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Ann Thorac Surg 1998;66:1224-1229
© 1998 The Society of Thoracic Surgeons
a Division of Thoracic Surgery, Allegheny University Hospitals, Allegheny General; and Allegheny University of the Health Sciences, Allegheny Campus, Pittsburgh, Pennsylvania, USA
Address reprint requests to Dr James Magovern, Division of Thoracic Surgery, Allegheny General Hospital, 320 E North Ave, Pittsburgh, PA 15212
Presented at the Poster Session of the Thirty-third Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Feb 3–5, 1997.
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Abstract |
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Methods. This retrospective study compares the morbidity, mortality, cost, and 6-month outcome of patients less than 80 years old undergoing elective left internal mammary artery to left anterior descending artery bypass grafting via MIDCABG (n = 60) or sternotomy (n = 55) between January 1995 and December 1996. There were no differences between the groups in mean age, sex distribution, or preoperative risk level. The left internal mammary artery was mobilized from the fifth costal cartilage to the subclavian artery in all patients. The anastomoses were done with a beating heart in the MIDCABG group and with cardioplegic arrest in the sternotomy group.
Results. There were no operative deaths in either group. The MIDCABG patients had a lower transfusion incidence (10/60 [17%] versus 22/55 [40%]; p 
0.02) and a shorter postoperative intubation time (2.1 ± 4.2 versus 12.6 ± 9 hours; p 0.0001). One patient in each group was reexplored for bleeding. Three sternotomy patients (3/55, 5%) required ventilatory support for greater than 48 hours, but no MIDCABG patient was ventilated for more than 24 hours. Median postoperative length of stay was 4 days for MIDCABG and 7 days for sternotomy. Estimated hospital costs were $11,200 ± 3100 for MIDCABG and $15,600 ± 4200 for CABG (p < 0.001). The reduced morbidity and cost of MIDCABG was found mostly in high-risk patients. At 6-month follow-up, 5 MIDCABG patients (5/60, 8%) had evidence of recurrent ischemia involving the left anterior descending artery, primarily the result of anastomotic stricture.
Conclusions. This analysis shows that MIDCABG reduces the initial morbidity and cost of coronary bypass, but some patients require subsequent reintervention. Long-term follow-up is needed before MIDCABG can be judged better than traditional bypass, but the initial results are promising, especially in high-risk patients.
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Introduction |
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Interventional cardiology procedures such as angioplasty and stenting have developed because of the well-known risks and complications of traditional CABG. These procedures are initially less morbid and less costly than an operation, but are associated with a significant incidence of recurrence that requires subsequent revascularization [5, 6]. However, patients and cardiologists usually choose catheter-based procedures as a first option rather than an operation, except in the circumstance of left main coronary stenosis or three-vessel coronary disease with depressed left ventricular function [7, 8].
Minimally invasive direct coronary artery bypass grafting (MIDCABG) has developed as a method to offer the advantages of surgical revascularization in combination with the reduced morbidity of interventional procedures. The procedure involves grafting the left internal mammary artery (LIMA) to the left anterior descending coronary artery (LAD) through an anterior thoracotomy incision without arresting the heart, which thereby avoids both a sternotomy and CPB [9, 10]. The anticipated benefits of this approach are reduced morbidity and cost, but concern has been raised about graft patency and late results. This article presents the morbidity, mortality, cost, and 6-month outcome of an initial series of patients who underwent MIDCABG. The results are compared with those of a historical group who underwent traditional LIMA to LAD grafting using sternotomy, CPB, and cardioplegia.
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Material and methods |
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Statistical analysis
The two groups of patients were compared with Student’s t test for unpaired data, 
2 test, or Fisher’s exact test where appropriate. A p value of 0.05 or less was considered significant.
