Ann Thorac Surg 2008;85:305-309. doi:10.1016/j.athoracsur.2007.05.073
© 2008 The Society of Thoracic Surgeons
New Technology
A Third Generation of Ascending Aorta Dacron Graft: Preliminary Experience
Ruggero De Paulis, MD*,
Raffaele Scaffa, MD,
Daniele Maselli, MD,
Andrea Salica, MD,
Alessandro Bellisario, MD,
Luca Weltert, MD
Cardiac Surgery Department, European Hospital, Rome, Italy
Accepted for publication May 29, 2007.
* Address correspondence to Dr De Paulis, Cardiac Surgery Department, European Hospital, Via Portuense 700, Rome, 00149, Italy (Email: depauli{at}tin.it).
| Dr De Paulis discloses that he has a financial relationship with Vascutek.
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Abstract
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Purpose: To develop a preassembled biological valved conduit, a Dacron conduit was modified to be stored in glutaraldehyde without loos of blood impermeability. This study reports the preliminary experience with this "third generation" aortic Dacron graft.
Description: Eight patients underwent ascending aorta or root replacement using the new Triplex prosthetic conduit (Vascutek Terumo, Renfrewshire, Scotland) consisting of three layers. The inner layer is a standard uncoated woven Dacron graft (DuPont, Wilmington, DE); the outer layer is a standard expanded polytetrafluoroethylene graft. Both layers are fused together by a central layer of self-sealing elastomeric membrane. For its peculiar characteristics this graft has unique properties that allow it to be maintained in glutaraldehyde solution as well as in various storage solutions.
Evaluation: None of the patients died or exhibited any neurologic event. The clinical inflammatory response was within the usual postoperative levels. The graft appeared slightly stiffer than the standard Dacron graft with similar handling and tailoring characteristics. Blood impermeability (even through the suture holes) was remarkably high.
Conclusions: This prosthetic graft appeared to combine good handling and tailoring characteristics with a striking reduction of blood oozing through the fabric and suture hole, even at full heparinization.
The ascending aorta was first replaced by Cooley and DeBakey [1] in 1956 by using an aortic allograft. As the need for conduits grew, so did the need for a suitable artificial conduit. The first fabric to be used was Vinyon N cloth by Blakemore and Voorhees [2]. Dacron (DuPont, Wilmington, DE) was subsequently introduced by DeBakey [3], and it soon became the "first generation" artificial conduit for aortic replacement. Although woven Dacron was generally preferred to the knitted version because of its lower porosity, the problem of blood oozing through the fabric was still an unresolved issue. A pre-clotting treatment with the blood from the patient or with albumin was then suggested. A "second generation" of woven Dacron grafts (Dupont) that were coated with protein (collagen-gelatin) to reduce the blood loss were first introduced in the 1990s. These coated woven Dacron grafts have greatly facilitated surgery and improved results [4].
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Technology
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The simultaneous replacement of the aortic valve and the entire ascending aorta with coronary reimplantation (ie, composite aortic root replacement better known as the Bentall procedure) [5] has become the accepted standard operation for all cases of aortic valve disease associated with aneurysm or dissection of the aortic root and ascending aorta. Many modifications of the standard surgical technique have been described through the years [6, 7]. The popularity and increased need for this type of operation have stimulated the development of composite valved conduits to facilitate and expedite the surgical procedure. For this reason, valved conduits coupling a mechanical heart prosthesis with a Dacron graft were realized. Initially the uncoated version of the graft was used, but it was soon replaced with the coated version of the Dacron graft when it became available. Because the biological valve prosthesis had to be preserved in glutaraldehyde, whereas the coated Dacron conduit had to be stored in a dry environment, producing a biological version of a valved conduit was not possible. Therefore, biological valved conduits (with stentless or stented valves) are still currently assembled by the surgeon at the time of surgery. However, age-related indication for the use of a biological valve in elderly patients in this setting indicates the increased need for a pre-assembled composite graft using a biological valve.
