Eur J Cardiothorac Surg 1998;14:S7-S12
© 1998 Elsevier Science NL
Single coronary artery bypass grafting – a comparison between minimally invasive 'off pump' techniques and conventional procedures
Johannes Bonattia,*,
Ruth Ladurnera,
Herwig Antrettera,
Christoph Hörmannb,
Guy Friedrichc,
Nico Moesc,
Volker Mühlbergerc,
Otto Dapunta
a University Clinic of Surgery/Cardiac Surgery, Anichstrasse 35, A-6020 Innsbruck, Austria
b University Clinic of Anesthesiology and Intensive Care Medicine, Anichstrasse 35, A-6020 Innsbruck, Austria
c University Clinic of Internal Medicine/Department of Cardiology, Anichstrasse 35, A-6020 Innsbruck, Austria
* Corresponding author. Tel.: +43 512 5042529; fax: +43 512 5042528; e-mail: johannes.o.bonatti@uibk.ac.at
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Abstract
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Objective: At present, few studies directly comparing minimally invasive and conventional coronary artery bypass grafting are available. The aim of the present study was to evaluate the clinical outcome of the two techniques. Methods: We retrospectively compared our first consecutive 20 patients undergoing minimally invasive coronary artery single bypass grafting on the beating heart (group I) with 23 consecutive patients receiving single coronary artery bypass via sternotomy using cardiopulmonary bypass and cardioplegia (group II). The procedures were performed during the period from Jan 1, 1994 to Feb 20, 1997. There were no significant differences in demographic data. Results: Statistically significant differences were found concerning total operative time (172.6 min in group I and 149.6 min in group II P=0.0009) and myocardial ischemic time (23.7 min local coronary occlusion time in group I and 17.6 min aortic cross-clamp time in group II P=0.03. Patients treated minimally invasive received significantly fewer blood transfusions (25.0% vs. 69.6% P=0.0035) and were discharged significantly earlier from the hospital (admission rate on the fifth postoperative day 68.4% in group I vs. 100.0% in group II P=0.0004). Conclusion: We conclude that minimally invasive coronary artery bypass grafting on the beating heart in comparison to conventional single coronary artery bypass grafting during the learning curve requires longer operative times but can reduce blood transfusion requirements and hospital stay.
Key Words: Coronary artery bypass grafting • Minimally invasive • Conventional • Results
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1. Introduction
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Minimally invasive coronary artery bypass grafting (CABG) after its introduction in 1994 [5]seems to gain wide spread acceptance although proof of its superiority versus conventional techniques is still lacking Few studies in the literature directly compare minimally invasive techniques with standard CABG and so far advantages of the former have been found concerning reduction of blood transfusion requirements, intubation time, hospital length of stay and reduction of cost [9, 11]The aim of the present study was a direct retrospective comparison of single coronary artery revascularizations performed off pump via left anterior minithoracotomy on the beating heart (minimally invasive direct coronary artery bypass, MIDCAB) with single CABG carried out via sternotomy using cardiopulmonary bypass (CPB) and cardioplegia.
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2. Methods
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From Jan 1, 1994 to Feb 20, 1997, 43 patients received single bypass grafting at our institution Demographic data of patients in both groups as well as procedure related data are listed in Table 1
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2.1 Operative technique
In 20 patients (group I) the procedure was carried out via a left anterior fourth or fifth interspace minithoracotomy. The internal mammary artery (IMA) was harvested via the mini-incision under direct vision. A new retraction device (IMA retractorTM, Cardio Thoracic Systems, Cupertino, CA) was used for this purpose in 8 cases. The IMA was harvested at least up to the cranial border of the second rib. All grafts were topically treated with diluted papaverine. After opening the pericardium the target vessel was inspected and then encircled proximally and distally to the planned anastomotic site with 3/0 Prolene sutures. Lateral 3/0 Prolene stabilizing sutures or the StabilizerTM device (Cardio Thoracic Systems, Cupertino, CA) were applied for mechanical immobilization of the heart. Using felt pledgets or pieces of silicone tube for protection of the anterior vessel wall the target vessel was snared for 5 min of ischemic preconditioning. After 5 min of reperfusion the coronary artery was opened longitudinally and an end to side anastomosis with the bypass graft was performed. A 7/0 Prolene running suture was taken to accomplish this. During the anastomosis the short acting ß-blocker Esmolol (500 µg/kg i.v. (bolus) followed by 100–300 µg/kg per min) was given in order to reduce heart rate and myocardial contractility. Hemostasis was checked and a chest tube was inserted. The minithoracotomy was then closed in layers. The procedure was performed by three different surgeons. Two patients who after initiation of a MIDCAB procedure were converted intraoperatively to CABG on pump using CPB and cardioplegia were excluded from the comparative study.
