Ann Thorac Surg 2000;70:1536-1540
© 2000 The Society of Thoracic Surgeons
Original articles: cardiovascular
The biocompound method in coronary artery bypass operations: surgical technique and 3-year patency
Heinz Robert Zurbrügg, MDa,
Friedrich Knollmann, MDa,
Michele Musci, MDa,
Markus Wieda,
Matthias Bauer, MDa,
Tito Chavez, MDa,
Andreas Krukenberg, MDa,
Roland Hetzer, MD, PhDa
a Deutsches Herzzentrum Berlin, Berlin, Germany
Address reprint requests to Dr Zurbrügg, Deutsches Herzzentrum Berlin, Augustenburger Platz 1, 13353 Berlin, Germany
e-mail: zurbruegg{at}dhzb.de
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Abstract
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Background. Complete arterial revascularization may be unsafe in patients with a high operative risk. In patients with varicose ectatic veins, the biocompound technique, which uses unsuitable autologous veins, enables the surgeon to influence the bypass graft wall stress levels and diameter. This report summarizes the 3-year patency of 53 patients, the survival rate of 200 patients, and operative technical considerations.
Methods. Biocompound grafts were used for aortocoronary bypass in 200 patients who were considered inappropriate subjects for complete arterial revascularization and who had unsuitable saphenous veins.
Results. The mortality rate (30 days) of 200 patients was 3.5%. The 3-year survival rate was 88.5%. The patency rate of the left internal thoracic artery (LITA) after 3 years was 97.3%, of the native vein was 68.7%, and of the biocompound graft was 68.3%. The LITA showed a superior patency rate (p = < 0.05).
Conclusions. The LITA is the first choice in coronary bypass operation. The biocompound technique is a reliable method to achieve complete revascularization in patients with a lack of suitable saphenous veins.
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Introduction
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Complete arterial revascularization may be unsafe in patients with a high operative risk. In cases in which no suitable saphenous vein is available, the decision making for the best operative strategy is difficult. Creating a biocompound graft with the patient’s own vein enables the surgeon to influence the bypass graft’s wall stress levels and diameter, particularly in patients with varicose ectatic veins. A biocompound graft is created by encasing the vein in extremely fine, highly flexible metal mesh tubing (biocompound graft application set, Alpha Research GmbH, Berlin, Germany) and affixing the two with fibrin sealant.
Since its initial implementation in 1994, the biocompound graft has been implanted in more than 950 patients in 38 centers worldwide. This report summarizes the 3-year patency of 53 patients, the survival rate of 200 patients, and operative technical considerations.
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Material and methods
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Patients
Biocompound grafts were used for aortocoronary bypass in 200 patients (Table 1). All patients thus handled were considered to be inappropriate subjects for complete arterial revascularization. The survival rate during the observation period was calculated as a percentage of the total number of patients. All patients underwent grafting with between one and four biocompound grafts. The intraoperative policy was to anastomose the left internal thoracic artery (LITA) to the left anterior descending coronary artery, and to target good or acceptable parts of the saphenous vein for the most viable coronary arteries for use in the first instance. Thereafter, the biocompound was used for less viable coronary arteries. However, the use of the LITA or native saphenous vein was not possible in all patients. Six patients underwent additional arterial grafting (3 with the right internal thoracic artery and 3 with the gastroepiploic artery). From 1995 until 1997, 53 unselected patients, who lived in the greater area of our institute, were restudied after consenting to an invasive examination. Graft patency was determined using ultrafast contrast computed tomography (Fig 1). The accuracy of the method for bypass occlusion (specificity, sensitivity) is reported in the literature to be more than 95% [1, 2]. The patency rates for each graft type over the implantation time were then calculated. Log rank statistical test analyses were applied.
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Fig 1. Three-dimensional reconstruction of an ultrafast contrast computed tomography examination at follow-up after 3 years. This patient (R.H., born in 1926) received one biocompound graft bypass to the first marginal branch and two native vein bypasses to the left anterior descending coronary artery and posterior descending coronary artery. The examination showed all bypasses to be open.
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Constructing the biocompound graft
A biocompound graft is created by sheathing the varicose or ectatic vein in a highly flexible metal mesh tubing and joining the two with fibrin sealant. The most appropriate, but still unsuitable, sections of the great or lesser saphenous veins are harvested using either a minimally invasive technique or a conventional technique. Arm veins have also been used in some cases (10 patients). Tributary or side branches are ligated with 5-0 polypropylene suture, but no metal suture clips are used, as the potential to damage the mesh tubing of the biocompound graft is considerable. Should the vein already have a substantial diameter, inflation of the graft for the purpose of checking for leakage is not recommended.
The harvested vein is ligated at the proximal end and the moistened balloon catheter of the application set is inserted into the distal end of the vein, in accordance with the anatomic direction of the venous valves (Fig 2). The vein must then be smoothed out carefully over the catheter (Fig 3A). Forced extension leads to a reduction in the caliber of the elastic vein and, should the balloon catheter be inflated to its maximum diameter of 3.5 mm, serious damage by overdilatation and microruptures of the vein wall may occur (Fig 3B). This technical fault can jeopardize the long-term prognosis inducing myointimal hyperplasia [3–8].
