TIMI Risk Score for STEMI

Age carries the highest point weight in the score (up to 3 points for ≥ 75 years), reflecting the strong independent association between advancing age and mortality following STEMI. Elderly patients have higher rates of mechanical complications, heart failure, and cardiogenic shock. They are also more likely to present late with atypical symptoms, reducing the window for effective reperfusion.

• < 65 years: 0 points. Lower baseline mortality risk, though complications can still occur, particularly with large anterior MIs or delayed presentation.
• 65–74 years: 2 points. A transitional group where comorbidity burden increases and cardiac reserve diminishes.
• ≥ 75 years: 3 points. The highest weighting. These patients have the highest mortality and complication rates, and decisions regarding invasive strategies must balance benefit against bleeding and procedural risk.

Hypotension at presentation carries the joint-highest weighting (3 points, equal to age ≥ 75), reflecting its strong association with cardiogenic shock, large infarct size, and haemodynamic compromise. A systolic BP below 100 mmHg may indicate extensive myocardial damage with reduced cardiac output, right ventricular infarction (especially in inferior STEMI), or mechanical complications such as acute mitral regurgitation or ventricular septal defect.

Hypotension should prompt immediate evaluation for these causes. Volume status assessment, echocardiography, and consideration of inotropic or mechanical circulatory support may be needed alongside reperfusion therapy.

Tachycardia at presentation is an independent predictor of mortality, reflecting sympathetic activation in response to pain, anxiety, reduced cardiac output, or incipient heart failure. In the context of STEMI, a heart rate exceeding 100 bpm may suggest a large area of myocardium at risk, evolving heart failure, or hypovolaemia.

It is important to distinguish sinus tachycardia (a compensatory response) from pathological arrhythmias such as atrial fibrillation with rapid ventricular response, which carry additional prognostic significance. Beta-blockade to control heart rate may be appropriate if there is no contraindication (hypotension, acute heart failure, bradycardia risk).

The Killip classification is a bedside assessment of heart failure severity in the setting of acute MI. It has been one of the most consistent predictors of mortality across multiple ACS scoring systems. In the TIMI STEMI score, any Killip class above I scores 2 points.

• Class I: No clinical signs of heart failure. No rales, no S3, no JVD. (0 points)
• Class II: Mild-to-moderate heart failure. Rales in the lower half of the lung fields, elevated JVP, or S3 gallop. (2 points)
• Class III: Acute pulmonary oedema. Rales extending above the lower half of the lung fields. (2 points)
• Class IV: Cardiogenic shock. Hypotension (SBP < 90 mmHg), signs of end-organ hypoperfusion (oliguria, altered mental status, cool extremities). (2 points)

Note that the original TIMI STEMI study excluded patients presenting with cardiogenic shock, so the score’s predictive accuracy in Killip class IV patients may be limited. However, the inclusion of Killip class II–III substantially improves discrimination across the population.

Low body weight has been consistently associated with increased mortality following STEMI, an observation reproduced across multiple ACS registries. The mechanism is multifactorial: lower body weight may reflect frailty, sarcopenia, or chronic illness burden. Additionally, low-weight patients may be at higher risk of bleeding complications from anticoagulant and antiplatelet therapy, and from catheterisation procedures.

This variable serves as a proxy for overall constitutional vulnerability. It is worth noting that women are more frequently below this threshold than men, which may partially explain sex-based differences in STEMI outcomes.

Anterior STEMI (ST elevation in leads V1–V4, with or without extension to V5–V6, I, and aVL) typically results from occlusion of the left anterior descending artery and involves the largest territory of myocardium at risk. Compared to inferior or lateral STEMI, anterior infarctions carry higher rates of heart failure, cardiogenic shock, ventricular arrhythmias, and death.

New LBBB in the setting of chest pain was historically treated as a STEMI equivalent, prompting emergent reperfusion. Current guidelines have evolved — new LBBB alone is no longer considered sufficient for emergent catheterisation lab activation unless other clinical features strongly suggest acute ischaemia. The modified Sgarbossa criteria can help identify acute MI in the setting of LBBB.

Delay from symptom onset to reperfusion therapy is a well-established determinant of infarct size and mortality. The adage “time is muscle” reflects the progressive, time-dependent loss of viable myocardium during coronary occlusion. The greatest absolute benefit from reperfusion is achieved in the first 2–3 hours, with a steep decline in benefit thereafter.

A treatment delay exceeding 4 hours reflects either late presentation by the patient, system-level delays in diagnosis and transfer, or both. In the era of primary PCI, this variable should be interpreted as symptom-onset to balloon time exceeding 4 hours, or symptom-onset to fibrinolytic administration exceeding 4 hours if a pharmacological strategy is used.

This composite variable captures the presence of any one of three major cardiovascular comorbidities: diabetes mellitus, hypertension, or prior angina pectoris. Each of these conditions independently increases the risk of adverse outcomes after STEMI through different but overlapping mechanisms.

• Diabetes mellitus is associated with diffuse coronary disease, impaired collateral circulation, autonomic neuropathy (which may mask ischaemic symptoms), and worse outcomes across all ACS presentations.
• Hypertension contributes to left ventricular hypertrophy, diastolic dysfunction, and increased myocardial oxygen demand, all of which impair recovery from acute infarction.
• Prior angina indicates pre-existing obstructive coronary disease, though paradoxically, some studies suggest that prior angina may confer a degree of ischaemic preconditioning that partially offsets its risk contribution.

Only 1 point is awarded regardless of how many of these conditions are present, reflecting their relatively modest independent contribution to 30-day mortality compared to haemodynamic variables.

The Global Registry of Acute Coronary Events (GRACE) score is a more complex model that predicts in-hospital and 6-month mortality across the full ACS spectrum (STEMI, NSTEMI, and unstable angina). It uses 8 variables including heart rate, systolic BP, creatinine, Killip class, cardiac arrest at admission, ST-segment deviation, elevated cardiac markers, and age. The GRACE score requires a computer or dedicated calculator for its nomogram-based computation, making it less practical at the bedside than the TIMI score.

The GRACE score generally provides superior discrimination for in-hospital mortality (c-statistic ≈ 0.83) compared to the TIMI STEMI score (0.78), but at the cost of greater complexity. The TIMI score’s advantage lies in its simplicity and ease of use at the point of care.

The Zwolle score was specifically developed for STEMI patients treated with primary PCI — unlike the TIMI score, which was derived in a fibrinolytic population. It includes 6 variables: Killip class, TIMI flow post-PCI, age, 3-vessel disease, anterior MI, and ischaemia time. The inclusion of angiographic data (TIMI flow, multi-vessel disease) means it can only be calculated after catheterisation, limiting its use for initial triage at presentation.

The Zwolle score is particularly useful for identifying very low-risk patients suitable for early discharge after primary PCI (within 48–72 hours).

The Dynamic TIMI Risk Score extends the original baseline score by incorporating in-hospital events — recurrent MI, arrhythmia, major bleed, stroke, heart failure, recurrent ischaemia, and renal failure — to provide an updated 1-year mortality estimate at discharge. The combined score ranges from 0 to 29 points. This allows reclassification of patients whose risk profile changed during hospitalisation, improving accuracy for post-discharge planning.

In the ExTRACT-TIMI 25 validation, 25.2% of patients were reclassified between risk categories when in-hospital events were added to the baseline score, with a net reclassification improvement of 33%.