Ann Thorac Surg 2009;87:1789-1794. doi:10.1016/j.athoracsur.2009.03.069
© 2009 The Society of Thoracic Surgeons
Original Articles: Adult Cardiac
Composite Freestyle Stentless Xenograft With Dacron Graft Extension for Ascending Aortic Replacement
Kostantinos Zannis, MDa,
Jean-François Deux, MDb,
Boyan Tzvetkov, MDa,
Kuniki Nakashima, MDa,
Daniel Loisance, MDa,
Alain Rahmouni, MDb,
Matthias E.W. Kirsch, MD, PhDa,*
a Department of Thoracic and Cardiovascular Surgery, Assistance Publique-Hôpitaux de Paris, Groupe Hospitalier Albert Chenevier-Henri Mondor, Créteil, France
b Department of Radiology, Assistance Publique-Hôpitaux de Paris, Groupe Hospitalier Albert Chenevier-Henri Mondor, Créteil, France
Accepted for publication March 25, 2009.
* Address correspondence to Dr Kirsch, AP-HP, Groupe hospitalo-universitaire Albert Chenevier–Henri Mondor, 51, avenue du Maréchal de Lattre de Tassigny, Créteil Cédex, 94 000, France (Email: matthias.kirsch{at}hmn.aphp.fr).
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Abstract
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Background: The present study was undertaken to evaluate clinical, hemodynamic, and morphologic results of composite stentless xenograft with polyethylene terephthalate fiber (Dacron; DuPont, Wilmington, DE) graft extension for combined replacement of the aortic valve, root, and ascending aorta.
Methods: Between 1997 and 2008, 55 consecutive patients (33 men, 71 ± 11 years) underwent ascending aortic replacement using Medtronic Freestyle with Dacron graft extension (DuPont). Indications included aneurysm (n = 31, 56%), dissection (n = 16, 29%), and endocarditis (n = 8, 15%). Associated procedures were performed in 25 patients (46%). Preoperative logistic EuroSCORE averaged 34% ± 28%. Mean cardiopulmonary bypass and aortic cross-clamp times were 244 ± 134 minutes and 162 ± 69 minutes, respectively.
Results: Clinical follow-up was 100% complete and averaged 2 ± 3 years. Early mortality was 0% (n = 0) in patients with a preoperative EuroSCORE of less than 20 (n = 26, mean expected mortality, 13% ± 5%) and 31% (n = 9) in those with preoperative logistic EuroSCORE of at least 20 (n = 29, mean expected mortality, 52% ± 28%). One- and 3-year survival rates were 83% ± 5% and 78% ± 7%, respectively. No major thromboembolic or spontaneous bleeding events were recorded. One patient (2%) required late reoperation for prosthetic valve endocarditis. Echocardiographic follow-up showed no valve dysfunction and low mean transvalvular gradients (7 ± 5 mm Hg). A 64-channel computed tomographic scan was performed in 33 patients at 32.4 ± 34 months and revealed two small pseudoaneurysms in a single patient.
Conclusions: Composite Freestyle with Dacron graft extension appears to be a safe option for bioprosthetic replacement of the aortic root and tubular ascending aorta. However, long-term results using this composite graft will have to be determined.
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Introduction
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Since its first description by Bentall and De Bono in 1968 [1], the technique for composite aortic valve and root replacement using a mechanical valved conduit has evolved to become the "gold standard" for the treatment of combined aortic valve and root disease. Although this operation provides excellent long-term survival and durability of repair, it exposes the patients to the risks of valve- and anticoagulation-related complications such as thromboembolism and bleeding. Thus, in a highly selected low-risk patient population, we have previously reported a sobering high linearized rate of minor thromboembolic events (10.3 per 100 patient-years; 95% confidence interval, 7.29 to 13.31) after elective Bentall procedure using a mechanical valved conduit [2].
Valve-sparing procedures such as David's reimplantation or Yacoub's remodeling procedures have become an increasingly appealing alternative in patients for whom lifelong anticoagulation is contraindicated or undesirable. These procedures have been shown to provide encouraging results, even in clinical settings such as bicuspid aortic valve, Marfan syndrome, or acute type A aortic dissection. However, these techniques are challenging and not always applicable in case of severe aortic valve disease. Other procedures designed for biologic replacement of the ascending aorta, such as aortic homografts or the Ross operation, cannot be considered as true alternatives owing to their limited availability and applicability.