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Fig 2. The balloon is inserted into the harvested vein and advanced up to the ligature at the proximal end. (Figure 2 is reproduced by kind permission of Alpha Research.)
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Fig 3. (A) Correctly smoothed out vein. The inflation of the balloon catheter to its maximal diameter (d) of 3.5 mm does not lead to an over-extension of the vein wall. (B) Forced lengthening of the vein. Stretching leads to a decrease of the overall diameter of the vein. Inflation of the balloon catheter to its maximal diameter (d) of 3.5 mm will lead to an extension in excess of physiologic limits.
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The applicator with the funnels is slipped over the vein and the mesh tubing is pushed off the applicator (Fig 4). The balloon is deflated and then filled with an isotonic solution. Its diameter remains constant (3.5 mm) throughout, similar to that of a dilatation balloon in an inflated condition. The mesh tubing with a diameter of 7.6 mm in a relaxed state is now smoothed out from the middle toward the ends of the vein. Complete congruity of the naturally irregular external diameter of the graft can be obtained through this maneuver. Filling the balloon before adaptation of the mesh tubing prevents possible indentations of tributary stumps. The bonding of the mesh tubing and the vein through the use of fibrin sealant facilitates intraoperative handling. This bonding is carried out by the application of the fibrinogen component, which the surgeon spreads evenly over the entire length, followed by the thrombin component. Once adhesion is complete, the graft is lubricated and then slipped off the balloon catheter.
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Fig 4. The mesh tubing is pushed off the applicator so that it does not become damaged by the sharp edge at the end of the applicator, which would happen if the mesh tubing were pulled. (Figure 4 is reproduced by kind permission of Alpha Research.)
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Implantation of the biocompound graft
After standard sternotomy and the harvesting of arterial and vein conduits, the biocompound graft is prepared. Cardiopulmonary bypass using an aortic and a single, two-stage, venous cannula is established. After standard cardioplegia maneuvers have been carried out, the pericardium over the target coronary vessel is incised and arteriotomy is performed. The biocompound graft is cut at an angle of 60 degrees. The anastomosis is constructed with a running 7-0 polypropylene suture technique. When presenting the vein, the assistant should take care not to grasp the mesh tubing itself as this could result in the mesh tubing separating from the vein wall. Because the graft with the mesh tubing has a degree of protection against compression, it can be grasped gently with forceps in its entirety and presented to the surgeon. Each suture bite should capture two rows of the mesh (Fig 5), to prevent the mesh from otherwise unraveling at the anastomosis (Fig 6).
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Fig 5. Construction of the coronary end-to-side anastomosis. The anastomosis is constructed with a running 7-0 polypropylene filament that integrates with the mesh tubing. (Figure 5 is reproduced by kind permission of Alpha Research.)
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Fig 6. The mesh tubing was not adequately integrated during suturing, thus it unravels from the anastomosis and the vein inflates to its original size. Angiography performed 6 months postoperatively (K.S., born in 1926).
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The mesh tubing frays slightly, which guarantees a high anastomotic compliance. The individual filaments usually turn toward the outside of the suture line due to the "memory" effect inherent in alloys. A high degree of hemostatic security is achieved by the capture of a small piece of epicardium with each suture bite and by the maintenance of a taut running suture. A purse-string effect is prevented through the elasticity of the biocompound graft wall, which widens the coronary arteriotomy. Before tying the suture, air is removed from the graft by injecting isotonic solution or blood. This procedure is followed by a check of the patency of the anastomosis; any leaks are repaired with fine simple or mattress sutures.
In sequential bypass grafting, the mesh is lifted from the vein wall and cut off tangentially with scissors. The venotomy of the mesh-free area may be parallel or perpendicular to the direction of the arteriotomy. The anastomosis is constructed with a 7-0 polypropylene suture, and a running suture technique is used. Here, the suture bites should capture only vein. Inclusion of the mesh into the suture pulls the graft down into the anastomosis and produces unfavorable indentation of the anterior wall and must therefore be avoided.
The measurement of the bypass length is then undertaken, and this length can be chosen generously, as the reinforced biocompound graft is not prone to kink. Tension on the graft dramatically reduces the internal diameter and must be avoided. After cross-clamp aortic release, the construction of the anastomosis to the aorta is undertaken with partial aortic occlusion. The graft is cut at an angle of 45 degrees. By the use of a 4.5-mm aortic punch and a 6-0 polypropylene running suture taking two or three rows of holes of the mesh tubing, the aortic anastomosis is completed. After making the anastomosis the mesh should be lifted from the vein on the outer curve of the graft for the first 2 cm and a longitudinal cut of 1.5 cm made through the mesh only. This technique prevents local shortening of the mesh tubing and the possibility that this may lead to graft stenosis (Fig 7). After removal of the side-biting clamp, any trapped air is expelled by inserting a 0.55-mm needle into the biocompound graft and massaging the air out through the needle hole.
