Ann Thorac Surg 2003;75:88-92
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
Graft of choice to right coronary system in left-sided bilateral internal thoracic artery grafting
Oren Lev-Ran, MDa*,
Rephael Mohr, MDa,
Gideon Uretzky, MDa,
Dmitry Pevni, MDa,
Chaim Locker, MDa,
Yosef Paz, MDa,
Itzhak Shapira, MDa
a Department of Cardiothoracic Surgery, The Tel Aviv Sourasky Medical Center and The Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
Accepted for publication July 31, 2002.
* Address reprint requests to Dr Lev-Ran, Department of Cardiothoracic Surgery, The Tel Aviv Sourasky Medical Center, 6 Weizmann St, Tel Aviv 64239, Israel
e-mail: orenlevran{at}hotmail.com
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Abstract
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BACKGROUND: The complementary graft of choice to the right coronary artery system in patients undergoing left-sided bilateral internal thoracic artery grafting has yet to be determined. Saphenous vein graft (SVG) was compared with right gastroepiploic artery (RGEA) as the supplemental conduit to the right coronary artery when left-sided bilateral internal thoracic artery grafting is implemented.
METHODS: From April 1996 to July 1999, 234 patients underwent bilateral internal thoracic artery grafting to the left coronary system with RGEA grafted to the posterior descending artery (RGEA group). They were compared with 127 patients with left-sided bilateral internal thoracic artery in whom SVG was used for grafting the right coronary system (SVG group).
RESULTS: Female sex (27% versus 14.5%), diabetic patients (40% versus 27%), emergency cases (21% versus 7.3%), and left main coronary artery disease (34% versus 23%) were more prevalent in the SVG group. Number of grafts per patient was higher in the SVG group (3.8 versus 3.5, p = 0.04). Thirty-day mortality was 3.9% in the SVG and 2.6% in the RGEA group (not significant). Occurrence of postoperative complications (myocardial infarctions, strokes, bleeding, and sternal infections) was similar. Return of angina was similar (1.6% versus 3.8% in the SVG and RGEA groups, respectively). Midterm follow-up (4 to 56 months) showed comparable 1-year and 4-year survival (Kaplan-Meier) for both groups (92.8% and 91.7% in the SVG group, and 94.7% and 88% in the RGEA group, respectively).
CONCLUSIONS: In patients undergoing left-sided bilateral internal thoracic artery grafting, the use of RGEA for revascularization of the right coronary system does not confer clinical benefits over SVG after midterm follow-up.
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Introduction
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The merits of bilateral internal thoracic artery (ITA) grafting for myocardial revascularization have been established [1–3]. Survival benefit has been particularly related to bilateral ITA grafting of the left coronary artery system, ie, the left anterior descending and circumflex arteries [4, 5]. Several conduits may be used to graft the right coronary artery (RCA) system when both ITAs are applied for left-sided revascularization. These include right gastroepiploic artery (RGEA) [6, 7], radial artery [8, 9], free right ITA grafts (connected proximally either to the left ITA in a T-graft configuration or constructed on the proximal aorta) [10, 11], and the traditional saphenous vein grafts (SVG). Nevertheless, the complementary conduit of choice to the RCA system has yet to be determined.
Despite satisfactory patency rate [6, 7], use of RGEA is deferred in conditions amenable to development of competitive flow [12]. Furthermore, concerns have been raised regarding insufficient flow capacity of RGEA, even in the presence of angiographically intact anastomosis [13]. Consequently, use of RGEA for myocardial grafting has been considerably limited. In addition, reduced ra-dial artery patency when grafted to distal RCA has been reported [14]. Recently, evaluation of SVG grafted to remote RCA territory revealed surprisingly good clinical and angiographic results after long-term follow-up [15]. Thus, the debate over the added value of complementary arterial grafts to the RCA system, when left-sided bilateral ITA grafting is applied, is pertinent.
