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Ann Thorac Surg 2001;71:1485-1490
© 2001 The Society of Thoracic Surgeons
a Department of Cardiovascular Surgery, Kumamoto Central Hospital, Kumamoto City, Japan
b Department of Cardiology, Kumamoto Central Hospital, Kumamoto City, Japan
c Department of Pathology, Kumamoto Central Hospital, Kumamoto City, Japan
Accepted for publication January 15, 2001.
* Address reprint requests to Dr Ura, Department of Cardiothoracic Surgery, St. George Hospital, Gray St, Kogarah, NSW 2217, Australia (Email: masashiura{at}hotmail.com).
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Abstract |
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Methods. To evaluate the technical aspects and outcome of revascularization of the proximal and distal major branches of the circumflex artery (obtuse marginal [OM] branch and posterolateral [PL] branch), a total of 145 patients who possessed a graftable branch of the circumflex artery were enrolled into the prospective project. There were 73 patients who had the PL branch as a primary target and 72 patients with OM branches, which were allocated by a blinded observer who reviewed the preoperative angiography.
Results. Changes of primary target vessels were required in 9 patients (6.2%), yielding an overall success rate of RITA grafting of 93.8%. The success rates of RITA grafting to the OM branch and the PL branch were 95.8% (69/72; CI 88.3% to 99.1%) and 91.7% (67/73; CI 83.0% to 96.9%), respectively. The univariate analysis identified grafting under hypothermic ventricular fibrillation as predictors of inability to use in situ RITA grafting for revascularization of the circumflex artery. RITA grafting to the PL branch is not identified as a predictor. Postoperative angiography in 136 patients revealed only one occlusion (0.75%) of the RITA graft anastomosed to the marginal artery. There were no significant differences in patency rates between left and right ITA grafts.
Conclusions. This prospective study showed that in situ RITA was, in most cases, able to reach most branches of the major circumflex artery and demonstrated an excellent patency rate.
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Introduction |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Patients and methods |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Of 225 patients undergoing CABG, the study population was selected using the following criteria: (1) patients who had an angiographically graftable branch of the circumflex artery, and (2) patients who were candidates for RITA grafting.
The exclusion criteria for RITA harvesting included severe chronic obstructive pulmonary disease, subclavian arterial stenosis (restriction of ITA flow), radiation therapy to the chest wall, and emergency surgery. Old age itself was not considered to be a contraindication for RITA harvesting. However, if the patient was older than 75 years, the decision to use RITA was performed on an individual basis. No patients were excluded for reasons of anatomic limitations suggested by angiography of in situ RITA grafting to the circumflex artery. Insulin-dependent diabetes mellitus was not considered as a contraindication for the use of RITA harvesting.
A total of 149 patients met the above criteria. During the operation, the RITA was injured and was thus used as a free graft in 3 patients, and was anastomosed to a more proximal artery in 1 patient. These patients were excluded from the study. Thus, ultimately 145 patients (94 men and 21 women; mean age of 62.5 years; range 13 to 77) were enrolled in the project.
All patients underwent a preoperative angiography. All the angiographical data were reviewed by independent observers (cardiologists S.O. and K.N.) who were unaware of the operative strategy. The PL and OM were defined by an independent observer based on the American Heart Association reporting system on patients for coronary artery disease [12]. The size of the perfusion areas of each major branch were qualitatively graded on a scale of 1 to 4 (large, medium, small, tiny). Graftable branches were defined as those having an area of 1 to 3 with more than 50% proximal stenosis.
The primary target branches of the circumflex artery for RITA grafting were selected preoperatively as follows. If the patient had two graftable branches, the branch with the larger perfusion area was selected as primary target. If the two branches had identical perfusion areas, the more distal branch (PL) was selected as the primary target. Thus, there were 73 patients who had the PL as a primary target, and 72 patients with OM, with the in situ LITA being anastomosed to the LAD in the conventional manner in 133 patients. The patients’ characteristics are summarized in Table 1.
