Eur J Cardiothorac Surg 2002;21:800-803
© 2002 Elsevier Science NL
Angiographic evaluation of the luminal changes in the radial artery graft in coronary artery bypass surgery: a concern over the long-term patency
Masahiro Ikeda*,
Hirokazu Ohashi,
Yasushi Tsutsumi,
Katsuaki Hige,
Takahiro Kawai,
Masateru Ohnaka
Department of Cardiovascular Surgery, Fukui Cardiovascular Center, Shinbo 2-228, Fukui 910-0833, Japan
Received 31 October 2001;
received in revised form 11 January 2002;
accepted 30 January 2002.
* Corresponding author. Tel.: +81-76-433-2222; Fax: +81-76-433-2274
e-mail: ikeda{at}toyama-med.jrc.or.jp
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Abstract
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Objective: The radial artery graft (RA) still involves two unsolved problems, namely, vasospasm and intimal hyperplasia, although satisfactory early and mid-term outcomes have been obtained recently. Methods: Two hundred patients underwent coronary artery bypass surgery with RA between October,1996 and December,2000. We made a comparison of the luminal diameters at early and mid-term periods in 23 patients who underwent mid-term angiographies after a mean follow-up of 27 months. The proximal anastomoses of the RA were the ascending aorta in these patients. The G/N ratio was determined as a ratio of the luminal diameter of the graft to that of the revascularized coronary artery so as to evaluate the luminal discrepancy between the graft and the native artery. Results: In the 122 patients who underwent angiographies about one month after the operation, the patency rate was 99% (144 of 145) in the RA, 97% (139 of 143) in the left internal thoracic artery graft (LITA), 96% (75 of 78) in the saphenous vein graft (SV). In the 23 patients who underwent mid-term angiographies, the patency rate was 91% (24 of 26) in the RA, 100% (23 of 23) in the LITA, and 83% (20 of 24) in the SV. The luminal diameters of the RA and LITA significantly increased from 2.15 to 2.52 mm, and from 1.75 to 1.97 mm, respectively. The luminal change from 3.78 to 3.33 mm in the SV was not significant. The G/N ratios changed from 1.10 to 1.31, from 1.01 to 1.13, and from 2.05 to 1.86 in the RA, LITA, and SV, respectively. The change of the RA alone was statistically significant. Conclusions: The angiographic early patency rate was almost the same in three kinds of graft material, but the mid-term patency rate of the RA was between those of the LITA and SV. The mid-term luminal dilatation of the RA could involve two conflicting characteristics, namely, a good intimal function and a propensity to increase in the luminal discrepancy. Therefore, a further observation is required to evaluate whether the clinical outcome of the RA could remain as good as that of the LITA in the long-term period.
Key Words: Luminal diameter • Radial artery graft • Coronary artery bypass grafting
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1. Introduction
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The benefits of the internal thoracic artery in coronary artery bypass surgery are undoubted for its excellent long-term patency [1]. Although the radial artery graft (RA) was introduced by Carpentier et al. in 1973 [2], this conduit was abandoned for its discouraging outcome due to hyperspasticity and intimal hyperplasia. Coupled with an increasing interest in total arterial revascularization in coronary surgery, however, the RA has been re-evaluated as an alternative arterial conduit and it was revived because of the availability in antispastic agents and the improvement in the harvesting technique [3]. Recently, good clinical and angiographic outcomes of the RA have been obtained [4–8]. Nevertheless, the two major problems are still unsolved entirely. In the present study, therefore, we evaluated the RA in coronary artery bypass surgery from the viewpoint of angiographic luminal changes in relation to the size of the native coronary artery in the mid-term period.
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2. Materials and methods
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In our hospital, the RA was introduced as a second order arterial graft next to the left internal thoracic artery (LITA) in October 1996. The way of selection of grafts was mainly determined by the vessel importance,; namely, LITA to LAD (the left anterior descending artery) in most cases, and RA to the second important vessel. Until December 2000, 200 patients underwent coronary artery bypass grafting with the RA. The negative result of a preoperative Allen test was a prerequisite to an indication of using the RA. The use of the RA was contraindicated when the patients could not tolerate the postoperative administration of antispastic agents or when there was no time sufficient to harvest the RA in emergency operations. In patients with renal dysfunction, it was not also used because of the potential need for an intraluminal shunt. The preoperative clinical characteristics of the patients are shown in Table 1.
