Aim The Thrombolysis in Myocardial Infarction (TIMI) risk score (range 0–7), used for emergency department (ED) risk stratification of patients with suspected acute coronary syndrome (ACS), underestimates risk associated with ECG changes or cardiac troponin elevation. A modified TIMI score (mTIMI, range 0–10), which gives increased weighting to these variables, has been proposed. We aimed to evaluate the performance of the mTIMI score in ED patients with suspected ACS.

Methods A multicentre prospective observational study enrolled patients undergoing assessment for possible ACS. TIMI and mTIMI scores were calculated. The study outcome was a composite of all-cause death, myocardial infarction or coronary revascularisation within 30 days.

Results Of the 1666 patients, 219 (13%) reached the study outcome. Area under the receiver operating characteristic curve for the composite outcome was 0.80 (0.76 to 0.83) for the mTIMI score compared with 0.71 (0.67 to 0.74) for the standard TIMI score, p<0.001, but there was no significant difference for death or revascularisation outcomes. Sensitivity and specificity for the composite outcome were 0.96 (0.92 to 0.98) and 0.23 (0.20 to 0.26), respectively, at score 0 for TIMI and mTIMI. At score <2, sensitivity and specificity were 0.82 (0.77 to 0.87) and 0.53 (0.51 to 0.56) for mTIMI, and 0.74 (0.68 to 0.79) and 0.54 (0.51 to 0.56) for standard TIMI, respectively.

Conclusions mTIMI score performs better than standard TIMI score for ED risk stratification of chest pain, but neither is sufficiently sensitive at scores >0 to allow safe and early discharge without further investigation or follow-up. Observed differences in performance may be due to incorporation bias.