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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 46  |  Issue : 3  |  Page : 163-171

Complete revascularization of patients with severe left ventricular dysfunction using mini extracorporeal circulation


1 Department of Cardiac Surgery, Saud Al-Babtin Cardiac Center(SBCC), Al-Dammam; Department of CardioThoracic Surgery, Tanta University Hospitals, Tanta, KSA
2 Department of Cardiac Surgery, Saud Al-Babtin Cardiac Center(SBCC), Al-Dammam, KSA

Date of Submission06-Feb-2018
Date of Acceptance26-Feb-2018
Date of Web Publication28-Feb-2019

Correspondence Address:
Ibrahim M Yassin
Department of Cardiothoracic Surgery, Facultyof Medicine, Tanta University, Tanta 31111
KSA
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DOI: 10.4103/tmj.tmj_7_18

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  Abstract 


Background and aim Mini extracorporeal circulation (MECC) when used as on-pump beating cardiac support during coronary artery bypass grafting can be a better alternative than the conventional cardiopulmonary bypass with aortic cross-clamping and cardioplegic arrest [(conventional cardiopulmonary bypass (cCPB)] in complete revascularization of patients with ejection fraction (EF) <30%.
Patients and methods A retrospective study was conducted on consecutive 50 patients with chronic stable severely impaired EF (< 30%) who underwent isolated coronary artery bypass grafting surgery using MECC from January 2011 to June 2016 (group I), and they were compared with another 50 matched patients randomized to similar group connected to cCPB from January 2009 to June 2014 (group II). Emergency, unstable, combined surgery and end-stage renal disease patients on dialysis are excluded.
Results There was no difference in CPB time, perioperative myocardial infarction (MI) or mortality between the two groups. Defibrillation was required in 10% in group I and in 82% in group II, with significantly lower cumulative energy of defibrillation (joules) (P<0.001). In group I, the requirement of inotropic support, incidence of atrial fibrillation (AF), the need for mechanical support, postoperative bleeding, the mean haematocrit value and the need for allogenic blood and products transfusion were significantly lower than in the group II (P<0.001), but the incidence of re-exploration was overall low (4% in group I) vs. 12% in group II), with a trend towards being significant (P=0.058). Postoperative creatine kinase MB isoenzyme and cardiac troponin I were significantly lower in group I (P<0.05) for 48 h. Lower postoperative creatinine (<0.01) was seen in group I. Duration of ventilation and length of ICU stay showed a trend towards being significant (P=0.053 and 0.057), but the total hospitalization time was significantly shorter in group I (P<0.05).
Conclusion On-pump beating heart revascularization of low EF patients using MECC is a safe procedure with better outcome than cCPB in low EF patients. It is followed by a diminished release of ischaemia markers, better early and smooth postoperative course and lower total hospitalization time than after cCPB, and both result in a satisfactory clinical outcome.

Keywords: coronary artery bypass grafting, mini extracorporeal, on-pump beating, ventricular dysfunction


How to cite this article:
Yassin IM, Oueida FM. Complete revascularization of patients with severe left ventricular dysfunction using mini extracorporeal circulation. Tanta Med J 2018;46:163-71

How to cite this URL:
Yassin IM, Oueida FM. Complete revascularization of patients with severe left ventricular dysfunction using mini extracorporeal circulation. Tanta Med J [serial online] 2018 [cited 2019 Mar 25];46:163-71. Available from: http://www.tdj.eg.net/text.asp?2018/46/3/163/253205




  Introduction Top


The number of patients with advanced left ventricular dysfunction who undergo coronary artery bypass grafting (CABG) is increasing with the advances in the interventional interference [1]. Although the recovery of the impaired myocardial function can occur in good percentage after CABG, contractile dysfunction remains a negative predictor of postoperative outcome [2]. It was also shown to be an independent predictor of operative mortality after CABG in this group of patients [3] and can also lead to the nightmare of the low cardiac output with different degrees of severity and its dramatic course, with the need for the inotropic or mechanical support for hours to days after surgery [4]. In the last decade, an improvement in surgical techniques and perioperative management has led to a better postoperative course and decreased postoperative mortality and morbidity rates in this group of patients [5],[6].