All operations were performed through median sternotomy. The harvest of the RA was simultaneous with that of the LITA. The RA was harvested together with its pedicle including the surrounding fat and satellite veins in the non-dominant forearm. After systemic heparinization, the RA was resected. For the graft pretreatment, papaverine chloride (4 mg/ml of saline) was used in the early period and was then switched to verapamil plus nitroglycerin solution, which provides good preservation of the endothelial function [9]. An intravenous administration of calcium-channel inhibitor was initiated after the anesthetic induction, and it was then prescribed orally in conjunction with wafarinization to all patients postoperatively. Diltiazem (intravenously; 2.5 mg/h, orally; 90 mg/day) was used in the first 52 patients. In the following 148 patients, it was switched to verapamil (intravenously; 0.5 mg/h, orally; 120 mg/day) [9]. In total, 195 of 200 operations were performed under cardiopulmonary bypass (CPB) with cardioplegic arrest. Myocardial protection was achieved by means of both antegrade and retrograde intermittent cold blood cardioplegias. The proximal anastomosis to the ascending aorta was performed during the cross-clamping time. In the other five patients, operations were performed without CPB because the preoperative computed tomography or intraoperative ultrasonic study demonstrated severe calcification and soft plaques in the aortic lumen. The operative data are shown in Table 2. The total number of the RA was 205 with 228 distal anastomoses because of its division and sequential anastomoses. In total, 197 RA were directly anastomosed to the ascending aorta. Of the residual eight RA, seven were anastomosed to the right ITA and one was anastomosed to the LITA as a prolongation. The distribution of the distal anastomoses is shown in Table 3.
The necessity and significance of postoperative coronary angiography were explained in all patients, and the angiography was performed if patients agreed.. The postoperative angiography about one month after the operation was performed in 122 patients (61%) with 145 RA, 143 LITA, and 78 saphenous vein (SV) distal anastomoses. By December 2000, survival of more than one year after the operation was achieved in 145 cases, and 23 patients of them agreed to enroll in the mid-term study. The mid-term angiography after a mean follow-up of 27±10 months was performed for 23 patients (12%) with 26 RA, 23 LITA, and 25 SV distal anastomoses, who were subjected to an evaluation of the angiographic luminal changes. In these 23 patients, the proximal anastomotic site of the RA was the ascending aorta. The occluded grafts were excluded from the comparison of the luminal changes. During angiography, all grafts were selectively catheterized and visualized. Angiographic images were measured using a special software (Stenosis Analysis ver. 2.01, mss, Japan). Measurement of the luminal diameter was carried out at near the proximal graft and the distal coronary artery to the distal anastomosis. In patients with sequential anastomoses of RA, the luminal diameter was measured at near the proximal graft and the distal coronary artery to the side-to-side anastomotic site. For an evaluation of luminal discrepancy between the graft and the revascularized coronary artery, we calculated the ratio of the luminal diameter of the graft to that of the revascularized native coronary artery, and we determined this value as the G/N ratio. All measurements were carried out separately by two different observers blinded to each other's treatment.
The data are expressed as mean±1 standard deviation. The quantitative data were compared using the paired t-test. P-value of less than 0.05 was considered significant. Cumulative cardiac events free and survival ratios were calculated by the Kaplan–Meier estimation. The statistical analysis was done with a special software (StatView ver. 5.0, SAS, USA).
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3. Results
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Hospital death occurred in five cases, and the causes were perioperative myocardial infarction, ventricular rupture, mediastinitis, and complication of intra-aortic balloon pumping. Late death occurred in seven cases due to heart failure, cancer, cerebrovascular event, and sudden death. The rate of freedom from cardiac events at 2-years, including recurrence of angina and heart failure and malignant arrhythmia, was 95%. The cumulative survival rate caused by cardiac events at 2-years was 98%.