Thus, several technical options have been devised to perform replacement of the ascending aorta (ie, aortic valve, root, and tubular ascending aorta) using a xenograft and have recently been reviewed by one of us [3]. Such a bioprosthetic approach would combine the benefits of avoiding lifelong anticoagulation with those of general applicability and low risk of technical failure. On the other hand, it exposes patients to structural xenograft deterioration and its associated risk of reoperation. Since 1997 we have been using the Freestyle (Medtronic Inc, Minneapolis, MN) stentless xenograft in full root replacement with polyethylene terephthalate fiber (Dacron; DuPont, Wilmington, DE) graft extension as originally described by Westaby and colleagues [4] and Akpinar and associates [5]. The Freestyle xenograft is prepared using a zero-pressure fixation process and anticalcification treatment using 
-amino oleic acid aiming to optimize hemodynamics and durability. Excellent flow characteristics and long-lasting freedom of structural deterioration have been demonstrated in several clinical studies for aortic valve or root replacement using the Freestyle xenograft [6, 7]. In contrast, only a few studies have evaluated the results of ascending aorta replacement using the Freestyle xenograft with Dacron tube graft extension [8–10]. The purpose of the present study was to evaluate clinical, echocardiographic, and scanning results of this procedure in our institution.
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Patients and Methods
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Patients
This retrospective cohort study was approved by our local ethics committee, which waived the need for patient consent because of its retrospective nature.
Between January 1997 and June 2008, 364 consecutive patients underwent aortic root and tubular ascending aorta replacement at Henri Mondor University Hospital. Most of these patients received a composite graft containing a tilting disk or a double-leaflet mechanical valve. In a subgroup of 55 patients (15%) constituting the present series, the procedure was performed using a composite Freestyle stentless xenograft with Dacron graft extension (DuPont). The choice of procedure was left to the discretion of the operating surgeon.
The series comprised 33 men (60%), and mean patient age was 71.2 ± 10.55 years (range, 26 to 86 years). Preoperative patient characteristics and operative risk assessment are shown in Table 1. Operative indications are listed in Table 2. Causative organisms for infectious endocarditis included Staphylococcus aureus (n = 3), enterococci (n = 3), streptococci (n = 1), and haemophilus (n = 1).
Surgical Technique
Median sternotomy and cardiopulmonary bypass were used in all patients. Arterial cannulation was performed through the proximal aortic arch or the common femoral artery depending on operative indication and extent of aneurysm. Venous drainage was achieved through a two-staged venous cannula in the right atrium in all but 2 patients who required bicaval cannulation. Myocardial protection was obtained by intermittent antegrade cold crystalloid cardioplegia. The ascending aorta was then transected. Aortic valve leaflets and the Valsalva sinuses were excised. Both coronary ostia were mobilized with limited aortic wall buttons.
Aortic root replacement
An appropriately sized Freestyle xenograft was chosen. Before the placement of the inflow suture line, the surgeon determined whether the Freestyle could be placed orthotopically depending on the relative positioning of the coronary ostia of the patients and the xenografts. If the xenograft could not be placed orthotopically, the valve was rotated counterclockwise by 120 degrees. Thus, the porcine left coronary sinus was aligned with the human noncoronary sinus, and the porcine right sinus with the patient's left sinus. The xenograft was then sutured within the left ventricular outflow tract, using 3-0 braided sutures. Once in place, the Freestyle was trimmed to create openings for the mobilized coronary ostia. Continuous 5-0 or 6-0 polypropylene sutures were used to reimplant coronary buttons.
Dacron graft extension
The size of the Dacron tube graft was chosen intraoperatively on the basis of the outer diameter of the distal end of the Freestyle and the diameter of the proximal aortic arch [20]. The Dacron tube diameter was larger than that of the Freestyle valve by 1.9 ± 2.3 mm. A double intussusception technique was used: the Freestyle was fitted inside the proximal end of the Dacron tube and the distal end of the Dacron tube was sutured inside the proximal aortic arch to obtain a telescope-like construction (Fig 1). Anastomoses were performed using running 5-0 polypropylene suture. A thin strip of polytetrafluoroethylene (Teflon) felt was incorporated into the distal suture line for reinforcement, creating a "sandwich-like" suture. Associated procedures and termination of operation were then performed in a standard manner. Associated procedures and intraoperative data are listed in Table 3.
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Fig 1. Morphometric measurements obtained by multislice computed tomography (CT) scans in 33 survivors.  = diameter.)
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Postoperative Antithrombotic Treatment
All patients received intravenous heparin until epicardial leads ablation, followed by oral anticoagulation using fluindione for the first 3 months. Thereafter, anticoagulation was suspended in the absence of other indications for oral anticoagulation indications. International normalized ratio was targeted between 2 and 3 for the first 3 months to be interrupted if no other concomitant pathologic process necessitated oral anticoagulation. Long-term administration of aspirin was recommended, but left to the discretion of the referring cardiologist.
Data Collection
Preoperative and operative data were prospectively recorded for all patients in a computerized data registry. Preoperative risk assessment was carried out according to the definitions of the European System for Cardiac Operative Risk Evaluation (EuroSCORE) [11].
