Ann Thorac Surg 2010;89:717-722. doi:10.1016/j.athoracsur.2009.12.004
© 2010 The Society of Thoracic Surgeons
Original Articles: Adult Cardiac
Off-Pump Right Coronary Artery Bypass With Saphaneous Vein or In-Situ Right Internal Thoracic Artery
Gijong Yi, MDa,
Young-Nam Youn, MDb,
Suk-Won Song, MDa,
Kyung-Jong Yoo, MDb,*
a Department of Thoracic and Cardiovascular Surgery, Gangnam Severance Hospital, Seoul, Korea
b Department of Thoracic and Cardiovascular Surgery, Yonsei Cardiovascular Center, Yonsei University College of Medicine, Seoul, Korea
Accepted for publication December 1, 2009.
* Address correspondence to Dr Yoo, Yonsei Cardiovascular Center, Yonsei University Health System, Shinchon-dong, Seodaemun-gu, Seoul 120-752, Korea (Email: kjy{at}yuhs.ac).
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Abstract
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Background: The ideal conduit for the right coronary artery (RCA) is yet to be determined. The purpose of this study was to compare the clinical results between the right internal thoracic artery (RITA) in situ with free saphenous vein (SV) graft for RCA in off-pump coronary artery bypass graft surgery (OPCABG).
Methods: Three hundred and fifty-eight patients who underwent isolated OPCABG with RCA anastomosis either by RITA in situ (n = 199) or free SV graft (n = 159) were included. We evaluated the graft patency and the incidence of RCA reintervention considering the degree of native RCA stenosis. The follow-up rate was 97.8%, and the mean follow-up duration was 57.6 months.
Results: The overall mortality and the incidence of major cardiac and cerebrovascular event showed no difference between the two groups (p = 0.495 and p = 0.338, respectively). The 5-year freedom from graft occlusion rate was 87.4% ± 3.2% in the RITA group and 94.3% ± 2.0% in the SV group (p = 0.011), with a statistically significant difference only in the moderate stenosis (< 75%) group (p = 0.020). The 5-year freedom from RCA reintervention rate was 95.7% ± 1.6% in the RITA group and 99.3% ± 0.7% in the SV group (p = 0.055).
Conclusions: Both RITA and SV showed favorable graft patency for the RCA system in OPCABG. The SV graft showed better patency in patients with moderate stenosis of RCA compared with RITA in situ. A longer follow-up period is necessary to clarify our current results.
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Introduction
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The left internal thoracic artery (LITA) has been known as an excellent bypass conduit for the left anterior descending artery (LAD) [1, 2]. But for the right coronary artery (RCA) system, the best bypass conduit has not been determined yet, and various conduits have been used: free saphenous vein (SV) graft from aorta, right gastroepiploic artery in situ or as a composite graft, radial artery from aorta or in a Y-graft configuration, right internal thoracic artery (RITA) in situ or as a composite graft, and so forth [3–6].
The SV graft from the ascending aorta is one of the most commonly performed graft strategy for the RCA system and showed quite favorable results [6]. Recently, as the benefit of arterial graft has been adopted by many surgeons, RITA has been used in many institutions and showed favorable clinical results [7, 8]. The RITA in situ has an advantage of arterial conduits, but few clinical outcomes of RITA in-situ grafting to the RCA system have been reported.
The RCA has different features compared with the left coronary artery (LCA), mainly characterized by relatively large size and worse graft patency after coronary artery bypass graft surery (CABG) [9]. The purpose of this study was to compare the clinical outcomes of RITA in situ and free SV graft from the ascending aorta for the right coronary system, which are our two main graft strategies in off-pump coronary artery bypass graft surgery (OPCABG), mainly focusing on the degree of native RCA stenosis.
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Patients and Methods
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Patients
From January 2001 to December 2005, 725 isolated OPCABG procedures were performed in our institution by a single surgeon, and 471 patients (65.0%) had one or more grafts to the right coronary system. After excluding the patients who received RCA bypass with composite or sequential anastomosis technique, 199 patients were enrolled in the RITA in-situ group (RITA group) and 159 patients were enrolled in the free SV graft from the ascending aorta group (SV group). Patient demographics are shown in Table 1. The two groups showed no difference in preoperative clinical characteristics, follow-up period, and follow-uprate.
Whether to use RITA or SV graft was decided by the surgeon's manual palpation and intraoperative transesophageal echocardiography [10]. During the operation, routine transesophageal echocardiography was performed to evaluate the degree of aortic atherosclerosis, and if the patient had atheroma by manual palpation or by transesophageal echocardiography (grade III or higher), RITA in situ was used to avoid side clamping of the ascending aorta; and if there was no evidence of atheroma, SV was anastomosed to the ascending aorta for the right coronary system bypass.