In this report, we compared the outcome of patients undergoing left-sided bilateral ITA revascularization, in whom either SVG or in situ RGEA was used to graft the distal right coronary branches.
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Material and methods
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Patients
Between April 1996 and July 1999, 234 consecutive patients underwent bilateral ITA grafting to the left coronary arteries (the left anterior descending and circumflex territories), with the RGEA as the complementary graft to the distal RCA system (RGEA group; Fig 1).
These patients were compared with 127 patients in whom the same techniques were used for left-sided bilateral ITA grafting, and SVG was used to graft the RCA system (SVG group; Fig 2). The RCA was grafted distal to the bifurcation, ie, the posterior descending artery.
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Fig 1. In situ bilateral internal thoracic artery grafting with right gastroepiploic artery (GEA) to posterior descending artery.
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Fig 2. Composite internal thoracic artery grafting with saphenous vein to posterior descending artery. (LITA = left internal thoracic artery; RITA = right internal thoracic artery.)
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Surgical techniques
Techniques used for left-sided bilateral ITA grafting included (1) in situ crossover arrangement (Fig 1) [16], and (2) a T-graft configuration, in which free right ITA was attached proximally on in situ left ITA (Fig 2)
[10]. The latter technique was performed when the in situ ITA arrangement was not technically feasible [16]. Internal thoracic arteries were uniformly mobilized as skeletonized vessels [17]. The benefits of this technique have been previously detailed [17]. The type of conduit selected for RCA grafting was not related to ITA configuration.
The RGEA was considered for use when degree of proximal stenosis of the target coronary was equal to or more than 70% reduction in the diameter of the coronary artery. This was intended to reduce the risk of developing competitive flow [12]. However, the final decision for using the RGEA was made during the operation, after palpating its pulse and evaluating its in situ size before harvesting.
Dissection of the RGEA [6] was performed after mobilization of both skeletonized ITAs. Ultrasonic scalpel (Harmonic Scalpel, Ethicon Endosurgery, Cincinnati, OH) was used in less than 5% of the cases. Care was taken to dissect fat tissue from the pedicle. The in situ RGEA pedicle was routed through a tailored incision in the right diaphragm.
Operations were performed with cardiopulmonary bypass through a midline sternotomy. Technique of myocardial preservation included intermittent tepid antegrade blood cardioplegia (30° to 32°C).
Distal RCA anastomosis was performed first in the sequence of grafting, with the proximal anastomosis constructed directly afterward; consequently, all anastomoses were performed on a single cross-clamp. Construction of ITA T graft was performed either before initiation of cardiopulmonary bypass or after distal ITA anastomoses were completed.
Postoperative protocol included high doses of intravenously administered isosorbide dinitrate (4 to 20 mg/h) for 2 days [16]. Cardiac enzyme analysis and electrocardiography were performed in all patients 8 hours after the operation, and at daily intervals for 3 days. All patients underwent a routine nuclear scan within 3 months after the operation, and have been examined by an independent cardiologist twice annually. Postoperative angiography was performed mainly in symptomatic patients (recurrent angina or undetermined chest pain), or in those patients with positive radionuclear scan. Patients’ data were collected and analyzed according to definitions of The Society of Thoracic Surgeons. Follow-up was obtained by a telephone questionnaire and ranged from 4 to 56 months (median, 36 months).
Statistical analysis
Data are expressed as mean ± standard deviation. The 
2 test and Fisher’s exact test were used to compare discrete variables. Two-sample Student’s t test was used to compare continuous variables. Cox proportional hazard model was used to evaluate the influence of preoperative and operative variables on late survival. Postoperative survival was expressed by the Kaplan-Meier method. All analyses were performed by SPSS 9 software (SPSS Inc, Chicago, IL).
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Results
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Preoperative and operative data are listed in Table 1.