Twenty-three patients described as group II received single coronary artery bypass grafting via median sternotomy. The majority of patients (n=20) in this group was operated before the start of our minimally invasive CABG program. Three patients received conventional operations thereafter because of contraindications for a minimally invasive procedure. After conventional take down of the IMA in a pedicle or harvesting of a piece of saphenous vein from the distal leg the pericardium was opened and the aorta and right atrium were cannulated for installation of cardiopulmonary bypass. In moderate hypothermia of 32°C ventricular fibrillation was induced and the target vessel was prepared for anastomosis. After aortic cross-clamping cold crystalloid cardioplegia (1000 ml of St. Thomas solution) was infused in an antegrade fashion via the ascending aorta. The target vessel was incised longitudinally and an end to side anastomosis with the bypass graft was performed using a 7/0 Prolene running suture. The aortic cross-clamp was then released. For central anastomosis of the vein grafts the ascending aorta was partially occluded. Cardiopulmonary bypass was discontinued and after insertion of a pericardial and mediastinal drain the sternotomy was closed in layers. The procedure was performed by six different surgeons. Three of them also operated on the patients in the minimally invasive group.
2.2 Statistical analysis
Data were obtained retrospectively from hospital records and entered into a computerized data base (dBASE for WindowsTM). They were then analyzed statistically using the SPSS for WindowsTM statistical software package. For comparison of categorical variables, the 
2-test or Fisher's exact test were applied as appropriate. Continuous variables were compared using the Mann–Whitney U-test, postoperative intubation rates and hospital admission rates were assessed by life table analysis and compared by the Wilcoxon (Gehan) test A P-value of less than 0.05 was regarded as significant.
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3. Results
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The total operative time (skin to skin) was 172.6 min in group I and 149.6 min in group II (P=0.0009). Myocardial ischemic time (local coronary occlusion time in group I and aortic cross-clamp time in group II) was 23.7 and 17.6 min, respectively (P=0.03). One patient in each group received inotropic support intraoperatively (P=NS).
No patient in group I required blood transfusions intraoperatively whereas 11 patients (47.8%) in group II were transfused during the procedure (P=0.0003). In group I hemoglobin levels fell from 14.2 g/l preoperatively to 10.9 g/l in the intensive care unit and in group II hemoglobin levels fell from 13.7 g/l preoperatively to 9.6 g/l in the intensive care unit (P=0.007). Further postoperative results are listed in Table 2
. A significantly lower blood transfusion rate could be seen in group II and a trend towards fewer arrhythmias and low output syndromes was noted in the minimally invasive patients.
As shown in Fig. 1
body temperature postoperatively fell to a mean of 36.1°C in the minimally invasive group. The corresponding temperature in the conventional group was 35.3°C (P=0.0046). In both groups a rise of body temperature to febrile values was noted thereafter with a return to normal on the fourth postoperative day.
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Fig. 1. Body temperature fell to a mean of 36.1°C in group I and to 35.3°C in group II. It then rose to the 37–38°C level in both groups. A slow decrease was then noted. PREOP, preoperatively; POSTOP, postoperatively; ICU, intensive care unit; POD, postoperative day. *P<0.05 minimally invasive vs. conventional.