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Operative procedures
The operative technique used was similar to that described in previous reports [5, 7, 9, 10]. After dissection, the ITA pedicle was wrapped with papaverine-soaked gauze (200 mg/50 mL of saline solution). No intraluminal papaverine injection was used. LITA grafting was performed in all patients except for 1 individual who had a poor-quality LITA. In 133 patients (91.7%), the in situ LITA was anastomosed to the LAD using standard methods.
To use the distal section of the RITA, which normally has good caliber, care is taken to obtain the maximum length by harvesting the RITA to near the origin of the subclavian artery and to obtain the shortest route by opening the pleura and incising the pericardium. The size of the ITA was measured at the anastomotic site before anastomosis was carried out. Only segments of the ITA of size over 1.5 mm were used. If the size of the ITA at the planned anastomotic site was not adequate (<1.5 mm), the recipient coronary artery was converted to a more proximal one or ITA was used as a free graft. If the graft was short by 1 to 2 cm, skeletonization of the RITA graft was performed to the extent of not overstretching the graft. The size of the recipient coronary artery was measured by passing through a metal probe (1.0, 1.5, 2.0, 2.5 mm) and the presence of calcification or plaque at the anastomotic site was also recorded.
Postoperative angiography
To evaluate the early patency rate, postoperative angiography was performed 2 to 3 weeks after surgery. All ITA grafts were evaluated for occlusion, development of string sign, or presence of significant stenosis (flow limiting or stenosis of more than 50% of the vessel diameter at any point along the body of the graft or at any anastomoses). Only grafts of good caliber, with no occlusion, string sign, or significant stenosis, were considered patent.
The graft/native coronary artery size matching ratio (GMR) was calculated as follows: GMR = graft size/native coronary artery size. All measurements were taken at the beginning of the QRS complex.
Pathological study
To clarify the pathological differences between both ITAs at the anastomotic site, the segments of ITA collected from each patient were fixed in formalin, embedded in paraffin blocks, and sectioned. The sections were stained with hematoxylin and eosin and Elastica van Gieson. Van Son and associates [13] have demonstrated that the ITA is an elastic conduit at most portions along its length except at its very distal sections, where it becomes an elastomuscular artery. The very proximal section of the superior epigastric artery and musculophrenic artery, which are the continuation of the bifurcation of the distal end of the ITA, are muscular with occasional elastic lamellae [13]. Because the number of elastic lamellae represents the elasticity of ITA graft [14], the number of elastic lamellae in the media of both ITAs at the anastomotic site was counted and recorded by an independent observer (Pathologist M.K.).
Statistical methods
Data are presented as means with 95% confidence intervals (CI). Univariate analysis was performed to determine the predictors of inability to use in situ RITA for grafting CX among the preoperative variables (gender, height, weight, body surface area [BSA], age, body mass index [BMI]), intraoperative data (grafting under hypothermic ventricular fibrillation), and angiographical data (the size [dominance of] of the left coronary artery system, and the primary target vessels). Univariate testing of variables was performed with the Fisher’s exact test for discrete variable comparisons. The Mann-Whitney U test was used for continuous variable comparisons. For multiple comparisons, a significant level of 0.0056 was set to ensure the whole type I error probability was less than 0.05, according to the Bonferroni method. All analyses were performed using commercial statistical software (version 6.12; SAS, Cary, NC).
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Results |
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Intraoperative data
To clarify the characteristics of RITA grafting, in 134 patients the intraoperative data on RITA grafting was compared with that for LITA grafting to the LAD or diagonal branch of the same patients (Table 3). As shown, in RITA to CX grafting, the more distal, smaller, and more muscular portion of ITA was used compared with conventional LITA-LAD or diagonal grafting. In addition, the recipient coronary arteries used for RITA grafting were significantly smaller in caliber and perfusion area than those used in LITA grafting (mainly the LAD). In general, in RITA grafting, the section of the RITA near the bifurcation was used for anastomosis (mean distance between anastomotic site of ITA and the bifurcation of ITA was 0.0 ± 1.1 cm), whereas in LITA grafting, anastomosis was performed at the ITA 2.7 ± 1.4 cm more proximally.
