Uric acid and prognosis in angiography-proven coronary artery disease

Transcription

1 DOI: /eci ORIGINAL ARTICLE Uric acid and prognosis in angiography-proven coronary artery disease Gjin Ndrepepa *, Siegmund Braun *, Lamin King *, Massimiliano Fusaro *, Tomohisa Tada *, Salvatore Cassese *, Martin Hadamitzky *, Hans-Ullrich Haase, Albert Sch omig *, and Adnan Kastrati * * Deutsches Herzzentrum, Technische Universit at, Munich, Germany, and I. Medizinische Klinik rechts der Isar, Technische Universit at, Munich, Germany ABSTRACT Background The optimal uric acid (UA) level associated with the lowest mortality and the strength of association between UA and mortality in various subgroups of patients with coronary artery disease (CAD) are unknown. Materials and methods This study included patients with angiographic confirmation of CAD and UA measurements available. The primary outcome analysis was 1-year mortality. Results Based on the receiver operating characteristic curve analysis, the best cut-off of UA for mortality prediction was 711 mg/dl. Using this cut-off, patients were divided into two groups: the group with UA 711 mg/dl (n = 9075) and the group with UA > 711 mg/dl (n = 4198). Cardiac mortality was 63% (256 deaths) in patients with UA > 711 mg/dl and 23% (201 deaths) in patients with UA 711 mg/dl [hazard ratio (HR) = 282, 95% confidence interval (CI) ; P < 0001]. After adjustment for cardiovascular risk factors, UA remained an independent correlate of cardiac mortality (HR = 120, 95% CI ; P = 0001, for each standard deviation increase in the logarithmic scale of UA). The relationship between cardiac or allcause mortality and UA showed a J-shaped pattern with lowest mortality in patients with UA between 517 and 676 mg/dl. UA predicted mortality across all subgroups of patients, with strongest association in women and patients without arterial hypertension. Conclusions UA predicted an increased risk of cardiac mortality across all subgroups of patients with CAD. The association between UA and cardiac or all-cause mortality had a J-shaped pattern with lowest risk of death in patients with UA levels between 517 and < 676 mg/dl. Keywords Coronary artery disease, mortality, uric acid. Eur J Clin Invest 2013; 43 (3): Introduction Uric acid (UA) an end product of purine metabolism has been implicated in the genesis of cardiovascular disease since 1879 [1], and more than 60 years ago, it was included in the protocols of Framingham study to be investigated as a potential risk factor for cardiovascular disease [2]. However, the nature of the relationship between UA and cardiovascular disease remains a subject of debate. Difficulties in determining whether UA should be considered a cardiovascular risk factor may be explained by its frequent association with other cardiovascular risk factors [3] for which UA is considered as a risk marker or epiphenomenon or even an adaptive change to protect from atherosclerosis due to its antioxidant properties [4] and the controversial and conflicting findings from epidemiological studies [3,5,6]. Apart from disputable causality, other aspects of the association between UA and cardiovascular disease remain poorly understood. Although a threshold effect in the association between UA and mortality has been described [7,8], the best cut-offs of UA for prediction of mortality remain unknown. A J-shaped association pattern between UA level and mortality (with an increase in mortality for lower and higher UA levels) has been described in population-based studies [9] and in various disease states [10 12]. However, the pattern of association between UA and mortality and the most optimal UA levels associated with lowest mortality in patients with coronary artery disease (CAD) remain unknown, even though a stronger association between UA and mortality in patients with a CAD history has been reported [13,14]. Moreover, conflicting 256 ª 2012 The Authors. European Journal of Clinical Investigation ª 2012 Stichting European Society for Clinical Investigation Journal Foundation

