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Ann Thorac Surg 2003;76:1498-1504
© 2003 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Washington University School of Medicine, St. Louis, Missouri, USA
* Address reprint requests to Dr Barner, Department of Cardiothoracic Surgery, Washington University School of Medicine, 11155 Dunn Rd, Office Building 1, St. Louis, MO 63136, USA
e-mail: barnerh{at}msnotes.wustl.edu
Presented at the Forty-ninth Annual Meeting of the Southern Thoracic Surgical Association, Miami Beach, FL, Nov 7–9, 2002.
Abstract
BACKGROUND: The radial artery (RA) can be used as either an aortocoronary (RA-Ao) or composite graft (T graft). Optimum use for the RA has yet to be established. We compared RA patency with these two techniques.
METHODS: Between October 1993 and June 2001, 1505 patients underwent coronary artery bypass grafting using the RA as either a composite (n = 1022) or RA-Ao graft (n = 483). Angiograms performed on 203 (13.5%) patients with signs or symptoms of ischemia at an average of 26.1 ± 18.5 months postoperatively were reviewed.
RESULTS: Patients with RA-Ao grafts had a greater incidence of postoperative angiography versus patients with composite grafts (19% versus 11%; p < 0.01). Patients receiving T grafts had a greater number of anastomoses per patient (4.1 ± 0.6 versus 3.0 ± 1.0; p < 0.01) and a higher incidence of total arterial revascularization (100% versus 41%; p < 0.01). Regardless of grafting strategy, patency was significantly worse for targets of the right coronary artery (58% T graft; 67% RA-Ao; p < 0.01 for both) and for targets with less than or equal to 70% stenosis (59% T graft; 57% RA-Ao; p < 0.01 for both). The site of proximal anastomosis failed to effect RA patency (relative risk, 1.2; 95% confidence interval, 0.7 to 1.8; p = 0.50).
CONCLUSIONS: The site of the proximal anastomosis does not appear to influence patency. Both RA-Ao and composite conduits are sensitive to target location and stenosis. Advantages of composite grafting include greater conduit length and minimizing aortic manipulation at the expense of increased complexity and the potential for hypoperfusion. These factors should be considered when choosing an RA grafting strategy.
Since its reintroduction by Acar and colleagues [1], the radial artery (RA) has generated significant interest as an alternative arterial conduit for coronary artery bypass grafting. The RA is an attractive conduit as it may be harvested simultaneously with the internal thoracic artery (ITA) and bilaterally if additional conduit is required. Its thick wall and diameter facilitate the performance of anastomoses, and its length is sufficient to accommodate most distal targets [2]. Although first described as an aortocoronary conduit by Carpentier and associates [3], the RA is used extensively as a composite graft with the pedicled ITA in a T or Y graft configuration [4]. Because of its versatility, the RA has become the second conduit of choice after the ITA for many surgeons [5]. Although several grafting strategies have been reported for this conduit, the optimal use of the RA has yet to be determined [1–8].
The purpose of this study was to compare the results for patients undergoing coronary artery bypass grafting with the RA when used as an aortocoronary conduit versus as a composite T graft with the ITA. It has been previously shown that both target location and proximal target stenosis are critical to the long-term patency of the RA when used as a composite T graft [9]. In this investigation, we have evaluated the impact of the proximal anastomosis, either to the ascending aorta as an aortocoronary conduit or to the pedicled ITA as a composite T graft, for its effect on RA patency. We have further investigated whether target location and stenosis remain significant predictors of RA patency when used as an aortocoronary conduit.
Material and methods
Study population
Between October 1993 and June 2001, 1,505 patients underwent coronary artery bypass grafting using the RA conduit. For 1,022 patients the RA was proximally anastomosed to the ITA as a composite T graft configuration, and in 483 patients it was anastomosed to the ascending aorta. Of these, 203 patients have undergone postoperative angiography for signs or symptoms of myocardial ischemia and 111 of 203 having a T graft configuration have previously been reported [8]. These patients constituted the study population. The patient demographics and perioperative (30-day) outcome data were collected prospectively in accordance with Society of Thoracic Surgeons database guidelines (Table 1). All data were collected under the guidelines of the institutional review board, and informed consent was obtained from each participant.
