Asian Cardiovasc Thorac Ann 2001;9:264-268
© 2001 Asia Publishing EXchange Pte Ltd
Flow Competition of Right Gastroepiploic Artery Graft
Lee Hyun Sung, MD,
Kwak Young Tae, MD,
Youn Young Nam, MD,
Park Hyung Dong, MD,
Chang Byung Chul, MD
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Division of Cardiovascular Surgery Yonsei Cardiovascular Center and Research Institute Yonsei University College of Medicine Seoul, Korea
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For reprint information contact: Chang Byung Chul, MD Tel: 82 2 361 7284 Fax: 82 2 313 2992 email: bcchang{at}yumc.yonsei.ac.kr Division of Cardiovascular Surgery, Yonsei Cardiovascular Center and Research Institute, Yonsei University College of Medicine, 134 Shinchon-dong, Seodaemun-ku, Seoul 120-752, Korea.
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ABSTRACT
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Right gastroepiploic artery is used as an in-situ arterial conduit in coronary revascularization, but flow competition has been reported. Between September 1998 and June 2000, 25 patients underwent coronary revascularization using right gastroepiploic artery. Coronary flow patterns were examined in 21 patients by postoperative angiography. Flow patterns were divided into 2 categories: right gastroepiploic artery-dependent (n = 16) and native coronary artery-dependent (n = 5). Flow competition was seen in 5 of the 21 patients (24%). The diameter of the right gastroepiploic artery was significantly larger in the right gastroepiploic artery-dependent group, whereas the diameter of the native coronary artery was larger in the native coronary artery-dependent group. Ten of 11 patients with 100% proximal coronary stenosis and all 3 who received a graft to the obtuse marginal branch showed a right gastroepiploic artery-dependent flow pattern. The flow pattern in the graft was determined by the size difference between the arterial conduit and the native coronary artery, the degree of proximal stenosis, and the site of the anastomosis. Further study is needed to evaluate the long-term results of coronary artery bypass grafting using right gastroepiploic artery.
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INTRODUCTION
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In coronary artery bypass grafting (CABG), internal mammary artery (IMA) grafts are used extensively because of ready availability and excellent long-term patency rates. Consequently, the current trend is to use as many arterial grafts as possible to improve the overall results of CABG.1,2 The right gastroepiploic artery (RGEA), an alternative in-situ arterial graft, has shown satisfactory medium- and long-term results, and it is used together with or in place of IMA when the latter is not readily available.3–7 One of the problems encountered with RGEA grafts is flow competition between the RGEA and the native coronary artery (NCA).8–10 The purpose of this study was to evaluate flow competition between the RGEA and NCA by early postoperative coronary angiography.
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PATIENTS AND METHODS
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From September 1998 to June 2000, 25 patients underwent CABG with RGEA grafts. There were 23 men and 2 women, with a mean age of 57.1 years (range, 40 to 73 years). Initially, the RGEA was used particularly in young patients, but with experience, it was used more freely. Preoperative characteristics are shown in Table 1
. Mean ejection fraction for the group was 0.57 ± 0.15. Preoperatively, the RGEA was not studied by angiography.
A standard median sternotomy incision was extended 5 to 10 cm caudally into the abdomen and the RGEA was evaluated by palpation. The RGEA was dissected with an Ultracision Harmonic Scalpel (Ethicon Endo-Surgery, Inc., Cincinnati, OH, USA) before harvesting the left IMA. The artery was dissected to the pylorus along the distal half of the greater curvature of the stomach. After systemic heparinization, the distal portion of the RGEA graft was divided, diluted papaverine (1 mg/150 mL of blood) was injected gently into the graft, and the distal end of the RGEA was clamped. The RGEA was brought up into the pericardial cavity, anterior to the pylorus and left lobe of the liver. The coronary anastomosis was performed using running 7/0 polypropylene sutures, and the pedicle was fixed to the epicardium with 5/0 polypropylene suture to prevent kinking of the graft.
