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Ann Thorac Surg 2001;71:1503-1507
© 2001 The Society of Thoracic Surgeons
a Oxford Heart Centre, Oxford, United Kingdom
b Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
Accepted for publication January 20, 2001.
Address reprint requests to Mr Pillai, Oxford Heart Centre, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom
| Abstract |
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Methods. Forty patients were prospectively randomized into either a minimally invasive (minimal) or traditional (open) saphenous vein harvest group. Smooth muscle contractile function was assessed by responses to potassium chloride and phenylephrine. Endothelial cell function was assessed by responses to serial escalations in concentration of acetylcholine, bradykinin, calcium ionophore, sodium nitroprusside, and N-nitro-L-arginine using isometric tension studies.
Results. Harvest times were similar for both groups. The total incision length in the minimal group was significantly shorter than in the open group. There were no differences in smooth muscle contractions to either receptor-independent or receptor-mediated agonists between the two groups. Similarly, vasorelaxation in response to both endothelium-dependent and endothelium-independent agonists were similar in both groups.
Conclusions. Minimally invasive saphenous vein harvesting is associated with similar medial smooth muscle and endothelial function as open harvesting. These findings suggest that minimally invasive harvesting techniques can be used without major detrimental effects on vascular integrity.
| Introduction |
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The use of minimally invasive saphenous vein harvesting has been advocated in an effort to minimize wound-related problems [57]. Some evidence suggests that these techniques may reduce leg wound complications such as pain and infection [7]. Several techniques are available for minimally invasive vein harvesting, but all require traction on the vein to maximize surgical visibility and enable side branch ligation. Although endothelial cell coverage appears grossly intact after such harvesting techniques [8, 9], the impact on endothelial and medial function in clinical situations is unclear.
Excessive surgical manipulation of saphenous vein conduits clearly impairs endothelial cell function and reduces the bioavailability of nitric oxide (NO) [1012]. Endothelial injury allows platelet and leukocyte adhesion that can result in graft thrombosis [13]. Furthermore, surgical preparation stimulates smooth muscle cell proliferation that exacerbates the intimal hyperplastic characteristic of accelerated atherosclerosis in diseased vein grafts [14, 15]. Thus, functional integrity of harvested saphenous vein has important implications for immediate and long-term graft survival.
We therefore sought to evaluate endothelial cell function and medial smooth muscle function in saphenous vein harvested by a minimally invasive technique compared with vein harvested by the open technique.
| Material and methods |
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Harvest techniques
A single surgeon (E.A.B.) carried out all operations. The minimally invasive SaphLITE System employs a modified bridging technique. The vein was identified through a longitudinal incision either proximal to the medial malleolus or distal to the groin. A dissection plane was established anterior and posterior to the vein by gentle clearing of subcutaneous fascia. The blade of the SaphLITE was placed into the wound, and the vein was progressively mobilized. The Genzarm (Genzyme Surgical Products, Cambridge, MA) was used to aid retraction. Side branches were ligated with Ligaclips (Ethicon, Somerville, NJ) and then divided. After dissection was carried as far as possible, an incision was made more distal to that point, and dissection was continued further up and down the limb. All incisions were closed in layers, and a pressure dressing was applied immediately.
In open harvesting, the vein was identified either just proximal to the medial malleolus or distal to the skin crease in the groin. The skin was incised along the whole length of the vein, and careful dissection was used to isolate the vein in situ, with attention given not to traumatize the vein or its branches. Side branches were ligated with 4-0 silk on the vein side and Ligaclips on the patients side. The leg wound was closed in layers and a full-length pressure dressing, applied.
Vasomotor studies
Saphenous vein segments were removed prior to distention and immediately rinsed without pressure, immersed in iced oxygenated Krebs-Henseleit buffer [16], and transported to the laboratory within 30 minutes. Vein segments were divided into three or four rings approximately 4 mm long and mounted in 25-mL organ baths (Linton Instrumentation, Diss, Norfolk, UK). The tension was recorded directly onto a computer (MP100 System; Biopac Systems Inc, CA and Acqknowledge software). Optimal resting tension was determined in baseline studies.
