malignant arrhythmias, or mechanical complications.

Risk assessment is intended to identify patients most likely to benefit from early coronary angiography and revascularization, while avoiding unnecessary procedural complications and bleeding in those at lower risk or in whom the hazards of revascularization outweigh its potential benefit. A routine invasive strategy does not reduce all-cause mortality across the overall NSTE-ACS population, but it reduces composite ischaemic outcomes, particularly among high-risk patients. The strategy may, however, increase peri-procedural complications and bleeding.

Clinical presentation

The available source material does not provide a detailed description of the presenting symptoms of NSTEMI. It does identify several clinical manifestations that indicate particularly high risk and should influence the urgency of management:

• Recurrent or ongoing chest pain despite medical treatment

• Acute heart failure presumed to result from ongoing myocardial ischaemia

• Haemodynamic instability or cardiogenic shock

• Life-threatening arrhythmias or cardiac arrest after presentation

• Mechanical complications of myocardial infarction

• Recurrent dynamic ECG changes suggestive of ischaemia, especially intermittent ST-segment elevation

Patients may initially stabilize and subsequently develop recurrent angina, recurrent ischaemic ECG changes, biomarker evidence of myocardial necrosis, or severe ischaemia on stress testing. Such developments may convert an initially selective or delayed approach into an indication for angiography and possible revascularization.

Initial evaluation and risk stratification

Clinical assessment

Assessment begins with the clinical context, the ECG, haemodynamic stability, and cardiac biomarker results. Patients with suspected ACS are categorized into a STEMI pathway or an NSTE-ACS pathway according to the initial ECG and clinical presentation.

For suspected NSTE-ACS, the immediate clinical questions are:

• Is there a very-high-risk feature requiring emergency angiography?

• Is there a high-risk feature supporting angiography within 24 hours?

• Is the patient stable without high-risk characteristics and therefore potentially suitable for a selective invasive approach?

• Is the clinical likelihood of true NSTE-ACS low enough that non-invasive evaluation is more appropriate?

The presence of extensive comorbidity may alter the balance between procedural risk and benefit. An early invasive strategy is not recommended when the risks of revascularization outweigh its expected benefits.

Haemodynamic and electrical status

Haemodynamic instability, cardiogenic shock, acute heart failure related to ongoing ischaemia, life-threatening arrhythmias, and cardiac arrest after presentation are markers of very high risk. They require immediate escalation because the priority is to identify and treat an obstructive coronary lesion without avoidable delay.

In contrast, haemodynamically stable patients without ST-segment elevation after successful resuscitation from out-of-hospital cardiac arrest should not routinely undergo immediate angiography. A selective or delayed approach is recommended in this setting unless other findings justify urgent intervention.

Risk scores

Several risk scores integrate clinical, ECG, and biomarker variables.

The GRACE score has the best discriminative performance among the scores specifically discussed for management decisions, and a value >140 is incorporated into current recommendations for early angiography.

Documented NSTE-ACS carries a broad early risk spectrum. The source material describes 30-day mortality ranging from 1–10% and recurrent ACS during the first year ranging from 5–15%. Risk is not uniform: patients with elevated troponin, dynamic ECG changes, diabetes, or a GRACE score >140 are among those in whom an early invasive strategy may provide the greatest benefit.

Electrocardiographic assessment

The ECG is central to triage and timing.

Findings supporting an immediate strategy

Recurrent dynamic ECG changes suggestive of ischaemia, particularly intermittent ST-segment elevation, are very-high-risk findings. They support emergency angiography as soon as possible.

Findings supporting an early strategy

The following are high-risk ECG findings:

• Dynamic ST-segment changes

• Dynamic T-wave changes

• Transient ST-segment elevation

These findings support consideration of angiography within 24 hours in an otherwise appropriate patient.

The source material also notes that ECG findings suggestive of left main stem involvement should prompt particularly rapid referral for coronary angiography.

ECG-negative presentations

A normal ECG does not exclude NSTE-ACS. In patients with suspected ACS who have no ECG changes, no recurrent pain, and non-elevated or uncertain high-sensitivity cardiac troponin, incorporation of coronary computed tomography angiography (CCTA) or non-invasive stress imaging into the initial evaluation should be considered.