Follow-up angiography of the RGEA graft was performed in 23 of the 25 patients (92%), from whom informed consent was obtained, between 5 and 21 days after CABG. The flow patterns of the RGEA and NCA were studied retrospectively in 21 of these 23 patients; one with a free RGEA graft and another who required emergency redo CABG with a vein graft were excluded. Flow patterns were divided into two types: RGEA-dependent and NCA-dependent (Figure 1).8 In the RGEA-dependent group, the RGEA graft perfused the entire NCA system, and in the NCA-dependent group, the RGEA was patent but the entire NCA system was perfused by the NCA itself (Figure 2). The relationship between these two flow patterns was analyzed in relation to the degree and location of the stenosis, the site of anastomosis, and the diameters of the RGEA and NCA. A digital image analyzer quantitatively measured the diameter of the coronary artery and the RGEA. The diameter of the RGEA graft was measured 1 cm proximal to the anastomosis; the diameter of the NCA was determined just distal to the anastomosis. Diameters were analyzed by the Mann-Whitney U method. The relationship between the degree and location of proximal stenosis was assessed by Fisher's exact test. A p value < 0.05 was considered statistically significant.
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Figure 1. Right gastroepiploic artery graft flow patterns found on postoperative angiography. NCA = native coronary artery, RGEA = right gastroepiploic artery.
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Figure 2. RGEA-dependent and NCA-dependent flow patterns seen on postoperative angiography. (A) RGEA-dependent anastomosis to the distal right coronary artery. (B) RGEA-dependent anastomosis to the obtuse marginal branch. (C) NCA-dependent anastomosis to the distal right coronary artery. A white arrow indicates the RGEA graft. NCA = native coronary artery, RGEA = right gastroepiploic artery.
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RESULTS
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In the study group of 25 patients, a total of 85 anastomoses (57 arterial and 28 saphenous vein grafts) were performed, the average number of distal anastomoses being 3.3 ± 0.99 per patient. There were 24 in-situ RGEA grafts (96%), and one case where the RGEA was used as a free graft. Three RGEA grafts (12%) were anastomosed to the obtuse marginal branch, 21 (84%) to the distal right coronary artery, and one (4%) to the diagonal branch. Minimally invasive CABG, off-pump CABG, and redoCABG were undertaken in 3, 2, and l patients, respectively.
One patient (4%) died from upper gastrointestinal bleeding on postoperative day 11. One patient had perioperative myocardial infarction (MI) in an area unrelated to the RGEA graft site. Gastric ulcers were found in two cases, which were managed medically. There was one case of postoperative superficial wound infection. One patient suffered a cerebrovascular accident and recovered without sequelae. In the 23 patients who had angiography postoperatively, the early patency rate of the RGEA graft was 100%. Of the 21 patients who were investigated for flow patterns, 16 showed the RGEA-dependent flow pattern and 5 showed the NCA-dependent pattern. Regarding the relationship between the degree of proximal stenosis and flow pattern, the RGEA-dependent flow pattern was seen in 10 of 11 grafts (91%) when the proximal stenosis was 100%, in 3 of 4 grafts (75%) when the stenosis was 90%, and in 3 of 6 grafts (50%) when the stenosis was less than 80%. All 3 grafts anastomosed to the obtuse marginal branch showed the RGEAdependent pattern, regardless of the degree of proximal stenosis (Table 2).
The diameter of the RGEA in the RGEA-dependent group was significantly larger than in the NCA-dependent group; likewise, the diameter of the NCA in the NCA-dependent group was considerably larger than its counterpart in the RGEA-dependent group (Table 3). The RGEA graft had the dominant flow pattern when its diameter was 1.5 mm or more (p = 0.004), when the NCA diameter was less than 2 mm (p = 0.003), or the RGEA/NCA diameter ratio was 1 or more (p < 0.001).
Minimally invasive direct CABG to the right coronary artery was performed using RGEA in a 53-year-old man who had 80% stenosis of the proximal right coronary artery, and an ejection fraction of 0.45. Preoperatively, he had suffered 2 episodes of MI in the right coronary territory, and he was taking amiodarone for ventricular tachycardia. CABG was performed uneventfully, but during the immediate postoperative period, he developed persistent ventricular arrhythmia and required aorto-coronary bypass with a saphenous vein graft distal to the anastomotic site of the RGEA, to correct myocardial ischemia causing the arrhythmia. Postoperative angi-ography showed a small but patent RGEA (Figure 3). Although the diameter of the RGEA was acceptable at 1.5 mm, that of the distal right coronary artery was too large at 3.8 mm. The ratio of RGEA to NCA diameter was 0.4. Thus, the flow pattern in this case was NCA-dependent.
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Figure 3. Postoperative angiography of a case of suspected native coronary artery-dependent flow pattern. An emergency redo aortocoronary bypass was performed with a saphenous vein graft. RCA = right coronary artery, RGEA = right gastroepiploic artery, SVG = saphenous vein graft.