Follow-Up
The referring cardiologists examined the patient at annual intervals. Clinical and echocardiographic information contained in their consultation letter was extracted and entered into our database. Postoperative events were compiled and analyzed according to the guidelines for reporting morbidity and mortality after cardiac valvular operations proposed by Akins and associates [12].
Clinical follow-up was 100% complete and averaged 21.2 ± 29.7 months (median, 4.7 months; 5th and 95th percentiles, 0.03 and 92.0 months). Echocardiographic follow-up was complete in 38 patients (86% of survivors) and averaged 22.5 ± 31.6 months (median, 5.3 months; 5th and 95th percentiles, 0.3 and 124.7 months). Only the latest echocardiographic data were considered for the present study. For all patients maximum and mean transvalvular gradients, effective orifice area, and left ventricular ejection fraction were obtained.
Computed tomography (CT) scans were obtained in 33 patients (75% of survivors). Computed tomography scans were performed after a mean of 30.8 ± 33.5 months after operation (median, 21.7 months; 5th and 95th percentiles, 1.7 and 127.0 months). Computed tomography scans were performed on an electrocardiogram-gated 64-detector CT scan (LightSpeed VCT, General Electric, Milwaukee, WI) using 90 mL of contrast medium injection (Iomeron 400, Bracco, Princeton, NJ). Measurements were performed on a dedicated platform (Advantage Windows 4.4, General Electric). Particular attention was paid to pseudoaneurysm formation in all suture lines, namely left ventricular outflow tract to Freestyle, Freestyle to coronary buttons, Freestyle to Dacron tube, Dacron tube to aortic arch (DuPont). Maximum diameters of these anastomoses, and of the innominate artery 1 cm distal to its origin and the aortic arch 1 cm distal to the innominate artery, were measured using multiplanar reconstruction techniques. Furthermore, coronary arteries and bypass grafts, when present, were explored for proximal stenoses.
Statistical Analysis
Statistical analysis was performed using SPSS Base 12.0 statistical software (SPSS Inc, Chicago, IL). Continuous variables were expressed as the mean ± 1 standard deviation and were compared using unpaired two-tailed Student's t tests. Categorical variables were expressed as percentages and compared with the 
2 test. A two-tailed probability value of less than 0.05 was taken to indicate statistical significance. Survival data were analyzed with standard Kaplan-Meier actuarial techniques for estimation of survival probabilities.
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Results
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Clinical Results
Mortality and long-term survival
Early mortality (
30 postoperative days) reached 16.4%. Causes of early mortality included heart failure (n = 4, 7%), septic shock (n = 2, 4%), multiple organ dysfunction syndrome (n = 2, 4%), and rupture of the aortic arch in a patient operated on for acute dissection. No patient with a preoperative EuroSCORE of less than 20 (n = 26; mean expected mortality, 12.9% ± 5%) died during the first 30 postoperative days. In contrast, patients with a preoperative logistic EuroSCORE of at least 20 (n = 29; mean expected mortality, 52% ± 28%) had a 30-day mortality of 31% (n = 9). Late mortality (>30 postoperative days) was noted in 2 patients (3.6%) and was related to traumatic hip fracture or unknown causes. Overall 1- and 3-year actuarial survival rates were 82.6% ± 5.4% and 78.3% ± 6.6%, respectively.
Postoperative morbidity
Early reoperations for hemostasis, sternal instability, or mediastinitis were required in 8 patients (15%). Other postoperative complications are listed in Table 4.
Embolism
No major thromboembolic events were recorded during the follow-up period. However, careful anamnesis revealed clusters of amaurosis fugax in 9 patients (20%).
Bleeding events
One patient experienced bleeding 45 months after operation. This patient had percutaneous prostatic biopsy complicated by hematoma of the major psoas muscle, which required transfusion and hospitalization. Of note, the patient was receiving oral anticoagulation for atrial fibrillation at the moment of bleeding.
Operated prosthetic valve endocarditis
One patient underwent reoperation for late prosthetic endocarditis in our department 23 months after the first operation. The infected xenograft and the Dacron tube were excised and successfully replaced by an identical composite graft.
Echocardiographic Results
No xenograft valve dysfunction was detected at follow-up echocardiography. Mean and maximal transvalvular gradients averaged 10 ± 5 mm Hg and 7 ± 5 mm Hg, respectively. Mean effective orifice area was 2.8 ± 1.3 cm2 and mean left ventricular ejection fraction was 0.53 ± 0.09.
Computed Tomography Scan Results
Morphometric measurements obtained on follow-up CT scans are shown in Figure 1. The observed diameter of the Freestyle xenograft measured at the level of the proximal suture line (inflow) was on average 5.9% ± 10.4% smaller than that indicated by the manufacturer on the size label. In contrast, the observed diameter of the Dacron graft was on average 11.8% ± 6.7% larger than that indicated by the manufacturer.