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70%), severely (71% to 89%), or critically (
90%) stenosed as determined by the results of preoperative angiography. Target location was classified as left anterior descending, circumflex (CX), or right coronary artery (RCA) on the basis of the anatomic relation to the major coronary arteries. Actual CX targets were obtuse marginal or posterolateral branches, whereas left posterior descending arteries were considered to be RCA targets (of which there were three). The ramus intermedius was considered a CX branch. The RCA was rarely the target (four in each group), which was usually the posterior descending (n = 79), the posterolateral (n = 10), or both (n = 11).
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Technique
For T grafting, the RA was harvested from its origin to the wrist crease by surgical assistants. Dissection with electrocautery was used superficial to the fascia whereas blunt and sharp technique was used for the RA pedicle with a shift to ultrasonic dissection midway through this experience. Branches were divided between clips or with ultrasound. Papaverine in saline was sometimes sprayed on the artery during harvest. Storage was in a wet sponge in saline or in heparinized blood with papaverine. Intraluminal papaverine (2 mg/mL of heparinized blood) was applied after the proximal or distal anastomosis; in the former the RA was allowed to dilate while exposed to arterial pressure. Perioperative nitrates or calcium-channel blockers were not systematically used nor were the latter used subsequently.
Follow-up
The clinical research staff obtained follow-up data for all patients with an RA graft between July 1998 and November 1, 2002, by means of postal questionnaire and telephone interview. The percent follow-up for both the composite T graft and aortocoronary group was more than 90% complete for both groups. A total of 203 patients (T graft, n = 111; aortocoronary, n = 92) were identified as having undergone postoperative angiography for signs and symptoms of myocardial ischemia. The angiographic results for this symptomatic group were reviewed.
Postoperative angiography
The results of postoperative angiography were obtained directly from the performing cardiologist or cardiac catheterization laboratory. Anastomotic failure was defined as occlusion or stenosis greater than or equal to 90%. The presence of extensive conduit narrowing or "string sign" was considered functionally occluded and recorded as nonpatent.
Statistical analysis
Statistical analysis was conducted using SAS version 7.0 software (SAS Institute, Inc, Cary, NC). Survival analysis methods were based on the incidence of anastomotic failure that was presumed to occur at the time of repeat angiogram. Kaplan-Meier analysis was used for comparisons of RA patency when used as a composite and aortocoronary conduit. Univariate analysis identified target variables that were significantly associated with RA anastomotic failure. Multivariate analysis with Cox regression identified the relative risk and 95% confidence intervals for significant independent predictors of RA patency based on the 
2 statistical analysis. Continuous data were expressed as mean ± standard deviation unless otherwise stated. All statistical analyses were reviewed by the Department of Biostatistics, Washington University, and are in agreement with the Uniform Requirements for Manuscripts Submitted to Biomedical Journals According to Biostatistics guidelines.
Results
The mean follow-up times for both the T graft and aortocoronary groups were 27.6 months (range, 2 to 71 months) and 29.2 months (range, 0.4 to 96 months), respectively. The patient demographics for these two groups were similar (Table 1) with only the incidence of tobacco use (p < 0.04) statistically different. The overall percentage of patients undergoing postoperative angiography was, however, significantly greater among the aortocoronary group when compared with patients who received a composite T graft 19% (92 of 483) versus 11% (111 of 1,022; p < 0.01). The differences in operative strategy stratified by grafting technique are shown in Table 2. This included more anastomoses performed per patient in the T graft group (p < 0.01) and a significantly greater incidence of total arterial revascularization among patients with an ITA/RA T graft (p < 0.01). Sequential grafting with the RA was also more common in the composite grafting group, resulting in a both a greater total number of RA anastomoses and RA anastomoses per patient in the T graft group (p < 0.01).