Complete revascularization of this group of patients without compromising its reserve is a crucial target for all cardiac surgeons, but this target mandates connecting the patient to the cardiopulmonary bypass for the safety of the patient. Over the past two decades, the concepts of miniaturized or minimal extracorporeal circulation were developed to reduce the adverse effects related to conventional extracorporal circulation (cCPB) leading to better perioperative outcome [7]. One of the major problems related to cCPB is haemodilution that deceases the oxygen carrying capacity which is not compensated owing to the loss of autoregulatory mechanisms leading to more end-organ hypoxia and damage. Shorting the length of the tube system in mini cardiopulmonary bypass systems together with low priming volume leads to better haematocrit value and avoidance of haemodilution [8]. This also reduces clotting factor consumption and complement activation that triggers the systemic inflammatory response owing to exposure to foreign surface [9]. Using the heparin-coated tubing systems also reduces systemic heparin requirements to half as well as provides more biocompatibility for blood components [7]. The Medtronic Resting Heart System (RHS) is a newly developed technology, consisting of a centrifugal pump, an oxygenator, and a heparin-coated, closed perfusion circuit. [10].


  Patients and methods Top


After the approval of ethics and research committee in our institution, Saud Al-Babtain Cardiac Centre (SBCC), KSA, a retrospective study was conducted on fifty consecutive patients with chronic stable elective severely impaired left ventricle [ejection fraction (EF) <30%] who underwent isolated CABG surgery from January 2011 to January 2016 using Resting Heart System machine, Resting Heart System (RHS; Medtronic Inc., Minneapolis, Minnesota, USA) (group I), and they were compared with another fifty matched randomized similar group connected to cCPB (group II) operated from January 2009 to January 2014 at our institution. Patient characteristics were similar in both groups. Emergency, unstable, combined surgery and end-stage renal disease patients on dialysis were excluded. The most interesting intraoperative details, early postoperative myocardial damage, the decrease of coagulation cascade, blood loss as well as in-hospital outcome were assessed. All cases were done by the same surgical team.

Surgical technique

In all patients studied, anaesthesia was induced with fentanyl (5–10 mcg/kg), propofol (2.0–2.5 mg/kg) and atracurium (0.5 mg/kg). Ventilation was controlled with oxygen in air (50%). Anaesthesia was maintained with continuous infusion of propofol (1–2 mg/kg/h), fentanyl (1–2 μg/kg/h) and atracurium 0.5 mg/kg/h. Each patient had a central venous catheter and  Swan-Ganz catheter More Details with invasive monitoring of blood pressure. All patients had median sternotomy. Single-stage venous cannula (size 32–34 F) was used to drain the venous blood from the right atrium. Tight atrial 3/0 Prolene purse is taken around the venous cannula in RHS patients as a special precaution to avoid air from entering circuit. Aorticpurse done by 4/0 Prolene along with a straight-tip arterial cannula. There was no difference regarding the surgical technique in both groups. The left internal thoracic artery was used in all patients.

Resting heart system (group I)

We used the Resting Heart System (RHS; Medtronic Inc., Minneapolis, Minnesota, USA) with CARMEDA AFFINITY NT oxygenator and a heparin-coated closed-loop (Carmeda BioActive Surface; Medtronic Inc.). The final priming volume of the circuit is 800–900 ml (excluding the tubing set and a filter, which is removed when the tubing set is connected to the arterial and venous cannula). The system is equipped with an active venous air detector and a removal device that detects and automatically removes venous air. In all RHS cases, we used the cell saver system (XTRA Auto Transfusion System; Sorin Group, Mirandola, Italy). After weaning, the shed blood during the operation was collected and washed in a cell saver together with the remaining blood from the RHS circuit and re-transfused to the patient. After induction and stabilization of the RHS, surgery was carried out without aortic cross clamp and cardiac arrest. Myocardial stabilization was performed with the help of the Octopus Evolution AS Tissue Stabilizer (Medtronic Inc.). Intracoronary shunts were used routinely while performing the distal anastomoses. Proximal anastomoses were constructed using tangential clamping of the ascending aorta while still being on-pump.