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As shown in Fig. 2
, the maximum heart rate rose to a mean of 106.0 beats/min (bpm) in group I and to 101.7 bpm in group II on the first postoperative day. It then came down to 82.6 bpm and 92.5 bpm, respectively, on the fourth postoperative day. Heart rate was significantly lower in minimally invasive patients from the second to fourth postoperative day.
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Fig. 2. Maximum heart rate showed a rise to above 100 beats/min (bpm) in both groups during the intensive care unit (ICU) stay. Thereafter a slow decrease was observed with a significantly earlier return to normal values in the MIDCAB group. PREOP, preoperatively; ICU, intensive care unit; POD, postoperative day. *P<0.05 minimally invasive vs. conventional.
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Although there was a significant difference in leukocyte count preoperatively, values were with normal limits in both groups. Leukocytes postoperatively rose to pathological levels in each group (13661.1 vs. 12430.4 g/l, P=NS) with normalization on the third postoperative day (Fig. 3
).
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Fig. 3. Leukocytes showed a rise to pathological levels in both groups with normalization on the fourth postoperative day. PREOP, preoperatively; ICU, intensive care unit; POD, postoperative day. *P<0.05 minimally invasive vs. conventional.
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Platelet count was within normal levels preoperatively in both groups but a significant difference was noted. Platelets fell significantly less in the MlDCAB group and reached normal levels earlier than in the conventional CABG group (platelet count 231 882 vs. 110 409 g/l in the intensive care unit P<0.0001) (Fig. 4
)
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Fig. 4. Platelets fell significantly less in the MIDCAB group and reached normal levels earlier than in the conventional CABG group. PREOP, preoperatively; ICU, intensive care unit; POD, postoperative day. *P<0.05 minimally invasive vs. conventional.
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As shown in Fig. 5
significantly higher postoperative serum creatine kinase (CK) levels in the minimally invasive group could be determined. On postoperative day number two the CK level was 235.8 U/l in group I and 128 9 U/l in group II (P=0.0123). CK-MB levels showed no rise to pathological levels in both groups (Fig. 6
) although statistical testing revealed a difference during the intensive care unit stay.
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Fig. 5. The time course of serum creatine kinase (CK) showed a significantly more pronounced postoperative increase in the minimally invasive group. PREOP, preoperatively; ICU, intensive care unit; POD, postoperative day. *P<0.05 minimally invasive vs. conventional.
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Fig. 6. The time course of the serum creatine kinase (CK) MB showed no rise to abnormal levels in both groups. PREOP, preoperatively; ICU, intensive care unit; POD, postoperative day. *P<0.05 minimally invasive vs. conventional.
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In Fig. 7
and Fig. 8
cumulative intubation rates and hospital admission rates are depicted. The intubation rate at 12 h was 45.0% in the minimally invasive group and 52.2% in the conventional group (P=NS). On the fifth postoperative day 68.4% of patients in group I were still admitted whereas this rate was 100.0% in group II (P=0.0004). Angiographic restudy which was carried out in 18 MIDCAB patients revealed a patent IMA graft in all cases. Two early reoperations however were necessary: one for an anastomotic stenosis and one for a stenosis of the target vessel distally to the LIMA to LAD anastomosis.
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Fig. 8. At 120 h (5 days) and 240 h (10 days) significantly more patients were discharged in the minimally invasive group.
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4. Discussion
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Promising results of minimally invasive CABG have so far been reported in observational studies but very few data on direct comparisons with conventional CABG are available at present. Magovern in a 1996 abstract [11]stated that minimally invasive direct coronary artery bypass grafting (MIDCAB) can reduce blood transfusion requirements, intubation time and hospital length of stay as compared with conventional CABG. In another abstract Fonger noted a significant reduction of cost [9]. When starting our minimally invasive CABG program in 1996 avoidance of CPB was the main goal of the project. This concept was underlined by experiences in the literature which noted a reduction of postoperative bleeding, low output syndromes, arrhythmias, pulmonary complications and neurologic events when performing CABG off pump [6, 13]. The technique used for minimally invasive coronary artery bypass grafting by our group has been described before [4, 7, 12].