2 URIC ACID AND PROGNOSIS IN CORONARY ARTERY DISEASE results have been reported regarding the association between UA and mortality in subgroups according to sex [5,15], diabetes [16,17] and kidney disease [18]. Despite data suggesting that elevated UA levels cause endothelial dysfunction [19] and may promote atherosclerosis and vascular thrombosis [20,21], evidence regarding the association between UA and myocardial infarction remains controversial [21,22]. We undertook this study in a large series of patients with CAD with a double objective: first, to assess the pattern of association between UA level and cardiac or all-cause mortality and find the most optimal UA levels associated with lowest mortality in patients with CAD; and second, to assess the strength of association between UA and mortality in various subgroups of patients with CAD. Methods Patients Between March 2000 and December 2009, consecutive patients with CAD underwent diagnostic angiography and percutaneous coronary intervention (PCI) in the Deutsches Herzzentrum in Munich. Those eligible for the study were patients with the clinical diagnosis of stable CAD or acute coronary syndromes (ACS) in whom the presence of significant CAD was confirmed by coronary angiography. Patients with no UA measurements (832 patients), acute infections (130 patients), renal disease (serum creatinine level 2 mg/dl; 312 patients) and known malignancies with life expectancy < 1 year (166 patients) were excluded. Thus, the present study included patients with angiographic confirmation of significant CAD and UA measurements available. Of these, 8149 patients had stable CAD, and 5124 patients had ACS (unstable angina in 2163 patients, acute non-st-segment elevation myocardial infarction in 1332 patients and ST-segment elevation myocardial infarction in 1629 patients). Detailed inclusion/exclusion of the patients and the diagnostic criteria of CAD are provided in prior publications from our group [8,23]. Patients gave written informed consent before recruitment in the study. The study was carried out in accordance with the Declaration of Helsinki and was approved by the institutional ethics committee. Reporting of the study conforms to STROBE along with references to STROBE and the broader EQUATOR guidelines [24]. Angiographic evaluation and definitions Digital angiograms were analysed offline with an automated edge-detection system (CMS; Medis Medical Imaging Systems, Nuenen, The Netherlands) in the core angiographic laboratory. Significant CAD was diagnosed in the presence of coronary stenoses 50% lumen obstruction in, at least, one of the three major coronary arteries. The complexity of lesions was defined according to the modified American College of Cardiology/ American Heart Association grading system [25]. Class B2 and C lesions were considered complex. Left ventricular ejection fraction was calculated with area length method using left ventricular angiograms [26]. Arterial hypertension was considered to be present when a patient was receiving active treatment with antihypertensive drugs or if, on two separate occasions, the systolic blood pressure was 140 mmhg or greater or the diastolic blood pressure 90 mmhg or greater. Hypercholesterolaemia was defined as a documented total cholesterol value 220 mg/dl or prior or ongoing treatment with a lipid-lowering agent. Smokers were defined as those currently smoking any tobacco. The requirements for a diagnosis of diabetes were as follows: active treatment with insulin or an oral hypoglycaemic agent on admission; documentation of an abnormal fasting blood glucose (> 125 mg/dl); blood glucose > 200 mg/dl at any time; or abnormal glucose tolerance test based on the World Health Organization criteria. Patients weight and height were measured, and body mass index was calculated. The glomerular filtration rate was estimated using the Cockcroft Gault formula [27]. Stent implantation and periprocedural care were performed according to standard criteria. Antiplatelet therapy consisted of clopidogrel (300 or 600 mg as a loading dose followed by 75 mg/day for at least 4 weeks) and aspirin (200 mg/day administered orally and continued indefinitely). Outcome definition and follow-up The primary outcome analyses were 1-year cardiac and allcause mortality. Secondary outcomes included vascular events such as nonfatal myocardial infarction and stroke. The followup protocol after discharge consisted of a phone interview at 1 month, a visit at 6 months and a phone interview at 12 months. The diagnosis of myocardial infarction was based on the development of new abnormal Q waves in 2 contiguous precordial or 2 adjacent limb leads, or an elevation of creatine kinase myocardial band (CK-MB) > 2 times (> 3 times for the 48 h after a PCI procedure) the upper limit of normal. Stroke required confirmation by computed tomography or magnetic resonance imaging of the head. Information about death was obtained from hospital records, death certificates or phone contact with relatives of the patient or referring physician(s). Cardiac death was defined according to Academic Research Consortium criteria and included any death due to proximate cardiac cause (e.g., myocardial infarction, low-output failure, faetal arrhythmia), unwitnessed death and death of unknown cause, and all procedure-related deaths, including those related to concomitant treatment [28]. Patients reporting cardiac complaints during follow-up underwent a complete clinical, electrocardiographic and laboratory evaluation. Collection of baseline characteristics of the patients, follow-up European Journal of Clinical Investigation Vol

