The TIMI Risk Score for STEMI (ST-Elevation Myocardial Infarction) is a validated clinical prediction model that quantifies 30-day all-cause mortality risk in patients presenting with STEMI who are candidates for fibrinolytic therapy. It was derived by Morrow and colleagues from the InTIME II trial dataset — a large-scale, double-blind randomised trial of fibrinolytic agents — and published in Circulation in 2000. The original TIMI-STEMI cohort comprised 14,114 patients enrolled across multiple international centres, providing a robust and diverse dataset for model derivation. The score incorporates nine independent clinical variables that were identified through multivariable logistic regression as the strongest predictors of 30-day mortality. These variables capture patient age, haemodynamic status, clinical history of cardiovascular risk factors, electrocardiographic findings, body habitus, and the time from symptom onset to treatment initiation. Points are assigned as follows: age ≥ 75 years scores 3 points; age 65–74 scores 2 points; systolic blood pressure < 100 mmHg scores 3 points; heart rate > 100 bpm scores 2 points; Killip class II–IV scores 2 points; a history of diabetes, hypertension, or angina scores 1 point; weight < 67 kg (148 lbs) scores 1 point; anterior ST elevation or left bundle branch block (LBBB) on ECG scores 1 point; and time to treatment > 4 hours scores 1 point. The total score ranges from 0 to 14, although scores above 8 are uncommon in practice. The TIMI STEMI score has been extensively externally validated in multiple independent fibrinolytic-era and primary PCI cohorts. While it was derived in the context of fibrinolytic therapy — which remains the reperfusion strategy in hospitals without primary PCI capability — the score retains prognostic value in primary PCI cohorts, where it continues to discriminate between low and high mortality risk. In clinical practice, it is primarily used to identify patients with very high short-term mortality risk who may benefit most from transfer to a PCI-capable centre, mechanical circulatory support, or more aggressive antithrombotic therapy.
TIMI STEMI Score = sum of all applicable criteria (range 0–14) • Age: ≥ 75 years → 3 points 65–74 years → 2 points < 65 years → 0 points • Systolic Blood Pressure < 100 mmHg → 3 points • Heart Rate > 100 bpm → 2 points • Killip Class II–IV (any sign of heart failure: crackles, S3 gallop, pulmonary oedema, or cardiogenic shock) → 2 points • History of diabetes, hypertension, or angina (any one present) → 1 point • Weight < 67 kg (< 148 lbs) → 1 point • Anterior ST elevation OR left bundle branch block (LBBB) on presenting ECG → 1 point • Time from symptom onset to treatment > 4 hours → 1 point Total Score: 0–14 points Each point increment is associated with an approximately 1.6-fold increase in 30-day mortality risk.
- 1Confirm the diagnosis of STEMI based on clinical presentation (ischaemic chest pain ≥ 20 minutes) and ECG criteria (ST elevation ≥ 1 mm in ≥ 2 contiguous limb leads, or ≥ 2 mm in ≥ 2 contiguous precordial leads, or new LBBB in the appropriate clinical context). Record the time of symptom onset and first medical contact, as this directly determines the time-to-treatment variable.
- 2Assess patient age precisely. Age carries the highest individual point contribution: patients aged ≥ 75 years score 3 points, reflecting the dramatically higher 30-day STEMI mortality in the very elderly due to reduced cardiac reserve, increased bleeding risk with antithrombotic therapy, and higher prevalence of comorbidities. Patients aged 65–74 score 2 points; those under 65 score 0.
- 3Measure systolic blood pressure (SBP) at presentation or first medical contact. SBP < 100 mmHg is the second most heavily weighted variable, contributing 3 points, and is a surrogate for haemodynamic compromise and cardiogenic shock physiology. This threshold corresponds to the clinical definition of significant hypotension in the ACS context and carries a particularly ominous prognosis.
- 4Measure heart rate at initial assessment. A heart rate > 100 bpm (tachycardia) contributes 2 points. Tachycardia in STEMI reflects sympathetic activation from pain and haemodynamic compromise, reduced stroke volume requiring compensatory rate increase, or the onset of atrial or ventricular arrhythmia. It is an independent predictor of 30-day mortality after adjustment for blood pressure and Killip class.
