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Ann Thorac Surg 2002;73:1189-1195
© 2002 The Society of Thoracic Surgeons
a Department of Thoracic and Cardiovascular Surgery, Örebro University Hospital, Örebro, Sweden
b Department of Thoracic and Cardiothoracic Surgery, University Hospital, Uppsala, Sweden
c Department of Molecular Pathology and Clinical Biochemistry and Surgery, The Royal Free and University College Medical School, Royal Free Campus, London, United Kingdom
Accepted for publication January 11, 2002.
* Address reprint requests to Dr Souza, Department of Thoracic and Cardiovascular Surgery, Örebro University Hospital, SE 701 85 Örebro, Sweden
e-mail: domingos.souza{at}orebroll.se
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Abstract |
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Methods. One hundred fifty-six patients who underwent coronary artery bypass grafting were randomized to three saphenous vein harvesting groups: group C (conventional)—the vein was stripped, distended, and stored in saline; group I (intermediate)—the vein was stripped, local application of papaverine was used instead of distention, and the vessel was then stored in heparinized blood; and group NT (no-touch)—the vein was harvested with surrounding tissue, not distended, and stored in heparinized blood. Surgical and clinical factors that might influence graft occlusion were recorded. One hundred twenty-seven vein grafts in group C, 116 in group I, and 124 in group NT, as well as 118 left internal mammary artery grafts, were angiographically assessed at 18 months mean follow-up time.
Results. The vein graft patency was 88.9% in group C, 86.2% in group I, and 95.4% in group NT. There was a statistically significant difference between the patency of the single-vein grafts in NT and the other two groups (p = 0.025). The higher the flow, the better the patency irrespective of the technique used. A higher attrition rate was found in vein segments taken from the knee area in group I. Poor vein quality affected patency in all groups. Forty-seven of all 51 sequential grafts (92.2%) were patent. The patency of left internal mammary artery grafts was 108 of 118 (91.5%).
Conclusions. We conclude that preservation of the surrounding tissue of the saphenous vein using this no-touch technique abolishes venospasm intraoperatively and plays an important role in maintaining vein graft function and patency.
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Introduction |
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Damage to the vessel wall occurring during graft preparation influences short-term and long-term patency [5, 6]. The LIMA graft is harvested with its pedicle of surrounding tissue and handled carefully during both preparation and grafting, whereas the SV is often stripped of its adventitial layer and distended to overcome spasm. These procedures are known to be the principal factors resulting in vein wall damage [7, 8]. Spasm requiring distention might therefore be a critical event triggering SV graft injury and subsequent occlusion [9, 10].
We have previously shown that when veins are harvested with a pedicle of surrounding tissue, the "no-touch" harvesting technique, they can be implanted without prior distention [11]. Two subsequent studies [12, 13] showed that veins harvested by this technique had better preserved endothelium.
In 1993 a prospective randomized study was initiated to compare this no-touch technique (group NT) with two other techniques: the conventional technique (group C) and an intermediate technique (group I). A high early patency rate was achieved with the no-touch graft [14]. The aim of this communication is to report the final results of the early angiographic assessment performed in 132 patients.
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Material and methods |
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Patient characteristics
There was no difference in baseline characteristics of the three patient groups (Table 1).
Patients who were on lipid-lowering drugs on admission or had serum cholesterol concentration above the normal range (2.6 to 5.0 mmol/L) were considered to have hyperlipidemia. Hypertension was defined as a diastolic blood pressure greater than 90 mm Hg or systolic blood pressure greater than 140 mm Hg. The left ventricular function was determined by the ejection fraction estimated by angiography.
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Harvesting technique
Group C: conventional technique
The SV was exposed by a continuous longitudinal incision, the perivascular tissue was stripped, and side branches were ligated with 3-0 silk. The vein was removed from the leg immediately after dissection and was manually distended with saline at 300 mm Hg for 1 minute, using a syringe connected to a manometer. After distention, the vein was stored in saline at room temperature.
Group I: intermediate technique
The SV was dissected as in group C. Instead of manual distention, the vein was left in situ and covered with a sponge moistened in saline-papaverine solution (1 mg/mL) until extracorporeal circulation was started. The vein was then removed and stored in blood obtained from the patient’s aortic cannula before cooling. Despite the use of papaverine, almost all vein grafts required gentle mechanical distention by finger massage to overcome residual spasm.
