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Annals of Clinical & Laboratory Science 39:372-377 (2009)
© 2009 Association of Clinical Scientists

Biochemical Changes Associated with Reperfusion After Off-Pump and On-Pump Coronary Artery Bypass Graft Surgery

Lal G. Chandrasena1,2, Hemantha Peiris2,3 and Hemant Digambar Waikar4
1 Department of Biochemistry and Clinical Chemistry, Faculty of Medicine, University of Kelaniya, Sri Lanka; 2 Nawaloka Metropolis Clinical Laboratories, Colombo, Sri Lanka; 3 Department of Biochemistry, Faculty of Medical Sciences, University of Sri Jayewardenepura, Sri Lanka; and 4 Department of Cardiothoracic Anesthesia, Nawaloka Hospitals, Colombo, Sri Lanka

Address correspondence to Prof. Lal G. Chandrasena, Nawaloka Metropolis Clinical Laboratories, 23 Deshamanya H.K. Dharmadasa Mawatha, Colombo 02, Sri Lanka; fax 94 11 243 0393; e-mail hempeiris{at}yahoo.com.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
A prospective study was performed to monitor the postoperative changes in biochemical markers associated with reperfusion injury following (i) cardiopulmonary bypass (CPB) with aortic cross-clamping and cardioplagia (CABG); (ii) CPB with a tissue stabilizing device (SUP.CPB); or (iii) surgery on beating heart (off-pump CABG or OPCABG). Of the 48 patients, 16 were subjected to CABG, 16 to SUP.CPB, and 16 to OPCABG. Arterial and venous blood samples drawn 10 min preoperatively and 0.2, 4, 24, and 48 hr after surgery were assayed for plasma lactate, total calcium, and ionized calcium and erythrocyte glutathione peroxidase (GPX) and superoxide dismutase (SOD). Results revealed that ionized calcium, SOD, and GPX levels of all patients increased at 4 hr following surgery but returned to baseline levels at 24 or 48 hr after surgery. Increased postoperative GPX levels reflect a cellular defense mechanism against oxidative damage during reperfusion, while lactate levels during reperfusion reflect delayed recovery of aerobic myocardial metabolism. The postoperative release of lactate, GPX, and SOD in patients undergoing the CABG (on-pump) technique was significantly higher compared to those subjected to OPCABG or SUP.CPB. There were no significant differences in postoperative patterns of release of biomarkers in patients with OPCABG vs SUP.CPB, suggesting that these surgical techniques are equally acceptable.

Keywords: coronary artery bypass graft, glutathione peroxidase, superoxide dismutase, lactate, calcium


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Coronary artery bypass grafting (CABG) is routinely performed (i) by cardiopulmonary bypass (CPB) with aortic cross-clamping and cardioplegia (CABG on-pump); (ii) by cardiopulmonary bypass without aortic cross-clamping using a tissue stabilizing device like the "Octopus" or "Starfish" device (supportive CPB or SUP.CPB); or (iii) on the beating heart, referred to as off-pump CABG (OPCABG) [1–3]. The relative advantages and disadvantages of these 3 surgical techniques are controversial due to the variable oxidative stress induced by overproduction of free radicals during reperfusion of coronary flow [4–6].

Reperfusion injury results from several interdependent mechanisms that are involved in the production of reactive oxygen species (ROS). The ROS formed during oxidative stress result in oxidation of proteins, lipid peroxidation, and inactivation of nitric oxide (NO), leading to endothelial injury and micro-vascular dysfunction [7,8]. This may delay the recovery of cardiac function following CABG. Generation of ROS disrupts the sarco-lemma and more specifically Ca2+-ATPase activity and interrupts ionized calcium homeostasis, suggesting that serum ionized calcium may be an important marker of oxidative stress [8].

Several hypotheses have been proposed for the delayed postoperative recovery of viable myocardium, involving cellular antioxidant defense activity and hypoxia due to tissue hypoperfusion (lactic acid production). Overproduction of ROS is neutralized by various antioxidant mechanisms, and among them, glutathione peroxidase (GPX) and superoxide dismutase (SOD) have been reported to be sensitive cardioprotective enzymes during ischemia-reperfusion injury [7]. In addition, N-acetylcysteine [9,10] has been reported to be a potent cardioprotective antioxidant [11,12].

