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Ann Thorac Surg 2000;69:728-731
© 2000 The Society of Thoracic Surgeons
a Department of Thoracic Surgery, Nagoya University School of Medicine, Nagoya, Japan
Address reprint requests to Dr Yasuura, Chuoudai 6-11-14, Kasugai City, Aichi 487-0011, Japan
| Abstract |
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Methods. An application of in situ GEA grafting to the right coronary artery (RCA) was studied by using a theoretical model. The theoretical model of CABG was given variables; ie, the diameters and the lengths of both in situ GEA and proximal segment of the RCA, and the degree of proximal stenosis in the RCA. According to the range of these variables obtained from clinical data, the ratio of the GEA flow to the flow of the RCA distal to the anastomosis was calculated.
Results. Main factors to determine the flows in the two parallel paths were the inner diameters of both vessels, and the degree of the proximal stenosis. When the inner diameters of the GEA were 0.5 mm larger than that of the RCA, the GEA carried more than 50% of the total flow of the RCA distal to the anastomosis despite a moderate stenosis in the RCA. When the inner diameter of the GEA was equal to, or 0.5 mm smaller than, that of the RCA, the GEA flow was dominated by the native RCA flow unless the proximal stenosis was critical.
Conclusions. If the inner diameter of the GEA is 0.5 mm larger than that of the RCA, CABG with the GEA can be applied more widely. If not, the application would basically be limited.
| Introduction |
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However, the GEA has two noteworthy characteristics in comparison with the ITA. One is the spasms associated with histologic distinction. Stronger spasm in the use of the GEA during operation is often encountered, and for prevention, topical use of papaverine and a systemic dose of nitroglycerin or calcium channel blockers are required [4]. Another characteristic is a limited flow reserve. The GEA branches off from a more distal portion of the aorta, is longer than the ITA, and varies more widely in diameter among patients, and hence it often causes a limited flow reserve. In regard to the use of in situ arterial grafts, if the proximal stenosis in the recipient coronary artery is marginal, postoperative angiography often shows "distal thread phenomenon" or "string sign" in ITA grafts and "thinning down phenomenon" in GEA grafts, leading to graft occlusion [68]. Flow competition between the GEA and the recipient coronary artery has been discussed, and the indications for use of the GEA in CABG remains controversial.
In this study, to clarify the indications of in situ GEA to the RCA as a bypass graft, we analyzed the effects of the lengths and the diameters of both the GEA and the proximal segment of the RCA, and the degree of proximal stenosis in the RCA on the ratio of the GEA flow to the flow of the RCA distal to the anastomosis under various conditions by using a theoretical model of the bypass system.
| Material and methods |
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From continuity, the flow in the GEA and native coronary artery combine to the total flow of the RCA distal to the anastomosis, and the source pressure of the two paths are the same:
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Clinical data
From January 1995 to December 1997, the in situ GEA was used for primary CABG in 26 patients. They were 24 males and 2 females, with a mean age of 60.3 years, and an average body surface area of 1.6 m2. Intraoperative data concerning both vessels showed that the length of their GEA pedicles were 15 to 20 cm, their Dg, measured with probes that were sized in 0.5 mm increments, were 1.5 to 2.5 mm, and Dc were 1.5 to 2.0 mm. The sites of their anastomoses ranged from the distal portion of the RCA to the posterior descending artery. According to these data, Lg for the calculation was set at 15, 17, and 19 cm; Dg at 1.5, 2.0, and 2.5 mm; Dc again at 1.5 and 2.0 mm; and Lc at 10 and 15 cm, which correspond to the distal portion of the RCA and the posterior descending artery, respectively. These values can be applied to the equations based on the theoretical model to calculate the ratio of flow through the GEA to the RCA flow distal to the anastomosis (Qg/Qd).
| Results |
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| Comment |
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Previous studies [9, 13] demonstrated that a bypass graft to a nonobstructed coronary artery does not increase the distal coronary flow, which arises from the proximal coronary artery and the bypass graft. Accordingly, there is an inverse relationship between the magnitude of flow arising from these two sources: the larger the native coronary flow, the less the bypass graft flow, and vice versa [10]. These considerations correspond with the fact that the arterial grafts are anatomically patent but physiologically nonfunctioning if the proximal stenosis in the recipient coronary artery is marginal [14]. The influence of the competitive flow on prognosis of the arterial graft has remained obscure. However, in regard to the ITA, the occluded graft immediately after operation was demonstrated to be patent when progression of disease in the recipient coronary artery occurred [15]. This report suggested the physiological adaptability of in situ ITA.
On the other hand, the GEA is the fourth branch of the aorta, whereas the left ITA is the second branch. Clinical investigations [16, 17] suggested that the pressure pattern of the GEA was different from that of the ITA and, consequently, flow competition may be by far more prone to occur. Particularly, in contrast with in situ ITA, there has been no report concerning restoration of patency in the occluded GEA with progressive change in the recipient coronary artery. Mills and colleagues [18] concluded that a setting with possible competition of flow should be avoided with in situ GEA grafts. If the flow competition associated with the use of in situ GEA is confirmed to be a major factor of occlusion for a long-term period, these results may point to the selection of grafts. Nevertheless, little investigation has been conducted concerning the strict indication of in situ GEA. In experimental animal studies, the size and the length of both grafts and the native coronary artery are so different from those of humans, that the results can not be applied to clinical practice. Our study, based on a mathematical model, makes for the first time the indication of in situ GEA for the revascularization of the RCA clear quantitatively. It suggests that the diameter of both vessels and the degree of proximal stenosis in the RCA are the major factors to determine whether the GEA flow becomes dominant over the flow of the proximal segment of the RCA. When the diameter of the GEA is 0.5 mm larger than that of the RCA, the GEA can be available even in moderate stenosis in the RCA, whether the GEA is longer or not, and the anastomitic site is distal or proximal. Therefore, the GEA can be widely used as a graft of choice. On the contrary, when the diameters of the GEA are smaller than that of the RCA, or the same, the indication of the in situ GEA graft should be strictly limited. In addition to such circumstances, if the proximal stenosis is not severe, a free GEA grafting may well be used.
Voutilainen and colleagues [19] reported that postoperative good function of GEA grafts had a significant correlation with the proximal stenosis. Hashimoto and colleagues [17] also demonstrated that stenosis more than 60% in diameter in the recipient artery is a critical line between functioning and nonfunctioning arterial grafts. These clinical reports are consistent with our conclusions calculated from a theoretical model. Review of abdominal angiograms in 202 cases showed that 152 cases (76%) have a diameter greater than 2.0 mm at the portion 20 cm distant from the origin of the GEA [20]. Therefore, the GEA may not always be indicated as an ideal bypass conduit if the criteria for use of the GEA are dependent on our theoretical model.
Our study also demonstrates that it is important to accurately measure the diameter of both vessels, and assess the degree of proximal stenosis in the RCA by preoperative angiography.
| References |
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