Ann Thorac Surg 2008;86:1444-1449. doi:10.1016/j.athoracsur.2008.06.055
© 2008 The Society of Thoracic Surgeons
Original Articles: Adult Cardiac
Preoperative Evaluation of the Right Gastroepiploic Artery on Multidetector Computed Tomography in Coronary Artery Bypass Graft Surgery
Keiji Kamohara, MD, PhD*,
Naoki Minato, MD, PhD,
Noritoshi Minematsu, MD,
Junji Yunoki, MD,
Takeshi Hakuba, MD,
Hisashi Satoh, MD,
Hiroyuki Morokuma, MD,
Yuichi Takao, RT
Department of Thoracic and Cardiovascular Surgery, Fukuoka Tokushukai Hospital, Kasuga City, Fukuoka, Japan
Accepted for publication June 17, 2008.
* Address correspondence to Dr Kamohara, Department of Thoracic and Cardiovascular Surgery, Fukuoka Tokushukai Hospital, 4-5 Suku-kita, Kasuga City, Fukuoka, 816-0871, Japan (Email: keijikamohara{at}hotmail.com).
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Abstract
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Background: The right gastroepiploic artery (GEA) is commonly used in coronary artery bypass grafting, but a method for preoperative assessment of the suitability of the GEA has not been established. Here, we assessed the efficacy of 64-slice multidetector computed tomography (MDCT) for this purpose.
Methods: Multidetector computed tomography was performed for 32 patients (24 males, 8 females; mean age, 65.9 ± 7.4 years) undergoing coronary artery bypass graft surgery. Preoperative MDCT criteria for GEA suitability were no significant stenosis or calcification and a diameter of 2.0 mm or more in the middle portion of the GEA. The skeletonized GEA was inspected in 30 patients to determine the accuracy of evaluation of arteriosclerosis by MDCT (2 patients were excluded owing to severe GEA stenosis). The internal diameter at the anastomotic site was compared with the diameters of the proximal, distal, and middle regions of the GEA on MDCT.
Results: The GEA was used to bypass a target coronary artery in 30 patients. The diameter of the middle of the GEA on MDCT correlated strongly with the actual internal diameter at the anastomotic site (r = 0.72, p < 0.0001). The diameter at the anastomotic site calculated from MDCT using the distance from the GEA origin to the anastomotic site and the actual diameter did not differ significantly (2.76 ± 0.6 versus 2.87 ± 0.5 mm, p = 0.06).
Conclusions: Preoperative MDCT imaging of the GEA is reliable for diagnosis, and a middle diameter of 2.0 mm or greater can be used to indicate GEA suitability for coronary artery bypass grafting.
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Introduction
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The internal thoracic artery (ITA) is utilized as the first bypass graft of choice in coronary artery bypass grafting (CABG) due to its excellent results in short- and long-term periods. In the present situation, the right gastroepiploic artery (GEA) is regarded as the second or third arterial conduits of choice [1–4], and is particularly suitable for circumflex and right coronary arteries [3, 4]. However, a method for preoperative assessment of the suitability of the GEA for use in CABG has not been established, resulting in the necessity of intraoperative small laparotomy and partial exposure of the GEA for the final determination. From our clinical experience for the past 5 years, the actual rate of the GEA suitability was calculated to be 93.6% in CABG patients with the preoperative intention of using the GEA, which means that an unnecessary laparotomy was performed in approximately 6.3% of the patients. Therefore, the preoperative quality evaluation of the GEA could play a very important role for these CABG patients.
From December 2006, we have performed routine evaluation of atherosclerotic changes in the whole aortic system using 64-slice multidetector computed tomography (MDCT) in patients scheduled for open-heart surgery. Image processing and compilation of data from MDCT allows construction of two- and three-dimensional images of the GEA that allow preoperative evaluation of the extent of arteriosclerosis in the GEA. The purpose of the current study was to evaluate the reliability and usefulness of preoperative MDCT imaging by comparing the GEA images with intraoperative findings.
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Patients and Methods
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Patients
Between December, 2006 and April, 2008 in our hospital, a total of 76 patients underwent CABG. There were 34 patients (44.7%) who were scheduled to undergo CABG using the GEA. In 2 of the 34 patients, the preoperative MDCT was avoided owing to moderate renal dysfunction (creatinine > 4 mg/dL and creatinine clearance < 30 mL/min) and history of severe allergic reaction to the contrast agent. In the remaining 32 patients, GEA images obtained from the MDCT data were used in the preoperative evaluation. This study was approved by the Ethical Committee of our institution. All patients gave written informed consent for use of their data.