Patient data were prospectively collected, and clinical follow-up data were retrospectively reviewed. Approval of the Institutional Review Board of Severance Hospital was obtained for the data collection and follow-up, and the individual patient consent was waived.
Operation Technique and Postoperative Management
The operation was performed under general endotracheal anesthesia with full sternotomy. The internal thoracic artery (ITA) was prepared using a semiskeletonized method. The SV was exposed by a continuous longitudinal incision, and all visible branches were divided using a ligature clip. Then the SV was removed together with the surrounding tissue, and gentle mechanical distention was applied to minimize residual spasm. All operations were performed under the off-pump method, and systemic heparinization was done to maintain an activated clotting time of more than 250 s during the operation. The Octopus system mechanical stabilizer (Medtronic, Minneapolis, MN) was used for cardiac displacement. For the LAD anastomosis, intracoronary shunt was used, and for the other left coronary system, proximal snaring technique was used. Regarding the RCA anastomosis, intracoronary shunt was used for the main RCA, and proximal snaring technique was used for the posterior descending artery or posterolateral branch. After confirmation of the absence of visible or palpable atheroma, side clamping of the ascending aorta was done, and aortotomy was performed using a 3.5-mm puncture device for the proximal anastomosis of the SV graft. When using RITA in situ, the distal portion RITA was anastomosed to RCA if the length of RITA was adequate for direct anastomosis (39 patients; 19.6% of the RITA group). In most cases of posterior descending or posterolateral branch anastomosis, the radial artery segment (130 patients; 65.3% of the RITA group) or SV (30 patients; 15.1% of the RITA group) was extended to the distal portion of RITA to ensure an adequate length for the anastomosis. To minimize any stenosis in the extension site, we used an end-to-side anastomosis technique at the distal portion of RITA, rather than an end-to-end anastomosis, and the distal end of RITA was obliterated with ligature clips. To avoid kinking or twisting of the extension site, fibrin glue agent was used for appropriate graft configuration. All patients received aspirin (100 mg daily) and clopidogrel (Plavix; Sanofi, New York, NY), 75mg daily, from the operation day and thereafter except for patients who had contraindications.
Follow-Up and Definitions
Patient follow-up was done in an outpatient clinic and by telephone interview from June 2008 to August 2008. Major adverse cardiac and cerebrovascular events (MACCE), defined as the occurrence of death of any cause, nonfatal myocardial infarction, stroke, and need for target vessel revascularization, were evaluated in the two groups. The primary endpoint was any MACCE during the follow-up period. Myocardial infarction was defined as creatine kinase-MB elevation with an appearance of new Q waves or ST-segment elevation of more than 2 mm on the electrocardiogram. Target vessel revascularization was defined as revascularization performed on a previously bypassed vessel. Diabetic patients were defined as patients receiving an oral hypoglycemic agent or insulin. Chronic renal failure patients were those who required hemodialysis, peritoneal dialysis, or whose preoperative serum creatinine level exceeded 2.0 mg/dL.
Patients were additionally assessed for cardiac events related to the RCA, which included occlusion of grafts to RCA and reintervention for RCA. Graft occlusion was defined as any occlusion confirmed by multislice computed tomography (CT) scan or by coronary angiography, and included competitive or nonfunctioning graft. For the evaluation of postoperative graft patency, multislice CT scan was taken routinely at postoperative day 7 unless the patient had renal insufficiency or economic hardship. An additional CT scan was performed 1 year after the surgery and then every other year thereafter as a routine, and additionally at any time when the patient had symptoms or signs of myocardial ischemia during the follow-up period. Three hundred twenty-three patients (90.2%) underwent postoperative CT scan, and 220 patients (61.5%) underwent CT scan more than two times. Follow-up angiography was performed when the patient had ischemic symptoms or when myocardial ischemia was suspected on CT scan or by the cardiologist's decision (101 patients; 28.2%). The degree of RCA stenosis was evaluated by more than two cardiologists, and the patients were classified into two groups: moderate and severe stenosis. Moderate degree of RCA stenosis was defined as stenosis of 50% to 74% in the native coronary artery, and severe degree of RCA stenosis was defined as stenosis of 75% or more.