Postoperative hyperlactatemia has been shown to correlate with increased postoperative morbidity [13–15]. Persistent lactate production after reperfusion reflects delayed recovery of aerobic metabolism. Hence monitoring of postoperative lactate levels may be useful for assessing the status of aerobic metabolism [10,13].

Measurements of cardiac troponins, malondialdehyde, heart fatty acid binding protein, and high sensitive C-reactive protein have been shown to be effective in identifying patients with several cardiac conditions including coronary interventions [8,16]. Clinical trials have established associations between increased postoperative concentrations of cardiac troponins and other cardiac-specific biomarkers and the increased postoperative morbidity and mortality following CABG [4,13,14]. The optimum sampling times for detection of biomarkers associated with reperfusion injury following CABG have not been clearly defined. This study was performed to compare the postoperative patterns of release of biochemical markers (eg, lactate, antioxidant enzymes, and ionized calcium) in patients after the CABG (on-pump), OPCABG, and SUP.CPB surgical techniques.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
A prospective comparative study was carried out from December 2007 to May 2008 at the cardiac surgery unit of Nawaloka Hospitals, Colombo, Sri Lanka. A total of 48 patients (21 females and 24 males) selected for multi-vessel coronary revascularization after angiographic evaluation were recruited to the study. Inclusion criteria were the presence of triple vessel coronary artery disease in the age group from 40 to 65 yr. Patients with a clinical history of diabetes mellitus, renal disease, or liver dysfunction were excluded from the study. Of the 48 patients, 16 were subjected to CABG (on-pump), 16 to SUP.CPB, and 16 to OPCABG (off-pump). Each treatment group consisted of 7 females and 8 males. Relevant data such as left ventricular ejection fraction (LVEF) before and after surgery, CPB time, and aorta cross-clamp time were recorded. In addition, 52 healthy subjects (age- and sex-matched, 27 females and 25 males) who came to the hospital for periodic health screening were recruited as controls. Medical histories and physical examinations were performed on all controls: none had clinical or diagnostic evidence of heart disease, diabetes mellitus, kidney disease, or liver dysfunction. Informed consent was obtained from the patients and controls prior to the study. Ethical clearance was given by the Ethics Committee of Nawaloka Hospitals.

Collection of samples.  Blood samples were drawn into heparin-coated tubes simultaneously from the radial artery and jugular vein of each patient 10 min preoperatively and 0.2, 4, 12, 24, and 48 hr after surgery to assess the arterial and venous pattern of release of biomarkers. The 4 hr postoperative samples were taken when the patients arrived at the cardiac intensive care unit (CICU). Venous blood samples were collected from the controls (healthy subjects) into heparin-coated tubes.

The blood samples were immediately separated into aliquots and one of them was centrifuged at 3000 g for 5 min to separate the plasma. GPX, SOD and calcium assays were performed within 3 hr after blood collection. Plasma calcium (total and ionized) was analyzed on a Konelab 20 clinical chemistry analyzer (Thermo, Finland). Plasma lactate assays were performed immediately after collection using a Stat Profile pHOx analyzer (Nova Biomedical, USA). Erythrocytes (pre-washed with ice-cold isotonic NaCl) were assayed for glutathione peroxidase (GPX) and superoxide dismutase (SOD) using Randox kits (Randox Laboratories Ltd., UK) and the Konelab 20 analyzer.

Reference intervals for lactate, GPX, SOD, and calcium (total and ionized) levels in control subjects were determined using 95% confidence intervals (CI’s). Owing to the skewed distributions of erythrocyte GPX and SOD activities, logarithmic transformations of these data were performed in calculating the 95% CI’s. Statistical analyses were performed using SPSS software (version 12.0) and results were reported as mean ± SD. Comparisons of data were done by ANOVA and p ≤0.05 was considered significant.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
General characteristics and variables of patients undergoing the 3 surgical techniques are given in Table 1Go, Patients in the 3 groups did not show any significant differences for age, BMI, or LVEF.


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  		Table 1. General characteristics and variables (mean ± SD) of patients undergoing the three surgical procedures.
 
Changes in arterial lactate, GPX, SOD, total Ca and ionized Ca concentrations at successive time intervals in patients subjected to the OPCABG, CABG (on-pump), and SUP.CPB procedures are shown in Figs. 1Go to 5GoGoGoGo. No significant arteriovenous differences were observed for biomarker levels in patients in any of the 3 treatment groups.