Surgical techniques: traditional coronary artery bypass grafting
Traditional CABG was done using a median sternotomy for access, CPB for circulatory support, and cold blood cardioplegia for myocardial preservation. In all cases central cannulation was employed using a single two-stage venous cannula in the right atrium and arterial return cannula in the ascending aorta. The CPB circuit contained a membrane oxygenator and a centrifugal pump. The prime volume was 1,800 mL and consisted of Plasma-Lyte (Baxter Healthcare, Deerfield, IL) plus 25 g of mannitol. Anesthesia was induced with etomidate (0.2 mg/kg) and curare (3 mg), and supplemented with fentanyl (5 to 10 µg/kg) and succinylcholine (2 mg/kg) for intubation. Anesthesia was maintained with isoflurane (1% to 2%), fentanyl (10 to 20 µg/kg), and midazolam (0.1 to 0.2 mg/kg). The core temperature was allowed to drift downward during CPB, and the patients were rewarmed until the bladder temperature was greater than 35°C before weaning from CPB. No specific methods were used to confirm anastomotic patency or graft flow.
Surgical procedure: minimally invasive direct coronary artery bypass grafting
Minimally invasive direct coronary artery bypass grafting is an operation in development. Technical reports have been published, but a brief outline of our technique is presented here. Anesthetic technique for MIDCABG was largely the same as for CABG, except that smaller doses of fentanyl (3 to 10 µg/kg) and midazolam (0.05 to 0.1 mg/kg) were used. Intercostal rib blocks (bupivicaine, 0.25%) and intravenous analgesia (ketolarac, 30 mg) were also routinely used to reduce early postoperative pain. A left-sided double-lumen endotracheal tube and transesophageal echocardiography were used in all cases. The double-lumen tube allowed collapse of the left lung, which facilitated LIMA takedown. Transesophageal echocardiography provided information on regional and global left ventricular function during coronary occlusion. A left submammary incision measuring 8 cm in length provided access to the heart. The chest was entered through the fourth interspace, after resection of the fourth costal cartilage. The LIMA was mobilized from the fifth rib up to the subclavian vessels under direct vision, which yielded a pedicled graft measuring approximately 15 cm in length. A variety of commercially available chest wall retractors were used to facilitate LIMA takedown under direct vision.
Attention was then directed to the heart. The pericardium was opened and suspended to the chest wall with sutures. The LAD was identified and exposed for a distance of 2 to 3 cm. The proximal and distal control of the LAD was achieved with silicone snares, which incorporated epicardial fat and myocardium to avoid trauma to the coronary artery. A 5-minute test occlusion was performed to determine the hemodynamic effect of LAD occlusion, and 5 minutes of reperfusion was then allowed. The coronary artery was reoccluded for construction of the anastomosis. During construction of the graft, cardiac motion was reduced by compression of the anterior and septal portion of the left ventricle with a retractor. Pharmacologic reduction of heart rate with ß-blockers, calcium blockers, or adenosine was not used. The coronary artery was opened with a standard coronary scalpel and scissors. The anastomosis was done with a continuous 7-0 polypropylene suture. Blood in the field was displaced by blowing carbon dioxide into the opened artery, which displaced blood and also distended the vessel.
Early in this series of patients no specific method was used to confirm graft patency. Starting in October 1996 (patient 50) a 20-MHz Doppler flow probe was used to evaluate systolic and diastolic flow velocity in the LIMA pedicle after construction of the anastomosis (Figs 1, 2).
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Results |
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Hospital stay and cost
The mean intensive care unit stay was 1.8 days (range, 1 to 18 days) for traditional CABG and 1.0 days (range, 1 to 2 days) for MIDCABG. The median length of stay for sternotomy was 7 days (range, 4 to 18 days) and 4 days for MIDCABG (range, 2 to 14 days). The estimated mean hospital cost for traditional CABG and MIDCABG were $15,600 ± 4,200 and $11,200 ± 3,100 (p < 0.001). The patients were also stratified into low, medium, high, and extremely high risk categories, as judged by a risk prediction model using preoperative information to analyze cost for different types of patients (Fig 3). Minimally invasive direct coronary artery bypass grafting was less expensive in each category, but the differences were greatest in the high-risk patients. That is, the difference between the two procedures was modest in low-risk patients, but marked in the high-risk patients. This was also true for postoperative length of hospital stay (Fig 4). The number of patients in the higher risk groups was relatively small, which precluded proper statistical analysis. To analyze these data, the patients were collapsed into two categories, which were low/medium-risk patients (clinical risk score 5) and high/very high risk patients (clinical risk score > 5). These data are shown in Table 3. Length of hospital stay and hospital costs were lower for MIDCABG than CABG in each of the two categories.