We measured contractions to both 60 mmol/L potassium chloride, (a receptor-independent agonist) and cumulative doses (10-9 mol/L to 10-4 mol/L) of phenylephrine hydrochloride (an
-1 adrenergic receptor agonist) [16]. After submaximal precontraction with phenylephrine (typically 3 x 10-6 mol/L), relaxations were serially determined to three endothelial-dependent agonistsacetylcholine (ACh), bradykinin, and calcium ionophore A23187and to an endothelial-independent agonist, sodium nitroprusside. Dose response curves to ACh, bradykinin, A23187, and nitroprusside were determined as previously described [16]. All experiments were performed in the presence of indomethacin (10 µmol/L) to inhibit vascular prostaglandin synthesis. Relaxation to nitroprusside was performed after addition of N-nitro-L-arginine (1 mmol/L) to inhibit endogenous NO synthesis [17].
Statistical analysis
Values are expressed as the mean ± the standard deviation or the standard error as appropriate. A p value of less than or equal to 0.05 was considered significant (Students t test or analysis of variance as appropriate). The sensitivity of each ring to the various agonists was expressed as the effective concentration that would produce 50% of the maximal response, or EC50 from a logarithmic dose-response plot. In all cases, n refers to the number of patients studied. An average of three rings was used from each patient.
| Results |
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Saphenous vein contractile function
To examine medial smooth muscle function after minimally invasive or open saphenous vein harvest, we determined contractions to potassium chloride (60 mmol/L), a receptor-independent agonist, and to the
-1 adrenergic receptor agonist phenylephrine. Vascular contractions were preserved in the two groups, and maximal contractions to both potassium chloride and phenylephrine were almost identical in veins harvested by the two techniques (Fig 1). Similarly, sensitivities to phenylephrine, determined by 50% effective concentration (EC50) were not significantly different (p = 0.3).
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| Comment |
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Preservation of saphenous vein function during minimally invasive harvest has important implications for the immediate functional integrity of venous conduits and for the long-term patency of venous bypass grafts. Surgical preparation of saphenous vein injures the endothelial and medial layers [1012, 14, 15, 20], reduces NO bioavailability [10], and results in platelet and leukocyte adhesion and smooth muscle cell migration into the intima [1214]. These changes contribute to the accelerated atherosclerosis, characteristic of mature vein grafts, that leads to vein graft vascular dysfunction [2123] and graft failure.
Although endothelial cell coverage appears grossly intact after minimally invasive harvesting techniques [8, 9], studies of endothelial function after minimally invasive vein harvesting have been limited. We found that ACh vasorelaxations in both groups ranged from 30% to 40%, results suggesting good preservation of endothelial cell function in both groups.
We studied relaxations to a range of agonists. Reliance on ACh relaxations alone may affect the precision of the results. We know that certain clinical details affect the production of NO [24]. Therefore, we were interested to find that plasma cholesterol, diabetes, and other risk factors for impaired vascular function were not significantly different between the groups (see Table 1). We also compared the response of the vessels to endothelium-independent agonists to check the response in more detail.
By using both ACh and bradykinin, we analyzed responses mediated by distinct receptor/G proteinmediated pathways. Furthermore, endothelial NO synthase activity in response to isometric contraction, assayed by the increase in tension in precontracted rings in response to the NOs synthase inhibitor N-nitro-L-arginine, was used to determine the activation of endothelial NO synthase by pathways that mediate the response to shear stress in vivo [17]. Finally, we used the receptor-independent agonist calcium ionophore A23187 to maximally stimulate endothelial NO synthase independent of any receptor-mediated pathway. In all of these studies, there was no difference in the bioavailability of NO between saphenous veins harvested by a minimally invasive technique versus an open technique, thus conclusively demonstrating preservation of NOmediated endothelial cell function across a broad range of cellular signaling pathways.
Assessment of medial smooth muscle cell contractile function is also important, as traction on the vein could cause overstretching of the medial layer and disrupt the contractile elements. In our study, there was no difference in contractile response between saphenous veins harvested by either the minimally invasive or open technique.
In conclusion, minimally invasive saphenous vein harvesting using the SaphLITE System preserves both endothelial and medial smooth muscle function as well as open harvest does. Vein conduits harvested by minimally invasive techniques should be no more prone to vascular dysfunction or failure than those collected by open technique.
| Acknowledgments |
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Drs Channon and West are supported by the British Heart Foundation.
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