Conventional cardio-pulmonary bypass (group II)

A nonpulsatile roller pump (Stöckert S3, SORIN STOCKERT, Denova Medical, Inc., USA) consisting of an open system with a nonheparin-coated tube system is used. The system was primed with Ringer’s Lactate, and mannitol 20% (total 1.8–2 l). Heparin (4000 units) was added to the prime volume. Blood was saved and collected in an open cardiotomy reservoir and transfused back to the patient. PrimO2x oxygenator (Sorin Group Inc., Milan, Italy) was used. After induction and stabilization of the cCBP, and aortic cross clamp, cardioplegia was applied via the aortic root. They received Buckberg-solution cooled at 4°C by a separate heat exchanger for 4 min [11], usually prepared by combining autologous blood obtained from the extracorporeal circuit while the patient is on cardiopulmonary bypass (CPB) with the crystalloid solution. The ratio of blood to crystalloid varies among centers; we use the most common ratio being 4 : 1 (flow 200 ml/min and in hypertrophied hearts increase to 300 ml/min). As in the IAWBC-group, an additional second or third shot of cardioplegia was administered each 20–25 min for a duration of 2 min (flow 200 ml/min). The solution consists of citrate–phosphate–dextrose (CPD), trishydroxymethylaminomethane (tham) or bicarbonate (buffers), and potassium chloride. The CPD is used to lower the ionic calcium, the buffer is used to maintain an alkaline pH of ∼7.8, and the final concentration of potassium is used to arrest the heart (∼16 mmol/l). During CPB at a mild systemic hypothermia of 33–34°C, the flow was maintained at 2.5 l/min/m2 and the arterial pressure between 50 and 60 mmHg. Using solitary as well as sequential grafts, distal anastomoses were performed during a single aortic cross-clamp time. Proximal anastomoses were constructed within the reperfusion interval using tangential clamping of the ascending aorta. After complete weaning of the CPB, whether RHS or cCPB, protamine sulphate dose is given to neutralize the heparin.

Ischemia markers

Quality of myocardial protection was assessed by ischemia markers cardiac troponin I (cTNI) and creatine kinase MB isoenzyme (CK-MB). For evaluation of postoperative enzyme kinetics, patients experiencing a myocardial infarction within the perioperative course were excluded to avoid interferences with incidence and enzyme release.

Definitions and data collection

Mortality was considered as death within 30 days after surgery (even after discharge) or during the same hospital stay whatever the duration. A diagnosis of postoperative myocardial infarction was through the development of new Q-waves in two or more contiguous ECG leads, poor R-wave progression, new left bundle-branch block and unstable ventricular rhythm. Values of the myocardial-specific cTNI were considered significant when reaching a reading of more than 10 ng/ml at 24 h postoperatively [12]. Cardiac enzymes and ECG were evaluated after admission to ICU at 6, 12, 24 and 48 h.

Statistical analysis

Values of continuous variables were expressed as mean±SD. Values of P less than 0.05 were considered significant. Statistical analyses were performed with computerized statistical packages (SPSS 18.0 software; SPSS Inc., Chicago, Illinois, USA).


  Results Top


Preoperative parameters and demographic data were comparable in both groups ([Table 1]).
Table 1 Preoperative and demographic parameters

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Operative analysis

CPB time was similar in both groups (P=0.44). There was no significant difference regarding the number of distal anastomoses (3.1±0.80 vs 3.2±1.05) or left anterior descending end-arterectomy (8 vs. 6%). Defibrillation was required in five (10%) patients in group I and in 41 (82%) patients in group II, with significantly lower cumulative energy of defibrillation (joules) (P<0.001).

In group I, the requirement of inotropic support and incidence of atrial fibrillation was significantly lower than in the group II (P<0.001). The need for mechanical support was significantly less in group I: intra-aortic balloon pump (IABP) (14 vs. 34%) and extra-corporeal membrane oxygenator (ECMO) (2 vs. 2%).