- 5Classify Killip class at presentation: Class I = no clinical signs of heart failure; Class II = mild-to-moderate heart failure with basal crackles, S3 gallop, or elevated JVP; Class III = acute pulmonary oedema with diffuse bilateral crackles and severe dyspnoea; Class IV = cardiogenic shock with systolic BP < 90 mmHg, cold extremities, oliguria, and altered mental status. Any Killip class of II or higher scores 2 points.
- 6Ascertain the three binary clinical history variables: (1) Prior diagnosis of diabetes mellitus, hypertension, or angina pectoris — any one of these three conditions present scores 1 point; (2) Patient weight < 67 kg (148 lbs) — lower body weight is associated with higher mortality, possibly reflecting lean body mass loss from chronic illness, greater drug concentration per kg, or reduced physiological reserve; (3) ECG shows anterior ST elevation (V1–V4) or new LBBB — these patterns indicate larger at-risk myocardial territory (LAD territory) and correlate with worse LV function post-infarction.
- 7Calculate the time from symptom onset to treatment. If the anticipated or actual time from first symptom to reperfusion (fibrinolysis or primary PCI balloon inflation) exceeds 4 hours, score 1 additional point. Prolonged ischaemic time allows progression of myocardial necrosis, increasing infarct size and 30-day mortality. This variable reinforces the importance of minimising pre-hospital and in-hospital delays in STEMI care pathways.
Low risk — priority reperfusion still required; primary PCI target door-to-balloon < 90 min
This 48-year-old male scores 0 on every TIMI STEMI criterion: he is under 65, haemodynamically stable (SBP 130, HR 78), in Killip class I, has no relevant cardiovascular history, is not underweight, presents with inferior rather than anterior ST elevation, and arrives within 2 hours of symptom onset. A TIMI STEMI score of 0 corresponds to approximately 0.8% 30-day mortality. Despite the low score, immediate reperfusion is still the priority — the score guides risk communication and adjunctive therapy intensity, not the decision to reperfuse.
Intermediate risk — anterior STEMI with moderate risk profile; consider adjunctive antithrombotic therapy and early PCI if available
This 62-year-old hypertensive male with anterior STEMI and delayed presentation accumulates 3 points: history of hypertension (1 pt) + anterior ST elevation (1 pt) + time to treatment > 4 hours (1 pt). He is haemodynamically stable and not in heart failure, keeping the score from rising further. A score of 3 corresponds to approximately 4–5% 30-day mortality. The anterior territory and delayed presentation support a strategy of primary PCI if available, with consideration of glycoprotein IIb/IIIa inhibitor or potent P2Y12 inhibitor as adjunctive therapy.
High risk — ICU-level care, primary PCI emergently; mechanical circulatory support evaluation
This 70-year-old diabetic woman with anterior STEMI accumulates significant risk: age 65–74 (2 pts) + HR > 100 (2 pts) + Killip II (2 pts) + diabetes (1 pt) + weight < 67 kg (1 pt) + anterior ST elevation (1 pt) + time > 4 hours (1 pt) = 10 points. Her SBP of 108 does not meet the < 100 threshold. A score of approximately 9–10 corresponds to 30-day mortality in the range of 15–20%. This patient requires immediate primary PCI, ICU-level haemodynamic monitoring, and early evaluation for intra-aortic balloon pump or other mechanical circulatory support if cardiogenic shock develops.
Maximal risk — immediate multidisciplinary STEMI team activation; haemodynamic support critical
Maximum TIMI STEMI score: age ≥ 75 (3 pts) + SBP < 100 (3 pts) + HR > 100 (2 pts) + Killip IV (2 pts) + DM/HTN (1 pt) + weight < 67 kg (1 pt) + LBBB (1 pt) + time > 4h (1 pt) = 14 points. This 79-year-old woman in cardiogenic shock with a new LBBB, severe hypotension, tachycardia, and prolonged ischaemic time has a predicted 30-day mortality of approximately 35–40%. Immediate multidisciplinary team activation, mechanical circulatory support, and primary PCI are required urgently. Advanced care planning discussions with the family are also appropriate given the extremely high mortality risk.