Preoperative GEA Evaluation Using MDCT
As a routine preoperative procedure, 64-slice MDCT (Aquilion 64; Toshiba Medical Systems, Tokyo, Japan) was used for detecting atherosclerotic changes, such as stenosis, atheroma formation, and calcification in the whole aortic system. The CT scan conditions are given in Table 1. After positioning the patient, an iodized contrast agent (1 mL/kg) was injected into a peripheral vein at a rate of 2.5 to 5.0 mL/s over 16 to 18 s. When the contrast agent reached the descending aorta at the level of the diaphragm and the CT contrast value was 100 HU (Hounsfield unit), patients were requested to hold their breath for 4 s, during which time scanning was performed from the level of the subclavian artery to the femoral artery. Image processing and compilation of MDCT data were used to reconstruct GEA images in curvilinear two-dimensional (Fig 1A) and voluminal surface three-dimensional (Fig 1B) modes using Ziostation v1.16g software (Ziosoft, Tokyo, Japan).
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Fig 1. (A) Two-dimensional and (B) three-dimensional right gastroepiploic artery images rebuilt using multidetector computed tomography data.
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The two- and three-dimensional images were used to assess the extent of GEA arteriosclerosis, including irregularity of the intimal surface, stenosis, and calcific deposits, and the proximal (CT-proximal) and distal (CT-distal) diameters were measured. The part of the GEA at about the midpoint of the greater omentum is generally chosen as the anastomotic site in our surgical experience, and therefore a model was established in which the crossing point of the vertical midline of the spine was considered to indicate the midpoint of the greater omentum. Using this model, the GEA diameter at the crossing point (CT-middle diameter) was obtained as an approximation of the actual internal diameter at the anastomotic site. The distance from the GEA origin to the point of measurement of the CT-middle diameter (CT-middle distance) was also determined.
A meandering two-dimensional image of the GEA was rebuilt by image processing, with the two-dimensional image as a straight line (Fig 2A). A GEA diagram was produced by plotting the GEA diameter at 1-cm intervals from the origin to the distal part of the GEA (Fig 2B). The GEA diameter at each point was calculated using the full width at half maximum method [5–7]. This approach may permit evaluation of the suitability of the GEA for use as a conduit, based on acute tapering of the GEA at or distal to the middle portion. The evaluation criteria used to indicate suitability of the GEA were as follows: no significant stenosis, no calcification, and a CT-middle diameter of 2.0 mm or greater.
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Fig 2. (A) Right gastroepiploic artery (GEA) diagram rebuilt by image processing, with the two-dimensional image in a straight line. (B) The GEA diagram produced by plotting the GEA diameter at 1-cm intervals from the origin to the distal part of the GEA.
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Intraoperative GEA Evaluation
After a median sternotomy and upper laparotomy, the GEA was skeletonized and harvested with a Harmonic Scalpel (Ethicon, Somerville, New Jersey) [8, 9]. After the distal end of the skeletonized GEA was divided, papaverine solution was injected intraluminally, and the GEA was then wrapped in a papaverine-saturated sponge to relieve spasm of the GEA, and ensure that the GEA became a maximally dilated, relaxed arterial conduit. In addition, intraoperative diltiazem drip infusion (1.0 to 1.5 µg · kg–1 · min–1) was performed routinely. The skeletonized GEA provided easy handling for anastomosis and also allowed evaluation of the extent of arteriosclerosis, based on inspection and palpation. The actual internal diameter of the GEA with no spasm at the anastomotic site (operative anastomic diameter: OP-anastomotic diameter) and the distance from the origin to the anastomotic site (OP-anastomotic distance) were measured by inserting dilator probes of 1 to 4 mm and using a paper ruler, respectively, before anastomosing the GEA to the target coronary artery. The GEA diameter at the anastomotic site on MDCT (CT-anastomotic diameter) was calculated retrospectively by overlaying the OP-anastomotic distance on the GEA diagram produced preoperatively using MDCT data.