As demographic data show, there were no significant differences between the two groups. Nevertheless a trend could be seen that in the minimally invasive group patients were slightly younger, more male and left ventricular function was slightly worse. The majority of procedures was performed for single vessel disease in both groups. The presence of double vessel disease in the two patient cohorts can be explained by the fact that in the conventional group in all these cases only one graftable target vessel could be found on angiography or intraoperatively. Another explanation is that three cases in the minimally invasive CABG group were carried out as `hybrid procedures' [3]combining MIDCAB with interventional techniques.
The intraoperative results regarding operative time and myocardial ischemic time seem to favour conventional CABG. Although a comparison of local coronary occlusion time with aortic cross-clamp time which involves global myocardial ischemia is problematic such a comparison was conducted in order to show that the anastomosis on the beating heart may be more difficult and more time consuming than on the arrested heart. We also attribute the longer intervals in group I to the learning curve which was present.
Concerning mortality, MIDCAB has to compete with a near zero percent mortality reported in the literature for single vessel coronary artery bypass grafting [2, 10]. There was one hospital death in our minimally invasive group due to concommitant aortic dissection type B. The case of myocardial infarction after MIDCAB occurred in a patient with an intramyocardial target vessel and postoperative angiography showed an anastomotic stenosis which lead to myocardial ischemia. Conventional CABG was performed and the patient recovered completely after prolonged stay in the intensive care unit.
As our data show, one of the major advantages of MIDCAB is significant reduction of blood transfusion requirements which primarily seems to be based on a less pronounced postoperative fall in platelets. Also a trend towards reduction of postoperative low output syndromes and atrial fibrillation could be noted. This is totally in accordance with previous off pump CABG experiences [6, 13].
The fact that MIDCAB leads to temperature elevation and postoperative rise of leukocytes might indicate that some kind of whole body inflammatory response which was described after on pump procedures [8]could as well be present after minimally invasive CABG off pump. The dose of diuretics required until the third postoperative day was similar in both groups maybe showing that some degree of capillary leakage might also be present in off pump CABG (Table 2).
We think that higher levels of serum CK without elevation of the CK-MB in the MIDCAB group could be explained by trauma to the pectoralis major muscle either by electrocautery or by compression and malperfusion during spreading of the mini-incision.
Very short intubation times and hospital admission have been reported following minimally invasive coronary artery bypass grafting [1, 7, 9, 11]. Longer intubation and hospital admission in our study groups compared with literature data can be explained by the fact that fast tracking of the patients was not intended during the initial experience with MIDCAB and not at all intended in conventionally operated patients. A trend that patients after minimally invasive CABG can be extubated earlier and a statistically significant earlier discharge from the hospital could be noted. In this retrospective study however, the significantly shorter hospital stay in the MIDCAB group might be due to bias and no definite conclusions can be drawn that MIDCAB really enables earlier hospital discharge. Further proof preferably by prospective randomized trials is warranted.
Angiographic restudy was carried out in 18 MIDCAB patients revealing two findings which required early reoperations. Routine postoperative angiography was not performed in conventionally treated patients. Therefore comparisons were not possible. Nevertheless relatively high rates of reoperations after MIDCAB have also been observed by others [7]and are a major point of criticism.
From this study we conclude that in comparison to conventional single coronary artery bypass grafting, minimally invasive CABG via minithoracotomy on the beating heart without cardiopulmonary bypass despite longer operative times which might be attributed to learning curve problems can reduce blood transfusion requirements. This is most likely due to a less pronounced postoperative reduction of platelet count. A whole body inflammatory response seems to be present after both MIDCAB and conventional CABG. Nevertheless earlier hospital discharge of patients treated minimally invasive can be possible.
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References
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Top
Abstract
1. Introduction