Risk stratification of STEMI patients in primary PCI centres to determine post-PCI monitoring intensity — score ≥ 5 typically warrants ICU admission rather than step-down unit care, early echocardiography within 24 hours, and consideration of mechanical circulatory support evaluation
Identification of very high-risk patients (score ≥ 7–8) who may benefit from early mechanical circulatory support (intra-aortic balloon pump or Impella) during primary PCI, particularly in the context of cardiogenic shock or haemodynamic instability
Guiding the urgency and route of inter-hospital STEMI transfers — high TIMI STEMI scores identify patients in whom the benefit of primary PCI over fibrinolysis is greatest, supporting urgent transfer even when PCI time will be slightly prolonged
Prognostic communication with patients and families — a calculated 30-day mortality estimate from the TIMI STEMI score (e.g., 15–20% for score 7–8) enables realistic prognostic discussions and informs advance care planning in elderly or very high-risk STEMI patients
Clinical research and STEMI registry benchmarking — the TIMI STEMI score is used in national and international cardiac audit programmes to risk-adjust in-hospital and 30-day STEMI mortality outcomes, enabling fair comparisons of performance across hospitals with different patient risk profiles
New LBBB and the STEMI diagnosis challenge
New or presumed new left bundle branch block (LBBB) on the presenting ECG represents a diagnostic and management challenge in suspected STEMI. The original Sgarbossa criteria and the modified Sgarbossa rules (Smith-modified) help identify patients with LBBB in whom STEMI is the underlying cause. However, LBBB masks the classic ST-elevation pattern, and the TIMI STEMI score appropriately counts LBBB as equivalent to anterior ST elevation (1 point). Clinicians must use clinical context (history of acute ischaemic symptoms, dynamic change on serial ECGs, biomarker rise) alongside ECG findings to determine whether immediate cath lab activation is warranted.
Very elderly patients — age ≥ 75 and treatment decisions
Patients aged ≥ 75 years score 3 points from age alone, often pushing them into high-risk TIMI categories before any haemodynamic variables are considered. This is appropriate — 30-day STEMI mortality in octogenarians exceeds 25% even in the primary PCI era. However, very elderly patients also have the highest absolute mortality benefit from successful reperfusion. Age alone is not a contraindication to primary PCI. Frailty assessment, comorbidity burden, renal function (affecting contrast and medication decisions), and patient/family preferences must be integrated with the TIMI score in shared decision-making.
Weight < 67 kg — drug dosing implications beyond scoring
The < 67 kg weight criterion in the TIMI STEMI score captures increased risk from lower physiological reserve and potentially higher drug concentrations per kilogram body weight. Beyond its scoring implication, weight < 67 kg directly influences clinical management: enoxaparin dosing uses weight-based calculation (1 mg/kg subcutaneously) with a cap of 100 mg per dose in patients < 100 kg; bivalirudin infusion rates are weight-based; and contrast volume for coronary angiography should be minimised in low-weight patients with reduced eGFR to prevent contrast-induced nephropathy. Female sex is associated with lower average weight and should prompt particular attention to weight-based dosing accuracy.
Time to treatment > 4 hours — fibrinolysis efficacy falloff
The time to treatment criterion reflects the well-established falloff in fibrinolytic efficacy beyond 4–6 hours from symptom onset, while primary PCI retains superiority over a longer ischaemic time window (up to 12 hours and sometimes beyond in patients with ongoing symptoms or haemodynamic instability). When the TIMI STEMI score was derived (InTIME II fibrinolytic trial), exceeding 4 hours from symptom onset was associated with meaningfully worse outcomes due to completed infarction and reduced likelihood of achieving TIMI 3 flow with thrombolytics. In the primary PCI era, the absolute cutoff of 4 hours is less binary, but symptom-to-balloon time of < 90 minutes (for direct presenters) and door-to-balloon < 60 minutes remain quality benchmarks.
TIMI STEMI score in women — sex differences in STEMI outcomes
Women with STEMI have consistently higher in-hospital and 30-day mortality than men across registries, partly explained by older average age at presentation, higher prevalence of hypertension, lower average body weight, and greater rates of bleeding complications with antithrombotic therapy. Women are more likely to score positive on the age ≥ 75 (3 pts) and weight < 67 kg (1 pt) criteria, contributing to higher average TIMI STEMI scores in female cohorts. Additionally, women with STEMI are more likely to have atypical presentations (dyspnoea, nausea, fatigue) leading to delayed recognition. The score should be calculated promptly in all patients once STEMI is confirmed, regardless of presentation atypicality.