3 G. NDREPEPA ET AL. information and adjudication of adverse events was performed by medical staff unaware of UA level. Biochemical measurements Detailed description of laboratory measurements has been previously shown [8,23]. Blood samples were obtained before angiography in all patients. Blood was collected into tubes containing lithium heparin as anticoagulant (S-Monovette 49 ml; Sarstedt, N umbrecht, Germany). The blood samples were immediately transported to the laboratory, centrifuged and analysed (median turn-around time min, 98% of results within 90 min). The UA concentration in plasma was determined with an enzymatic colorimetric test on a Cobas Integra 800 analyzer (Roche Diagnostics, Mannheim, Germany). The measuring range in plasma is mg/dl ( lm). Lower detection limit of the test is 020 mg/dl (119 lm). The reference range for men is mg/dl ( lm) and for women mg/dl ( lm). Plasma concentrations of high-sensitivity C-reactive protein (CRP) were measured using a fully automated latex-enhanced immunoturbidimetric assay on a Cobas Integra (Roche Diagnostics). The CRP assay has an analytical sensitivity of 0085 mg/l and a measuring range up to 160 mg/l. The upper limit of the reference range in healthy adults is 5 mg/l. Creatinine was measured using a kinetic colorimetric assay based on the compensated Jaffe method. Laboratory personnel were unaware of clinical, angiographic or follow-up data of the patients. Statistical analysis Data are presented as median (interquartile range), counts or proportions (%). One-sample Kolmogorov Smirnov test was used to assess the data distribution. Continuous data with skewed distribution (shown as medians with interquartile range) were compared with the Kruskal Wallis rank sum test. Categorical data were compared with chi-square test. Receiver operating characteristic (ROC) curve was constructed to assess the best UA cut-off value regarding the prediction of cardiac mortality whilst maximizing sensitivity and specificity through minimizing the square root of (1 sensitivity) 2 + (1 specificity) 2. Survival analysis was performed by applying the Kaplan Meier method and log-rank test. Multivariable Cox proportional hazards model was used to assess the association between UA and cardiac or all-cause mortality whilst adjusting for cardiovascular risk factors and other relevant clinical variables. The following variables were entered into the model: age, sex, body mass index, diabetes, arterial hypertension, hypercholesterolaemia, smoking status, previous myocardial infarction, previous coronary artery bypass surgery, clinical presentation (stable CAD vs. ACS), glomerular filtration rate, CRP, left ventricular ejection fraction, multivessel disease and UA. UA was entered into the model as a continuous variable after logarithmic transformation. Area under the ROC curve showing the performance of UA to predict cardiac mortality was calculated after covariate adjustment. The same variables as for the Cox model were entered into the model. The discriminatory power of the model regarding mortality was assessed by calculating the integrated discrimination improvement (IDI) according to Pencina et al. [29] Differences in the association between UA and mortality across various subgroups of patients were investigated by performing interaction testing. All analyses were performed using S-plus statistical package (S-PLUS; Insightful Corp, Seattle, WA, USA). A two-tailed P < 005 was considered to indicate statistical significance. Results Characteristics of patients The ROC curve analysis of UA predicted 1-year cardiac mortality with an unadjusted area under the curve of 0650 with 95% confidence interval (CI) between 0616 and 0675 (P < 0001; Fig. 1). The best cut-off value of UA regarding mortality prediction was 711 mg/dl. Using this cut-off, patients were divided into two groups: group with UA level 711 mg/dl (n = 9075 patients) and group with UA level True-Positive Rate (Sensitivity) 1 0 Unadjusted AUC = 0 650, 95% CI [ ]; P< Uric acid 7 11 mg/dl Uric acid level = 7 11 mg/dl Sensitivity = 56% Specificity = 69% False-Positive Rate (1-Specificity) Figure 1 Receiver operating characteristic (ROC) curve showing the accuracy of uric acid to predict cardiac mortality. Adjusted area under the ROC curve was 0666, 95% confidence interval ; P < ª 2012 The Authors. European Journal of Clinical Investigation ª 2012 Stichting European Society for Clinical Investigation Journal Foundation