Lower postoperative creatinine in group I was also noted (98.2±58.0 vs. 149.1±85.25) (P<0.01).

The mean haematocrit value and the need for allogenic blood and products transfusion were significantly less in group I (P<0.001). The average total amount of postoperative bleeding was significantly less in group I (P<0.001), but the incidence of reoperations owing to bleeding was overall low, RHS 4% (n=2) versus cCPB 12% (n=6), with a trend towards significant difference between the two groups (P=0.058).

PT and PTT were significantly less in group I (P<0.001) (98.2±58.0 vs. 149.1±85.25 and 37.52±4.57 vs. 48.19±5.09).

Duration of ventilation and length of stay in the intensive care unit were statistically NS, though a trend towards being significant between the two groups (P=0.053 and 0.057)([Table 2]), but the total hospitalization time was significantly shorter in group 1 (P<0.05) ([Table 3]).
Table 2 Intra-operative data

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Table 3 Clinical outcome

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There was no difference in incidence of perioperative myocardial infarction between the two groups (NS).

Total length of stay (LOS) in the hospital (days) was significantly lower in group I (RHS) (P<0.05). There were no significant differences (NS) regarding major complications, mediastinitis (2 vs. 4%) and stroke (4 vs. 6%).

Echocardiographic (TTE) measurements on discharge including EF and Segmental Wall Motion Scoring Index (SWMSI) showed no significant difference between the two groups. There was no significant difference (NS) in mortality between the two groups (2 vs. 4%).

Postoperative ischaemia markers, creatine kinase isoenzyme MB (CK-MB) and cTnI, were significantly lower in group 1 (P<0.05) for 6, 12, 24 h postoperatively, and this difference declines till becoming NS after 48 h. There was no significant difference in the total creatinine phospho kinase (TCPK) all through the measurements ([Table 4] and [Figure 1], [Figure 2]).
Table 4 Myocardial markers

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Figure 1 Creatine kinase MB isoenzyme difference in the mean value between the two groups at 6, 12, 24 and 48 h postoperatively.

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Figure 2 Cardiac troponin I difference in the mean value between the two groups at 6, 12, 24, and 48 h postoperatively.

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Postoperative WBC count was lower in group I (P<0.05) for 6, 12, 24 h postoperatively, and this difference declines steadily with time but was statistically nonsignificant (NS) ([Table 5], [Figure 3]).
Table 5 White blood cells count difference in the mean value between the two groups at 6, 12, 24, and 48 postoperatively

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Figure 3 White blood cells count difference in the mean value between the two groups at 6, 12, 24, and 48 h postoperatively.

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  Discussion Top


The conventional well-known CPB is still the cornerstone of the cardiac surgery in general and also in CABG surgery. It is a safe, well-known and established technique with a low risk and mortality rate [13],[14]. The feasibility to most cardiac surgeons and good exposure of the target vessels allow for complete re-vascularization, which is a crucial point especially in patients with severely impaired LV function.

However, the morbidity owing to CPB is still significant [15],[16],[17]. Besides neurological events, which may at least be partially related to the use of CPB, and the uncompensated haemodilution owing to loss of autoregulatory mechanisms leading to more end-organ hypoxia and damage [8], as well as clotting factor consumption and complement activation which triggers the systemic inflammatory response owing to exposure to foreign surface [9], the ideal myocardial protection is still a matter of debate during CPB. For these reasons, CABG on the beating heart (OPCAB) has been accepted and become an alternative to CABG with conventional CPB because all potential complications related to CPB may be eliminated. Nevertheless, despite some advantages, off-pump myocardial revascularization is considered controversial mainly owing to the less optimal operative field, which may result in incomplete or unsatisfactory procedures [18], which is highly critical in patients with severely impaired LV function.