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Only one RITA graft anastomosed to the OM was found to be occluded. String-like artery and significant stenosis were present in 1 patient and 2 patients, respectively, for a patency rate of RITA grafts of 96.6%. The patency rate of LITA grafts was 97.6%. There were no significant differences in patency rates between LITA and RITA grafts.
Predictors of inability to use in situ RITA grafting to the CX
Among the preoperative and intraoperative variables, univariate analysis identified grafting under hypothermic ventricular fibrillation to be predictors of inability to use in situ RITA for grafting CX (p < 0.001). RITA grafting to the postero-lateral branch was not identified as a predictor.
RITA grafting to the postero-lateral branches in the case of dominant left coronary artery
RITA grafting to the theoretical most distal branch, the postero-lateral branches in the dominant left coronary artery, was feasible, with a success rate of 83.7%, lower than in other groups (Table 2). In this technically demanding group, size discrepancy between the graft and the recipient artery (GMR < 6.0) was noted more frequently. Of 16 RITA grafts revealed by early angiography to have completely opacified, there were four RITA grafts with a size discrepancy with the coronary artery, as demonstrated in Figure 2, whereas there were eight grafts with a size discrepancy among 101 grafts (p < 0.05) in the other patients.
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Comment |
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Although previous anatomic studies have demonstrated that any coronary artery can be reached with an in situ ITA graft [4], Tatoulis and associates observed that pedicled RITA grafts were often not able to reach the more distal circumflex marginal arteries [3]. Some have advocated free RITA to overcome the anatomic limitations of the in situ RITA [2, 3]. In Buche and associates’ report, patients receiving in situ RITA via the transverse sinus represent only 52% of the patients undergoing bypass grafting to the circumflex arterial system [6]. They did not, however, mention the exact percentage of in situ RITA grafts that could not be used due to anatomic limitations in the remaining 48% of patients in their study. Previous reports of in situ RITA grafting were based on selected patients, and there is concern regarding to what extent in situ RITA grafting can be applied successfully to patients with a graftable major branch of the circumflex artery, especially the more distal circumflex branch (postero-lateral branch). Our prospective study demonstrated that in situ RITA grafting via the transverse sinus was performed successfully in 91.7% of cases involving the graftable postero-lateral branch, and in 95.8% of cases involving the other more proximal branch, indicating the broad applicability of this technique to patients with graftable major branches of the circumflex artery.
Dietl and associates [11] reported an increased rate of RITA graft failure when it was used to bypass the right coronary and posterior descending arteries. They attributed this problem to spasm of the distal end of the RITA graft and tension on the graft. Morin and associates reported that the patency rate is low (58.5%) for the two terminal branches of the ITA used to bypass two arteries in a Y configuration [16]. Two branches of the ITA are muscular arteries, with occasional elastic lamellae, although the midportion of the main ITA is more elastic. Elastomuscular media were observed in the proximal and distal segments of the ITA (which had a mean of six elastic lamellae), whereas the media of the mid-segment was almost purely elastic (with a mean of nine elastic lamellae) [14]. He and associates [17, 18] reported increased contractility of the ITA toward the distal end. They noted that occlusion of the bifurcation is due not only to its smaller diameter, but possibly more importantly to its greater tendency to demonstrate contraction or spasm, and emphasized that the distal end of the ITA should not be used for grafting. However, as mentioned in their study, there are not enough data to show that extensive use of the distal section of the ITA increases the likelihood of spasm or graft failure. Indeed, our pathological data demonstrate that the distal section of the RITA (RITA at the anastomotic site) is more muscular than the LITA used in the conventional way (LITA-LAD); and more distal section had to be used for RITA anastomosis than LITA. However, the patency rate of RITA anastomosis was not different and no patient experienced low cardiac syndrome (defined as progressive deterioration of cardiac output with a concomitant rise in pulmonary wedge pressure) or poor ITA perfusion syndrome postoperatively that could be attributed to RITA grafting.