Biomarkers and laboratory findings

High-sensitivity cardiac troponin

High-sensitivity cardiac troponin (hs-cTn) is used in diagnostic algorithms for suspected NSTEMI. The source material refers to the ESC 0-hour/1-hour and 0-hour/2-hour algorithms, in which the initial hs-cTn concentration and its change over time determine whether the patient enters a rule-out, observation, or rule-in pathway.

Patients with a confirmed NSTEMI based on the recommended hs-cTn algorithms are classified as high risk and should be considered for an early invasive strategy within 24 hours, provided that no very-high-risk feature mandates immediate angiography.

The source material does not provide specific hs-cTn thresholds or delta values. These should therefore be applied according to the relevant validated assay-specific diagnostic algorithm rather than inferred from a generic value.

Troponin and risk

Positive or rising troponin values identify a group with greater risk of adverse events. In studies comparing early with delayed angiography, patients with positive troponin and those with a GRACE score >140 appeared to derive greater benefit from an early approach, although some subgroup interaction tests were inconclusive.

Troponin elevation is not synonymous with type 1 NSTEMI. The overall clinical situation, ECG, symptoms, and haemodynamic state remain essential for determining whether the presentation represents NSTE-ACS and whether invasive management is appropriate.

In older adults, hs-cTn retains excellent diagnostic performance, but specificity is lower than in younger patients because elevations are more frequently associated with conditions other than ACS.

Other biomarkers

Multimarker assessment incorporating hs-cTn and brain natriuretic peptides is described as an evolving approach that may help characterize pathophysiology and refine risk stratification. The source material does not provide specific brain natriuretic peptide thresholds or treatment implications.

Imaging and non-invasive testing

Coronary angiography

Coronary angiography is the central diagnostic procedure for patients selected for an invasive strategy. Its purpose is to define coronary anatomy and permit PCI when appropriate. Depending on the anatomy, coronary artery bypass grafting (CABG) or continued medical therapy may instead be selected.

The timing of angiography is determined by risk category:

• Immediate angiography for very-high-risk NSTE-ACS

• Early angiography within 24 hours for high-risk NSTE-ACS

• Inpatient invasive management before discharge for patients with a high index of suspicion who do not meet immediate or early criteria

• Selective invasive evaluation for patients without high-risk features and with a low index of suspicion

CCTA and stress imaging

In suspected ACS with uncertain or non-elevated hs-cTn, no ECG changes, and no recurrent pain, CCTA or non-invasive stress imaging should be considered as part of the initial work-up.

A selective invasive strategy may also be based on evidence of obstructive coronary artery disease on CCTA or inducible ischaemia on stress testing. Coronary angiography is then reserved for patients in whom the non-invasive evaluation indicates a need for anatomical definition or revascularization.

Categories of invasive management

Three broad strategies are used.

Immediate invasive strategy

An immediate invasive strategy means emergency coronary angiography as soon as possible, followed by PCI if indicated. The guideline material describes a target of less than two hours whenever possible.

It is recommended for patients with a working diagnosis of NSTE-ACS and at least one of the following:

• Haemodynamic instability or cardiogenic shock

• Recurrent or ongoing chest pain refractory to medical treatment

• Acute heart failure presumed secondary to ongoing myocardial ischaemia

• Life-threatening arrhythmias or cardiac arrest after presentation

• Mechanical complications of myocardial infarction

• Recurrent dynamic ECG changes suggestive of ischaemia, particularly intermittent ST-segment elevation

These patients require urgent clinical stabilization and emergency angiography. Revascularization is performed if the coronary anatomy and clinical circumstances support it.

Early invasive strategy

An early invasive strategy consists of routine angiography, with PCI if required, within 24 hours of presentation.

It should be considered in patients with at least one of the following high-risk criteria:

• Confirmed NSTEMI using the current ESC hs-cTn diagnostic algorithms

• Dynamic ST-segment or T-wave changes

• Transient ST-segment elevation

• GRACE risk score >140

The 2023 revision described in the source material changed the recommendation from a stronger earlier formulation to a Class IIa recommendation, despite retaining a high level of evidence for this group.

Inpatient invasive strategy before discharge

Patients who do not meet very-high-risk or high-risk criteria may still require inpatient angiography when there is a high index of suspicion for NSTE-ACS, particularly suspected unstable angina.

The decision should be individualized according to the degree of clinical suspicion, recurrent symptoms, ECG evolution, biomarker results, non-invasive testing, comorbidity, and procedural risk.

