1Department of Clinical Therapeutics, University of Athens, Alexandra Hospital, Vas. Sofias 80, Athens 11528, Greece
2Imperial College School of Medicine, National Heart & Lung Institute, Cardiology Department, Hammersmith Hospital, London, UK
Received 27 September 2004; revised 30 December 2005; accepted 3 February 2005; online publish-ahead-of-print 30 March 2005.
* Corresponding author. Tel: +30 210 338 1497; fax: +30 210 777 0473. E-mail address: ignoik{at}otenet.gr
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Methods and results MCSF and CRP were measured in 100 patients with chronic CAD. Of 95 (33%) patients, 31 who completed the 6 year follow-up presented adverse events (death, myocardial infarction, and unstable angina). In multivariable analysis (including traditional risk factors and medications), the upper tertiles of MCSF (814 pg/mL) and CRP (
2.5 mg/L) levels were independently associated with a 13- and 6-fold increase in risk of events, respectively (P<0.01). Patients with combined high CRP and MCSF had a higher absolute risk of events than patients with elevated MCSF or CRP alone (75 vs. 59 vs. 32%, respectively, P<0.01). The mean event-free time was 39, 64, and 52 months in patients with elevated MCSF, elevated CRP, and their combination, respectively.
Conclusion In patients with chronic CAD, the prognostic value of MCSF is independent and complementary to that of CRP. MCSF is a particularly useful prognostic marker when CRP levels are low, but also provides additional information concerning risk and time-course of events in patients with elevated CRP.
Key Words: Inflammation Coronary artery disease Long-term prognosis
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Circulating CRP and MCSF levels have been associated with death and recurrent ischaemic events in patients with acute coronary syndromes.1721 In addition, CRP predicts outcome in patients with chronic coronary artery disease (CAD).1719 However, it remains unclear whether CRP and MCSF have an independent or additive prognostic value in patients with chronic CAD during a long-term follow-up period. We, therefore, prospectively compared the prognostic significance of CRP to that of MCSF or their combination in patients with chronic CAD during a 6 year follow-up period.
![]() |
Methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Laboratory assays
Plasma MCSF was measured by enzyme-linked immunoassay (human MCSF Quantikinine, sensitivity 20 pg/mL, R&D system, Minneapolis, MN, USA). CRP was measured using particle-enhanced immunonephelometry (N Latex CRP mono, Behring Diagnostics). The assay detects a range of values between 0.175 and 1100 mg/L. The intra-assay coefficients of variation were <5% for both tests.
Follow-up
Of the 100 patients, 95 (95%) completed a mean follow-up of 6 years (72±3 months). The remaining five were lost to follow up and were considered as censored cases. Patients were followed as outpatients at 612 month intervals, starting from the day of blood sampling. The clinical endpoints considered in our analysis were the occurrence of cardiac death, acute myocardial infarction (MI), and hospital admission for unstable angina. Elective percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) was not considered, as they were not thought to represent an acute coronary event. Of the 100 patients (23%), 23 had a revascularization procedure (6 PCI and 17 CABG) during the 6 year follow-up. Deaths of cardiac origin were confirmed by death certificates and were verified by medical record review or primary care physician interview. Non-cardiac death was not included in the analysis. MI was confirmed by ST-elevation or non-ST elevation changes on ECG and diagnostic increases in serum cardiac enzymes. Unstable angina was diagnosed by the occurrence of rest angina with non-ST segment elevation ischaemic ECG changes or with a positive troponin T test without concomitant increase in serum creatine kinase levels.
Statistical analysis
Inflammatory indices are presented as medians and interquartiles, as the data were not normally distributed. Stata 8.0 (Stata Corporation, College Station, TX, USA) software was used. Differences within and among groups were analysed by Wilcoxon signed rank test, MannWhitney U test, or analysis of variance (KruskalWallis and Friedman test). Simple relations were assessed by Spearman's rank correlation. Multiple relations were assessed by linear regression analysis after logarithmic transformation of MCSF and CRP. Categorical variables were compared by contingency 2 test.