Figure 1
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  		Fig. 1. Arterial plasma lactate concentrations in patients undergoing the OPCABG, On-pump, and SUP.CPB techniques. ** Significantly different at p <0.01.

 

Figure 2
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  		Fig. 2. Arterial glutathione peroxidase (GPX) activity in patients undergoing the OPCABG, On-pump, and SUP.CPB techniques. * Significantly different at p <0.05.

 

Figure 3
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  		Fig. 3. Arterial superoxide dismutase (SOD) activity in patients undergoing the OPCABG, On-pump, and SUP.CPB techniques. * Significantly different at p <0.05.

 

Figure 4
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  		Fig. 4. Arterial plasma total calcium concentrations in patients undergoing the OPCABG, On-pump, and SUP.CPB techniques. ** Significantly different at p <0.01.

 

Figure 5
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  		Fig. 5. Arterial plasma ionized calcium concentrations in patients undergoing the OPCABG, On-pump, and SUP. CPB techniques. * Significantly different at p <0.05.

 
The reference intervals determined in the healthy controls were as follows: plasma lactate, 1.2–2.0 mmol/L; plasma total calcium, 8.8–10.2 mg/dl; plasma ionized calcium, 1.17–1.29 mmol/L; erythrocyte GPX, 7.0–12.9 U/L; and erythrocyte SOD, 110–152 U/ml, respectively. No significant differences of biomarker levels were observed between the preoperative patients vs the controls.

Plasma lactate levels.  Compared to the preoperative levels, the mean values of arterial plasma lactate changed significantly (p <0.01) following the 3 surgical techniques with the greatest increase in patients with the CABG (on-pump) procedure. In patients undergoing the OPCABG (off-pump) and SUP.CPB techniques, plasma lactate levels were normalized (<2.0 mmol/L) within 48 hr after surgery when compared with those undergoing the CABG (on-pump) procedure (Fig. 1Go). The peak lactate value was observed 4 hr following reperfusion and the duration of hyperlactatemia was comparable to the pattern of release of antioxidant enzymes in the 3 surgical groups (Figs. 2Go and 3Go). However, patients undergoing the CABG (on-pump) technique remained hyperlactatemic (>2 mmol/L) even at 48 hr following surgery.

Erythrocyte glutathione peroxidase (GPX) and superoxide dismutase (SOD) activities.  At 4 hr after surgery, the GPX and SOD activities in patients undergoing CABG (on-pump) were significantly higher (p <0.05) than those in the OPCABG and SUP.CPB groups (Figs. 2Go and 3Go). No significant difference was found for postoperative activities of GPX and SOD in the OPCABG vs SUP.CPB groups. Although elevated activities of GPX and SOD were observed at 4 hr in all groups of patients following reperfusion, the activities returned to their baseline values at 48 hr.

Plasma total calcium and ionized calcium (Ca2+) levels.  Total and ionized calcium values in the patients subjected to the CABG (on-pump) technique showed significant increase (p <0.01 and p <0.05, respectively) at 4 hr following reperfusion compared to those undergoing the OPCABG and SUP.CPB procedures. However, the serum total and ionized calcium concentrations in all study groups returned to the respective baseline values at 48 hr after surgery (Figs. 4Go and 5Go).


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Off-pump surgery (OPCABG) has been shown to result in less organ-specific dysfunction than CABG (on-pump) surgery, and therefore, OPCABG is considered to have clinical advantages over the conventional on-pump technique [3,11]. In the CABG (on-pump) technique, a controlled cardiac arrest is induced using cardioplegia to minimize damage to myocytes by slowing ATP expenditure. Even though the myocytes are subjected to reduced temperature and an anti-contraction chemical environment, some hypoxia occurs, which leads to production and release of many biochemical metabolites [11,12].

Direct estimation of blood oxidant levels is difficult because of the short half-life of free radicals; however, oxidative stress can be estimated indirectly by measuring antioxidant levels in blood. There is substantial evidence that reperfusion results in the release of antioxidants in patients undergoing CABG (on-pump), due to overproduction of ROS [17]. Excess production of free radicals such as superoxide anions and hydroxyl radicals soon after CABG may be the result of increased GPX and SOD activities in patients. In the present study, the postoperative GPX and SOD values were less in the OPCABG and SUP.CPB groups compared to those in the CABG (on-pump) group, suggesting that the OPCABG and SUP.CPB surgical techniques cause less oxidative stress during surgery.