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There was one death in the MIDCABG group in a high-risk patient at 3 months after the operation of gastrointestinal bleeding complicated by multiorgan system failure. Stress perfusion radionucliotide scans were obtained on MIDCABG patients at 2 to 4 months after the operation. Catheterization was done for recurrent angina or abnormal stress perfusion tests. Recurrent angina developed in 5 patients (5/60, 8%). Three patients were found to have anastomotic strictures, which were successfully treated with angioplasty. One patient had a patent anastomosis but obstruction of the distal LAD, probably from a snare injury. One patient had an occluded graft. Two patients had abnormal stress thallium scans in the absence of symptoms, and subsequent angiography showed normal grafts. The remainder of the patients showed no ischemia in the distribution of the LAD. The overall incidence of recurrent angina in the two groups was 1.8% (1/55) for CABG and 8% (5/60) for MIDCABG. This difference was not statistically significant (p = 0.20) because recurrent angina was uncommon in both groups.
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Comment |
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Our data show that MIDCABG is as safe as traditional CABG for single-vessel coronary artery disease. There were no operative deaths and no deaths resulting from cardiac causes in the first 6 months after operation in either group. We have also shown that MIDCABG is less morbid than standard CABG, because fewer patients have postoperative complications such as stroke, pulmonary insufficiency, and renal failure. It also appears that MIDCABG patients have a shorter length of stay and decreased overall cost. The difference in morbidity and cost between MIDCABG and CABG was particularly striking for high-risk patients undergoing operation. Older patients with depressed left ventricular function or multiple comorbid conditions tolerate MIDCABG well, but they are prone to major complications with traditional surgical revascularization. Information has been published in recent years that allows identification of high-risk patients before operations, but it is not simple to reduce complications in these patients. Our results suggest that MIDCABG can be done with low morbidity, even in high-risk surgical candidates, which is an important finding. The differences in cost, length of stay, and complications were present but less striking in low- and medium-risk patients undergoing MIDCABG, which is not surprising because these are ideal candidates for traditional CABG.
The major concern with MIDCABG is immediate and long-term graft patency. Harvesting of the LIMA, exposure of the LAD, and construction of the anastomosis are more challenging in this procedure than when sternotomy, CPB, and cardioplegic arrest are employed. We did not use routine postoperative angiography in this initial series to evaluate graft patency because there were no instances of obvious postoperative ischemia. However, complete clinical follow-up of all patients in this series was obtained at 6 months after the operation and all MIDCABG patients underwent stress perfusion tests to identify myocardial ischemia. There was an 8% incidence of recurrent ischemia in this group. Thus, there appears to be a definite incidence of early graft problems with MIDCABG caused primarily by anastomotic stricture. This can also occur in a LIMA to LAD graft done with the traditional CABG procedure, but it is an uncommon event [12]. From our data we cannot determine whether the grafts were abnormal from the start or were compromised by a restenosis phenomenon. However, based on this experience we are now obtaining routine intraoperative angiography as well as Doppler flow analysis of the bypass grafts. Only with these data can this new procedure be validated and established as an effective form of revascularization.
