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Interact CardioVasc Thorac Surg 2009;9:832-836. doi:10.1510/icvts.2009.206466 © 2009 European Association of Cardio-Thoracic Surgery
Minimal extracorporeal circulation and off-pump compared to conventional cardiopulmonary bypass in coronary surgery
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| Abstract |
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Key Words: Coronary artery disease; Minimal extracorporeal circulation; Off-pump coronary artery bypass; Conventional cardiopulmonary bypass; Coronary artery bypass grafting
| 1. Introduction |
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Momentary benefits and advantages of OPCAB and CCPB are under discussion.
Recent studies show or suggest inferior patency rates and incompleteness of revascularization in OPCAB [1, 4, 5], whereas CCPB is being questioned with regard to longer hospital stay, the use of blood and blood products and the occurrence of systemic inflammatory reactions and its associated occurrence of neurocognitive disorders [6–9].
Therefore, in this study, we evaluated the results of our center comparing MECC, CCPB and OPCAB regarding completeness of revascularization, the occurrence of arrhythmia, defined as atrial fibrillation or atrial flutter and the use of blood and blood products. Packed cells (red blood cells) were given only when the hematocrit levels were <26% (0.26 mg/dl). Fresh frozen plasma was applicated when the INR (International Normalized Ratio) was bigger than 2.0. Platelets were only given then when platelets level was <90 Gpt/l after the patient was weaned from ECC.
| 2. Material and methods |
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Total surface of the MECC system was ~3 m2 compared to 13 m2 in CCPB. These 13 m2 is the calculated surface of the lines including the surfaces of the filters and deforming agents.
All patients were recorded prospectively. Prior to the operations Aspirin and Plavix was stopped at least seven days in advance of surgery in all groups. Therefore, there was no indication to give plasma, coagulation factors or platelets as prophylaxis at the end of the operation. Mean body surface area of the patients in the MECC group was 1.95 (±0.19) compared to 2.00 (±0.20) in the CCPB group and 2.02 (±0.24) in the OPCAB group. Mean preoperative hemoglobin levels were, respectively, 9.6 mmol/l in the MECC group, 9.8 mmol/l in the CCPB group and 9.7 mmol/l in the OPCAB group. All patients were operated using the left internal mammary artery (LIMA) in combination with vein grafts.
All patients were operated on by the same team of four experienced surgeons and five perfusionists.
Perioperative morbidity, hospital stay, the use of blood and blood products, the occurrence neurocognitive disorders, the occurrence of postoperative arrhythmia (atrial fibrillation or -flutter) and the completeness of revascularization was assessed up to December 2007 by studying the medical dossiers of our population after patients provided informed consent.
During the period from 2004 to 2007, no major changes were made in the surgery and anesthesiology protocols.All patients received a median sternotomy. Parallel to harvesting the LIMA, one, two or three vein grafts were being harvested. The vena saphena magna was being used in all patients. The venectomy wounds were closed prior to the arterial and venous cannulation in case of MECC or CCPB.
Antegrade multidose normothermic bloodcardioplegia was given through the aortic root. Cell Saver® was being used as suction device in OPCAB and MECC. In CCPB, conventional cardiotomy suction was used. Cell Saver® was not used in the intensive care unit (ICU) for retransfusion of shed blood.
After connection of CPB using MECC and after cardiac arrest was obtained, bypass grafting was performed similarly to CCPB. After release of the cross-clamp, and after the proximal anastomoses were performed and the patient was in a hemodynamic stable situation with a stable rhythm, flow was reduced and the patients were disconnected from CPB.
In case of OPCAB surgery the heart was stabilized by a Medtronic® stabilizer after one or multiple pericardial deep stitch(-es) was/were placed to luxate the heart. When the heart was luxated the patients were positioned with their head lower than the legs (Trendelenburg). During OPCAB surgery, a heart–lung machine was available/stand by in case of emergency conversion to CPB.
All three techniques MECC, CCPB and OPCAB require training and they have a learning curve to perform these techniques safely and routinely.
All operations were being performed by the same team of experienced surgeons who were trained to use all three techniques on a routine base.
Although MECC is a new technique and many end points can be studied in this study we focussed on the completeness of revascularization, the occurrence of arrhythmia, neurocognitive disorders and the use of blood and blood products in the perioperative period (defined as the first 30 days after surgery).Completeness of revascularization was defined as three or more distal anastomoses with at least one or more grafts/distal anastomoses on at least one major branch of each, significant stenosed, coronary artery.
Arrhythmia was defined as the occurrence of atrial fibrillation or atrial flutter within 30 days after surgery.
Neurocognitive disorders were defined through a neurological test MMSE (Mini Mental State Examination according to Folstein) taken preoperatively and on the 2nd postoperative day and the 7th postoperative day. This test was taken in a quiet surrounding by the physician. Especially on the 2nd day the test was taken after release from the ICU. If patients were still on the ICU on day 2 the test was taken at a moment when the patient was alone in the room in the intensive care.
The use of blood and blood products was measured by the necessity to acquire packed cells, plasma or platelets postoperatively defined as mean transfusions per patient.
2.3. Follow-up and postoperative controlling
From the moment of admission in our hospital until the 30th postoperative day, details of the course of each patient were monitored prospectively.Preoperatively and postoperatively a stroke scale was documented for each patient to observe postoperative neurocognitive disorders. Furthermore, the occurrence of atrial fibrillation/-flutter, the use of blood and blood products per patient and completeness of revascularization were documented specifically for each patient.
Follow-up was completed for ~99% of the population.
All data were included prospectively and were processed using Excel.
Continuous variables were expressed as mean±S.D. Categorical variables were expressed as percentages. The two-tailed unpaired t-test for continuous variables and
2-test for discrete variables were used for group comparisons. Non-normally distributed data were expressed as median with range.