| Score | Risk Category | 30-Day Mortality | Clinical Action |
|---|---|---|---|
| 0 | Very Low | ~0.8% | Standard primary PCI pathway; routine post-PCI monitoring |
| 1 | Very Low | ~1.6% | Standard care; telemetry monitoring; early mobilisation |
| 2 | Low | ~2.2% | Standard primary PCI; consider potent P2Y12 inhibitor |
| 3 | Low-Intermediate | ~4.4% | Prioritise rapid PCI; cardiology review of adjunctive therapy |
| 4 | Intermediate | ~7.3% | Aggressive antithrombotic therapy; post-PCI HDU monitoring |
| 5 | Intermediate-High | ~12.4% | ICU post-PCI; echocardiography within 24h; MCS evaluation |
| 6 | High | ~16.1% | ICU care; haemodynamic monitoring; early echo; MCS standby |
| 7 | High | ~23.4% | ICU; MCS consideration; multidisciplinary STEMI team activation |
| 8+ | Very High | >26–36% | Immediate multidisciplinary activation; MCS; advanced care planning |
What does the TIMI STEMI score predict, and over what time frame?
The TIMI STEMI score predicts all-cause 30-day mortality in patients presenting with ST-elevation myocardial infarction (STEMI) who are candidates for reperfusion therapy. It was derived in the context of fibrinolytic therapy in the InTIME II trial, so the absolute mortality estimates most directly reflect that treatment context. However, the score retains prognostic value in primary PCI cohorts, where it continues to discriminate between low and high 30-day mortality risk. Unlike the TIMI UA/NSTEMI score, which predicts a 14-day composite endpoint (death, MI, and urgent revascularisation), the TIMI STEMI score specifically predicts mortality as a single endpoint at 30 days.
How does the TIMI STEMI score differ from the TIMI UA/NSTEMI score?
The TIMI STEMI and TIMI UA/NSTEMI scores are entirely different tools despite sharing a name. The STEMI score was derived from the InTIME II fibrinolytic trial and uses 9 variables (including SBP, HR, Killip class, weight) to predict 30-day mortality. The UA/NSTEMI score was derived from the TIMI 11B/ESSENCE trials and uses 7 different binary variables to predict a 14-day composite of death, MI, and urgent revascularisation. The scores are not interchangeable — applying the NSTEMI score to a STEMI patient or vice versa is clinically incorrect. Scores and thresholds differ substantially, and they should always be applied to the correct ACS subtype.
Was the TIMI STEMI score derived in a primary PCI or fibrinolysis population?
The TIMI STEMI score was derived from the InTIME II trial, in which all patients received fibrinolytic therapy (lanoteplase vs alteplase). Primary PCI was not available to most patients in that era (1997–1999). Consequently, the absolute 30-day mortality estimates associated with each score tier reflect outcomes in the fibrinolytic-era population. In contemporary primary PCI cohorts, absolute mortality rates are lower across all score categories due to more complete and faster reperfusion. However, the score's discriminative ability (ability to rank patients by relative risk) remains valid in primary PCI populations.
Why is SBP < 100 mmHg weighted so heavily (3 points)?
Systolic blood pressure < 100 mmHg at STEMI presentation is a surrogate for cardiogenic shock or impending haemodynamic collapse. Cardiogenic shock complicates approximately 5–8% of STEMI presentations but accounts for over 70% of in-hospital STEMI mortality. In the InTIME II derivation cohort, hypotension was one of the strongest independent predictors of 30-day death after multivariable adjustment, hence its 3-point weighting — equal to very advanced age (≥ 75 years). Patients with SBP < 100 mmHg require immediate assessment for cardiogenic shock, intra-aortic balloon pump or Impella support, and primary PCI over fibrinolysis.
What is the clinical significance of the anterior ST elevation or LBBB criterion?
Anterior ST elevation (V1–V4) indicates occlusion of the left anterior descending (LAD) artery, which typically supplies the largest myocardial territory of any single coronary vessel. LAD occlusions are associated with larger infarcts, worse left ventricular ejection fraction post-MI, higher rates of heart failure, and greater 30-day mortality compared with right coronary artery (inferior STEMI) or circumflex (lateral/posterior STEMI) occlusions. New left bundle branch block (LBBB) can obscure ST changes, may indicate massive anteroseptal infarction with conduction system involvement, and should be treated as a STEMI equivalent per most guidelines when the clinical context is consistent with acute MI.
