The TIMI risk score for ST-elevation myocardial infarction (STEMI) is a bedside tool that converts 8 pieces of information already available at presentation into a single 0-14 number estimating 30-day mortality risk. It was designed to be calculated quickly, without delaying the emergent reperfusion therapy that all STEMI patients need regardless of score.

How the TIMI STEMI risk score works

Unlike some risk scores where every criterion is worth the same number of points, the TIMI STEMI score assigns different weights based on how strongly each factor predicted mortality in the derivation cohort. Age contributes up to 3 points (2 for 65-74, 3 for 75 and older), systolic blood pressure below 100 mmHg contributes 3 points, heart rate above 100 bpm and Killip class II-IV each contribute 2 points, and the remaining criteria — diabetes/hypertension/angina history, low body weight, anterior involvement, and treatment delay — each contribute 1 point. The resulting 0-14 total maps to a published 30-day mortality rate ranging from 0.8% at a score of 0 up to 35.9% at a score above 8.

The 8 criteria

The criteria fall into three rough groups: baseline vulnerability (age, prior diabetes/hypertension/angina, low body weight), acute hemodynamic severity (low blood pressure, high heart rate, Killip class), and infarct characteristics (anterior location or LBBB, and treatment delay). Hemodynamic instability and low blood pressure carry the heaviest weights because they most directly reflect the degree of myocardial compromise at presentation.

Scope and limitations

The TIMI STEMI risk score was derived and validated in patients with ST-elevation MI enrolled in the InTIME II trial — it is a distinct tool from the TIMI risk score for UA/NSTEMI, which uses different criteria and predicts a different outcome. Calculating this score should never delay time-critical reperfusion therapy; it is intended for risk stratification and communication after treatment has been initiated, not as a gate to treatment. Like any clinical risk score, it estimates population-level risk and does not replace individualized clinical judgment.