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Fig 7. Shortening of the graft due to tension on the bypass may lead to proximal stenosis. A longitudinal cut of 1.5 cm made only through the mesh prevents this effect. (Figure 7 is reproduced by kind permission of Alpha Research.)
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After weaning the patient from cardiopulmonary bypass, closure of the chest is undertaken in the standard fashion. After 6 hours 500 mg acetylsalicylic acid in an injectable solution is administered. Oral anticoagulation is begun on the second or third postoperative day. After 3 months the oral anticoagulation is terminated and aspirin administration (100 mg/day) is begun as a lifelong therapy.
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Results
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The mortality rate (30 days) of the 200 patients was 3.5% (7 patients). Autopsy showed that in 3 patients all of the bypasses had remained open. In the other 4 patients autopsies were not performed. The cause of death in 3 patients was low-cardiac output syndrome. In 4 patients, the cause of death was not of cardiac origin. One patient had cerebral apoplexy. The cause of death was unclear in 1 patient (W.C., born in 1919). One patient (B.G., born in 1927) had acute respiratory distress syndrome. The fourth patient (A.L., born in 1924) died from a pulmonary failure as a result of a bacterial pneumonia.
The 3-year survival rate was 88.5%. One patient died during the second and 1 patient during the third postoperative year (Fig 8). None of the patients who received a biocompound graft constructed from arm veins died. In 2 patients the cause of death was noncardiac, in 1 patient it was suspected to be cardiac, but an autopsy was not performed. Of the 53 patients (34 men, 19 women) that were available for invasive control, using ultrafast computed tomography, patency rates per graft type were calculated (Fig 9). After 3 years the patency rate of the LITA was 97.3%, of the native vein was 68.7% (saphenous veins only), and of the biocompound graft was 68.3%. None of the target vessels was statistically significantly at a higher risk for graft occlusion. The patency rates of the veins and the biocompound grafts did not differ significantly (p = 0.67, log rank test), whereas the LITA showed a superior patency rate (p < 0.05).
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Fig 9. Three-year patency rates curve for 53 patients with 82 biocompound grafts (BCG), 37 left internal thoracic arteries (LITA), and 48 native vein bypasses (VEIN). Log rank test showed no significant difference (p = 0.67) between veins and BCG.
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Comment
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The biocompound graft method was used at our institution for the purpose of aortocoronary bypass in 200 patients. The graft received approval for implantation in Switzerland in 1994 and in Germany in 1995. In 1997, the biocompound graft satisfied the requirements of the European Council Directive 93/42/EEC, which concerns medical devices (Communauté Européanne regulations) and was therefore approved for implantation in the European Union.
All patients operated on were selected on a restrictive, that is, negative, basis because at the beginning of this series the long-term patency of the biocompound graft was unknown [9–11]. This was reflected in the mortality rate of 3.5% (7 patients) when compared with an overall mortality rate in isolated coronary artery bypass operation in Germany of 2.8% [12]. An analysis of the risk factors of this series is published elsewhere [13]. Although superior survival rates for patients with LITA bypasses are known, only in 70.5% of all patients was revascularization with an arterial graft performed. This restriction is justified, as the positive influence of the LITA bypass to the patients survival is small when compared with the use of vein bypasses only [14], but the use of the LITA almost doubles the operative mortality [15]. Moreover, this rate of LITA use is acceptable when compared with 66.1% of the German Summary Statistic [12] or with 19.1% of The Society of Thoracic Surgeons’ Database of 1997 [15]. Therefore, the LITA was not utilized when relative contraindications were present or the arterial graft turned out to be unsuitable intraoperatively. However, the patency rate of the LITA of 97.3% after 3 years emphasizes, as in other studies [16], that the LITA should nevertheless be the conduit of first choice when used with a reasonable operative risk. The patency rates of the veins and the biocompound grafts did not differ, but were not compared with a control group with varicose veins. Of course, one would expect lower patency rates of varicose veins, but data are not available in the literature. Therefore, it is unclear whether the method enhances the patency rate of varicose veins. Because of previous experimental results [7, 17–19], it was not justified to establish a control group with bypasses performed with varicose veins. Moreover, a reliable classification for the quality of veins is not known and, therefore, comparison of patients is not useful.
Complete revascularization is the major goal of bypass operation. In patients with a high operative risk this goal is easier to achieve with the biocompound technique than with complete arterial revascularization. After 3 years, the patency rate of the different types of bypasses is comparable with those of other series [16, 20, 21]. Considering the intraoperative policy of using inferior quality veins for the construction of the biocompound graft and anastomosing it to target vessels of the second or third choice, the comparable patency rates of veins and biocompound grafts after 3 years are encouraging.
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References
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Accepted for publication April 24, 2000.
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Abstract
Introduction
