High-sensitivity C-reactive protein (hs-CRP) and tumor necrotizing factor-alpha (TNF-alpha) after on- and off- pump coronary artery bypass grafting.

INTRODUCTION: Coronary artery bypass grafting (CABG) is one of the most frequently performed operations around the world. The aim of this study is to evaluate high-sensitivity C-reactive protein (hs-CRP) and tumor necrosis factor-alpha (TNF-alpha) differences between on-pump and off-pump coronary surgery.
METHODS: In this prospective study, 90 patients with coronary artery disease referred for CABG were enrolled from July 2006-November 2007. Levels of hs-CRP and TNF-alpha were measured by ELISA using commercial kits
RESULTS: hs-CRP levels significantly (p<0.001) increase after CABG. But no difference between off-pump and on-pump groups was noted for hs-CRP and TNF-alpha levels (p=0.4, p=0.8).
CONCLUSIONS: There was no difference in high-sensitivity C-reactive protein (hs-CRP) and TNF-alpha between on-pump and off-pump CABG surgery.

Introduction

Coronary artery bypass grafting (CABG) is commonly performed worldwide and any improvement in the safety and efficacy of the procedure would have an impact on outcome in absolute terms [1,2].

It is well accepted that cardiopulmonary bypass (CPB) during on-pump CABG and pulmonary-myocardial reperfusion activates the immune system. The extent of this immune reaction has been correlated to clinical and post-operative complications. [3,4] It has been proposed that avoiding CPB and myocardial ischemia-reperfusion significantly reduces the postoperative systemic complications which negatively affect the perioperative course after surgical myocardial revascularization [5,6,7].

The aim of this study is to evaluate differences in high-sensitivity C-reactive protein (hs-CRP) and tumor necrotizing factor-alpha (TNF-alpha) between on-pump and off-pump coronary surgery.

We hypothesize that serum concentrations of both C-reactive protein and TNF-alpha are lower in patients who undergo CABG without using CPB.

Methods

This prospective case-matched study was conducted in Tabriz Shahid Maddani Hospital from July 2006-November 2007. The study protocol was approved by the Tabriz University of Medical Sciences (TUMS) ethics committee, which was in compliance with the Declaration of Helsinki. Ninety patients with coronary artery disease who were referred for CABG were enrolled in the study: 45 were enrolled in the on-pump group and 45 were enrolled in the off-pump group.

All patients signed a consent form before being included in the study. Inclusion criteria were: age between 35-55 years; no sign of current/previous neoplasm, including benign and malignant cancers; no history of steroidal or non-steroidal anti-inflammatory drug (NSAID) therapy during the past 2 weeks; no history of respiratory system failure (including asthma, adult respiratory distress syndrome, prolonged mechanical ventilation, acute lung injury); no history of rheumatologic diseases (including gout, lupus and related subtypes dermatomyositis, polymyositis, sclerodermia, rheumatoid arthritis, osteoarthritis); no autoimmune neurologic diseases (such as myasthenia gravis, multiple sclerosis); no chronic hemathologic and oncologic diseases (such as hemolytic anemia, idiopathic and thrombotic thrombocytopenic purpura); no insulin dependent diabetes, acute/chronic renal failure, or active infectious diseases during the past month.

Presence of any complication during 24 hours after surgery (including acute tubular necrosis, cardiac arrest), inability to obtain serum samples and prolonged operation time were considered exclusion criteria.

Anesthesia was induced with etomidate (200-300 mg/kg) and fentanyl (20-30 μg/kg). After muscle relaxation with cisatrocurium (0.15 mg/kg) and endotracheal intubation, anesthesia was maintained using fentanyl, midazolam, and isoflurane (0.4-1.5%).

On-pump patients were managed as follows: CPB equipment included nonpulsatile roller pumps (Stoeckert, Munich, Germany) and membrane oxygenators (Affinity, Avecor Cardiovascular, Plymouth, USA).