The GPX results in this study were consistent with other findings of postoperative release of GPX in patients following CABG (on-pump) surgery, suggesting that GPX plays an important role in ischemia-reperfusion injury [7,18]. This is thought to be a defense response to increased levels of cellular oxidation and to minimize oxidative damage during reperfusion [7,19,20].

Plasma lactate levels were measured as a means of evaluating tissue hypoxia. The cardioplegia used in CABG (on-pump) arrest induces anaerobic myocardial metabolism with a net production of lactate from glycolysis [13]. However, persistent lactate release during reperfusion suggests a delay in recovery of normal aerobic metabolism and inadequate post-operative myocardial function in patients undergoing CABG surgery [15]. Therefore, plasma lactate levels, while not specific for oxidative damage during reperfusion, may reflect the transition from anaerobic to aerobic myocardial metabolism [14]. A 100% survival rate was reported in patients whose serum lactate levels were normalized (<2 mmol/L) within 24 hr, while a low survival rate (14%) was reported in patients who took more than 48 hr to normalize the lactate level following multiple trauma [15]. Thus, the high lactate levels observed in patients subjected to the CABG (on-pump) technique is suggestive of a slow transition from anaerobic to aerobic myocardial metabolism following reperfusion, when compared with the OPCABG and SUP.CPB techniques.

Plasma ionized calcium plays a vital role in the regulation of vascular tone and cardiac rhythm. Excessive production of ROS disrupts the sarcolemma and more specifically, ATPase-Ca2+ transport activity, which subsequently disrupts Ca2+ homeostasis [10,21]. In the present study, the increased antioxidant enzyme activities suggest that production of ROS during CABG (on-pump) may have caused the increased serum ionized calcium levels.

In conclusion, the present study suggests that persistent release of lactate is attended by delayed recovery of aerobic myocardial metabolism, especially in patients undergoing the CABG (on-pump) technique when compared to those subjected to SUP.CBP or OPCABG. Hence, postoperative plasma lactate levels may be a clinically useful marker for delayed recovery of aerobic myocardial metabolism in patients undergoing CABG. Timely monitoring of postoperative lactate levels and correction of hyperlactatemia may facilitate rapid recovery of aerobic metabolism and reduce postoperative complications. Increased GPX levels in postoperative patients are suggestive of increased antioxidant activity against the oxidative damage incurred during reperfusion. Hence, postoperative GPX levels may be of value in assessing the oxidative stress induced during reperfusion. The present study suggests that the SUP.CBP technique using the Octopus tissue stabilizer is useful in the surgical armamentarium. The SUP.CBP technique using Octopus tissue stabilizer without aortic cross-clamping during surgery appears to equal the OPCABG technique with respect to the biochemical markers tested for reperfusion injury.