4 URIC ACID AND PROGNOSIS IN CORONARY ARTERY DISEASE Table 1 Baseline characteristics Characteristic Uric acid (UA) 711 mg/dl (n = 9075) > 711 mg/dl (n = 4198) P value Age (years) 670 [592; 743] 684 [604;756] < 0001 Females 2389 (263) 714 (170) < 0001 Diabetes 2409 (265) 1296 (309) < 0001 Insulin requiring 751 (83) 436 (104) < 0001 Body mass index (kg/m 2 ) 265 [243; 291] 278 [256; 306] < 0001 Arterial hypertension 6269 (691) 2844 (677) 0123 Current smoking 1450 (160) 642 (153) 0314 Hypercholesterolaemia 6387 (704) 2904 (692) 0159 Previous myocardial infarction Previous coronary artery bypass surgery 2751 (303) 1458 (347) < (143) 698 (166) < 0001 Clinical presentation Stable coronary artery disease 5541 (611) 2608 (621) 0011 Acute coronary syndrome 3534 (389) 1590 (379) High-sensitivity C-reactive protein (mg/l) 21 [09; 60] 32 [13; 86] < 0001 Creatinine (mg/dl) 09 [08; 11] 11 [09; 13] < 0001 Glomerular filtration rate (ml/min) 828 [641; 1039] 721 [524; 958] < 0001 UA (mg/dl) 58 [50; 64] 81 [76; 90] < 0001 No. of coronary arteries narrowed (186) 625 (149) < (274) 1031 (246) (540) 2542 (605) Multivessel disease 7385 (814) 3573 (851) < 0001 Complex lesions 6869 (757) 3191 (760) 0688 Left ventricular ejection fraction (%) 580 [490; 630] 540 [430; 610] < 0001 Vessel treated Left main coronary artery 390 (43) 197 (47) < 0001 Left descendent coronary artery 3640 (401) 1563 (372) Left circumflex coronary artery 2189 (241) 1010 (241) Right coronary artery 2518 (278) 1197 (285) Bypass graft 338 (37) 231 (55) Type of intervention Coronary stenting 8221 (906) 3786 (902) 0461 European Journal of Clinical Investigation Vol

5 G. NDREPEPA ET AL. Table 1 Continued Characteristic Uric acid (UA) 711 mg/dl (n = 9075) > 711 mg/dl (n = 4198) P value Balloon angioplasty 854 (94) 412 (98) Drug-eluting stents 6239 (759)* 2822 (745)* 0109 Data are number of patients (%) or median [25th; 75th percentiles]. Data on body mass index, glomerular filtration rate, C-reactive protein and left ventricular ejection fraction were available in 997% (n = ), 997% (n = ), 992% (n = ) and 879% (n = ) of the patients, respectively. The remaining data are complete. *Refers to patients with implanted stents only. > 711 mg/dl (n = 4198 patients). With the exception of the proportions of patients with arterial hypertension, current smoking, hypercholesterolaemia or complex lesions and the type of therapy, all other characteristics differed significantly amongst patients in both groups (Table 1). Clinical outcome Overall, there were 646 deaths (49%) within the first year following PCI. Of these, 457 deaths (34% of patients or 707% of deaths) were of cardiac origin. Deaths of cardiac origin occurred in 256 patients with UA level > 711 mg/dl and in 201 patients with UA level 711 mg/dl [Kaplan Meier estimates of mortality 63% and 23%, respectively; hazard ratio (HR) = 282, 95% CI ; P < 0001; Fig. 2a]. Allcause deaths occurred in 345 patients with UA level > 711 mg/dl and in 301 patients with UA level 711 mg/ dl (Kaplan Meier estimates of mortality 84% and 36%, respectively; HR = 254, 95% CI ; P < 0001; Fig. 2b). Nonfatal myocardial infarction occurred in 139 patients with UA level > 711 mg/dl and in 281 patients with UA level 711 mg/dl (Kaplan Meier estimates, 34% and 31%, respectively; HR = 108, 95% CI ; P = 0449). Stroke occurred in 35 patients with UA level > 711 mg/dl and in 59 patients with UA level 711 mg/dl (Kaplan Meier estimates, 09% and 07%, respectively; HR = 130, 95% CI ; P = 0806). Distribution pattern of mortality according to UA level Cardiac and all-cause mortality was assessed according to deciles of UA concentration (Table 2 and Fig. 3). For UA levels between 517 and < 676 mg/dl (3rd to 6th deciles), cardiac and all-cause mortality was lowest [19% (100 deaths) and 30% (160 deaths), respectively]. For patients with UA levels 517 mg/dl (the first 2 deciles), the risk of cardiac (76 deaths, 29%) or all-cause (108 deaths, 41%) mortality was significantly higher than for patients in the 3rd to 6th deciles [odds ratio (OR) = 153, 95% CI ; P = 0005 for cardiac mortality and OR = 136 ( ); P = 0013 for (a) (b) Probability of mortality (%) Probability of mortality (%) Patients at Risk UA>7 11 mg/dl Patients at Risk Months UA>7 11 mg/dl UA 7 11 mg/dl UA 7 11 mg/dl P<0 001 P<0 001 UA>7 11 mg/dl UA 7 11 mg/dl UA>7 11 mg/dl UA 7 11 mg/dl Months Figure 2 Kaplan Meier curves of cardiac (a) and all-cause (b) mortality according to UA level > or 711 mg/dl. UA, uric acid. all-cause mortality]. For patients with UA levels > 676 mg/dl (7th to 10th deciles), the risk of cardiac (281 deaths, 53%) or all-cause (378 deaths, 71%) was significantly higher than for patients in the 3rd to 6th deciles [OR = 290 ( ); 260 ª 2012 The Authors. European Journal of Clinical Investigation ª 2012 Stichting European Society for Clinical Investigation Journal Foundation