The pump was primed with a standard electrolyte solution containing 5000 IU heparin, 1000 mL Ringer's lactate, 500 mL NaCl 0.9%, and 250 mL of a 15% mannitol solution (Osmofundin 15%w, Braun Melsungen, Melsungen, Germany). Heparin (300 IU/kg) was administered immediately before vascular cannulation. After the institution of CPB at a flow rate of 2.4-3 L/m2 per min, the aorta was cross-clamped and a bloody warm cardioplegic solution was injected.

Off-pump patients were managed as follows: once the pericardium was opened, an initial heparin dose of 2 mg/kg was administered. Intravenous heparin then was used to maintain an activated clotting time (ACT) of more than 350 s until the anastomoses were created. An Octopus stabilizer system (Medtronic Inc., Minneapolis, MN) was used during the operation. After incision of the coronary artery, an intracoronary shunt was inserted and an anastomosis was performed.

Following revascularization, the heparin effect was reversed with protamine sulphate (at a ratio of 1.5:1) in all patients. Cefazoline was given for perioperative antibiotic prophylaxis.

Venous blood samples were taken immediately before surgery and 24 hours post-surgery. Samples were collected in sterile tubes, centrifuged at 3000 rpm for 10 minutes at 4°C, and then stored at -79°C until assayed.

Demographic data included age, sex, weight, height, body mass index (BMI), history of hypertension, diabetes, and hyperlipidemia, history of drug use, smoking, and alcohol, family history, number of coronary arteries involved, graft type, and ejection fraction (EF).

Serum levels of total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), creatinine (Cr), blood urea nitrogen (BUN) and uric acid (UA) levels were measured using an automated chemical analyzer (Abbott analyzer, Abbott laboratories, Abbott Park, North Chicago.IL) with commercial reagents obtained from Pars Azmoon Laboratories Ltd. (Tehran, Iran). Low-density lipoprotein cholesterol (LDL-C) was calculated using the Friedewald equation [8].

Levels of hs-CRP and TNF-alpha were measured by ELISA using commercial kits (hs-CRP by Monobind Inc., 100 North Point Drive, Lakeforest, California ( 92630 ), USA, Lot No: EIA-1K2L7, and TNF-alpha by Human INF-alfa ELISA, Bender MedSystems, GmbH, Campus Vienna Biocenter, 1030 Vienna, Austria) as directed by the manufacturer. Light absorbance was read at 450 nm.

Statistical analyses were performed using the SPSS Statistical Package version 13.0 (SPSS Inc, Chicago, IL). The results are presented as mean ± standard deviation (SD).

The Kolmogorov-Smirnov test was used for checking the normality. Independent sample t-test, paired t-test and Wilcoxon signed rank tests were used to assess the differences between stages, as appropriate. Comparison of qualitative data was done by chi-square test. The null hypothesis was rejected if the p value was less than 0.05.

Results

The groups were well matched for demographic characteristics and comorbidities (Table 1), concomitant medications (Table 2) and preoperatively blood tests (Table 3).

Demographics and surgical characteristics.

Medication history of the participants according to their surgical group.

Comparison of biochemical parameters between On-pump and off-pump.

In both off-pump and on-pump groups, hs-CRP level after CABG surgery increased significantly (p<0.001, p<0.001), but comparison of hs-CRP level increase (DhsCRP= hsCRP after CABG-hsCRP before CABG) between off-pump and on-pump groups revealed no significant difference (Table 4).

Comparison of hsCRP and TNF-alpha levels between study groups.

TNFα levels after CABG, in both off-pump and on-pump groups, were not increased significantly (p=0.2, p=0.7), and comparison of TNFa levels increase between off-pump and on-pump groups revealed no significant difference (Table 4).

Discussion

In this study, we aimed to compare TNF-alpha and hs-CRP levels in off-pump and on-pump groups before and after CABG. Although hs-CRP and TNF-alpha levels after CABG were increased in both off-pump and on-pump groups, this increase was statistically significant only in hs-CRP level. Comparison of the increase in hs-CRP and TNF-alpha levels between off-pump and on-pump groups revealed no significant difference.