Our present study demonstrated that use of the distal section of the ITA does not increase graft failure rate, at least in the early period, as long as an ITA with adequate caliber is used. We conclude that the high graft failure rate of bypass using branches is due not to a greater likelihood of contraction or spasm but to technical difficulties such as small diameter, or increased tension on the limbs of the Y grafts as mentioned in their original article [16]. Several investigators have raised concerns about the increased tendency toward intimal thickening in the distal segment of the ITA, which may jeopardize the long-term patency of the ITA graft [17]. We and other investigators have recently reported the good long-term patency of in situ RITA bypass via the transverse sinus for revascularization of the circumflex and diagonal arteries. Although the study population was different from that in the present study, excellent results in patients in which the same technique was used in the same institution suggest that there is minimal or negligible effect on long-term patency as a result of the use of the distal section of pathologically inferior ITAs.
In Tatoulis and associates’ report, of 1,454 free RITAs, 552 were directed to the OM1, and 166 to OM2 [3]. OM1 and OM2 were the two main target vessels in their report, but in our experience, we do not find in situ RITA grafting of OM difficult. This may result from the difference in our strategy of RITA grafting or our RITA harvesting technique. In our institution, in order to use the distal section of the RITA with good caliber, care is taken to obtain the maximum length by harvesting the RITA to near the origin of the subclavian artery and to obtain the shortest route by opening the pleura and incising the pericardium. Although some authors claim reduction of pulmonary function as a result of pleurotomy carried out during ITA harvesting [19], a recent study suggests that pleurotomy does not affect postoperative function [20, 21]. In our experience, although prolonged ventilation was noted in 7 patients, 3 were related to postoperative strokes. We consider that entering both pleura does not increase operative morbidity.
Recently, the use of skeletonized bilateral internal thoracic artery (BITA) conduits has been reported to be potentially useful to expand the use of ITAs, in terms of the number of anastomoses per patient and of reducing the incidence of sternal complications [22]. The main drawbacks of this operative technique are that harvesting the skeletonized arterial graft is more time consuming than the conventional one and less is known about the late results of skeletonized grafts, whereas there are abundant short- and long-term results about the conventional pedicled grafts. However, sequential grafting of several branches of CX by skeletonized RITA could be a useful method, and should be considered once long-term patency rate is confirmed.
The study revealed that under aortic cross-clamping, in situ RITA is able to reach most branches of the major CX, even the most distant type of coronary artery (the postero-lateral branches in the dominant left coronary artery), although its success rate is lower (83.7%) than with closer anastomoses. In this technically demanding group, size discrepancy between the graft and the recipient artery (GMR < 6.0) was noted more frequently (4 of 16; 25%), whereas there were eight grafts with size discrepancy among 101 grafts in the other patients (p < 0.05). Spence and associates reported in an experimental study that relative ITA graft flow is proportional to the relative diameter of the ITA graft to the native coronary artery [23]. Future study is required to clarify whether an ITA with size discrepancy relative to the native artery can provide enough blood flow to meet the demand of the recipient artery.
Study limitations
This was not a randomized study. The target vessels were determined mainly by the perfusion area of the recipient artery and not selected randomly. But clearly, such randomization would require the unnecessary choice of grafting the ITA to the second largest branches, which could reduce the clear benefit of revascularizing the most important branch of the CX with another ITA. Although the study group was not selected randomly, the two groups were identical in terms of preoperative variables, including those of the target vessels (apart from the branches), which, we believe, satisfactorily demonstrated that in situ RITA grafting is feasible in a wide variety of patients with diseased CXs.
Conclusions
Although in situ RITA grafting without cross-clamping is often difficult due to insufficient ITA length, if anastomosis is performed under aortic cross-clamping, the RITA is, in most cases, able to reach most branches of the major CX and shows an excellent patency rate. This study supports the continued use of this method of ITA grafting, which has the potential to be applied to a wide variety of patients with diseased CXs.
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