Technical refinements of CPB-circuits may partly counterbalance the negative aspects of CPB. Mini-ECC system, a minimalization of the CPB system, has the potential to reduce blood transfusion requirements and blood–air interactions. This system was developed and introduced successfully in clinical routine by the group of Regensburg [19]. The circuit has a reduced tubing length because the cardiotomy reservoir and the conventional suction device have been eliminated. The decrease in priming volume from 1800 to 600 ml helps to reduce the negative effects. The advantage of these minicircuits was shown in many studies [9],[20],[21]. The Medtronic Heart System is one of these newly developed minicircuits with initial good outcomes [22].

The idea of coronary revascularization using on-pump beating heart surgery was developed since long time in high-risk patients, such as those with severely impaired LV with good results [23], and we agree with the possibility of using this system to support the heart and performing the surgical procedure, as an on-pump beating can allow us to get the benefit of the good exposure and complete revascularization, maintaining good haemodynamics during revascularization of the severely impaired LV function patients, as well as avoiding the undesirable effects of the cCPB and the cardioplegic arrest. [24]. So, we started our experience with these mini-ECC systems during the last five years in our centre, SBCC, in high-risk patients, and nowadays, we consider it as an indication for revascularization of patients with severely impaired LV.

cTnI is well known nowadays to be a very sensitive and specific marker of myocardial damage during open heart surgery [25],[26],[27]. Moreover, cTnI is used as a prognostic marker, and high cTnI-values were shown to be associated with a worse mid-term outcome [27]. OPCAB significantly reduces postoperative cTnI levels in comparison with coronary revascularization using cardioplegic arrest [28],[29].

In our study, postoperative ischaemia markers, creatine kinase isoenzyme MB (CK-MB) and cTnI were significantly lower in group 1 (P<0.05) for 6, 12, 24 h postoperatively, and this difference declines till it becomes NS after 48 h. These values in the mini-ECC group are on the level recently reported by Alwan et al. [28] in patients who underwent beating heart surgery.

The necessity of defibrillation and the cumulative energy of defibrillation was significantly less in group 1 (RHS) (10 vs. 42% and 5.4±10.8 vs. 11.8±20.6) (P<0.001).

Our results may not be influenced by the higher rate of perioperative defibrillation to restore sinus rhythm in patients operated with CPB, as only minor or even no cTnI elevations have been reported after defibrillation by others [30],[31].

To our mind, just avoiding of the cardioplegic arrest, reperfusion injury, electrolyte disturbances and minimizing the incidence of air bubbles in the coronaries and other precipitating factors to ventricular fibrillation necessitating defibrillation to restore the sinus rhythm are a major advantage. Moreover, the low cumulative energy needed in group I mainly to convert the heart from atrial fibrillation to sinus rhythm and not from ventricular fibrillation as in group II is another major advantage. Both contribute to smooth, short ICU and subsequent total hospital stay.

In group I, the incidence of atrial fibrillation and the requirement of inotropic support was significantly lower than in the group II (P<0.001). This might be owing to a decrease in the usual volume shift observed in patients undergoing CPB and may be one aspect for the significant reduction in the length of stay observed in group I.

The need for mechanical support was significantly less in group 1, i.e., IABP (14 vs. 34%) and ECMO (2 vs. 2%), denoting good operative cardiac protection.

The hazards of blood transfusion [32] are known in general and were mentioned particularly in the field of coronary surgery to reduce the long-term survival [32],[33]. The mean haematocrit value and the need for allogenic blood and products transfusion were significantly less in group 1 (P<0.001). The average total amount of postoperative bleeding was significantly less in group I (P<0.001). Overall requirement of blood transfusion was in favor of group I; transfusions in the CPB group were mainly performed during CPB because of the priming volume related to intra-operative hemodilution and partially in the postoperative period owing to more blood loss in group II.

Blood–air interaction is practically completely eliminated with the mini-CPB smart system. The venous reservoir is removed, the modified optoelectrical suction system prevents any air–blood contact, and no vent is required on the ascending aorta. These factors contribute to less derangement of the whole coagulation cascade system [34]. In our study, PT and PTT were significantly less in group 1 (P<0.001) (98.2±58.0 vs. 149.1±85.25 and 37.52±4.57 vs. 48.19±5.09).