The patency rates in the early postoperative period were 99% (144/145) in the RA, 97% (139/143) in the LITA, and 96% (75/78) in the SV. One occluded RA showed a diffuse narrowing unrelated to the anastomotic line, which was probably caused by spasm. The mid-term patency rate was 91% (24/26) in the RA, 100% (23/23) in the LITA, and 83% (20/24) in the SV. One occluded RA showed a diffuse narrowing, which had been occluded in the postoperative period. The other occluded RA showed complete occlusion just from the proximal anastomotic line. The luminal diameter and the G/N ratio of each graft are shown in Table 4. The luminal diameter significantly increased from 2.15 to 2.52 mm in the RA, and from 1.75 to 1.97 mm in the LITA in the mid-term period. A demonstrative case of change in the luminal diameter of the RA is shown in Fig. 1
. Obscure graft disease of the SV was detected in two2 patients in the mid-term period. The luminal diameter of the SV changed from 3.78 to 3.33 mm, and this change was not significant. The G/N ratio of the RA significantly increased from 1.10 to 1.31. The G/N ratio of the LITA changed from 1.01 to 1.13 and that of the SV from 2.05 to 1.86, and these changes were not significant.
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Fig. 1. Postoperative angiographies in the early (a) and mid-term periods (b) in a demonstrative case of change in the luminal diameter of the radial artery graft.
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4. Discussion
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The RA has been revived because of the availability of the antispastic agents as well as the improvement of the harvesting technique [3]. Anatomically, the RA is a muscular artery whereas the ITA is an elastic artery [10]. Therefore, there has been a functional problem about hyperreactivity to various external stimuli, which not only could result in vasospasm with a possible fatal deterioration in the postoperative hemodynamics but also could influence the graft patency. Fibrous intimal hyperplasia is another major problem of the RA due to focal damage to the intima [11]. In addition, intimal hyperplasia is likely to develop especially when the RA is anastomosed directly to the ascending aorta [4,10]. However, even when the RA was directly anastomosed to the ascending aorta, good clinical and angiographic outcomes have been demonstrated [5–8]. Therefore, we also anastomosed the RA proximally to the ascending aorta when the aorta was intact. The early and mid-term patency rates were 99 and 92%, respectively, which were similar to other authors’ results [5–8].
In the present study, the luminal diameter of the RA significantly increased from 2.15 to 2.52 mm in the mid-term follow-up. This result suggested that the RA could be a living conduit with a good intimal function such as nitric oxide production and could have a capacity of growth depending on increased myocardial blood flow demand in the mid-term period. Because the RA is a free graft, sympathetic denervation could also cause luminal dilatation. A simple gradual liberation from vasospasm of the RA could result in this luminal enlargement. Namely, even when the RA was patent with antispastic agents in the immediate postoperative angiography, more release from vasospasm could gradually occur. Possati et al. [7] also demonstrated luminal dilatation of the RA from 2.09 to 2.58 mm in the 5-year follow-up and concluded that the hyperspastic characteristics gradually declined with time.
In the present study, we evaluated not only the luminal changes per se, but also the G/N ratio of each graft. The G/N ratios in the RA and LITA were nearly 1 in the immediate postoperative period. Twenty seven months later, the G/N ratio of the RA significantly increased from 1.10 to 1.31, whereas that of the LITA remained at nearly 1. The extent of nitric oxide-dependent vascular relaxation of the RA is reported to be greater than that of the ITA [12]. Therefore, these results could be explained as an over-reaction of the RA to nitric oxide. The mean wall shear stress (
) is calculated as a variation of the Hagen–Poiseuille equation: =4
Q/
r3, where is the blood viscosity, Q is the blood flow, and r is the graft lumen radius, and 
can cause endothelial production of vasoactive mediators such as nitric oxide and prostacyclin which have vasodilatory as well as antiplatelet effects [13,14]. According to this formula, excessive luminal enlargement of the graft diameter could lead to a deterioration in the graft patency through the decrease in the shear stress [6,15,16]. The excellent long-term patency of the LITA may be attributed to its anatomical characteristics [11] and good intimal function as well as to its luminal size which is just fit for the revascularized coronary artery. Therefore, the statistically significant increase in the G/N ratio of the RA may cause deterioration of the long-term patency as compared to that of the LITA. On the other hand, the G/N ratio of the SV was consistently as high as 2. This result could demonstrate that the SV has an inferior intimal function as well as a more extensive luminal discrepancy as compared with the arterial conduits. Considering the gradual excessive increase in the luminal diameter of the RA, there is a fear of gradual deterioration of the patency rate in the long-term period. The mid-term patency rate of the RA was between those of the LITA and SV in the present study. Therefore, it is quite interesting to investigate whether the clinical outcome of the RA could remain between those of the LITA and SV in the long-term follow-up period, and thus further studies are necessary.
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Top
Abstract
1. Introduction