Statistical Analysis
Continuous variables were mean ± SD, and for the comparison of two variables, the Student t test and 
2 test were used. For survival and event-free survival, the Kaplan-Meier method was used, and the differences were assessed with the log-rank test. A significance level of 0.05 was used throughout the test. For all statistical analyses, SPSS 13.0 software (SPSS, Chicago, IL) was used.
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Results
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Patient Characteristics and MACCE
Patient characteristics of the two groups (RITA and SV) are shown in Table 1. There was no difference in the incidences of hypertension, diabetes mellitus, chronic renal failure, acute coronary syndrome, left main coronary disease, left ventricular ejection fraction (%), mean distal anastomosis number, and so forth, between the two groups. The overall operative mortality was 0.8% (3 patients), and no difference was found between the two groups (p = 0.119). All 3 operative mortalities occurred in the RITA group (2 multiorgan failures and 1 cerebral hemorrhage). The overall follow-up rate was 97.8%, and 8 patients were lost to follow-up including 3 patients who went abroad. The follow-up duration was 57.6 ± 18.7 months (range, 0 to 89) and was similar between the two groups (p = 0.597). The overall mortality was 5.3% during the follow-up period, and there was no difference between the two groups (p = 0.495; Fig 1). The overall MACCE rate was 14.1% in the RITA group and 10.7% in the SV group, which showed no significant difference between the two groups (p = 0.338).
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Fig 1. Survival curve comparing saphenous vein (SV) group (top line) and right internal thoracic artery (RITA) group (bottom line) using the Kaplan-Meier method.
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Graft Patency
The overall graft patency was 89.4% in the RITA group and 93.1% in the SV group (p = 0.231, Table 2). The 5-year freedom from graft occlusion rate was 87.4% ± 3.2% in the RITA group and 94.3% ± 2.0% in the SV group (p = 0.011 by log-rank test; Fig 2A). Regarding the degree of native coronary artery stenosis, the SV group showed a lower incidence of occlusion only in the moderate stenosis group compared with the RITA group (Fig 2B). In the moderate stenosis group, the 5-year freedom from occlusion rate was 81.3% ± 6.9% in the RITA group and 94.0% ± 2.9% in the SV group (p = 0.020); and in the severe stenosis group, it was 91.6% ± 2.8% and 94.6% ± 2.6%, respectively (p = 0.201; Fig 2C).
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Fig 2. Freedom from graft occlusion rate comparing saphenous vein (SV) group (top line) and right internal thoracic artery (RITA) group (bottom line) in the overall population, moderate stenosis group, and severe stenosis group. (A) Comparing SV group with RITA group in overall patients. (B) Comparing SV group with RITA group in moderate right coronary artery stenosis patients. (C) Comparing SV group with RITA group in severe right coronary artery stenosis patients.
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Reintervention of RCA
The overall RCA reintervention rates were 3.5% in the RITA group and 0.6% in the SV group (p = 0.067). The 5-year freedom from RCA reintervention rate was 95.7% ± 1.6% in the RITA group and 99.3% ± 0.7% in the SV group (p = 0.055; Fig 3A). Regarding the degree of RCA stenosis, both subgroups (moderate and severe stenosis group) showed a lower incidence of RCA reintervention in the SV group, without statistical significance (p = 0.133 and p = 0.202, respectively; Fig 3B, C).
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Fig 3. Freedom from right coronary artery (RCA) reintervention rate comparing saphenous vein (SV) group (top line) and right internal thoracic artery (RITA) group (bottom line) in overall population, moderate stenosis group, and severe stenosis group. (A) Comparing SV group with RITA group in overall patients. (B) Comparing SV group with RITA group in moderate RCA stenosis patients. (C) Comparing SV group with RITA group in severe RCA stenosis patients.
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Comment
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There has been much debate over an ideal conduit for the right coronary system in surgical coronary revascularization. Although various conduits, such as SV, radial artery, gastroepiploic artery, and RITA, have been recommended for the right coronary system and showed favorable results [3–6], graft patency of RCA showed worse clinical results compared with that of LCA [11]. Besides conduit type, various factors must be considered for the selection of RCA conduit: competition flow, composite or sequential grafting technique, degree of stenosis in the native coronary artery, size of the native coronary artery, and so forth [9, 12]. These numerous factors made evaluation of RCA graft patency more difficult, whereas LITA to LAD has been used as an ideal bypass strategy in almost all institutions. To simplify these various factors to consider, we tried to compare RITA in-situ graft, which is our most commonly used arterial graft for the RCA, with free SV graft from the ascending aorta considering the degree of stenosis in native coronary artery, while excluding composite or sequential grafting technique.