There was no difference in the incidence of perioperative myocardial infarction between the two groups (NS). Duration of ventilation and length of stay in the intensive care unit were statistically NS, though a trend towards being significant between the two groups (P=0.053 and 0.057) ([Table 2]), but the total hospitalization time was significantly shorter in group 1 (P<0.05) ([Table 3]).

Fortunately, the incidence of reoperations owing to bleeding was overall low, RHS 4% (n=2) vs. cCPB 12% (n=6), with a trend towards significant difference between the two groups (P=0.058), but these results may be changed if the study is on larger population of study. Subsequent increase in the duration of ventilation and ICU stay can be a usual anticipation. The incidence of some other major complications may also be changed rather than in our current study which was of no statistically significant difference (2 vs. 4%).

In our study, lower postoperative creatinine in group I was also noted (98.2±58.0 vs. 149.1±85.25) (P<0.01). The association between the low haematocrit during conventional CPB besides the other deleterious effects of the variability of the haemodynamic status and the mediators of the systemic inflammatory response was mentioned in other studies [8]. In our opinion, more selective studies on larger population regarding the effects of the mini-CPB systems on the renal function are still needed.

In our opinion, mini-ECC is technically less demanding for the surgeon as well as the anaesthesist than OPCAB surgery and allows to maintain peripheral (cerebral) safe perfusion in contrast to a certain risk in off-pump procedures. This impression is through our large experience with OPCAB, and in accordance with our anaesthesia team, as we started OPCAB in our centre, SBCC, 10 years ago. The brain oximetry is being used routinely in all of our cases. The overall incidence of stroke in our two groups was low (two patients in group I and three patients in group II), and mini-CPB could effectively maintain the haemodynamics of the patients all through the procedure. These strokes are mostly related to the preoperative bilateral carotid extensive atherosclerosis, which was even expected from the readings of the brain oximetry in contrast with the maintained mean arterial blood pressure over the entire operation. The effect of these minimized CPB was also shown in other studies [35]. The small series of our study, involving both the groups, and the low euro-score of both and our routine preoperative routine carotid endarterectomy for significant bilateral carotid stenosis patients are the main clear limitations to show the difference in the outcome neurologically.In our study, postoperative WBC count was lower in group I for 6, 12, 24 h postoperatively, and this difference declines steadily with time but was statistically nonsignificant (NS) ([Table 5], [Figure 3]). This is mostly related to the decrease in the systemic inflammatory response in group I (RHS) [8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24],[25],[26],[27],[28],[29],[30],[31],[32],[33],[34],[35],[36],[37]. Evaluation of the systemic inflammatory response was not shown significantly in the study as it did not include the factors and cytokines related to this issue, which is considered another limitation of this study.

The number of distal anastomoses, in our study, is not reduced (3.1±0.80 group I vs. 3.2±1.05 group II) owing to technical limitations, when revascularization areas are difficult to expose owing to hemodynamic instability, and complete revascularization was achieved in almost 100% of cases in both groups even those who required end-arterectomy to the left anterior descending [four (8%) patients in group 1 vs. three (6%) patients in group II]. So, there was no significant difference in CPB time in both groups (NS). Distal as well as proximal anastomoses were done during being on CPB in both groups. However, in RHS (group I) the heart is not completely unloaded during the procedure, and the persistent coronary flow is managed by the routine use of intracoronary shunt during the distal anastomoses. The time difference owing to this little difficulty in performing the distal anastomoses is compensated by the time taken to give the cardioplegia. This was for the purpose of the study, but in our opinion, revascularization of the entire anterior wall can be done when using RHS, before going on CPB. This will definitely make the CPB time much shorter and the benefit much more or even doubled than in our study.


  Conclusion Top


RHS when used in on-pump beating heart revascularization of low EF patients is a safe procedure and is followed by a diminished release of CK-MB and cTnI, less incidence of postoperative atrial fibrillation, bleeding, re-exploration and magnitude of allogenic blood and products transfusion, better early and smooth postoperative course and total hospitalization time than after cCPB, and both result in a satisfactory clinical outcome.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

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