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Technique
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In an effort to develop a preassembled and ready to use biological valved conduit, a Dacron conduit (woven polyester graft) was modified to be stored in glutaraldehyde, while at the same time maintaining its blood impermeability feature. The new aortic conduit (Triplex; Vascutek Terumo, Renfrewshire, Scotland) was specifically designed for this purpose and has been primarly used for simple replacement of the ascending aorta in its straight form or associated with a biological valve for complete root replacement in its modified "Valsalva" design [8].
The aim of the study is to report the initial clinical experience with this "third generation" Dacron graft for ascending aortic replacement.
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Clinical Experience
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Eight consecutive patients (6 males and 2 females; mean age, 71 ± 7) underwent ascending aorta or root replacement using the new Triplex prosthetic conduit (Vascutek Terumo) in our department between July 2006 and December 2006. The inclusion criteria were the ascending aorta aneurysm or ascending aorta dissection, isolated or associated to aortic valve disease. All patients were included irrespective of concomitant ischemic heart disease or associated noncardiac pathology. All patients gave informed consent to participate in this study that was approved by the ethical committee of our institution.
Prosthetic Aortic Graft Description
The new Triplex vascular graft, (Communauté Européenne approval, restricted from sale in Canada; Vascutek Terumo, Renfrewshire, Scotland), consists of three layers or membranes (Fig 1). The inner layer that is in contact with blood is a standard uncoated woven Dacron graft, known as the "first generation" of vascular conduits; the outer layer is a standard expanded polytetrafluoroethylene graft. These two layers are fused together by a central layer of self-sealing elastomeric membrane (Fig 2). Grafts using this middle adhesive layer (ie, thermoplastic elastomer Styrene-Ethylene-Propylene-Styrene) have been implanted in animals for extended periods of time; analysis of the explants has shown no loss of the material in the bloodstream or change in its composition. The outer expanded polytetrafluoroethylene layer along with the central elastomeric membrane ensure a complete water and blood proof vascular prosthesis, whereas the Dacron layer is still the only one in contact with the blood of the patient. Those three layers allow total impermeability; in vitro tests show that the Triplex vascular graft has a water leakage value of 0,68 mL/cm2/min, which is significantly lower than a standard Gelweave coated vascular graft (Vascutek Terumo), which is rated at 15 mL/cm2/min. For its particular characteristics of high intrinsic impermeability, this graft does not require coating; therefore it can be maintained in glutaraldehyde solution as well as in various storage solutions. Furthermore, the graft showed high tensile, burst strength and suture retention (Table 1) during bench testing while at the same time maintaining a high biocompatibility derived from the high porosity of the inner layer of standard uncoated woven Dacron. In its Valsalva configuration, the Triplex graft consists of three segments joined together: (1) the collar with horizontal corrugation, (2) the skirt with radially expandable vertical corrugation, and (3) the body with horizontal corrugation as extensively described and shown in previous publications [8].
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Fig 1. A schematic drawing of the three-layer structure of the Triplex vascular graft (Vascutek Terumo, Renfrewshire, Scotland). The inner layer is a standard un-coated woven Dacron graft (DuPont, Wilmington, DE); the outer layer is a standard expanded polytetrafluoroethylene graft. These two layers are fused together by a central layer of self-sealing elastomeric membrane.
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Patient Population
Isolated supra-coronary ascending aorta replacement was performed on 2 patients and the Bentall procedure with Valsalva design and bioprosthesis was performed on 2 patients. A combined biological aortic valve and supra-coronary ascending aortic replacement (Wheat procedure) was performed in the remaining 4 patients. Associated mitral valve repair and coronary artery bypass were performed on 2 patients. Ascending aorta replacement was performed as an emergency procedure on 1 patient. Another patient had previous cardiac surgery.