The target characteristics were also significantly different dependent on the grafting strategy used (Table 2). Whereas the RA aortocoronary conduit was used primarily for targets of the left anterior descending coronary artery and CX, T graft anastomoses were directed principally toward targets of the CX and significantly more often for targets of the RCA distribution (p < 0.001). Similarly, T graft targets frequently had moderate stenosis whereas aortocoronary grafts were used more frequently for vessels with either severe or critical stenosis (p < 0.01). Too few grafts were placed to the RCA versus its branches for a meaningful assessment (for aortocoronary conduits, two of four occluded; for T grafts, three of four occluded).
There were no significant differences in the perioperative complications between the T graft and aortocoronary groups. The respective incidences of perioperative bleeding requiring reexploration (5.4% versus 3.3%), stroke (2.7% versus 2.2%), or myocardial infarction (3.6% versus 3.3%; p > 0.05 for all) were similar. The incidences of deep sternal wound infection (0.9% versus 1.1%) or hypotension requiring intraaortic balloon pump placement (2.7% versus 4.3%) were no different between the two groups (p > 0.05 for all).
Regardless of grafting strategy chosen, target location and proximal target stenosis were both identified as significant predictors for anastomotic failure. As shown in Table 3, univariate analysis demonstrated superior patency for targets of the left anterior descending coronary artery and progressively worse patency for the CX and RCA distributions. Radial artery patency was similarly affected by proximal target stenosis. Actuarial patency for the RA was lowest for vessels with moderate stenosis ('70%) and increased steadily with increasing target stenosis (Table 3). The average target stenosis for patent aortocoronary RA anastomoses was 85% ± 13% as compared with 78% ± 18% for occluded anastomoses (p < 0.001). The average target stenosis for patent T graft RA anastomoses was 82% ± 15% as compared with 71% ± 18% for occluded vessels (p < 0.001). The choice of proximal anastomosis (Table 3), ITA versus ascending aorta, failed to show any statistical difference.
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A principal finding of this investigation was the similar patency of the RA regardless of grafting strategy chosen [10, 11]. It has been suggested that the RA, as a third-order or fourth-order vessel, is better suited to an ITA anastomosis rather than the ascending aorta. Anastomosis of any arterial conduit to a thicker walled aorta requires a small hole in the latter, which can narrow during healing or by intimal hyperplasia.
The patients receiving T grafts in this series did have a greater number of anastomoses per patient and a higher incidence of total arterial revascularization. Although acknowledging that the T graft patients had fewer postoperative catheterizations when compared with the aortocoronary group, determining the specific benefit of arterial revascularization is not easily demonstrated in this retrospective analysis. Whereas prophylaxis against progression of native disease may be one factor [12], any other benefits of arterial revascularization may require longer follow-up as suggested by others [13, 14]. From a technical standpoint, composite grafting did provide sufficient length as a result of the T graft construct to perform a complete arterial revascularization with only two conduits. This "no-touch" technique with respect to the ascending aorta should also theoretically provide the additional benefit of minimizing aortic manipulation and, if combined with off-pump techniques, has the potential to further reduce aortic trauma and subsequent stroke [15, 16], which was not realized in this experience.
We have previously shown that the RA, when used as a composite graft, is particularly sensitive to both target location and proximal target stenosis [8]. The results of the present investigation have demonstrated that the RA aortocoronary conduit appears equally sensitive to these same factors. Indeed proper target selection appears to be the principal determinant of RA patency rather than grafting strategy chosen. The results of this study are consistent with other reports suggesting that the RA should not be used for targets with less than 70% stenosis [8, 11, 17, 18], which has become our practice.
The impact of target location has similarly been addressed by several investigators for both arterial and venous conduits [11, 19–22]. The superior patency for targets of the left anterior descending coronary artery and CX distributions appears to be the result of improved anastomotic outflow into the larger vascular beds supplied by the anterolateral circulations. The RCA distribution frequently supplies a smaller healthy myocardium requiring less flow [23]. The relatively poorer RA patency to targets of the RCA has been demonstrated by others [11]. The nonsignificant superior patency of aortocoronary conduits in this study (75% versus 70%) was most likely the result of greater use of the T graft for moderately stenosed targets of the RCA (Table 2) rather than any particular benefit from the aortic anastomosis.