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DISCUSSION
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The IMA is clearly the first choice of conduit in CABG because of its availability and excellent long-term patency rates. The RGEA is second best; although postoperative intimal hyperplasia and problems caused by arterio-sclerosis are rarely seen in RGEA grafts, flow competition with the NCA is more frequent than with IMA.8 Histologically, the RGEA contains a thick medial layer of smooth muscle cells, whereas the IMA has a large number of elastic fibers.11 This difference in structure may explain why the RGEA is more susceptible to intense vascular spasm than the IMA. In addition, blood flow in the in-situ RGEA graft is influenced by the gastric contents.12 Tedoriya and colleagues13 reported that diastolic and mean pressures in the RGEA were signi-ficantly lower than in the IMA graft. This pressure difference may be due to the fact that the RGEA is the 4th branch away from the aorta, whereas the left IMA is the 2nd branch. These 3 characteristics of RGEA (intense spasm, influence by gastric contents, and lower systemic pressure) may explain the lower blood flow in the RGEA compared to the left IMA.
Blood flow in arterial grafts is influenced by the size and length of the graft, blood pressure within the graft, and factors related to the NCA system; if the coronary stenosis is more proximal and not too severe, blood flow in the NCA may overcome the flow in the RGEA graft.10 However, in this study, the degree of proximal occlusion of the NCA had no significant effect on the flow pattern, and flow patterns did not correlate with the location of stenosis. These results might be due to the small number in the study population. However, patients with total occlusion of the proximal coronary artery had a smaller NCA diameter than those with partial occlusion (p = 0.007), but there was no significant difference in the RGEA diameters (p = 0.657).
Uchida and Kawaue10 reported that the preoperative diameter of the RGEA was fairly uniform (2.27 ± 0.33 mm) and suggested that since the resistance posed by each graft is almost the same, graft flow is largely dependent on the condition of the distal coronary artery. However, in our study, there was a significant difference in the sizes of the RGEA and NCA between the RGEA-dependent and the NCA-dependent groups. In a study of flow competition in patients with left IMA grafts, the graft diameter was much smaller when there was flow competition, showing string signs in some patients.14 Consequently, the mean calculated flow volume of the group with flow competition was nearly 10% of that in patients with a left IMA-dependent flow pattern. However, the mean flow velocity in these patients was a quarter of that in a left IMA-dependent flow pattern. These results suggest that graft diameter reduction adapting to flow demand could be a contributory factor in maintaining graft flow velocity at a relatively high level. This situation may be applied to the flow competition of in-situ RGEA grafts.
It is interesting to note that all grafts anastomosed to the obtuse marginal branch produced the RGEA-dependent flow pattern, regardless of the degree of proximal stenosis and the sizes of the NCA and RGEA. It is postulated that the RGEA-dependent flow pattern was the result of the small size of the obtuse marginal artery. All 4 grafts anastomosed to areas of old MI, and 7 grafts in 8 patients (88%) with unstable angina resulted in the RGEAdependent pattern, regardless of the degree and location of coronary stenosis. The mean diameter of the RGEA was significantly larger in the group with an old MI (2.88 ± 0.38 mm) than in the group without previous MI (1.99 ± 0.81 mm, p = 0.049). Myocardium damaged by an old MI lesion requires less blood flow, resulting in diminished blood flow in the NCA system. However, when CABG is performed in such patients, the increased myocardial contraction in the infarcted area requires an increased blood supply, while myocardial viability remains unchanged.15 It is possible that the decreased vascular resistance in the distal ischemic area maintains good flow in the graft, even in the face of low blood pressure and a small-sized graft. For these reasons, the RGEA is a suitable conduit for CABG for a patient with an old MI with viable myocardial tissue.
Competitive blood flow from the NCA may induce changes in an in-situ arterial graft, causing graft failure or occlusion. However, in studies with IMA grafts, Cosgrove and colleagues16 reported no significant difference in 1- to 2-year patency rates between grafts placed on coronary arteries with less than 50% stenosis and those placed on arteries with greater than 50% stenosis. An additional concern with RGEA is that flow competition of the graft may produce myocardial ischemia due to the steal phenomenon.
It was concluded from this study that flow competition between the RGEA graft and the native coronary system depends on the size difference between the RGEA and the NCA, the degree of proximal coronary artery stenosis, and the site of graft anastomosis. These factors should be taken into account when RGEA is considered as a conduit in CABG. Further studies are needed to evaluate the long-term results after RGEA grafting with the NCAdependent flow pattern, in view of its physiological adaptability in common with IMA.