6 URIC ACID AND PROGNOSIS IN CORONARY ARTERY DISEASE Table 2 Cardiac and all-cause mortality according to uric acid (UA) deciles Deciles of UA UA level (mg/dl) Number of patients Mortality (number of patients; %) Cardiac All-cause 1st 130 to < (227) 48 (363) 2nd 452 to < (446) 60 (452) 3rd 517 to < (119) 31 (245) 4th 560 to < (196) 40 (291) 5th 600 to < (265) 51 (386) 6th 637 to < (171) 38 (282) 7th 676 to < (233) 38 (305) 8th 720 to < (364) 70 (509) 9th 780 to < (513) 88 (645) 10th (992) 182 (1368) Data are range(s) or number of patients (%). Mortality(%) Cardiac mortality All-cause mortality Uric acid Deciles Figure 3 Cardiac and all-cause mortality according to deciles of uric acid. P < 0001 for cardiac mortality and OR = 180 ( ); P < 0001 for all-cause mortality]. Thus, the relationship between mortality and UA level in patients with CAD showed a J-shaped pattern (Fig. 3). UA and adjusted risk of mortality The Cox proportional hazards model was used to test the association between UA level and mortality whilst adjusting for potential confounders (see Methods for variables entered into the model). Results of multivariable analysis are shown in Table 3. After adjustment for traditional cardiovascular risk factors and relevant clinical variables, including renal function (glomerular filtration rate) and inflammation status (CRP), UA remained an independent correlate of cardiac mortality (adjusted HR = 120, 95% CI ; P = 0001) and all-cause mortality (adjusted HR = 119, 95% CI ; P < 0001) for each standard deviation increase in the logarithmic scale of UA. Adjusted risk of mortality was also calculated for each 1 mg/ dl increase in the UA level. For each 1 mg/dl increase in the UA level, the adjusted risk of cardiac and all-cause mortality was increased by 10% (adjusted HR = 110, 95% CI ; P < 0001) and 11% (adjusted HR = 111, 95% CI ; P < 0001), respectively. The inclusion of UA in the multivariable model was associated with a trend for an improvement of the discriminatory power of the model regarding prediction of cardiac mortality (absolute IDI = 0004, relative IDI = 25%; P = 0074) and a significant improvement of discriminatory power of the model regarding all-cause mortality (absolute IDI = 0005, relative IDI = 30%; P = 0022). UA and mortality in various subgroups of patients The association between UA and cardiac or all-cause mortality was assessed in various subgroups of patients. For this analysis, patient subgroups were obtained by dividing patients according to age (cut-off, 65 years), sex, diabetes, arterial hypertension, glomerular filtration rate (cut-off, 60 ml/min), body mass index (cut-off, 30 kg/m 2 ), left ventricular ejection fraction (cut-off, 50%) and CRP (cut-off, 5 mg/l). This analysis showed that UA predicted an increased risk of cardiac and all-cause mortality across all subgroups. An interaction was observed between UA and sex demonstrating a stronger European Journal of Clinical Investigation Vol

7 G. NDREPEPA ET AL. Table 3 Results of multivariable Cox proportional hazards model regarding cardiac and all-cause mortality Characteristic Uric acid (for each SD increase in the natural logarithm) Cardiac mortality All-cause mortality HR [95% CI] P value HR [95% CI] P value 120 [ ] [ ] < 0001 Age (for 10-year increase) 112 [ ] [ ] 0006 Female sex 114 [ ] [ ] 0212 Body mass index (for 5 kg/m 2 increase) 111 [ ] [ ] 0412 Diabetes 160 [ ] < [ ] < 0001 Arterial hypertension 055 [ ] < [ ] < 0001 Hypercholesterolaemia 079 [ ] [ ] 0009 Current smoking 093 [ ] [ ] 0724 Previous myocardial infarction 083 [ ] [ ] 0274 Previous coronary artery bypass surgery 075 [ ] [ ] 0379 Clinical presentation (ACS vs. stable CAD) 225 [ ] < [ ] < 0001 Glomerular filtration rate (for 30 ml/min decrease) 204 [ ] < [ ] < 0001 C-reactive protein (for 5 mg/l increase) 102 [ ] < [ ] < 0001 Left ventricular ejection fraction (for 10% decrease) 161 [ ] < [ ] < 0001 Multivessel disease (vs. single-vessel disease) 187 [ ] [ ] 0001 ACS, acute coronary syndrome; CAD, coronary artery disease; CI, confidence interval; SD, standard deviation; HR, hazard ratio. association with mortality in women than in men (P for interaction = 0059 for cardiac mortality and P for interaction = 0019 for all-cause mortality) and between UA and arterial hypertension demonstrating a stronger association between UA and mortality in patients without arterial hypertension than in patients with arterial hypertension (P for interaction = 0050 for cardiac mortality and P for interaction = 0064 for all-cause mortality). The