Comprehensive Evaluation
The reliability of GEA images from MDCT was evaluated based on intraoperative GEA findings and statistical comparison of the OP-anastomotic diameter with the diameters measured with MDCT (CT-proximal, CT-distal, CT-middle, and CT-anastomotic diameters). All data are expressed as means ± SD. A Student t test was used to assess differences between the OP-anastomotic and CT-anastomotic diameters, and the correlation coefficient (r) of the OP-anastomotic diameter with each MDCT diameter was calculated by regression analysis. Differences were considered significant at the level of p less than 0.05. Statistical analyses were conducted using StatView for Windows version 5.0 (SAS Institute, Cary, North Carolina). To evaluate the quality of bypass grafting by the GEA, a 3.0-mm transonic flow probe (Model SB-3.0 mm; Transonic Systems, Ithaca, New York) was placed around the GEA to measure flow, and catheter angiography was performed on postoperative day 7 to assess the patency of the GEA.
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Results
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The clinical characteristics of the 32 patients are shown in Table 2. Elective surgery for effort angina or postinfarction angina was performed in all patients. Preoperative cardiac function was well maintained, with a mean ejection fraction of 57.8% ± 10.9%, and only 4 patients had an ejection fraction less than 50%. Two of the 32 patients who underwent preoperative MDCT imaging did not meet the criteria for evaluation of the GEA and were excluded from the study.
The two- and three-dimensional GEA images (Fig 1A, B) allowed comprehensive preoperative evaluation of the diameter and extent of arteriosclerosis of the GEA, including the presence of significant stenosis and calcification. The GEA diagram (Fig 2A) enabled calculation of the diameter of the proximal, middle, and distal portions (Table 3) and evaluation of the presence of acute tapering. In the 30 patients who met the CT criteria for GEA suitability, the mean CT-proximal and CT-middle diameters were 4.21 ± 1.4 and 2.80 ± 0.7 mm, respectively. In the 2 patients who were excluded from study, the CT-middle diameter was small (1.2 to 1.7 mm) with severe arteriosclerosis in the GEA (Fig 3A, B).
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Table 3 Right Gastroepiploic Artery (GEA) Variables on Multidetector Computed Tomography (MDCT) and in Operations
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Fig 3. (A) Two-dimensional and (B) three-dimensional right gastroepiploic artery (GEA) images in a patient with a gastroepiploic artery that was unsuitable for use as a conduit owing to severe arteriosclerosis.
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Operative variables are shown in Table 4. Except for 4 patients who required mitral valvuloplasty or long onlay patch grafting, off-pump CABG was performed with a mean number of distal anastomoses of 3.6 ± 0.9. Complete revascularization was achieved in 28 patients, and 2 patients with a long diffusely diseased coronary artery required subsequent transmyocardial laser revascularization. There were no operative deaths.
In the 30 patients who met the CT criteria, the quality of the skeletonized GEA was satisfactory in terms of size and extent of arteriosclerosis and was used as a conduit. The operative variables related to the GEA are shown in Table 3. The GEA bypassed the distal right coronary artery with a mean bypass blood flow of 51.7 ± 23.8 mL/min. The mean value of the OP-anastomotic diameter was 2.87 ± 0.5 mm, and the mean OP-anastomotic distance was 18.2 ± 2.3 cm, resulting in calculation of a mean CT-anastomotic diameter of 2.76 ± 0.6 mm using the GEA diagram. The postoperative patency of each graft was determined by catheter angiography in 27 patients. The remaining 3 patients did not undergo angiography owing to their personal preference or moderate postoperative renal dysfunction. The results were as follows: ITAs 100% (35 of 35), GEA 100% (27 of 27), radial artery 95% (21 of 22), and saphenous vein graft 100% (2 of 2). As for the FitzGibbon classification of the patent grafts, all grafts except 1 (grade B) were grade A. One occluded graft was grade C.
The CT-middle and CT-anastomotic diameters showed a strong linear correlation with the OP-anastomotic diameters (r = 0.72, p <0.0001; r = 0.81, p <0.0001, respectively; Table 5). There was a weak correlation between the OP-anastomotic and CT-proximal diameters (r = 0.41, p = 0.02), but no correlation between the OP-anastomotic and CT-distal diameters. There was no significant difference between the OP-anastomotic and CT-anastomotic diameters (2.87 ± 0.5 mm versus 2.76 ± 0.6 mm, p = 0.06), although the CT-anastomotic diameter tended to be underestimated compared with the OP-anastomotic diameter.