Group NT: no-touch technique
The SV was also exposed using a continuous incision. All visible side branches were ligated approximately 0.5 cm from the vein wall with 3-0 silk ligatures. Then the vein, together with a pedicle of surrounding tissue, was isolated from its bed. The vein was left in situ covered with sponges moistened in saline until extracorporeal circulation was started. It was then stored in blood collected from the patient’s aortic cannula before cooling. No form of mechanical distention was needed or applied.
Surgical aspects
Cardiopulmonary bypass with moderate hypothermia (28° to 30°C) and only cold blood intermittent cardioplegia (4°C) through the coronary sinus was routinely used. Malleable calibrated probes were used to measure the diameter of target coronary arteries. The distal anastomoses were performed first. To check for leakage the proximal end of the grafts in groups I and NT was briefly connected to the arterial cannula of the cardiopulmonary bypass. The grafts were therefore neither flushed nor dilated with a syringe. Figure 1
shows a sequential no-touch graft being tested for leakage. However, in group C, leakage was checked manually using a syringe and saline. All LIMAs were anastomosed as a single graft to the left anterior descending coronary artery. The proximal anastomosis was performed after release of the aortic cross-clamping.
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Angiography
Selective graft angiograms were performed according to the technique of Judkins [16]. Low osmolarity Visipaque contrast medium, 320 mg iodine/mL, (Nycomed Amersham AB, Stockholm, Sweden) was used. Both the SV graft and LIMA were visualized in two projections. Angiographic assessment was performed in a blinded-way by one radiologist. Graft patency and significant localized or diffuse changes were recorded. Occlusion was identified by visualization of a remaining stump by selective injection or by lack of opacification after a 50-mL bolus injection of dye in the ascending aorta.
Statistical methods
Patency of graft, an outcome with two states, ie, patency or occlusion, was analyzed with logistic regression models. The main predictor variable was the three different harvesting techniques: conventional, intermediate and no-touch. Before reaching the final model we examined the possibility that the chosen predictor variable had significant interactions, in particular with the main predictor variable, the harvesting technique. In the final model we also calculated the goodness-of-fit of the model to the observed data by using the likelihood ratio criterion. Basic references for our modeling approach are Rogers [17] and Cnaan and associates [18].
Additional predictor variables were examined individually, and those showing a significant relation to the outcome and also having an uneven distribution across the three harvesting techniques were selected and used in the final model.
The logistic regression model was analyzed with graft as the unit of analysis with a total of 316 grafts. However, 118 of 132 patients had more than one graft, with a maximum number of three grafts per patient. Multiple grafts per patient might introduce dependencies between the observations, a violation of one basic assumption for calculation of standard errors used for computation of probability values and confidence intervals. A special form of the logistic regression model was therefore used to allow for clustered observations, in which the patient was the cluster and dependencies among observations within a cluster were considered in the computation of the standard errors. The probability values and confidence intervals shown are in this way corrected for the problem with correlated observations.
The outcome variable of interest in the logistic regression model is the odds ratio (OR). An OR of 1.0 indicates no effect in the analyzed category compared with the chosen reference category. An OR above 1.0 indicates increased chance for patency, an OR below 1.0, less chance. As patency is a common and occlusion a seldom-occurring event, the OR approximates the relative risk well in this study.
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Results |
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Surgical data
The mean duration of cardiopulmonary bypass and aortic cross-clamp time was 121 minutes (range, 59 to 187 minutes) and 64 minutes (range, 34 to 95 minutes), respectively, for group C; 126 minutes (range, 90 to 180 minutes) and 69 minutes (range, 41 to 117 minutes), respectively, in group I; and 139 minutes (range, 88 to 195 minutes) and 72 minutes (range, 41 to 113 minutes), respectively, in group NT. Thus, there was a slightly longer aortic cross-clamp time and duration of cardiopulmonary bypass in the NT group.
The mean (± standard deviation) time for the vein in situ for group I was 24.92 ± 10.18 minutes and for group NT was 28.10 ± 14.65 minutes, which was not significantly different (p = 0.27). The mean storage time for group C was 88.22 ± 20.27 minutes, for group I was 53.51 ± 14.39 minutes, and for group NT was 57.42 ± 17.57 minutes; this variable showed a statistically significant difference between group C and the other two groups (p < 0.001).
The majority of patients in all groups received three vein grafts, which included sequential vein grafts as well as a mammary artery. A total of 127 of vein grafts and 41 LIMAs were used in group C, 116 vein grafts and 35 LIMAs in group I, and 124 vein grafts and 42 LIMAs in group NT. Left internal mammary artery grafts were considered not suitable in 5 patients in group C, 5 in group I, and 3 in group NT.