All surgical procedures were performed by full median sternotomy and normothermic cardiopulmonary bypass; intermittent antegrade warm cardioplegia (ie, the blood of the patient plus potassium) was used as myocardial protection. A short period of hypothermic circulatory arrest was used in a patient affected by acute type A aortic dissection. Polypropylene 4-0 running sutures were used to perform the anastomoses between the aortic wall and the Triplex graft (Vascutek Terumo) and Ticron 2-0 pledgetted sutures (Tyco, Waltham, MA) were used for aortic valve replacement or for proximal anastomosis in the Bentall procedure. In the last instance, the coronary ostia were attached in the usual manner with Polypropylene 6-0. Clinical results were evaluated in terms of survival (both operative and 30-day mortality), neurologic events (evaluated early and at 30 days), and whole inflammatory response (evaluated in terms of C-reactive protein, erythrocyte sedimentation rate, white blood cells count, and fever). Prosthetic graft evaluation included surgical comfort in graft suturing, tailoring, and stretching, as well as hemostasis (evaluated in terms of time, postoperative bleeding, and need for chest re-entry). Postoperative pericardial effusion was also evaluated by transthoracic echocardiography.
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Results
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None of the patients died or showed major or minor neurologic events; clinical inflammatory response was within the routinely observed postoperative values (Table 2).
None of the patients at the discharge echocardiography evaluation exhibited significant pericardial effusion or developed fever or postoperative infections.
The prosthetic graft seemed slightly stiffer than the Dacron graft currently used (Fig 3). However, this increased stiffness due to the three layers configuration did not seem to decrease the ability of the graft to properly conform to the native aorta, even for finer anastomosis like coronary button sutures; therefore, it should not influence the workload of the heart. Graft handling and tailoring did not differ from that of the common Dacron conduit (Table 3). However, upon graft pressurization, a significant and clear advantage of this conduit seemed evident (ie, the ability of the graft to immediately stop any bleeding even from the suture holes).
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Fig 3. The picture compares a Triplex graft (Vascutek Terumo, Renfrewshire, Scotland) (top) with a current commercial model (bottom) mimicking the arch of the aorta. Note that the slightly increased rigidity of the Triplex graft is not ideal in case of sharp angles that are more easily reconstructed with a standard Dacron graft (DuPont, Wilmington, DE).
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Furthermore, the unique three-layer structure allows the surgeon to punch the graft with a very large bore needle that heals spontaneously in term of seconds. Graft sutures were never required. The time needed to obtain a complete and good hemostasis at the anastomoses was greatly reduced, even in presence of full heparinization.
One patient was re-explored for bleeding from the arterial cannulation site 12 hours after surgery. The mean 48 hours of bleeding for all the other patients was 487 ± 137 mL. These figures compared favorably with a consecutive series of 68 patients undergoing the Bentall operation or supra-coronary valve replacement during a 1- year period in which the average 48 hours of bleeding was 690 ± 210 mL). The average number of transfused blood units was 1.3 ± 0.3. Other blood products were not used. All patients were discharged from the postoperative intensive care within 24 hour of surgery. Computed tomographic scans performed 3 months after surgery showed a complete absence of peri-prosthetic effusion.
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Comment
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In the last few years there has been an increase in heart surgeries performed on elderly patients. This has reflected a significant increase in the use of biological prosthetic valves. There has also been a parallel increase in the number of aortic root replacements that require the use of a biological valve. Therefore, the availability of a preassembled and ready to use biological-valved conduit similar to mechanical-valved conduits could be very beneficial to surgeons. However, to store the conduit in glutaraldehyde, along with a biological valve, precludes the use of coating with proteins like albumin or gelatine. The need for a Dacron conduit that could be stored in glutaraldehyde and at the same time demonstrate an extremely high impermeability without the need of coating with proteins resulted in the creation of the new Triplex aortic conduit.