The SV graft has been most widely used for the RCA. But these days, the usage of SV graft has somewhat decreased as arterial graft became more popular in many institutions. The conventional graft patency rate of SV has been reported to be 60% at 10 years [13, 14], although quite favorable results have been reported recently [6]. Although a competitive flow leading to the graft dysfunction is not related to the SV graft, atherosclerotic change of the vein graft, especially 5 years after the operation and thereafter, leads to questions for better bypass conduit for the RCA.
These days, total arterial grafting with aorta no-touch technique using the off-pump method has been adopted by many surgeons. We strongly support this surgical strategy and try to use as many arterial grafts as possible. In our institution, we use LITA for LAD bypass and radial artery as a composite graft for the other left coronary system. For the right coronary system, the use of RITA in situ was increased to fulfill the aforementioned graft strategy, so we tried to compare the RITA with widely used SV graft. Although this study is not a randomized trial, we could have similar subgroups of patients because whether to use RITA or SV was mainly determined by the degree of native aortic atherosclerosis and not by the preoperative conditions of the patients.
As pointed out in many reports, arterial graft has a tendency for competition flow when the degree of stenosis in the proximal native coronary artery decreases [9, 12, 15–19]. The major problem of ITA competition flow is that it may aggravate progressive constriction of ITA and finally lead to arterial atrophy and occlusion. Sabik and others [9] reported that decreasing stenosis in the proximal coronary artery is related to reduced ITA patency, especially when ITA is anastomosed to RCA compared with LAD, and that the only situation in which SV graft patency is superior to ITA patency is early after the operation (less than 5 years) when grafting the RCA with moderate stenosis. The results of our present study strongly support these data. The RITA group showed worse graft patency compared with SV group in overall population, and the significant difference was made in the moderate stenosis group. In the stud by Sabik and others [9], a small number of ITA graft to RCA territory (n = 80) was compared with a relatively large number of vein grafts (n = 4,028), but in ours, two relatively similar groups with comparable patient population were compared. Based upon the preliminary result from this study, we now use the SV graft in patients, especially the elderly, with moderate stenosis of RCA (less than 75%). Additionally, although statistically insignificant, we could find a trend for a decrease in the incidence of occlusion as the degree of stenosis increases in RITA group, which may be a favorable evidence for arterial graft in patients with severe degree of stenosis.
Regarding the graft patency, long-term follow-up is essential. In our study, the mean follow-up duration was 58 months, which is not long enough to verify the conclusions. The long-term failure of SV conduit has been reported in the literature [13, 14]. Early SV graft failure has been explained by thrombosis and intimal hyperplasia, which lead to 80% to 90% graft patency 1 year after the operation. The patency rate sharply declines after 5 years, and by 10 years, only 60% of the SV grafts are patent, of which only half are free of stenosis [13, 14]. Poor patency with increasing time in the SV graft is attributed to the arteriosclerosis that worsens stenosis and occlusion. Conversely, several observational studies have demonstrated the recovery of arterial graft function a long time after having been found nonfunctional (string sign) at early follow-up, which is not found in venous graft [20]. This characteristic of arterial graft may be related to the endothelial protective function. An arterial graft autoregulates blood flow according to the metabolic demands; thus, ITA flow may increase as the native coronary disease worsens. The aforementioned benefits of arterial graft will be clarified a long time after the operation, which emphasizes long-term results for the graft patency. Although we identified better SV patency in moderate RCA stenosis with a mean follow-up period of 4.8 years, several more years of follow-up will be helpful in the selection of the ideal graft for RCA.
We could not find any statistically significant difference in the incidence of reintervention for RCA, although the SV group showed a low incidence of RCA reintervention rate (p = 0.055). Only 1 patient in the SV group and 7 patients in the RITA group underwent RCA reintervention after the operation, which can be explained by the small numbers in our study and different strategy in percutaneous intervention by each cardiologist. A longer follow-up period with a larger population is needed to verify this result.
There are several limitations to our study. This is an observational study with retrospective review. A relatively small sample size and single-center experience with similar surgical strategy including graft harvesting technique may limit generalizability. Also, competing risk of mortality was not considered in this study. Regarding the degree of stenosis, we did not use regression analysis because the two subgroups (RITA and SV group) had a similar number of moderate and severe stenosis patients.
In conclusion, both RITA and SV showed favorable graft patency for the right coronary system in off-pump surgical revascularization. The SV graft showed better graft patency in patients with moderate degree of stenosis in the native RCA compared with RITA in situ in mid-term follow-up after OPCABG. Longer follow-up is necessary to clarify our current conclusions.
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References
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Abstract
Introduction