Another issue raised by MIDCABG is whether the beating heart approach can be applied to multivessel CABG. Initially this will require a sternotomy incision, because access to the right coronary and circumflex marginal branches is not satisfactory through an anterior thoracotomy unless the heart is decompressed with CPB. Single-vessel disease constitutes a small percentage of all CABG operations, and ultimately MIDCABG will not be significant unless it can be applied to multivessel disease. A recent report suggests that long-term graft patency with beating heart techniques is not as good as with conventional methods [13]. This is in contrast to other reports that show good results with this approach [14, 15]. None of the published studies provide rigorous postoperative analysis of graft patency or myocardial ischemia. It seems clear that a prospective study of traditional versus beating heart CABG for multivessel disease is needed to delineate the risks, benefits, and late outcome of these two approaches before traditional CABG is abandoned. The group with the most to benefit from beating heart procedures are the patients judged to be high-risk candidates for traditional CABG.
Several limitations of this study are apparent. First, this was a retrospective analysis of the results of two operations rather than a prospective, randomized study, which introduces the question of systematic bias. For example, the anesthetic management and extubation protocol for the two operations were different, which accounts for much of the differences in intubation time between the groups. In addition, the MIDCABG patients were anticipating early discharge after operation, whereas the CABG patients were expecting a 5 to 7 day hospitalization. Certainly preoperative expectations have a strong effect on the length of hospital stay.
However, bias also exists in the other direction. These results compare the initial clinical experience with MIDCABG with results of an operation that has been developing for more than 25 years. The results of MIDCABG will improve as experience and dedicated equipment grows. For example, we no longer use snares that constrict or pull up on the coronary artery, because we and others have seen new stenoses develop at the site of coronary snares. In addition, objective confirmation of graft flow with Doppler methods and angiography will improve early graft patency to 100%. Finally, adoption of patient selection criteria that exclude patients with very small (1 mm) or intramyocardial target vessels from MIDCABG will also improve the results of this procedure.
Another factor is that the MIDCABG results have been examined more critically than those of CABG. None of the CABG patients had routine stress perfusion scans or angiography, and therefore we do not know the 6-month patency rate of these grafts. Cardiac surgeons like to assume 100% patency for LIMA to LAD grafts, but few early angiography data are available for analysis. A recent report examined early graft patency for CABG in a trial of aprotinin versus placebo [16]. In this study, 645 patients with an LIMA to LAD anastomosis underwent angiography at a mean of 10.8 days after traditional CABG. Patency of the LIMA was 98.8%, but 7.8% had a graft stenosis of more than 50%, which yielded a widely patent graft rate of 91%. Thus, graft stenosis is not necessarily a problem seen only with MIDCABG.
There is a common perception that traditional CABG for single-vessel coronary artery disease is a uniformly low-risk procedure, but there are no data to support this view. Age, left ventricular function, comorbid diseases, and unstable status are commonly recognized factors that influence the outcome of CABG, but the number of grafts is not a factor for predicting postoperative complications, transfusion, hospital stay, or mortality [11, 17–19]. The mean hospital stay for single-vessel CABG in the CABG group was 7 days, which is typical for CABG in this region. Most low- or medium-risk patients were discharged sooner than this, but several high-risk patients had a prolonged hospital stay because of postoperative complications, which increased the mean overall length of stay of the entire group.
Judging the success of a treatment or procedure depends on the end points that are chosen for analysis. Surgeons typically choose survival, graft patency, and long-term outcome as the most important criteria, whereas patients and referring physicians value low procedural morbidity and ease of recovery, in addition to survival. A recent randomized trial compared LIMA to LAD bypass grafting with angioplasty for single-vessel LAD disease [20]. Cardiac event-free survival was 97% for operation but only 76% for angioplasty. Nonetheless, most patients continue to choose angioplasty over traditional CABG because of the reduced morbidity and shorter recovery. Using similar logic, some patients may prefer MIDCABG or beating heart CABG over traditional CABG because of the reduced morbidity and improved comfort, even if there is a small incidence of graft stenosis. At this point it seems fair to conclude that MIDCABG is less morbid than CABG. Prospective studies that include evaluation of early and late graft patency are needed to prove that effective long-term revascularization is achieved.
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