Our primary purpose was to first test its noninferiority compared with the commonly used coated Dacron graft in standard situations such as a simple ascending aortic replacement or sutured on site to a biological valve in a Bentall configuration. In fact, clinical evaluation of an aortic conduit is rather simple and is clearly based on the perception made by the surgeon of good handling characteristics, suture holding, and ease of tailoring and adapting the graft to the particular anatomy of the patient. In this initial stage, apart from a slightly increased stiffness of the conduit, there were no major differences observed in comparison with a standard Dacron graft. Needle penetration, suture holding, and the ability of the graft to conform to the aortic wall were excellent and were very similar to what is normally customary. However, one striking aspect that is a clear advantage of this type of three-layer graft is its impermeability (Fig 4), which was evident not only through the graft body but also at the level of the suture holes when the patient was still on full heparinization. As a consequence, the anastomoses could be immediately checked for potential point of bleeding without waiting for protamine administration that is usually necessary to stop the typical oozing through the suture holes. This results in a much quicker time to obtain optimal surgical hemostasis and could be particularly advantageous in case of dissection in which the blood coagulation is often more impaired for a certain period of time.
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Fig 4. Intraoperative view of the graft that exhibits the very high impermeability of the prosthetic conduit.
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Because only the Dacron layer is in contact with blood, no differences were expected in terms of inflammatory response or blood hemolysis; therefore its high porosity should maintain an excellent "endothelial re-habitation" (biocompatibility) of the inner graft surface.
Although the number of cases might seem limited, they seemed sufficient to judge the handling characteristics as well as the overall surgical performance and initial testing of the noninferiority of this graft compared with standard ones. The three-layer configuration of the new graft seemed to combine impermeability with good handling characteristics. The long-term performances of the graft remain to be seen.
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Disclosures and Freedom of Investigation
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The clinical study for the evaluation of the new Triplex vascular graft (Vascutek Terumo, Renfrewshire, Scotland) for ascending aorta replacement was not financially supported by the manufacturer. Therefore, the vascular grafts were not donated by the company; they were acquired by our own institution at the regular cost. All authors had full control of the design of the study, methods used, outcome measurements, analysis of the data, and production of the written report. None of the authors has a financial agreement with the company Vascutek Terumo for the Triplex conduit. Dr De Paulis discloses he owns a patent licensing agreement with Vascutek regarding the Valsalva design of the graft.
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Footnotes
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Disclaimer The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.
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References
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- Cooley DA, DeBakey ME. Resection of the entire ascending aorta in fusiform aneurysm using cardiac bypass JAMA 1956;162:1158.[Abstract/Free Full Text]
- Blakemore AH, Voorhees AB. Aneurysm of the aorta: review of 356 cases Angiology 1954;5:209.[Free Full Text]
- Westaby S, Cecil B. Surgery of the thoracic aortaIn: Westaby S, editor. Landmarks in Cardiac Surgery. Oxford, United Kingdom: Isis Medical Media; 1997. pp. 223.
- Franke U, Jurmann MJ, Uthoff K, et al. In vivo morphology of woven, collagen-sealed dacron prostheses in the thoracic aorta Ann Thorac Surg 1997;64:1096-1098.[Abstract/Free Full Text]
- Bentall H, De Bono A. A technique for complete replacement of the ascending aorta Thorax 1968;23:338-339.[Abstract/Free Full Text]
- Kouchoukos NT, Karp RB. Resection of ascending aortic aneurysm and replacement of aortic valve J Thorac Cardiovasc Surg 1981;81:142-143.[Medline]
- Cabrol C, Pavie A, Mesnildrey P, Gandjbakhch IG, Laughlin L, Bors B, Corcos T. long-term results with total replacement of the ascending aorta and reimplentation of the coronary arteries J Thorac Cardiovasc Surg 1986;91:17-25.[Abstract]
- De Paulis R, De Matteis GM, Nardi P, Scaffa R, Colella DF, Chiarello L. A new aortic Dacron conduit for surgical treatment of aortic root pathology Ital Heart J 2000;1:457-463.[Medline]
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Abstract
Introduction