There were 107 single grafts, 16 double sequential grafts, and 4 triple sequential grafts in group C. In group I, 100 single grafts, 14 double sequential grafts, and 2 triple sequential grafts were used, and in group NT there were 109 single grafts and 15 double sequential grafts. The single grafts had the proximal anastomosis to the aorta and the distal anastomosis to a target artery. Each sequential graft was considered as one entity irrespective of the number of touchdowns and they were not included in Tables 2 and 3. It was necessary to perform thromboendarterectomy in two posterior descending coronary arteries in group C and one posterior descending coronary artery in group I, but no thromboendarterectomy was performed in group NT.
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The vein graft patency rate was 118 of 124 (95.4%) in group NT compared with 113 of 127 (88.9%) in group C and 100 of 116 (86.2%) in group I.
The complete data regarding characteristics of the target coronary arteries, vein grafts and their relationship to the harvesting technique, and the patency rate are given in Table 2. Low flow associated with small-sized coronary arteries (
1.5 mm) reduced the patency in all groups, and low flow alone had a greater influence on the patency rate for grafts in group I. The poor quality of target coronary artery had no influence on the patency in any group. Both grafts that were anastomosed to the posterior descending coronary artery after thromboendarterectomy in group C were patent, but not the graft in group I.
The patency rate for veins of poor quality before implantation was 6 of 10 (60.0%) in group C, 13 of 19 (68.4%) in group I, and 26 of 29 (89.7%) in group NT. In all groups, most of the proximal portions, the vein from the thigh, were anastomosed to the right coronary artery; the central portions, the vein from the knee area, were anastomosed to the diagonal branches; and the distal portions of the vein were anastomosed to the circumflex branches. The majority of occluded vein grafts in group I were from the central portion of the vein.
Table 3 shows a logistic regression analysis of the most important factors that affected the graft outcome, ie, the patency rate. Odds ratios obtained with no multivariate adjustment and from the final, multivariate model are shown. A statistically significant difference in patency rate was found between the NT group and group C (p = 0.025), and the poorest result was observed in group I. The OR for group NT in comparison with group C was 3.9, with a 95% confidence interval of 1.2 to 12.6. The analysis showed a high OR for increasing coronary artery diameter (OR, 4.7 for diameter 
2.0 mm compared with 1.0 mm) and increased flow (OR, 4.9 for flow 41 mL/min compared with 20 mL/min). Poor vein quality gave a low OR (0.2). Odds ratios of 0.2 were observed for central and proximal parts compared with distal parts of the vein. All these variables were based on multivariate adjustment and were statistically significant.
All sequential grafts in the NT and I groups were patent, whereas in group C two sequential grafts were totally occluded and two others were partially occluded. The partially occluded grafts were a double and a triple sequential graft, and in both grafts the occluded segment corresponded to the distal segment. Accordingly, 47 of 51 (92.2%) sequential grafts were completely patent.
One narrowing of approximately 40% at the anastomotic site between the aorta and the SV graft was observed in group NT. Narrowing of approximately 50% at the coronary anastomosis was observed in four anastomoses in group C, in three anastomoses in group I, and one anastomosis in group NT.
Mild-to-moderate diffuse narrowing was observed in 2.4% in group NT versus 5.5% in group C and 6.0% in group I.
All patients were recommended to follow lifelong antiplatelet medication. At the time of the angiographic examination, 42 patients in group C were receiving 160 mg/d aspirin, 3 were taking 75 mg/d, and 1 was not taking antiplatelet aggregation drug therapy. In group I, 35 were taking 160 mg/d, 3 were taking 75 mg/d, and 2 were not receiving drug therapy. In group NT, 35 patients were receiving 160 mg/d, 7 patients were taking 75 mg/d, and 3 were not taking any antiplatelet drug therapy.
Only a few patients developed minor wound complications, such as cellulitis and superficial wound infection, associated with harvesting of SV graft. Two of 46 patients (4.3%) in group C, 3 of 41 patients (7.3%) in group I, and 5 of 45 (11.1%) in group NT had wound complications. There was no major complication that required subsequent surgical intervention.
No association among vein graft occlusion and classic clinical factors that are reported to influence the graft patency such as age, preoperative infarctions, cholesterol level, smoking habits, or hypertension was observed in any group.
The results from the patients in group NT have been separately evaluated in a recent article [14].
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Comment |
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TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
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This is the first study to show that the surrounding tissue of the SV contributes to high early patency rate of SV grafts compared with preparation of SV grafts with conventional technique. We have investigated whether preservation of the perivascular tissue, including the adventitial layer, might improve venous graft patency rate by comparing early angiographic results between the no-touch and two other techniques. Our results show a significant improvement of vein graft patency using this new no-touch technique, with patency rates comparable to LIMA grafts.