   Acknowledgments
 
This research was funded by Nawaloka Hospitals Sri Lanka Research Grant No: NH/R/2006/02. The authors thank: (i) the staff of the Division of Clinical Chemistry, Nawaloka Metropolis Clinical Laboratories for technical assistance; (ii) Prof. A. R. Wickramasinghe and Dr. Janani Pinidiyapathirage, Department of Public Health, University of Kelaniya, for assistance with data analysis; and (iii) the cardiothoracic surgeons, Dr. A. J. Jayakrishnan and Dr. Y. K. M. Lahie, for their invaluable contributions to this study.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Raja SG, Dreytus GD. Current status of off-pump coronary artery by-pass surgery. Asian Cardiovas Thorac Ann 2008;16:164–173.
  2. Singh SK, Mishra SK, Kumar D, Yadave RD, Sinha SK. Multivessel total revascularization via left thoracotomy. Asian Cardiovas Thorac Ann 2004;12:30–32.
  3. Khan NE, De Soyza P, Mister R, Flather M, Clague J, Davies S, Collins P, Wang D, Sigwart U. Pepper J. Randomized comparison of off-pump and on-pump multivessel coronary artery bypass surgery. NEJM 2004; 350:21–28.[Medline]
  4. Chowdhuri UK, Malik V, Yadav R, Seth S, Ramakrishnan L, Kalaivani N, Reddy SM, Subramaniam GK, Govindappa R, Kani M. Myocardial injury in coronary artery bypass grafting: on-pump versus off-pump comparison by measuring high-sensitive C-reactive protein, cardiac troponin I, heart-type fatty acid-binding protein, creatine kinase-MB and myoglobin release. J Thorac Cardiovas Surg 2008;135:1110–1119.[Abstract/Free Full Text]
  5. Raja, SG, Dreytus GD. Modulation of systemic inflammatory response after cardiac surgery. Asia Cardiovas Thorac Ann 2005;13:382–395.
  6. Raja SG, Berg GA. Impact of off-pump coronary artery bypass surgery on systemic inflammation. Current best available evidence. J Cadiac Surg 2007;22:445–455.
  7. Blankenberg S, Rupprecht HJ, Bickel C, Torzewski M, Hafner G, Tiret L, Smiega M, Combien F. Glutathione peroxidase 1 activity and cardiovascular events in patients with coronary artery disease. NEJM 2003; 349:1605–1613.[Medline]
  8. Wim BG, van Boven WJP, Boss DS, Haas FJ, van Dongen EP, Aarts LP. Malondialdehyde in plasma, a biomarker of global oxidative stress during mini-CABG compared to on-pump and off-pump CABG surgery: a pilot study. Interactive Cadiovas Thorac Surg 2006;5:27–31.
  9. Orhan G, Yapici N, Yuksel M, Sargin M, Senay S, Yalcin AS, Aykac Z, Aka SA. Effects of N-acetylcysteine on myocardial ischemia reperfusion injury in bypass surgery. Heart Vessels. 2006;21:42–44.[Medline]
  10. Verma S, Fedak PWMS, Weisel RD, Butany J, Rao V, Maitland A, Dhillon B, You TM. Fundamentals of reperfusion injury for the clinical cardiologist. Circulation 2002;105:2332–2345.[Free Full Text]
  11. Santosh S, Kumud G, Pawan K, Neela P. Myocardial cellular damage and antioxidant status in off-pump versus on-pump coronary artery bypass grafting–A prospective study. Vasc Dis Prevent 2005;2:267–271.
  12. Richard OC. Role of nitric oxide in cardiovascular disease: Focus on the endothelium. Clin Chem 1998;44:1809–1819.[Abstract/Free Full Text]
  13. Yurvati O, Blair JL, Naig M, Mallet RJ. Pyruvate-enhanced cardioprotection during surgery with cardiopulmonary bypass. J Cardiothorac Vasc Anesth 2003;17:715–720.[Medline]
  14. Rao V, Ivanov J, Weisel RD, Richard DW, Gideon C, Michael A, Weisal RD, Coren G, Borger MA, Mickle DAG. Lactate release during reperfusion predicts low cardiac output syndrome after coronary bypass surgery. Ann Thorac Surg 2001;71;1925–1930.[Abstract/Free Full Text]
  15. Abramson D, Scalea TM, Hitchcock R, Trooskin SZ, Henry SM, Greenspan J. Lactate clearance and survival following injury. J Trauma 1993;35:584–588.[Medline]
  16. Schnabel R, Blankenberg S. Oxidative stress in cardiovascular disease. Circulation 2007;116:1338–1340.[Free Full Text]
  17. Boven WJP, Gerritsen WB, Driessen AH, Morshuis WJ, Waanders FG, Haas FJ, Dengen EPV, Aarts LP. Myocardial oxidative stress and cell injury, comparing three different techniques for coronary artery by-pass grafting. J Cardio-Thorac Surgery 2008;34:969–975.
  18. Espinola-Klein C, Rupprecht HJ, Bickel C, Schnabel R, Genth-Zotz S, Torzewshi M, Lackner K, Munzel T, Blankenberg S. Glutathione peroxidase-1 activity, atherosclerosis burden, and cardiovascular prognosis. Amer J Cardiology 2007;99:808–812.
  19. Poling J, Rees W, Klans S, Bahlmann L, Hubner N, Hantovani V, Warnecke H. Myocardial metabolic monitoring with the microdialysis technique during and after open heart surgery. Acta Anaesth Scand 2007; 51:341–344.[Medline]
  20. Luyten CR, van Overveld FJ, De Backer LA, Sadowska AM, Rodrigus ZE, de Hert SG, de Backer WA. Antioxidant defence during cardiopulmonary bypass surgery. Eur J Cadiothorac Surg 2005;27:611–616.[Abstract/Free Full Text]
  21. Gross GJ, Kersten JR, Warltier DC. Mechanisms of postischaemic contractile dysfunction. Ann Throac Surg 1999;68:1898–1904.




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