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. 2009 Nov 23;4(11):e7947.
doi: 10.1371/journal.pone.0007947.

Does simplicity compromise accuracy in ACS risk prediction? A retrospective analysis of the TIMI and GRACE risk scores

Krishna G Aragam  1 , Umesh U Tamhane, Eva Kline-Rogers, Jin Li, Keith A A Fox, Shaun G Goodman, Kim A Eagle, Hitinder S Gurm
Affiliations

Does simplicity compromise accuracy in ACS risk prediction? A retrospective analysis of the TIMI and GRACE risk scores

Krishna G Aragam et al. PLoS One. .

Abstract

Background: The Thrombolysis in Myocardial Infarction (TIMI) risk scores for Unstable Angina/Non-ST-elevation myocardial infarction (UA/NSTEMI) and ST-elevation myocardial infarction (STEMI) and the Global Registry of Acute Coronary Events (GRACE) risk scores for in-hospital and 6-month mortality are established tools for assessing risk in Acute Coronary Syndrome (ACS) patients. The objective of our study was to compare the discriminative abilities of the TIMI and GRACE risk scores in a broad-spectrum, unselected ACS population and to assess the relative contributions of model simplicity and model composition to any observed differences between the two scoring systems.

Methodology/principal findings: ACS patients admitted to the University of Michigan between 1999 and 2005 were divided into UA/NSTEMI (n = 2753) and STEMI (n = 698) subpopulations. The predictive abilities of the TIMI and GRACE scores for in-hospital and 6-month mortality were assessed by calibration and discrimination. There were 137 in-hospital deaths (4%), and among the survivors, 234 (7.4%) died by 6 months post-discharge. In the UA/NSTEMI population, the GRACE risk scores demonstrated better discrimination than the TIMI UA/NSTEMI score for in-hospital (C = 0.85, 95% CI: 0.81-0.89, versus 0.54, 95% CI: 0.48-0.60; p<0.01) and 6-month (C = 0.79, 95% CI: 0.76-0.83, versus 0.56, 95% CI: 0.52-0.60; p<0.01) mortality. Among STEMI patients, the GRACE and TIMI STEMI scores demonstrated comparably excellent discrimination for in-hospital (C = 0.84, 95% CI: 0.78-0.90 versus 0.83, 95% CI: 0.78-0.89; p = 0.83) and 6-month (C = 0.72, 95% CI: 0.63-0.81, versus 0.71, 95% CI: 0.64-0.79; p = 0.79) mortality. An analysis of refitted multivariate models demonstrated a marked improvement in the discriminative power of the TIMI UA/NSTEMI model with the incorporation of heart failure and hemodynamic variables. Study limitations included unaccounted for confounders inherent to observational, single institution studies with moderate sample sizes.

Conclusions/significance: The GRACE scores provided superior discrimination as compared with the TIMI UA/NSTEMI score in predicting in-hospital and 6-month mortality in UA/NSTEMI patients, although the GRACE and TIMI STEMI scores performed equally well in STEMI patients. The observed discriminative deficit of the TIMI UA/NSTEMI score likely results from the omission of key risk factors rather than from the relative simplicity of the scoring system.

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Conflict of interest statement

Competing Interests: Dr. Eagle has received research support from the Mardigian Foundation, Sanofi-aventis, Pfizer, and the Department of Internal Medicine, University of Michigan. Dr. Goodman has received research grant support and speaker/consulting honoraria from Sanofi-aventis, the sponsor for the ESSENCE and TIMI 11B trials, and the GRACE project. Dr. Gurm has received research support from Blue Cross Blue Shield Foundation of Michigan, and the NIH. The remaining authors report no conflicts.

Figures

Figure 1
Figure 1. Comparison of TIMI UA/NSTEMI and GRACE risk scores in UA/NSTEMI patients.
Receiver operating characteristic curves of (A) the TIMI UA/NSTEMI and GRACE in-hospital risk scores for predicting in-hospital mortality, and (B) the TIMI UA/NSTEMI and GRACE 6-month risk scores for predicting 6-month mortality in patients surviving to hospital discharge.
Figure 2
Figure 2. Risk score distributions of UA/NSTEMI patients for in-hospital mortality.
(A) GRACE in-hospital and (B) TIMI UA/NSTEMI risk score distributions for surviving versus deceased UA/NSTEMI patients for in-hospital mortality.
Figure 3
Figure 3. Risk score distributions of UA/NSTEMI patients for 6-month mortality.
(A) GRACE 6-month and (B) TIMI UA/NSTEMI risk score distributions for surviving versus deceased UA/NSTEMI patients for 6-month mortality.
Figure 4
Figure 4. Comparison of TIMI STEMI and GRACE risk scores in STEMI patients.
Receiver operating characteristic curves of (A) the TIMI STEMI and GRACE in-hospital risk scores for predicting in-hospital mortality, and (B) the TIMI STEMI and GRACE 6-month risk scores for predicting 6-month mortality in patients surviving to hospital discharge.
Figure 5
Figure 5. Modifications to the TIMI UA/NSTEMI risk model.
Receiver operating characteristic curves of the TIMI UA/NSTEMI risk score, the TIMI UA/NSTEMI refitted multivariate model, and a modified TIMI UA/NSTEMI model including heart failure and hemodynamic variables for predicting (A) in-hospital mortality and (B) 6-month mortality in patients surviving to hospital discharge.
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