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Comment
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Satisfactory short- and long-term outcomes have been reported with use of the GEA as an alternative arterial conduit in CABG [1–4]. In our institution, the ITA and radial artery are utilized as the first and second grafts of choice, respectively, and the GEA has been used as the third choice. Concerning preoperative assessment of these arterial conduits, the ITA and radial artery can be evaluated by ultrasonography and catheter angiography with generally high reliability. However, an accurate method for preoperative evaluation of the GEA has not been established. There are cases in which the GEA is found to be unsuitable only after partial harvesting following an upper laparotomy, and an improved method of preoperative evaluation is required to eliminate the need for intraoperative small laparotomy. We have used MDCT imaging for this purpose since the introduction of 64-slice MDCT, but there have been few reports evaluating this approach, despite the establishment of MDCT for postoperative assessment of bypass patency [4, 10].
The widespread use of a Harmonic Scalpel for skeletonizing the GEA provides a method to prolong the usable length of the GEA, makes it easier to handle the GEA for anastomosis, and allows assessment of the extent of GEA arteriosclerosis [4, 8, 9, 11–13]. In the 30 patients who met the CT criteria, the quality of the skeletonized GEA was satisfactory and bypass grafting using the GEA was achieved as planned preoperatively, indicating that MDCT for preoperative GEA evaluation is useful and reliable. In addition, the GEA diagram built using MDCT data was helpful for showing tapering of the GEA. The average length from the origin to the actual anastomotic site was 18.2 cm (15 to 25 cm) in this cohort, and therefore the GEA diagram allows estimation of the internal diameter at the probable anastomotic site by measuring the diameter 18 cm from the GEA origin.
The diameter of the middle portion of the GEA obtained from MDCT showed a strong linear correlation with the actual internal diameter at the anastomotic site (r = 0.72, p < 0.0001). Furthermore, there was no significant difference between the diameter at the anastomotic site calculated using the GEA diagram based on MDCT and the internal diameter at the anastomotic site (p = 0.06). These results show the reliability of preoperative GEA evaluation by MDCT and suggest that our preoperative criteria for the suitability of the GEA (no significant stenosis or calcification with a diameter of the middle portion of the GEA 
2.0 mm) are reasonable.
There are two limitations of this study. The full width at half maximum was used for diameter measurements on MDCT images, and that may have caused the CT-anastomotic diameter to be underestimated compared with the OP-anastomotic diameter. However, since the full width at half maximum is widely used in the radiologic field [5–7] to minimize the scatter of values determined in different measurements, we consider that the use of this method is acceptable. The second limitation emerges from the choice of the measuring point of the CT-middle diameter as the crossing point of the vertical middle line of the spine and the GEA on a two-dimensional image. The GEA around the midpoint of the greater omentum has generally been used as the anastomotic site, and an approximate point for this site on the two-dimensional image was required. However, the crossing point is not necessarily similar to the midpoint of the great omentum owing to morphologic differences of the stomach and the extent of dilatation of the stomach during acquisition of MDCT data. The CT-middle distance varied from 9.8 cm to 25.3 cm, indicating the need for a more reliable measuring point on the two-dimensional image for estimation of the GEA diameter at the anastomotic site. Use of a foaming agent before MDCT to dilate the stomach and allow determination of the midpoint of the greater omentum may be considered in a future series to improve the accuracy of the diameter at the anastomotic site on MDCT images. Alternatively, as the average of the OP-anastomotic distance was 18.2 cm in the current series, the best approach to obtain this diameter may be to make a measurement 18 cm from the GEA origin on the GEA diagram.
In conclusion, our results indicate the reliability and sensitivity of preoperative MDCT imaging for the diagnosis of GEA arteriosclerosis, and a middle diameter of 2.0 mm or greater on MDCT images can be used as a criterion to predict the suitability of the GEA for CABG. This method is based on rebuilding MDCT data that are acquired in routine preoperative evaluation of whole-body atherosclerotic changes and does not place an additional financial or medical burden on the patient.
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Acknowledgments
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We thank Ms Emi Miyazaki and Mrs Saori Matsuo for their technical assistance with image processing.
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Abstract
Introduction
