Relationship between interleukin 6 and mortality in patients with unstable coronary artery disease - Effects of an early invasive or noninvasive strategy

Context Inflammatory activity is associated with high rates of long-term mortality in unstable coronary artery disease (CAD). Interleukin 6 (IL-6) induces C-reactive protein and fibrinogen, systemic markers of inflammation. Objectives To determine whether plasma levels of IL-6 are predictive of mortality and to evaluate the interaction of IL-6 levels with the effects of invasive vs noninvasive treatment strategies in unstable CAD patients. Design, Setting, and Patients The prospective, randomized Fragmin and Fast Revascularisation During Instability in Coronary Artery Disease II trial, conducted among 3489 patients, 3269 of whom had plasma samples analyzed for IL-6 levels, with diagnosed unstable CAD (67% male, median age, 67 years) at 58 Scandinavian hospitals between June 1996 and August 1998. Interventions Patients were randomly assigned to receive either an early invasive (n = 1222) or a noninvasive treatment strategy (n = 1235). The fatter group, as well as 666 patients with contraindications to invasive therapy, were further randomized to 90-day treatment with low-molecular-weight heparin (dalteparin, 5000-7500 IU twice per day, n = 1140) or placebo (n = 1127). Main Outcome Measure Mortality at 6 and 12 months in the medically and interventionally randomized cohorts, respectively, in relation to IL-6 levels, measured at randomization. Results Plasma levels of IL-6 that were at least 5 ng/L compared with levels lower than 5 ng/L were associated with greatly increased mortality in the noninvasive group (7.9% vs 2.3%; relative risk [RR], 3.47; 95% confidence interval [CI], 1.94-6.21) and in the placebo-treated group (7.9% vs 2.5%; RR, 3.19; 95% CI, 1.77-5.74). The association remained significant after adjustment for most established risk indicators. An early invasive treatment strategy strongly reduced 12-month mortality among those with elevated IL-6 levels (5.1% absolute reduction; P=.004) whereas mortality was not reduced among patients without elevated IL-6 concentrations. Those taking dalteparin with elevated IL-6 levels experienced lower 6-month mortality than those who did not take dalteparin (3.5% absolute reduction; P=.08). Conclusions Circulating IL-6 is a strong independent marker of increased mortality in unstable CAD and identifies patients who benefit most from a strategy of early invasive management.