What is the TIMI (Thrombolysis In Myocardial Infarction) risk score, its component variables, risk categories, and recommended management for patients presenting with unstable angina or non‑ST‑segment‑elevation myocardial infarction?

TIMI Risk Score for Unstable Angina/NSTEMI

Overview and Components

The TIMI risk score is a validated 7-point bedside tool that stratifies patients with unstable angina/NSTEMI into risk categories for death, myocardial infarction, or urgent revascularization within 14 days, with event rates ranging from 4.7% to 40.9%. 1, 2

The score assigns 1 point for each of the following 7 variables present at admission 1:

• Age ≥65 years 1, 2
• ≥3 risk factors for coronary artery disease (hypertension, diabetes, hyperlipidemia, family history, current smoking) 1, 2
• Known coronary stenosis ≥50% (prior catheterization showing significant disease) 1, 2
• ST-segment deviation ≥0.5 mm on presenting ECG 1, 2
• ≥2 anginal events in the prior 24 hours 1, 3
• Aspirin use in the prior 7 days 1, 2
• Elevated cardiac biomarkers (troponin or CK-MB) 1, 2

Risk Stratification and Event Rates

The composite endpoint (all-cause mortality, new or recurrent MI, or severe recurrent ischemia requiring urgent revascularization through 14 days) increases progressively with higher scores 1:

• TIMI 0-1: 4.7% event rate (low risk) 1
• TIMI 2: 8.3% event rate (intermediate risk) 1, 2
• TIMI 3: 13.2% event rate (intermediate-high risk) 1
• TIMI 4: 19.9% event rate (high risk) 1, 2
• TIMI 5: 26.2% event rate (high risk) 1, 2
• TIMI 6-7: 40.9% event rate (very high risk) 1, 2

The score has been validated across multiple international trials including TIMI 11B and ESSENCE, maintaining consistent predictive ability across all cohorts 1, 2. It performs well in routine clinical practice and proves superior to ECG changes plus troponin alone for risk stratification in unselected emergency department patients with possible ACS 2, 4.

Management Recommendations Based on Risk Score

High-Risk Patients (TIMI ≥4)

Patients with TIMI scores ≥4 mandate early invasive strategy with coronary angiography and revascularization. 1, 2 This includes 1, 2:

• Early invasive strategy (coronary angiography within 24-48 hours) 1
• Intensive antiplatelet therapy with glycoprotein IIb/IIIa inhibitors 2, 3
• Low-molecular-weight heparin preferred over unfractionated heparin 2, 3
• Dual antiplatelet therapy with aspirin and P2Y12 inhibitor 1

Additional high-risk features that favor invasive strategy regardless of TIMI score include 1:

• Recurrent angina or ischemia at rest or with low-level activities despite intensive medical therapy 1
• Signs or symptoms of heart failure or new/worsening mitral regurgitation 1
• Hemodynamic instability 1
• Sustained ventricular tachycardia 1
• PCI within 6 months or prior CABG 1
• Reduced left ventricular function (LVEF <40%) 1

Low-Risk Patients (TIMI 0-2)

Patients with TIMI scores 0-2 can be managed with a conservative strategy including medical therapy and stress testing before discharge. 1, 2 However, patient and physician preference should be considered in the absence of high-risk features 1, 2.

For patients with TIMI score of 0, only 1.8% experience a cardiac event within 30 days (sensitivity 97.2%, specificity 25.0%) 4. The TIMI risk score should not be used as the sole means of determining patient disposition, as it requires integration with clinical judgment 4.

Practical Implementation

Calculate the TIMI risk score immediately at presentation using readily available clinical data without requiring computer assistance. 2 The calculator is available at www.timi.org for verification 1, 2.

The score remains a significant predictor of events and is relatively insensitive to missing information, such as knowledge of previously documented coronary stenosis 1. The model's predictive ability remains intact with the age cutoff of 65 years 1.

Important Caveats

• The TIMI risk score was originally derived for unstable angina/NSTEMI patients 3. A separate TIMI risk score exists for STEMI patients using different variables (age, systolic blood pressure, heart rate, Killip class, weight, anterior MI location, time to treatment, diabetes/hypertension/angina history) to predict 30-day mortality 2, 5
• The predictive ability of the TIMI risk score for nonfatal coronary heart disease risk is only moderate 1
• The score effectively predicts not only 14-day outcomes but also 1-year cardiovascular events in emergency department patients with chest pain 6
• With increasing TIMI risk score, progressively greater benefits are observed with specific treatments including low-molecular-weight heparins, glycoprotein IIb/IIIa inhibitors, and early invasive strategy 1, 3