Only the first event of the combined primary outcome variable (cardiac death, non-fatal MI, and unstable angina) was counted as an endpoint. On the basis of an annual event rate of 2% for the primary end-point in patients with stable angina,23 an overall sample of 80 patients was required to detect a 10% increase of the event rate in the group of patients with high concentrations of inflammatory markers using a two-tailed test with a significance level of 5%, a power level of 90%, a drop-out rate of 5%, and a total follow-up period of 6 years. We prospectively stratified patients into three groups, on the basis of the tertiles of the measured biochemical indices (MCSF: <449 pg/mL, n=34; 450813 pg/mL, n=34; 814 pg/mL, n=32; CRP: <1.09 mg/L, n=33; 1.12.4 mg/L, n=33;
2.5 mg/L, n=34),18 and cardiac event-free survival curves were constructed by KaplanMeier analysis.18 Differences among curves were assessed using the log rank test. Because the outcomes for the first and second tertile of MCSF and CRP plasma levels were not statistically different, they were combined for the final KaplanMeier and Cox proportional hazard analyses.18,24 Univariate Cox proportional hazard analysis24 was used to assess the predictors of cardiac events for the following covariates: age, gender, smoking status, hypertension, hyperlipidaemia, parental CAD, previous (>6 months) MI, multivessel disease (two and three vessel disease), non-use of ß-blockers, calcium blockers, nitrates, angiotensin-converting enzyme inhibitor, lipid-lowering medication, MCSF
814 pg/mL, and CRP
2.5 mg/L. The covariates with a P-value <0.10 at univariate analysis were entered in the multivariable model.24 Cox multivariable analysis with a stepwise selection method was used to estimate the final predictors of cardiac events. Significance between models was calculated by the likelihood ratio test. In multivariable analysis, a P<0.05 was considered statistically significant.
Interactions between MCSF, CRP, smoking, and multivessel disease were also assessed in the multivariable analysis. To adjust the final model for other atherosclerotic risk factors and for medication, a forced entry approach was used.24 The results of the Cox regression analysis are expressed as hazard ratios (HR) and corresponding 95% confidence intervals (CI). The appropriateness of the risk assumption was examined by preparing the log (log) plots of the survival function. The final multivariable model was validated by plotting the residuals against the fitted values (generalized CoxSnell residuals) and testing the goodness of fit. Receiver operating characteristic curve analysis was also used to compare the predictive value of MCSF vs. CRP levels. The curves were constructed by plotting sensitivity against (one-specificity). The area under the curve (AUC) for MCSF or CRP was also calculated, in addition to the standard risk factors (age>60 years, sex, smoking, hypelipidaemia, and hypertension) using logistic regression analysis. Wilcoxon's signed rank test for dependent samples was used for comparisons between the unadjusted AUCs, and one-sample test of proportions for comparisons between the adjusted AUCs.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Association of MCSF and CRP with atherosclerotic risk factors
By multivariable regression analysis, MCSF and CRP levels were related to smoking (r=0.37 and r=0.28 respectively, P<0.01) and MCSF additionally to multivessel disease (r=0.21, P=0.035), among age, gender, body mass index, hypertension, hyperlipidaemia, family history of CAD and medications. MCSF levels were related to those of CRP (r=0.47, P<0.05).
Cardiac events
Thirty-one patients presented cardiac events within the follow-up period. Of these, 6 died, 9 suffered a non-ST segment elevation MI, and 16 had an episode of unstable angina. The median time from the start of follow-up to the occurrence of cardiac events was 24 (1268) months.
Of the 31 (23%), patients with cardiac events, 7 had a revascularization procedure (two PCI and five CABG) at a median time of 13 (1221) months of follow-up or at a median time of 16 (951) months before the adverse event. Moreover, 16 of the 69 patients without events (23%) had a revascularization procedure (4 PCI and 12 CABG) at a median time of 14 (1246) months of follow-up. There was no difference in revascularization rate between patients with or without events (P=0.178).
Predictors of outcome
KaplanMeier life-time analysis for MCSF and CRP
Survival tables showed that the absolute risk (%) of cardiac events was 75% in patients with combined high CRP (>2.5 mg/L) and MCSF (>814 pg/mL), 59% in patients with high MCSF alone, 32% in patients high CRP alone, and 8% in patients with MCSF and CRP levels lower than the corresponding upper tertiles (Figure 1), suggesting a complementary role of MCSF and CRP.