Selective invasive strategy

A selective invasive, ischemia-guided, or conservative strategy begins with medical management and close observation. Angiography is performed if one of the following develops:

• Haemodynamic instability

• Recurrent rest pain or recurrent ischaemia

• Recurrent ST-segment or T-wave changes

• New biomarker evidence of myocardial necrosis

• Obstructive coronary disease detected by CCTA

• Severe inducible ischaemia on stress testing

This strategy is recommended for patients without very-high-risk or high-risk characteristics who have a low index of suspicion for NSTE-ACS. It is also appropriate for patients with NSTEMI or UA who are not considered suitable candidates for coronary angiography.

Timing algorithm

Evidence informing timing

A routine invasive approach reduces composite ischaemic endpoints, particularly in high-risk patients, but does not consistently reduce all-cause mortality in the overall NSTE-ACS population. It may increase peri-procedural complications and bleeding.

Meta-analyses comparing early with delayed angiography have shown:

• A reduction in recurrent or refractory ischaemia with early angiography

• A shorter hospital stay

• A reduction in myocardial infarction during long-term follow-up in one analysis

• No consistent overall reduction in mortality

• Greater apparent benefit in patients with GRACE scores >140 and in some analyses in those with positive troponin

The largest meta-analysis described in the source material found that early angiography in unselected NSTE-ACS patients reduced recurrent ischaemia and duration of hospitalization but did not significantly reduce all-cause mortality, myocardial infarction, heart-failure admission, or repeat revascularization. Interpretation is limited by variation in the timing of angiography in the delayed-treatment groups and by the fact that many earlier trials did not use contemporary hs-cTn diagnostic algorithms.

Observational data are broadly concordant, without a strong universal signal that early angiography is superior to delayed angiography in all patients. The balance of evidence therefore supports risk-directed rather than indiscriminate acceleration of invasive management.

Cardiogenic shock and haemodynamic instability

Cardiogenic shock is an uncommon but particularly high-risk complication of NSTEMI. The source material reports an incidence below 3% and an in-hospital mortality of 35% in a large US national database. In that population, the risk-adjusted mortality was reduced by more than 50% with an invasive strategy.

Shock or unstable haemodynamics is therefore an indication for immediate angiography and, where appropriate, revascularization. Such patients were excluded from major randomized ACS trials, so management recommendations are based on the very high observed risk and available clinical evidence rather than on the same trial framework used for stable NSTE-ACS.

Cardiac arrest and arrhythmia

Life-threatening arrhythmias or cardiac arrest occurring after presentation are very-high-risk features requiring immediate invasive management in the context of NSTE-ACS.

A different approach applies to patients successfully resuscitated from out-of-hospital cardiac arrest who are haemodynamically stable and have no persistent ST-segment elevation or equivalent. Routine immediate angiography is not recommended in this group. A delayed or selective invasive approach should be used unless other clinical or diagnostic findings indicate a need for urgent intervention.

For adults who remain unresponsive after return of spontaneous circulation following either out-of-hospital or in-hospital cardiac arrest, temperature control with continuous core-temperature monitoring and active prevention of fever above 37.7°C is recommended.

Revascularization after angiography

Angiography is performed with the intention of proceeding to revascularization when appropriate. The options include:

• PCI

• CABG

• Continued medical therapy when revascularization is not indicated or is not suitable

Coronary anatomy, comorbidity, renal function, haemodynamic status, and procedural complexity influence the choice. In patients with multivessel disease, single-stage PCI may be considered when cardiogenic shock, severe comorbidity such as acute kidney injury, and unfavorable or high-risk anatomy are absent. Complex anatomy may require Heart Team assessment for CABG versus complex PCI.

Antithrombotic and medical treatment

The source material states that anti-ischaemic and antithrombotic treatment should be initiated before or alongside the invasive strategy, but it does not provide a complete drug regimen, specific doses, or detailed contraindication tables for NSTEMI. Accordingly, specific doses for anticoagulants, antiplatelet agents, nitrates, beta-blockers, or other anti-ischaemic therapies are not stated here.

The guideline material does provide the following antiplatelet recommendations from the revised recommendations table:

• In a primary PCI strategy, pre-treatment with a P2Y12 receptor inhibitor may be considered.

• After stent implantation in patients treated with dual antiplatelet therapy (DAPT), aspirin discontinuation after 3–6 months should be considered according to the balance between ischaemic and bleeding risk.

