Impact of renal dysfunction on the prognostic value of the TIMI risk score in patients with non-ST elevation acute coronary syndrome

Abstract

The thrombolysis-in-myocardial-infarction risk score (TRS) is a validated risk-assessment tool based on randomized clinical trials. Its applicability to an unselected group of patients seen in general clinical practice may be limited as renal dysfunction was an exclusion criteria in the original trials upon which the TRS was determined. Consecutive patients with non-ST elevation acute coronary syndrome were stratified based on renal function. Normal renal function was defined as a creatinine clearance (CrCl) of more than 60 ml/min, moderate renal dysfunction was defined as a CrCl of at least 30 ml/min but 60 ml/min or less, and severe renal dysfunction was defined as a CrCl of less than 30 ml/min. A TRS was calculated using the original seven criteria (TRS-7) which did not consider renal function. A second TRS was calculated using the original seven criteria plus the addition of renal dysfunction if the CrCl was 60 ml/min or less (TRS-8 ≤ 60). A third TRS was calculated using the original seven criteria plus renal dysfunction if the CrCl was less than 30 ml/min (TRS-8<30). In the calculation of both of the TRS-8, the presence of renal dysfunction was given weight equal to each of the original seven criteria. Comparisons between groups stratified by renal function were made using Pearson's χ² test or Fisher's exact test for categorical variables (presented as counts and percentages) and the unpaired t-test for continuous variables (presented as the mean ± standard deviation). The χ² test was used to compare the statistical differences between each of the three TRS and the percentage of patients achieving the primary composite outcome during the index hospitalization. The primary outcome was the composite of cardiovascular death, nonfatal myocardial infarction, or urgent coronary revascularization for documented myocardial ischemia. Of the 798 patients included in the analysis, 281 (35%) patients had renal dysfunction (26% had moderate dysfunction and 9% had severe dysfunction). When considered categorically, patients with moderate or severe renal dysfunction had significantly higher rates of the primary composite outcome. The three TRS (TRS-7, TRS-8 ≤ 60, and TRS-8<30) were significantly correlated with the primary composite outcome. With a calculated TRS of 5 or less, the TRS-8 ≤ 60 and the TRS<30 were not associated with a significantly higher prevalence of the composite outcome (all comparisons P>0.05). At a calculated TRS of 6 or 7, the TRS-8<30 was associated with a significantly greater prevalence of the composite outcome compared with the TRS-7 (P=0.02) and the TRS-8 ≤ 60 (P=0.02). There was no significant difference in the frequency of the composite outcome with a calculated TRS of 6 or 7 using the TRS-7 compared with the TRS-8 ≤ 60 (P=0.79). At a calculated TRS of 8, both the TRS-8<30 and TRS-8 ≤ 60 had a significantly higher prevalence of the composite outcome compared with a calculated TRS of 7 using the TRS-7 (P=0.002 for the TRS-8<30 and P=0.045 for the TRS-8 ≤ 60). At a TRS of 8, the TRS-8<30 was associated with a significantly higher composite outcome compared with the TRS-8 ≤ 60 (P=0.035). The addition of renal dysfunction to the TRS-7 as an eighth clinical criterion was associated with a higher prevalence of the primary composite outcome primarily at scores of 6 or more. When considered in the context of clinical practice, the use of the TRS-8 ≤ 60 and TRS-8<30 rather than the TRS-7 would not be expected to substantially change the management strategy for patients presenting with non-ST elevation acute coronary syndrome.