This investigation further supports the utility of the RA when used as either a composite or aortocoronary graft inasmuch as the perioperative morbidity and mortality were acceptably low for either grafting strategy. Although the safety of the RA has been well established [2, 4, 6, 7], the RA may provide even better intermediate-term outcomes when compared with saphenous vein grafts [24]. Compared with other arterial conduits, the RA has the advantage of being easily and safely harvested, avoiding sternal devascularization, and providing excellent length. If used appropriately, RA patency approaches that of the ITA when directed to proximal targets with more than 70% stenosis [7, 10, 11, 18, 25]. The limitations of target selection for the RA must be recognized and alternative strategies considered for those targets associated with reduced patency.
Limitations of this nonrandomized retrospective study are that it was spread over 8 years and resulted in two very different groups of patients despite the fact that the demographics were similar. Grafting strategies varied significantly among the 13 surgeons, although in the T graft group there was consistency of philosophy and technique because 1 surgeon performed 89% of operations, whereas the other surgeons were selective in their use of the RA. This singular commitment to the T graft resulted in more RA grafts to lateral and inferior targets with lesser degrees of stenosis (50% to 70%).
The indication for angiography was symptoms or signs of ischemia, but we do not have data on whether some patients with the same symptoms or signs were not studied. In this regard, it has been found that graft patency is 15% to 20% lower in symptomatic patients versus symptomatic patients [26].
An additional limitation is imposed by the assumption that the time to graft failure is assumed to be the same as the date of postoperative cardiac catheterization. In the absence of serial control angiography, this assumption permits the use of the Cox model for analysis of patency within a longitudinal study.
Acknowledgments
This article would not have been possible without the dedicated efforts of the clinical research staff and their tireless commitment to patient follow-up.
Discussion
DR CLAUDIO MUNERETTO (Brescia, Italy): Let me congratulate the authors for the interesting presentation that provides additional information about the physiology of the radial artery. Several authors already reported that the radial artery is sensitive to both location and target stenosis.
Doctor Sundt, who is here, demonstrates that the radial artery may be very sensitive to the location. Your study provides important information about the proximal anastomosis but unfortunately did not give enough information about the role of distal anastomosis.
I would like point out that the sensitivity of the radial artery to the location may also be related to a wrong quantification of the degree of coronary lesion, expecially in the case of a proximal lesion of the right coronary artery. In such cases, the degree of stenosis asserted by observational angiography may be critical and up to 80% to 90%, but it could be associated with a reduction of coronary flow because of the large diameter of the vessel. This creates the condition for a competitive flow with the radial artery graft.
For the above mentioned reason, I would like to know how many patients who had occlusion of the radial artery had a proximal lesion. Besides, did you find any differences in radial artery patency with regard to the type of final anastomosis, side-to-side versus side-to-end?
Thank you very much.
DR MANIAR: Thank you for your questions. I do agree with you, there have been several investigations now that have shown that the radial artery is particularly sensitive to both target location as well as target stenosis. We had previously reported on some of this data at the American Association for Thoracic Surgery a few years ago.
The interest in performing this study was really twofold: one, to see whether patency rates were different when used as an aortocoronary conduit versus a T graft construction, and two, to see whether the same factors, which appeared to be significant in a T graft construction, applied as well to the aortocoronary graft. And I think we are fairly convinced that the impact of both target stenosis and target location apply to the radial artery when used either as a T graft or an aortocoronary graft.