|
|
|
|
The multivariable Cox regression model included gender, smoking, multivessel disease, and elevated MCSF and CRP, as only these variables were significant at P<0.1 at univariate analysis among traditional risk factors and medication. Using the backwards stepwise selection method, smoking status was removed from the model. Then, using the forward stepwise selection method, the non-significant covariates previously examined in univariate analysis were added. No new significant covariates were added in the multivariable model at the end of this analysis. At this point, interactions between inflammatory indices and smoking or multivessel disease were examined in the multivariable model. A significant interaction emerged between the subgroups of MCSF and CRP (P=0.03 for interaction), suggesting that the adjusted HR for cardiac events was different between each subgroup of MCSF and CRP. The interaction term between MCSF and CRP remained significant after using the backward selection procedure (P=0.02). However, multivessel disease became non-significant (P>0.05) and, thus, was removed from the final model. The final multivariable model was therefore constructed by male gender, MCSF levels 814 pg/mL, CRP levels
2.5 mg/L, and their interaction term, as summarized in Table 2.
Cox proportional hazard analysis showed that patients with high MCSF (814 pg/mL) alone had a 13.17-fold (95% CI: 4.1442) higher risk of cardiac events compared with patients with low MCSF and low CRP (P=0.0001), whereas patients with high CRP levels (
2.5 mg/L) alone had a 6.24-fold (95% CI: 1.7422.42) higher risk of cardiac events compared with patients with low CRP and low MCSF levels (P=0.005, Table 2).
After adjustment for other potential confounders such as age, hypertension, hyperlipidaemia, parental CAD, previous MI, and medications, the HR associated with elevated MCSF and CRP did not change: 14 (95% CI: 3.660) for MCSF and 6.29 (95% CI: 1.4627) for CRP (P=0.001).
Comparison of the usefulness of MCSF and CRP as predictors of cardiac events
Receiver operating characteristic curve analysis showed a greater AUC for plasma MCSF levels than for CRP levels [80% (95% CI: 70 to 91) vs. 61% (95% CI: 55 to 74), z=8.419, P=0.00001 for the unadjusted AUC and z=2.605; P=0.009 for the adjusted AUC], suggesting a superior prognostic value of MCSF than of CRP for predicting cardiac events (Figure 4).
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
MCSF, CRP, and acute cardiac events
In the present study, male gender, multivessel disease, smoking status, and the upper tertiles of MCSF and CRP levels were significant predictors of prognosis by univariate analysis. However, in multivariable analysis only male gender and the upper tertiles of MCSF and CRP levels retained their prognostic value among age, smoking, hypertension, hyperlipidaemia, family history of CAD, and multivessel disease. Because atherosclerotic risk factors promote cytokine production14,22,25,26 and, consequently, CRP release,12,27,28 these findings suggest that inflammatory indices may serve as a surrogate marker of the cumulative effect of traditional risk factors on the prognosis of patients with chronic CAD. However, it is possible that MCSF and CRP may directly contribute to plaque rupture, thrombosis,4,6,7,10,15,16 and thus, to the genesis of acute cardiac events.1721 Our findings are in agreement with those of others18 who found that CRP levels independently predicted cardiac events in patients with stable and unstable angina during a 2 year follow-up period. Saito et al.21 showed the prognostic significance of increased MCSF levels for future cardiac events in a mixed population of patients with stable and unstable angina during 14 months of follow-up. However, in their study, increased MCSF levels on admission and incidence of future events were associated with the diagnosis of unstable angina at inclusion, indicating that the results of their study were mainly driven by the subgroup of patients with unstable angina. Conversely, in the present study, we showed that high MCSF levels predicted an adverse outcome in patients with chronic CAD.
Moreover, in this study, patients with CRP levels <2.5 mg/L, who are considered at low risk of cardiac events,17 had a 13-fold risk of future events when their MCSF levels were >814 pg/mL compared with when they were <814 pg/mL. Thus, in the presence of low CRP levels, MCSF becomes particularly useful in distinguishing patients at a substantially lower or higher risk of cardiac events.
Furthermore, patients with the combined elevation of MCSF and CRP levels had a higher absolute and relative risk of future events when compared with patients with elevated levels of a single inflammatory factor or to patients with low levels of both inflammatory indices. Thus, high MCSF provided additional prognostic information in patients with high CRP levels and vice versa.
Our results suggest that MCSF and CRP levels may be synergistic and complementary predictors of adverse outcome in patients with chronic CAD. Indeed, both CRP and MCSF induce apoptosis of vascular smooth muscle cells4,15 and tissue factor expression10,16 in atherosclerotic lesions and, consequently, may cause a synergic increase in plaque thrombogenicity and instability.