The incidence of life threatening morbidity and mortality after CPB has decreased significantly in recent years; however, the inflammatory effects still are commonly recognized. The systemic inflammatory response, with an increased release of cytokines and adhesion molecules after conventional CABG with CPB, has been shown to provoke postoperative organ dysfunction [1,2,4]. Systemic inflammation now is known to result in activation of coagulation, downregulation of physiological anticoagulant mechanisms, and inhibition of fibrinolysis. For instance, IL-6 affects the coagulation cascade at different levels, increasing tissue factor and factor VIII mRNA levels in monocytes and liver cell lines, enhancing platelet production, and increasing the transcription of fibrinogen gene [4]. Some of these effects also may be mediated by other inflammatory markers such as C-reactive protein [3].

It is known that CABG elicits a normal inflammatory reaction in the early hours after surgery. Interestingly, some inflammatory markers (IL-1, IL-6, some leukocyte subsets) show similar behavior in both on-pump and off-pump techniques, whereas others (TNF-alpha, IL-8, IL-10, and elastase) show earliest and highest peak levels in CABG during the time span between the final steps and the very early hours after the surgical procedure. Afterwards, the differences in the inflammatory profile progressively fade and finally cancel out [7].

The strong relationship between postoperative changes in the levels of IL-6, but not of TNF-alpha, with that of C-reactive protein and fibrinogen, similar in both techniques, suggests a link between these variables. Because these variables were unaffected by the use of CPB, it suggests a possible link between inflammatory and haemostatic pathway activation. Indeed, fibrinogen, besides being an acute phase protein and a risk factor for future cardiovascular events, strongly affects hemostasis, blood microcirculation, platelet aggregation, and endothelial function [9]. In conclusion, this study shows that there is a protracted postoperative activation of the inflammatory pathways after coronary bypass surgery performed both on- and off-pump. These findings may be of pathophysiological and therapeutic interest in the treatment of patients undergoing coronary bypass surgery, whichever revascularization strategy (on- or off-pump) is chosen.

Off-pump coronary artery bypass is a surgical technique under clinical evaluation for its role and indications in ischemic heart disease. The avoidance of CPB may protect from perioperative systemic activation of inflammation and reduce hemostasis changes. In retrospective studies this has been shown to be associated with a varying degree of improvement of the early morbidity and mortality in the off-pump group when compared to the on-pump group [5,6].

Consistent advantages of off-pump over on-pump are limited to some inflammatory markers and to the time span between the final steps and the very early hours after the surgical procedure. Some inflammatory markers (activated complement factors, TNF-alpha, IL-8, IL-10 and elastase) increase compared to baseline in both on-pump and off-pump, but the peak levels are highest in on-pump. Afterwards, the difference in the inflammatory profile fades progressively and finally cancels out [10]. In the early phase, CPB is the major determinant of the onset of the inflammatory reaction, but in the late phases, the surgical trauma itself likely plays a predominant role. Evidence about other markers (IL-1, IL-6, some leukocyte subsets) is less consistent, and in some cases, even contradictory [10]. Overall, it can be hypothesized that CPB itself only minimally influences the circulating levels of these markers.

The trauma resulting from the surgical procedure likely may be the major determinant of inflammatory reaction.

The activation of the inflammatory system, although less marked than those of CPB cases, during vascular and non-cardiac thoracic surgery further supports this hypothesis [11,12].

In summary, the analysis of the available data shows that, in terms of biological impact, there are non-significant differences between off-pump and on-pump, and the general surgical trauma may play a role more significant than CPB. We have to recognize that in most of the studies quoted in the present discussion, the CPB was structured and conducted in a standard way, i.e. using mild or moderate systemic hypothermia, cold cardioplegia, uncoated circuits, without the administration of anti-fibrinolytic drugs or of any other inflammation modulating drug and using the cardiotomy suction devices. However, during the last decade, the practice of CPB has undergone major refinements and improvements in the field of biocompatibility, such as the introduction of warm heart surgery, coated circuits, antifibrinolytic drugs and the elimination of cardiotomy suction devices. Warm cardioplegia seems to reduce the oxidative stress [13,14,15,16,17,18] and inflammatory response [19,20].

In summary, the analysis of the available data shows that, in terms of biological impact, there are subtle differences between off-pump and on-pump, and the general surgical trauma may play a role more significant than CPB.