With respect to your question regarding where the exact location was for the right coronary artery, I think this is a very good question. I can tell you, although I do not have the exact numbers here, the majority of the anastomoses to the right coronary were fairly distal anastomoses, meaning it was a very rare exception when the graft was placed very proximally on the right coronary artery. I think it is something worth looking into, and it is definitely a subset of patients we can not analyze, and obviously the patency for right coronary arteries, for right coronary targets, or perhaps for several reasons, not only is a result of I think what you are alluding to, proximal target stenosis, but also the bed in which that graft flows into, meaning the outflow for that particular target.
And lastly, the majority of these, at least with the T graft construction, were performed by 2 surgeons at our institution who performed, at least in almost its entirety, a side-to-side or parallel anastomosis. So it is difficult to give you some meaningful data with regard to a comparison with that.
DR THORALF SUNDT (Rochester, MN): I enjoyed that very much, Hersh, and congratulations on pulling those data together. It is not easy to do once you have gone back to your clinical responsibilities, particularly at another institution, and I do not underestimate that.
I am committed to the notion of arterial grafting in general and have expended a good bit of energy in radial artery grafts in particular. At this point, however, we have a good 10 years' experience with the radial artery as a conduit and need to step back and objectivly answer the question "How good is the radial artery as a second arterial conduit?" What is the best additional arterial graft to the left internal thoracic artery, is it the right internal thoracic artery or is it the radial artery?
I am concerned about your late patency data. In particular, I am concerned about the shape of the curve for the radial arteries, which, regardless of the target, looks more like saphenous vein patency than it does like internal thoracic artery patency. We are used to seeing the curves for the internal thoracic artery in which there are some early failures and then an almost flat line, whereas vein patency continues to decline during the study interval. It does not look like radial arteries are going to behave like internal thoracic arteries. So I wonder whether you could comment on whether you think that our choice for the second artery ought to be the internal thoracic artery or the radial artery?
Thanks.
DR MANIAR: Thank you, Dr Sundt. I agree with you it is discouraging on some of the graphs you saw, particularly the last one, which was only a Kaplan-Meier curve, where we looked at radial artery patency and it seemed remarkably similar to the saphenous vein graft. I think we have to remember that that is, unfortunately, a univariate analysis when we are looking at the Kaplan-Meier curve. And I think of particular interest is that it took almost 10 years to show the improved patency with results of bilateral internal thoracic artery grafting. I think there is room to suggest that the other internal thoracic artery may be a better conduit but that the differences that we will see between radial artery patency and saphenous vein graft may require greater time for further follow-up.
The majority of our follow-up, although it extends as far as 8 years postoperatively, is still the median or mean of around 3 to 4 years. And ideally, although like you mentioned, we would like to see the curve drop off, if it is going to drop off quickly with the radial artery and then flat line out, it is unclear whether that flat line is still yet to come or whether it is going to continue to deteriorate as the saphenous vein graft. So I do not have a good answer for you. But I think the comparison with the opposite internal thoracic artery, the right internal thoracic artery, would be an excellent comparison for a randomized trial.
DR JOHN M. KRATZ (Charleston, SC): Thank you for doing this work. Many of us follow your group's work to give us a guide as to which kind of arterial grafts to use where and how. One thing I am concerned with about your data is there is only a smaller percentage of people that you actually have data on from your overall group of patients, that is, those who are symptomatic and had angiograms. Does this really tell us anything about the entire group and what is going on in the patency rates of the entire group?
DR MANIAR: Thank you for your question, and I am glad you brought that up. I think it is important to stress that the patency that we are seeing here is only in patients who are having difficulty. There are two ways to look at it. It is a small subset and perhaps that is a good reason, that it is a small subset, meaning the patients who are not getting catheterized are doing well with these constructs. The alternative would be to perform routine angiography to look at these data, at least in this setting, and obviously that is something that is not amenable at this current day.
The only alternative then would be other methods to evaluate these grafts, either looking for ischemia with stress thallium or some other imaging study, making sure that these grafts are patent and open.
But I think in the absence of being able to do a controlled angiographic study, which is done I think in some other centers, particularly in Europe and Australia, we are somewhat limited in having to make inferences as best we can from a symptomatic data set.
References
This article has been cited by other articles:
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