The intermediate group was devised to demonstrate the importance of the surrounding tissue to vein grafts, inasmuch as after dissection, handling of the SV was identical to that of the no-touch group except for the vessel being stripped. Removal of surrounding tissue generally resulted in pronounced spasm, and mechanical distention was required despite the local application of papaverine. In contrast, grafts retaining a pedicle of surrounding tissue required neither pharmacologically induced relaxation nor mechanical distention.
The no-touch group provides both an improvement in endothelial protection and a higher patency rate than the other two groups. However, an unexpected finding in the present study was that veins harvested conventionally showed a higher patency rate than the intermediate technique despite our previous observation that the endothelial lining is better protected in the intermediate group than in the conventional group [12]. This suggests that it is not only the endothelial layer that plays an important role in protecting the grafts from occlusion, but that the adventitial layer also makes a significant contribution to improved graft patency.
The majority of the occluded grafts in the intermediate group corresponded to those grafts obtained from the central portion of the veins. This is probably related to the vein being implanted with residual spasm, and this may be an important cause of occlusion, especially in small-bore vein segments that require a higher degree of distention.
In agreement with other studies [20, 21], the graft flow rate and diameter of the lumen of the target coronary arteries are important factors in predicting the outcome of the grafts, irrespective of the method of vein harvesting used. We corroborate a previous study [22], which reported an improved patency rate for sequential grafts. Poor vein quality affected the patency rate in all three groups. Other surgical aspects, such as the quality of the coronary arteries and the length of the vein graft used, had no influence on graft patency. In agreement with a recently published article [23], traditional cardiovascular risk factors for arteriosclerosis did not seem to predict the early fate of SV grafts. However, it is likely that arteriosclerotic changes will become more evident at long-term follow-up.
The mechanisms underlying the early success of our novel no-touch technique are unclear. One important contributing factor is likely to be related to the preservation of endothelial structure and function. However, preservation of the cushion of surrounding tissue may well be the most important factor contributing to the high patency rate of this technique. Previous studies have suggested that vein graft failure may be caused by the inability of the vein to adapt to altered shear stress and high aortic arterial pressure after grafting [24]. In an in vitro model, the detrimental effect of pulsatile aortic pressure was reduced by external stenting of the vein graft [25], which resulted in a decrease in early medial and neointimal thickening. Our previous study also showed that the tissue surrounding the SV is rich in collagen and connective tissue, suggesting that this pedicle of surrounding tissue may act as a natural external support to the vein, protecting it against the effects of aortic shear stress [13]. Furthermore, this cuff supports excessively long vein grafts and prevents them from kinking. By harvesting the vein with its surrounding tissue, the adventitia is left intact together with its network of functioning vasa vasorum, and this may reduce ischemic injury [26]. The combination of these factors may have contributed to the observed improvement in early patency rates of this no-touch technique. The long-term fate of the no-touch vein graft remains to be assessed.
The operation time is somewhat longer using the no-touch technique than the other techniques. Damage to the saphenous nerve is inevitable when harvesting the SV by this technique; however, this also occurs frequently when using the conventional technique [27].
No major wound complication occurred, and we attribute this to our exclusion criteria, which did not include older patients or patients with peripheral vascular disease or insulin-dependent diabetes mellitus who are at a higher risk of wound complications. Also, the patients had a good left ventricular function and did not require intraaortic balloon pump assistance. It is expected that wound complications are more likely to occur in patients who have their veins harvested by the no-touch technique; therefore, we recommend certain approaches to avoid serious complications. First, in addition to a meticulous surgical technique, the no-touch technique should be avoided in high-risk patients, in particular those with peripheral vascular disease. Second, preoperative SV mapping using ultrasonographic imaging the day before the operation to mark the course of the vein should be performed. This will allow the incision to be made exactly above the vein, avoiding a long flap of subcutaneous tissue that might be a major cause of wound complication.
We conclude that in addition to improved preservation of vein graft endothelium, the intact adventitial layer contained within the cushion of surrounding tissue when harvesting the vein by this no-touch technique is also an important contributing factor to improved graft function and patency. The adventitial layer possesses both mechanical and functional properties that protect the vein from spasm. In contrast, removal of surrounding tissue results in spasm that requires mechanical distention with resultant vascular trauma. Although early-term results are encouraging, long-term results remain to be established.
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Acknowledgments |
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