Can the TIMI STEMI score be used to decide whether to give fibrinolysis versus primary PCI?
The TIMI STEMI score should not be used as the primary tool for choosing between fibrinolysis and primary PCI. That decision is governed by the time from first medical contact to PCI balloon inflation: if PCI can be achieved within 120 minutes (or 90 minutes for very early presenters or very large infarcts), primary PCI is preferred regardless of TIMI score. If PCI is not available within these time windows, fibrinolysis should be initiated promptly if there are no contraindications. However, a very high TIMI STEMI score may reinforce the decision to transfer even if PCI time will be slightly delayed, given the higher mortality benefit of mechanical reperfusion in high-risk patients.
What is Killip classification and how is it assessed clinically?
Killip classification describes the degree of acute left ventricular failure in MI: Class I = no clinical signs of heart failure (clear lungs, no S3, no elevated JVP; in-hospital mortality ~5%); Class II = mild-to-moderate heart failure — bibasal crackles up to 50% of lung fields, S3 gallop, or elevated JVP (mortality ~12%); Class III = acute pulmonary oedema — diffuse bilateral crackles throughout both lung fields, severe respiratory distress, oxygen saturation falling (mortality ~40%); Class IV = cardiogenic shock — SBP < 90 mmHg with cold clammy extremities, oliguria, and altered mentation (mortality ~55–80%). Clinical assessment requires careful auscultation of the lung bases, assessment of jugular venous pressure, and evaluation of peripheral perfusion. The TIMI STEMI score assigns 2 points for any Killip class II or higher.
How does the TIMI STEMI score guide adjunctive therapy decisions?
While reperfusion (primary PCI or fibrinolysis) is the cornerstone of STEMI management regardless of TIMI score, the score helps risk-stratify patients for the intensity of adjunctive antithrombotic therapy and monitoring. High-risk patients (TIMI STEMI ≥ 5–7) may derive greater absolute benefit from potent P2Y12 inhibitors (ticagrelor or prasugrel over clopidogrel), glycoprotein IIb/IIIa inhibitors in selected cases, and anticoagulation with unfractionated heparin or bivalirudin during PCI. Very high-risk patients (score ≥ 9) should be considered for ICU admission post-PCI, early IABP or Impella evaluation, and early echocardiography to assess post-procedural LV function.
Pro Tip
The TIMI STEMI score is most actionable as a tool for escalating care intensity rather than as a reperfusion decision tool — all STEMI patients require immediate reperfusion therapy regardless of score. Use the score to identify patients who need ICU-level post-PCI monitoring (score ≥ 5), early echocardiography (score ≥ 4), evaluation for mechanical circulatory support (score ≥ 7), and more intensive antithrombotic therapy (consider switching from clopidogrel to ticagrelor or prasugrel in higher-risk patients without contraindications). Always document the score at initial presentation and reassess clinical status if haemodynamic deterioration occurs.
Did you know?
The TIMI (Thrombolysis in Myocardial Infarction) group at Brigham and Women's Hospital, led by Eugene Braunwald, is one of the most prolific clinical trials networks in cardiovascular medicine, having published landmark trials including TIMI 2, TIMI 11B, InTIME II, and TRITON-TIMI 38. The TIMI name now graces not only risk scores but also the universally used TIMI flow grade system (0–3) for assessing coronary artery patency after reperfusion — a grading system used in every cardiac catheterisation laboratory worldwide. TIMI 3 flow (full, brisk coronary flow equivalent to a normal vessel) remains the primary angiographic efficacy endpoint in virtually every reperfusion trial conducted since 1985.
References
- ›Morrow DA et al. TIMI Risk Score for ST-Elevation Myocardial Infarction: A Convenient, Bedside, Clinical Score for Risk Assessment at Presentation — Circulation 2000
- ›Antman EM et al. The TIMI Risk Score for Unstable Angina/Non-ST Elevation MI: A Method for Prognostication and Therapeutic Decision Making — JAMA 2000
- ›Ibanez B et al. 2017 ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation — Eur Heart J 2018
- ›O'Gara PT et al. 2013 ACCF/AHA Guideline for the Management of ST-Elevation Myocardial Infarction — J Am Coll Cardiol 2013
- ›Thrane PG et al. 15-year follow-up of the TIMI STEMI Risk Score — Eur Heart J Acute Cardiovasc Care 2018