Presented at the 8th Annual Meeting of The Asian Society for Cardiovascular Surgery, Fukuoka, Japan, September 6–8, 2000.
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Acknowledgments
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We would like to thank Miran Lee and Mi Hyun Shin for preparing the manuscript, and Dr. Pill Whoon Hong, MD, and Dr. Jae Hee Soh, MD, for critically reviewing the manuscript.
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REFERENCES
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Loop FD, Lytle BW, Cosgrove DM, Stewart RW, Goormastic M, Williams GW, et al. Influence of the internal mammary artery graft on 10-year survival and other cardiac events. N Engl J Med
1986;314:1–6.[Abstract]
-
Sergeant P, Lesaffre E, Flameng W, Suy R. Internal mammary artery: methods of use and their effect on survival after coronary bypass surgery. Eur J Cardio-thorac Surg
1990;4:72–8.[Abstract]
-
Suma H, Wanibuchi Y, Terada Y, Fukuda S, Takayama T, Furuta S. The right gastroepiploic artery graft. Clinical and angiographic midterm results in 200 patients. J Thorac Cardiovasc Surg
1993;105:615–23.[Abstract]
-
Mills NL, Everson CT. Right gastroepiploic artery: a third arterial conduit for coronary artery bypass. Ann Thorac Surg
1989;47:706–11.[Abstract]
-
Grandjean JG, Boonstra PW, den Heyer P, Ebels T. Arterial revascularization with the right gastroepiploic artery and internal mammary arteries in 300 patients. J Thorac Cardiovasc Surg
1994;107:1309–16.[Abstract/Free Full Text]
-
Lytle BW, Cosgrove DM, Ratliff NB, Loop FD. Coronary artery bypass grafting with the right gastroepiploic artery. J Thorac Cardiovasc Surg
1989;97:826–31.[Abstract]
-
Suma H, Isomura T, Horii T, Sato T. Late angiographic result of using the right gastroepiploic artery as a graft. J Thorac Cardiovasc Surg
2000;120:496–8.[Abstract/Free Full Text]
-
Nakao T, Kawaue Y. Effect of coronary revascularization with the right gastroepiploic artery. Comparative examination of angiographic findings in the early postoperative period. J Thorac Cardiovasc Surg
1993; 106:149–53.[Abstract]
-
Nishida H, Endo M, Koyanagi H, Koyanagi T, Nakamura K. Coronary artery bypass grafting with the right gastroepiploic artery and evaluation of flow with transcutaneous Doppler echocardiography. J Thorac Cardiovasc Surg
1994;108:532–9.[Abstract/Free Full Text]
-
Uchida N, Kawaue Y. Flow competition of the right gastroepiploic artery graft in coronary revascularization. Ann Thorac Surg
1996;62:1342–6.[Abstract/Free Full Text]
-
He GW, Yang CQ. Comparison among arterial grafts and coronary artery. An attempt at functional classification. J Thorac Cardiovasc Surg
1995;109:707–15.[Abstract/Free Full Text]
-
Suma H, Fukumoto H, Takeuchi A. Coronary artery bypass grafting by utilizing in situ right gastroepiploic artery: basic study and clinical application. Ann Thorac Surg
1987;44:394–7.[Abstract]
-
Tedoriya T, Kawasuji M, Sakakibara N, Ueyama K, WatanabeY. Pressure characteristics in arterial grafts for coronary bypass surgery. Cardiovasc Surg
1995;3:381–5.[Medline]
-
Shimizu T, Hirayama T, Suesada H, Ikeda K, Ito S, Ishimaru S. Effect of flow competition on internal thoracic artery graft: postoperative velocimetric and angiographic study. J Thorac Cardiovasc Surg
2000;120:459–65.[Abstract/Free Full Text]
-
Kobayashi S, Takaba T, Kume M, Kashima T, Michihata T. Efficacy of coronary artery reconstruction in maintaining myocardial viability: quantitative determination of local myocardial circulation with 13NH3 myocardial positron emission tomography. J Jpn Assoc Thorac Surg
1996; 44:459–66.
-
Cosgrove DM, Loop FD, Saunders CL, Lytle BW, Kramer JR. Should coronary arteries with less than fifty percent stenosis be bypassed? J Thorac Cardiovasc Surg
1981; 82:520–30.[Medline]
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ABSTRACT
INTRODUCTION