• In patients who remain event-free after 3–6 months of DAPT and who are not at high ischaemic risk, single antiplatelet therapy, preferably with a P2Y12 receptor inhibitor, should be considered.

The duration and composition of antithrombotic therapy must therefore be individualized to ischaemic risk, bleeding risk, stent-related considerations, and comorbidity.

Persistent hyperglycaemia in ACS should prompt consideration of glucose-lowering therapy, while hypoglycaemia should be avoided. The source material does not specify a drug, dosing regimen, or a universal glucose target; the target should be adapted to comorbidities.

Special populations

Older adults

Age is a major predictor of adverse outcome after ACS. Adults aged ≥75 years are frequently under-represented in clinical trials and have a higher prevalence of frailty, multimorbidity, and both ischaemic and bleeding risk.

In older patients, decisions about invasive management should incorporate:

• Ischaemic risk

• Bleeding risk

• Life expectancy

• Comorbidities

• Frailty

• Cognitive and functional status

• Quality of life

• Potential need for non-cardiac surgery

• Patient values and preferences

• Estimated procedural benefit and risk

A small randomized study in patients aged ≥80 years with NSTE-ACS found that an invasive strategy reduced a composite of myocardial infarction, urgent revascularization, stroke, and death, but did not reduce all-cause mortality. The benefit became less pronounced with increasing age.

Hs-cTn remains diagnostically useful in older adults, although reduced specificity requires careful integration with the clinical presentation and ECG.

Diabetes

The indications and timing of revascularization for patients with diabetes and NSTE-ACS should not differ from those for patients without diabetes. Diabetes is, however, associated with poorer prognosis, and some analyses suggest that patients with diabetes may derive greater benefit from an early invasive approach.

Renal dysfunction and comorbidity

Patients with chronic kidney disease were among groups in which benefit from an early invasive strategy was observed in some analyses. Nevertheless, severe comorbidity, acute kidney injury, and unfavorable anatomy may substantially increase procedural risk and influence the choice between PCI, CABG, delayed evaluation, or medical management.

Guideline recommendations

The principal recommendations can be summarized as follows:

• An invasive strategy is recommended for patients with ACS, with timing determined by clinical risk.

• Immediate angiography is recommended for very-high-risk NSTE-ACS, including shock or haemodynamic instability, refractory chest pain, ischaemic acute heart failure, life-threatening arrhythmias or cardiac arrest, mechanical complications, and recurrent dynamic ischaemic ECG changes.

• An early invasive strategy within 24 hours should be considered for confirmed NSTEMI, dynamic ST/T changes, transient ST elevation, or GRACE score >140.

• Patients without very-high-risk or high-risk criteria but with a high suspicion of UA should undergo inpatient invasive evaluation.

• Patients with a low index of suspicion and no high-risk features should undergo selective evaluation, incorporating CCTA or non-invasive stress imaging where appropriate.

• Routine immediate angiography is not recommended in haemodynamically stable patients without persistent ST elevation after resuscitated out-of-hospital cardiac arrest.

• Risk scores are useful in management; the GRACE score is specifically incorporated into the decision to pursue early angiography.

• In older adults, invasive treatment should be individualized according to frailty, comorbidity, life expectancy, quality of life, and the balance of ischaemic and bleeding risks.

Prognosis and follow-up

The prognosis of NSTE-ACS varies widely. Early mortality and recurrent ACS risk are substantial, particularly among patients with biomarker-positive disease, dynamic ECG changes, haemodynamic compromise, heart failure, arrhythmia, diabetes, or a high GRACE score.

An invasive strategy may reduce recurrent ischaemia, myocardial infarction, composite ischaemic outcomes, and length of hospitalization, with the greatest benefit concentrated in higher-risk patients. It does not consistently reduce mortality in unselected NSTE-ACS populations, and it carries potential peri-procedural and bleeding hazards.

Long-term risk assessment should continue after hospital discharge. Risk scores may help identify patients requiring more intensive secondary prevention, particularly those with greater risk of recurrent atherothrombotic events. The source material does not provide a detailed schedule for outpatient follow-up, rehabilitation, lipid targets, blood-pressure targets, or specific long-term pharmacological doses. These elements therefore require application of the broader ACS and secondary-prevention guidance relevant to the individual patient.