The prevalence of female sex (27% versus 14.5%), diabetic patients (40% versus 27%), patients with left main coronary artery disease (34% versus 23%), emergency operations (20.5% versus 7.3%), and preoperative intraaortic balloon (6.3% versus 0.99%) was significantly higher in the SVG group (Table 1). Bypass time and aortic cross-clamping time were similar in both groups (87 ± 47 and 70 ± 35 minutes compared with 80 ± 39 and 70 ± 33 minutes in the SVG and RGEA groups, respectively). Number of grafts per patient was higher in the SVG group (3.8 versus 3.5, p = 0.04).
Thirty-day mortality was 3.9% in the SVG group and 2.6% in the RGEA group (p = 0.074). Multivariable logistic regression analysis identified age and diabetes mellitus to be the only predictors of early mortality. Odds ratio for 70 years of age or older was 5.84 (95% confidence intervals, 1.35 to 25.27), and odds ratio for diabetes mellitus was 4.47 (95% confidence intervals, 1.28 to 17.73). Use of SVG or RGEA grafts was not found to be a predictor of early mortality.
There was no significant difference in the incidence or distribution of postoperative myocardial infarctions (0% versus 0.9%), rate of perioperative strokes (0.8% versus 0.9%), reexploration for bleeding (0.8% versus 1.7%), and sternal infections (0.8% versus 1.3%) between the two groups (Table 2).
Abdominal complications after RGEA harvesting were not observed. Similarly, there were no major wound complications associated with the limited SVG incision.
Late follow-up was available in 98% of the surviving patients. There were three late deaths in the SVG group (2.4%) and 14 in the RGEA group (6%; p = 0.121). Late cardiac mortality included two deaths in the SVG group (6 and 24 months after the operation), and 10 deaths in the RGEA group (5 to 21 months postoperatively). This difference did not reach statistical significance (p = 0.178). One-year and 4-year survival (Kaplan-Meier) were comparable for both groups (92.8% and 91.7% in the SVG group, and 94.7% and 88% in the RGEA group, respectively; p = 0.79, log-rank test; Fig 3).
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Fig 3. Survival curves (Kaplan-Meier). SVG group versus RGEA group. (RGEA = right gastroepiploic artery; SVG = saphenous vein graft.)
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Using the Cox regression with follow-up time as a dependent variable and postoperative death as the censored variable, none of the explanatory variables, including age, sex, diabetes mellitus, and the use of RGEA or SVG, was found to have a significant effect on survival.
There was no difference in the rate of return of angina. Return of angina occurred in 2 patients from the SVG group (1.6%; 10 to 15 months postoperatively), and in 9 patients from the RGEA group (3.8%; 6 to 27 months after the operation; p = 0.23). Only 26 grafts to the posterior descending artery were demonstrated angiographically (6 to 27 months after the operation). This included 15 RGEA grafts and 11 SVGs. All SVGs were defined as intact; however, five RGEA grafts were nonfunctioning. Of the latter, angiographic "string sign," related to competitive flow, was observed in 2 patients. Two grafts were occluded and one was severely stenosed. None of the SVG group and only 1 patient of the RGEA group (0.4%) required postoperative reintervention.
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Comment
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In this study, the use of RGEA (complete arterial revascularization) did not confer any benefit over SVG when grafted to remote RCA territory in patients undergoing left-sided bilateral ITA grafting. Early complications were comparable, and return of angina, reintervention rate, and survival were similar.
Several studies have advocated the use of left-sided bilateral ITA grafting as the single factor most associated with survival benefit after coronary artery bypass grafting [4, 5]. Thus, the question of the preferred conduit to the RCA is pertinent, particularly when bilateral ITA grafting is applied to the left coronary system. The radial artery has been proposed for RCA grafting [8, 9]. However, when connected proximally to the aorta, its added benefits over the SVG are still debatable [14, 15]. Despite the assumption that improved patency is conferred by the construction of left ITA–radial artery T graft, a recent report demonstrated disappointing patency rate when grafted to the RCA [14]. Furthermore, many surgeons defer the use of the radial artery owing to concerns related to graft spasm and coronary competitive flow [9, 18]. Similarly, the in situ right ITA graft is also associated with less than optimal patency rate when grafted to the distal RCA [19].