Survival tables showed that the mean event-free time was 39 months in patients with elevated MCSF when compared with 64 months in patients with elevated CRP and 52 months in patients with combined elevation of CRP and MCSF. This finding suggests that increased MCSF levels alone or combined with elevated CRP levels may predict the incidence of future coronary events occurring at an earlier time when compared with elevated CRP levels alone.
Atheroslerotic risk factors1,22,25 or infections2 may trigger increased MCSF production, mainly by endothelial cells,2 in the initial process of atherosclerosis.31 Moreover, MCSF-activated macrophages produce further amounts of MCSF that can enter the systemic circulation.2 MCSF promotes the release of IL-6,11 which drives CRP production.12 Thus, MCSF production by endothelial cells and resident macrophages at atherosclerotic lesions may precede the cytokine-mediated release of CRP by hepatocytes.12 As a result, MCSF may promote apoptosis of smooth muscle cells,4 release of metalloproteinases,7 platelet activation,8,9 tissue factor expression10 and, consequently, plaque instability at an earlier time than CRP. Although CRP and MCSF have been detected in human atherosclerotic lesions,28,29 CRP is not present in the normal vessel wall,2,28 suggesting a role of CRP in the advanced phases of atherogenesis. Recent evidence suggests that a balance of prothrombotic15 and anti-thrombotic effects of CRP30,31 on the vessel wall may be important in the development of adverse cardiac events.32 Increased MCSF production may disrupt this balance towards increased apoptosis and plaque thrombogenicity at an early stage of atherosclerosis by enhancing the apoptotic effects of CRP.4,15 Alternatively, MCSF may facilitate the structural modification of the native, pentameric, CRP to monomeric subunits which are required for proinflammatory actions on endothelial cells.33 Through this action MCSF may enhance and accelerate the proinflammatory effects of circulating CRP on vascular tissues so that these are augmented and become evident at an earlier time than they would have become in the presence of elevated CRP levels alone. The above pathophysiological mechanisms may explain the greater risk of future events and the shorter event-free time in patients with combined high CRP and MCSF levels compared with patients with elevated CRP levels alone observed in the present study. Thus, the measurement of MCSF provides additional prognostic information on the risk and time-course of events compared with the measurement of CRP in patients with chronic CAD.
In this study, a head-to-head comparison between the predictive value of MCSF and of CRP showed that the upper tertile of MCSF levels was associated with an approximately two-fold higher absolute (59 vs. 32%) and relative (13.17 vs. 6.24) risk of events, as well as with a shorter event-free time (39 vs. 64 months) than the upper tertile of CRP levels. In addition, by receiver operating curve analysis, the predictive value for acute cardiac events of MCSF levels was higher than that of CRP levels (area under the curve 80 vs. 61%). MCSF is directly related to myocardial ischaemia during effort and daily life activities,9,27 as well as to the angiographic extent of CAD in patients with chronic stable angina.21,27 Conversely, CRP is modestly related to the anatomic extent of CAD in these patients.34 Thus, increased MCSF may signal patients with more aggressive CAD and, therefore, with a higher risk for acute ischaemic events at an earlier follow-up time compared with patients with elevated CRP alone. Our results are in line with those of other investigators who found that MCSF but not CRP was an independent predictor of in-hospital and short-term outcome in patients with unstable angina.20 For these reasons, MCSF levels may be considered a reliable alternative marker of outcome in patients with chronic stable CAD.
Study limitations
The following limitations should be acknowledged. Inflammatory indices were measured in peripheral blood. This does not allow firm conclusions on the release of these factors within the coronary circulation. Medications may affect plasma levels of the measured inflammatory indices.19,27 However, the study subgroups did not differ in antianginal, antiplatelet, or lipid lowering treatment at enrolment or at the end of the follow-up period. Thus, any possible influence of medications on cytokine plasma levels was evenly distributed within the study subgroups. The sample size of our study population is relatively small, though adequately powered (>80%) for the differences reported between the various study subgroups. The study population comprised a high proportion of smokers and male patients and thus our results should be interpreted in view of this. Finally, the number of patients using ß-blockers and lipid lowering drugs was relatively low; thus, our study population may not be representative of the current patient population, in whom the current widespread use of ß-blockers and statins may influence the prognostic value of the measured inflammatory markers.
![]() |
Conclusion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
Acknowledgement |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|