results of subgroup analyses are shown in Figs 4 and 5. Discussion In this study, we investigated the pattern of association between UA and mortality (cardiac and all-cause) in a large series of patients with CAD and the strength of this association in various subgroups of patients. The main findings of the study can be summarized as follows: (i) UA predicted an increased risk of cardiac and all-cause mortality independent of traditional cardiovascular risk factors, left ventricular function, CRP and renal function across the whole spectrum of patients with CAD. (ii) The association between UA and cardiac or all-cause mortality followed a J-shaped pattern with a significant increase in the risk of death in patients with the lowest and highest UA levels. UA levels between 517 and < 676 mg/ dl were associated with the lowest risk of mortality (both cardiac and all-cause). There was a significant increase in the risk of death for UA levels either < 517 mg/dl or higher than 676 mg/dl. (iii) UA predicted an increased risk of cardiac and all-cause mortality across all subsets of patients defined by age (younger or older than 65 years), sex, diabetes, arterial hypertension, obesity, CAD presentation, renal function, left ventricular systolic function or CRP level. However, the strongest association between UA and mortality was observed in women and patients without arterial hypertension. Prior studies in patients with known CAD have shown that UA is an independent correlate of mortality [30,31]. Of note, it has also been suggested that the presence of CAD strengthens the association between UA and mortality [13,14]. The present study is the largest one to provide support for an independent association between UA and both cardiac and all-cause mortality in patients with known CAD. We also 262 ª 2012 The Authors. European Journal of Clinical Investigation ª 2012 Stichting European Society for Clinical Investigation Journal Foundation

8 URIC ACID AND PROGNOSIS IN CORONARY ARTERY DISEASE Cardiac mortality No. of Events/Total (%) Uric acid 7 11 mg/dl >7 11 mg/dl All Patients Age >65 years 201/9075 (2 3) 161/5203 (3 2) 256/4198 (6 3) 212/2114 (8 3) 65 years 40/3872 (1 1) 44/1584 (2 8) Sex Women 69/2389 (3 0) 76/714 (11 0) Men 132/6686 (2 0) 180/3484 (5 3) Diabetes 85/2409 (3 7) 105/1296 (8 4) No Arterial hypertension 116/6666 (1 7) 151/2902 (5 3) 104/6269 (1 7) 107/2844 (3 8) No 97/2806 (3 5) 149/1354 (11 3) Clinical presentation ACS 143/3534 (4 1) 193/1590 (12 5) Stable CAD 58/5541 (1 1) 63/2608 (2 5) GFR<60 ml/min 113/1816 (6 4) 176/1446 (12 6) No 86/7239 (1 2) 75/2737 (2 8) BMI>30 kg/m 2 28/1730 (1 7) 47/1214 (4 0) No 171/7325 (2 4) 203/2968 (7 0) LVEF 50% 106/2132 (5 1) 144/1330 (11 2) >50% 52/6016 (0 9) 37/2186 (1 7) CRP> 5mg/L 121/2594 (4 8) 164/1591 (10 7) No 78/6413 (1 2) 90/2572 (4 6) Hazard ratio (95% Confidence Intervals) 2 82 [ ] 2 70 [ ] 2 71 [ ] 3 88 [ ] 2 66 [ ] 2 37 [ ] 3 04 [ ] 2 30 [ ] 3 31 [ ] 3 15 [ ] 2 32 [ ] 2 03 [ ] 2 32 [ ] 2 43 [ ] 3 01 [ ] 2 25 [ ] 1 97 [ ] 2 30 [ ] 2 90 [ ] P int Hazard ratio Figure 4 Cardiac mortality in various subgroups of patients with CAD. ACS, acute coronary syndrome; BMI, body mass index; CAD, coronary artery disease; CRP, C-reactive protein; GFR, glomerular filtration rate; LVEF, left ventricular ejection fraction; No., number; P int, P for interaction. showed that the association between UA and mortality has a J-shaped pattern with higher mortality rates for patients with high and low UA levels. Based on our analysis, 60% of patients with CAD had suboptimal UA levels (the first two deciles too low and the upper four deciles too high) in terms of association with mortality. The association between elevated levels of UA and mortality from cardiac disease has been the subject of intense research, and a host of putative mechanisms to explain it has been proposed and recently reviewed [32]. In brief, an association with a more adverse cardiovascular risk profile and the possibility that UA per se may promote atherosclerosis or vascular events leading to cardiovascular deaths have been proposed to explain increased risk of death associated with elevated UA levels. Evidence available suggests that UA may have atherogenic actions. Thus, it has been suggested that UA causes endothelial dysfunction [19,33], proliferation of vascular smooth muscle cells [34], and it promotes inflammation in vascular tissue [33], acts as pro-oxidant in atherosclerotic environment [35], and enhances lipid peroxidation [36]. UA and xanthine oxidase have been identified in atherosclerotic plaques and involved in the aetiology of atherosclerosis [37]. However, the Hill s criteria of causality for UA as a risk factor for cardiovascular disease [38] are only partially fulfilled at best [39]. Reasons for an association between low UA levels and mortality are unknown. In a recent study of patients on hemodialysis by Lee et al. [40], an UA level < 52 mg/dl (very close to our cut-off point of 517 mg/dl) was associated with a > 2-fold increased risk of death in the first year of dialysis. Low UA levels were also associated with more comorbid conditions and markers of protein energy wasting, suggesting a higher oxidative stress due to reduced antioxidant combat mechanisms conferred by low UA level. These factors were proposed as putative mechanisms for increased risk of death in these patients [40]. Other studies have implicated malnutrition as a causative factor for low UA level, which also affects mortality [41]. Reduced UA levels have been linked to several neurological diseases such as multiple sclerosis, Parkinson s disease, Alzheimer s disease and optic neuritis [42]. Although the risk conferred by these diseases in our patients remains unaccounted for, any substantial contribution in mortality by these diseases would seem unlikely. Moreover, because patients with impaired renal function (serum creatinine level 2 mg/dl) were excluded from the study, mechanisms that may be operative in a patient population with renal failure and dialysis may not be applicable in explaining the increased risk of death with low UA levels in our patients with CAD. European Journal of Clinical Investigation Vol

9 G. NDREPEPA ET AL. All-cause mortality No. of Events/Total (%) Uric acid All Patients 7 11 mg/dl 301/9075 (3 6) >7 11 mg/dl 345/4198 (8 4) Age >65 years 247/5203 (4 8) 283/2114 (10 0) 65 years 54/3872 (1 4) 62/1584 (4 0) Sex Women 102/2389 (4 4) 102/714 (14 6) Men 199/6686 (3 0) 243/3484 (7 1) Diabetes 114/2409 (4 9) 150/1296 (12 0) No 187/6666 (2 8) 195/2902 (6 8) Arterial hypertension 167/6269 (2 7) 164/2844 (5 9) No 134/2806 (4 8) 181/1354 (13 6) Clinical presentation ACS 209/3534 (6 0) 241/1590 (15 4) Stable CAD 92/5541 (1 7) 104/2608 (4 1) GFR<60 ml/min 171/1816 (9 6) 232/1446 (16 4) No 125/7239 (1 7) 105/2737 (4 0) BMI>30 kg/m 2 36/1730 (2 1) 68/1214 (5 8) No 260/7325 (3 6) 268/2968 (9 2) LVEF 50% 148/2132 (7 1) 183/1330 (14 1) >50% 84/6016 (1 4) 62/2186 (2 9) CRP> 5mg/L 180/2594 (7 1) 224/1591 (14 5) No 119/6413 (1 9) 118/2572 (4 7) Hazard ratio (95% Confidence Intervals) 2 54 [ ] 2 36 [ ] 2 84 [ ] 3 55 [ ] 2 39 [ ] 2 54 [ ] 2 44 [ ] 2 20 [ ] 2 92 [ ] 2 71 [ ] 2 42 [ ] 1 78 [ ] 2 24 [ ] 2 74 [ ] 2 62 [ ] 2 05 [ ] 2 04 [ ] 2 12 [ ] 2 50 [ ] P int Hazard ratio Figure 5 All-cause mortality in various subgroups of patients with CAD. ACS, acute coronary syndrome; BMI, body mass index; CAD, coronary artery disease; CRP, C-reactive protein; GFR, glomerular filtration rate; LVEF, left ventricular ejection fraction; No., number; P int, P for interaction. Subgroup analyses performed in the setting of present study showed that UA level predicts an increased risk of cardiac and all-cause mortality across all subsets of patients with CAD. We believe that these findings are novel and important in the light of existing controversy regarding the association between UA and mortality in various diseases [16 18]. Although, UA level predicted mortality across all subgroups, differences in the strength of association were observed. Specifically, a stronger association of UA with mortality was observed in women and patients without arterial hypertension. Whilst the association between UA and mortality was observed in both sexes, the finding of a stronger association in women in our study is in line with prior studies showing a stronger association of UA with mortality in women than in men [15]. A recent meta-analysis by Kim et al. [43] showed that association between hyperuricemia and CAD incidence and mortality was significant in women but not in men. Moreover, in recent studies by Strasak et al. [44,45], a higher mortality due to CAD was observed only in women. To our knowledge, finding of a stronger association between UA and cardiac mortality in patients without arterial hypertension is novel. In the Rotterdam study, the association between UA and stroke was weakened by the presence of arterial hypertension [21]. The magnitude of differences in the risk estimates (HRs) in subgroup analyses (Figs 4 and 5) provides a signal for a stronger association between UA and mortality in the absence of cardiovascular risk factors. Specifically, trends for a stronger association of UA with cardiac mortality were observed in patients without arterial hypertension, diabetes, obesity and in those with low CRP. Although, this finding may be a signal for causality in the relationship between UA and cardiovascular disease, which