The authors had full access to and took full responsibility for the integrity of the data.
All authors have read and agree to the manuscript as written.
| 3. Results |
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Perioperative mortality was equal in all three groups: 1.8% in the MECC group, 2.3% in the CCPB group and 1.7% in the OPCAB group.
The mean number of distal anastomoses was 3.2±0.6 in the MECC group, 3.4±0.7 in the CCPB group and 1.9±0.8 in the OPCAB group (P=0.01). Completeness of revascularization was achieved in both the MECC group and the CCPB group.
Postoperative arrhythmia (atrial fibrillation/-flutter) occurred in 25% of the MECC group and in 35.6% of the CCPB group (P=0.05). Arrhythmia occurred in 21.7% of the OPCAB group (Fig. 2). Neurocognitive disorders were found in seven patients of the MECC group (3%), in 74 patients of the CCPB group (7%) and in three patients of the OPCAB group (3%) (Fig. 3).
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| 4. Discussion |
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The MECC concept is based on previous research on the heparin-coated circuit with a reduction of the systemic heparin dose, a reduction of the total surface area from 13 m2 to 3 m2 of the circuit, a reduction of priming volume from 1500 ml to ~700 ml and avoidance of cardiotomy suction in order to get less activation of platelets and granulocytes. These developments of the heart–lung machine technology are resulting in a reduction of the necessity to use blood and blood products perioperatively [8, 9, 11, 12]. Furthermore, MECC has been associated with rapid postoperative mobilization of the patients after cardiac surgery [1, 8, 13, 14], a superior global organ protection [15–17] and reduction of the need to use blood and blood products in comparison with CCPB. Furthermore, MECC is safe and feasible and offers complete extracorporeal perfusion without increased perioperative morbidity [18, 12]. MECCs' perioperative morbidity rates is equal to that of the established technique of OPCAB.
Some authors have discussed whether there are benefits in cognitive and cardiac outcome if CCPB is avoided [2].
Complete revascularization, however, might not be achieved using the OPCAB technique in all patients due to hemodynamic instability and due to the complex anatomy of coronary lesions. Taken together, the evidence suggests that OPCAB and MECC should be considered equivalent tools with respect to reduction of postoperative morbidity. Although these conclusions are provisional and warrant further investigation, MECC may be used in patients with complex anatomy of coronary lesions, hemodynamic instability in which situations OPCAB is considered technically unreasonable/unsuitable.
Although there is no clinical evidence at the moment with regard to major adverse cardiac events (MACE) that there is a statistically significant benefit from MECC over OPCAB at 1-year follow-up [1], larger sample sizes need to be studied to give a definite answer on this specific issue.
Another topic which needs to be discussed is the matter of graft patency in OPCAB surgery. Recent studies underscore OPCAB [4] in comparison to on-pump surgery. OPCAB is said to have significantly increased graft occlusion rates, particularly those of venous grafts [4]. Furthermore, OPCAB is said to provide a lower revascularization rate and, therefore, incomplete revascularization [5, 19].
CABG with MECC has shown in recent studies to be associated with a lower perfusion defect rate and graft occlusion rate [1].
Furthermore, MECC reduces the systemic inflammatory reaction providing a better organ protection which is associated with the closed system and reduction of blood–air contact and the reduction of the total length of the circuit which is associated with blood cell activation. Schöttler and colleagues investigated a group of 60 patients who had coronary artery disease (CAD) and underwent CABG surgery. Thirty of them were operated using the MECC technique and 30 of them were operated using CCPB. They found no statistically significant benefit in clinical or laboratory outcome between the two groups. If we take a closer look at this study we recognize that 60% of the MECC patients receive blood or blood products for example compared to 76% of the CCPB group. To get statistically significant results these cohorts were simply too small for the questions they tried to answer [20]. Bigger groups and perhaps a subgroup analysis of risk groups will show evidence of the benefits of MECC like in our population.
In this study, we found that perioperative morbidity rates as well as the perioperative mortality rates for all three groups were equal.
The mean number of distal anastomoses was significantly higher in the MECC and CCPB groups in comparison to the OPCAB group. However, ~60% of the patients of the OPCAB group had two- or three-vessel disease (53.4% with two-vessel disease and 6.4% with three-vessel disease) compared to 91.3% in the CCPB and 89.7% in the MECC group. Therefore, severe patient selection was avoided so that this suggested bias of patient selection did not influence our results.
Furthermore, we found a significant difference in the occurrence of postoperative arrhythmia between the CCPB group on one side in comparison to MECC and OPCAB. From the MECC and OPCAB groups, respectively, 80% and 83.3% of the patients could be released to the ward within one day after surgery whereas this was the case in only 65.6% of the CCPB patients. We found a significant difference in occurrence of neurocognitive disorders between the MECC and OPCAB group on one side compared to CCPB. The perioperative use of blood and blood products was slightly less in the OPCAB group but was almost equal compared to that of the MECC group. Patients of the CCPB group received significantly more blood and blood products perioperatively.
Although the intraoperative use of blood and blood products was less in the OPCAB group, the benefits of longer patency rates and completeness of revascularization favor MECC over OPCAB in our hands.
Overall MECC, using cardioplegic arrest, appears to be an equal or even superior strategy in modern coronary surgery in comparison to OPCAB and CCPB, because it is associated with a reduction of peri- and postoperative morbidity.
MECC offers a surgical setting in which completeness of revascularization is warranted and high-risk patients can be operated upon relatively safely. Branches of the obtuse margin vessels can be reached and operated upon without the risk of hemodynamic instability as often is seen in OPCAB surgery. Further investigations have to be done to draw a definite conclusion.
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