Coronary competitive flow [12, 20, 21] and insufficient flow capacity [13] may limit the use of the RGEA. The relationship between RGEA patency and competitive flow has been documented [18]. Consequently, most authors recommend a degree of proximal coronary stenosis of at least 70% to achieve optimal graft patency [6, 12]. However, angiographic patency is not the sole factor for adequate grafting.
Ochi and colleagues [13] demonstrated insufficient RGEA flow capacity in the presence of angiographically intact patent graft, and concluded that only RGEA grafts of 2.6 mm or more in luminal diameter would be consistently adequate. However, the average internal diameter of the RGEA is usually smaller (mean 2.2 mm) [22].
Thus, if these strict criteria are applied, the RGEA would be inadequate for grafting in a substantial number of patients undergoing coronary artery bypass grafting. Unfortunately, RGEA size is associated with wide individual variability, and no reliable method exists for predicting its size before harvesting. In our experience, the RGEA could be applied in only 30% to 40% of the cases; moreover, if more strict criteria are set, as recently advocated [13], this number may be further reduced.
Early results of both groups were similar. The trend toward higher early mortality in the SVG group may reflect on the higher prevalence of high-risk patients in this group (more female patients, diabetic patients, and emergency operations, and higher prevalence of left main coronary artery disease). The construction of a proximal SVG anastomosis on the ascending aorta did not affect the rate of perioperative stroke (compared with the RGEA group, in which no proximal anastomoses were performed).
Return of angina was similar in both groups. This was true for the overall groups, as well as for the adjusted groups after exclusion of patients with angiographic problems in the ITA grafts. At midterm follow-up, return of angina was not affected by the type of graft to the distal RCA system (SVG or RGEA). In a comprehensive study, in which complementary SVGs were used to graft remote myocardial areas, Dion and associates [15] demonstrated a low rate of return of angina and surprisingly good patency rate of the SVG. The authors question the added value of arterial grafts to remote posterior descending artery areas. In our study group, coronary angiography was performed only in symptomatic patients or patients with positive postoperative scans. Overall, 26 grafts were demonstrated. These limited data do not allow conclusions to be drawn with regard to patency rate. Nevertheless, this was not reflected in the reintervention rate (0.3%).
It has been advocated that the average RCA is not the clinical equivalent of left-sided coronary branches [4, 23]. Thus, despite the fact that the attrition rate of the SVG is progressive and particularly demonstrated over 5 years, it is unclear whether supplemental SVGs used to graft the RCA would negatively influence cardiac morbidity when both ITAs are used for left-sided revascularization. From current knowledge, late survival would not be affected [1–5]. To date, this question remains unresolved.
This study should be viewed with its own limitations. The two groups differed in the degree of right coronary stenosis, and SVG patients constituted a higher-risk group. This stems from the tendency to prefer SVG over the RGEA in higher-risk subgroups, and may reflect the latter being surgically more demanding. Hence, case selection could be influenced toward younger and healthier patients in the RGEA group. However, although this study has a nonrandomized design, the influence of patient selection bias is limited because individual anatomic variations (degree of proximal RCA stenosis and RGEA intraluminal diameter), rather than the complexity of the surgical technique, determined whether RGEA would be used.
Whether arterial grafts to the RCA system, and particularly RGEA, can further improve clinical results of left-sided bilateral ITA grafting will probably be established after longer periods of follow-up. However, inasmuch as this question is repeatedly debated in daily practice, it is our belief that additional information is currently warranted.
In conclusion, in patients undergoing left-sided bilateral ITA grafting, the use of the RGEA for revascularization of the RCA system does not confer clinical benefit when compared with SVG. Nevertheless, this statement is limited to midterm follow-up.
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References
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Abstract
Introduction