may be more evident in the absence of masking effects of risk factors, further studies are needed to confirm this hypothesis. The present study may have implications. In particular, this study may strengthen the need for interventional studies with UA-lowering therapies to maintain UA levels in the range associated with the lowest mortality. Although current guidelines recommend an UA level 6 mg/dl [46], these target concentrations are reached in < 50% of the patients [47]. Moreover, allopurinol a xanthine oxidase inhibitor has been shown recently to significantly improve endothelial function and abolish vascular oxidative stress [48], has a clinically relevant antiischaemic effect and has been well tolerated in patients with angina [49]. In analogy with homocysteine-lowering therapy, 264 ª 2012 The Authors. European Journal of Clinical Investigation ª 2012 Stichting European Society for Clinical Investigation Journal Foundation

10 URIC ACID AND PROGNOSIS IN CORONARY ARTERY DISEASE interventional studies with UA-lowering agents, apart from exploring clinical benefits of these agents, may provide valuable additional information regarding causality in the UA cardiovascular disease relationship. We recognize several limitations of the present study. First, a follow-up longer than 1 year would be desirable. However, the curves of mortality were diverging, and the difference in mortality rates expanding throughout the first year suggests that even greater differences in mortality would be expected in the years to come. Second, when analysing the results of subgroup analyses, the impact of errors introduced by multiple testing should be considered. However, all subgroup comparisons of UA mortality association had P < 0001, which almost excludes the possibility of chance findings. Although, in general, subgroup analyses suffer from limited numbers of subjects/patients due to division into subgroups, large number of patients in the present study allowed us to perform subgroup analyses with large numbers of patients per subgroup. Third, the study has an observational design and is based on a single UA measurement. Thus, eventual changes in UA level during the follow-up remain unaccounted for. Finally, patients with advanced renal disease and those with malignancies with life expectancy < 1 year are not included in this analysis. In conclusion, UA level predicted an increased risk of cardiac and all-cause mortality across all subsets of patients with CAD with the strongest association observed in women and patients without arterial hypertension. The association between UA level and cardiac and all-cause mortality followed a J-shaped pattern with a significant increase in mortality for UA levels < 517 and > 676 mg/dl. Specifically designed interventional studies are needed to confirm these findings. Author contribution Drs Ndrepepa and Kastrati involved in the conception and design of the study. Drs Ndrepepa, Braun, King, Fusaro, Tada, Cassese, Hadamitzky and Haase involved in the acquisition of the data, analysed and interpreted the data. Drs Ndrepepa, Kastrati and Sch omig involved in the writing and critiquing of drafts of the manuscript. Drs Ndrepepa, Braun, King, Fusaro, Tada, Cassese, Hadamitzky, Haase, Sch omig and Kastrati approved the final manuscript for submission. Conflicts of interest None. Sources of funding None. Address Deutsches Herzzentrum, Technische Universit at, Lazarettstrasse 36, M unchen, Germany (G. Ndrepepa, S. Braun, L. King, M. Fusaro, T. Tada, S. Cassese, M. Hadamitzky, A. Sch omig, A. Kastrati); 1. Medizinische Klinik rechts der Isar, Technische Universit at, Munich, Germany (H.-U. Haase, A. Sch omig). Correspondence to: Gjin Ndrepepa, MD, Deutsches Herzzentrum, Lazarettstrasse 36, M unchen, Germany. Tel.: ; fax: ; ndrepepa@dhm. mhn.de Received 25 May 2012; accepted 29 November 2012 References 1 Mohamed FA. On Bright s disease, and its essential symptoms. Lancet 1879;1: Dawber TR, Meadors GF, Moore FE Jr. Epidemiological approaches to heart disease: the Framingham Study. Am J Public Health Nations Health 1951;41: Culleton BF, Larson MG, Kannel WB, Levy D. Serum uric acid and risk for cardiovascular disease and death: the Framingham Heart Study. Ann Intern Med 1999;131: Davies KJ, Sevanian A, Muakkassah-Kelly SF, Hochstein P. Uric acid-iron ion complexes. A new aspect of the antioxidant functions of uric acid. Biochem J 1986;235: Fang J, Alderman MH. Serum uric acid and cardiovascular mortality the NHANES I epidemiologic follow-up study, National Health and Nutrition Examination Survey. JAMA 2000;283: Niskanen LK, Laaksonen DE, Nyyssonen K, Alfthan G, Lakka HM, Lakka TA et al. 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