In one asymptomatic patient, CT scan performed at 49 months detected two false aneurysms. The first (maximum diameter, 7 mm) developed on the anastomotic line between the Freestyle and the left main coronary artery (Fig 2A). The second (maximum diameter, 14 mm) developed on the anastomotic line between the Freestyle and the proximal end of the Dacron tube (Fig 2B). No other false aneurysms were detected in this patient series.
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Fig 2. Asymptomatic pseudoaneurysms (arrows) developed in the same patient on the anastomotic lines between (A) the left coronary button and the Freestyle bioprosthesis and (B) between the Freestyle xenograft and the Dacron tube (DuPont, Wilmington, DE).
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No stenoses were detected on the reimplanted proximal segment of the coronary arteries. However, a stenosis of a saphenous venous graft to the second marginal artery was observed.
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Comment
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In contrast to mechanical valved conduits or aortic valve-sparing procedures, xenograft replacement of the ascending aorta combines the benefits of avoiding lifelong anticoagulation with those of wide applicability and low risk of technical failure. Although some bioprosthetic valved conduits have been commercialized, most groups currently use homemade composite grafts, constructed either with stented or stentless xenografts [3]. Intraoperative construction of a composite valved conduit using a stented xenograft appears as a straightforward approach and has yielded excellent long-term results [13]. Other groups, however, advocate the construction of composite valved conduits using a stentless xenograft to take advantage of their superior hemodynamics. Thus, Urbansky and coworkers [14] describes a composite graft consisting of a stentless xenograft incorporated within a Dacron tube. However, great care has to be taken during the construction of the graft to avoid prosthetic valve distortion with subsequent regurgitation. Alternatively, some stentless xenografts can be implanted using the full-root method, which might reduce this risk. However, the commercially available stentless xenografts are usually too short to replace the ascending tubular aorta and require interposition of a short segment of Dacron tube graft between the bioprosthetic root and the aortic arch.
The choice of the diameter of the Dacron tube graft is often reported in relation to the size of the bioprosthetic root. Thus, Akpinar and colleagues [10] preferred using a Dacron graft one size smaller than the Freestyle valve. In contrast, we and others [8, 9] prefer to oversize it, typically in a range from 1 to 3 mm. However, choosing the diameter of the Dacron graft with respect to the labeled diameter of the valve might be confusing. Indeed, the manufacturer's size label corresponds to the diameter of the proximal Dacron reinforced rim of the bioprosthesis and not to its distal diameter. We believe that the size of the Dacron interposition graft should be determined intraoperatively by (1) the outer diameter of the distal end of the bioprosthetic root and (2) the diameter of the proximal aortic arch. The diameter of the interposition graft can then be chosen to correct, at least in part, any size discrepancies between the bioprosthetic aortic root and the proximal aortic arch. Thus, less beveling of the distal suture line is required in case of moderate arch dilatation. This two-step reconstruction of the ascending aorta allows a tailored approach to each patient's anatomy.
One limitation of this technique is that it adds one suture line between the xenograft and the proximal end of the Dacron tube graft. This additional suture line obviously prolongs the aortic cross-clamp time for a few minutes, but this can hardly be expected to influence overall results. The most important concern, however, is about the fate of this suture line, which might be at risk for early bleeding or late dehiscence with false aneurysm formation especially in light of the increased aortic wall stresses observed in the root after ascending aortic replacement [15, 16]. Indeed, the distal end of the Freestyle is made of friable glutaraldehyde-treated tissue not reinforced with Dacron. Additionally, both prosthetic tissues probably have different compliances, increasing the stress at the level of the anastomosis even more. Finally, Dacron grafts have a tendency to dilate when implanted in the ascending aortic position. Etz and associates [17] have described a median graft diameter increase of 17% on early postoperative CT scans with a further dilatation of 2.8% per year in the long term. Our CT scan measurements have shown a 6% decrease of the diameter of the Freestyle inflow contrasting with a 12% increase of the diameter of the Dacron tube diameter. Consequently, some authors advocate the use of strips of felt or pericardium to reinforce the suture line between the bioprosthetic root and the Dacron graft. Alternatively, surgical glues can also be applied on this suture line for additional reinforcement. We perform this anastomosis without additional reinforcement, but take care to invaginate the distal end of the bioprosthetic root into the proximal end of the Dacron tube graft. Thus, only one of our patients developed a small false aneurysm on this suture line and did not require additional intervention to date.
An unexpected finding of our study was the occurrence of amaurosis fugax clusters in 20% of survivors. These transient but repetitive events might have an impact in cognitive functions and the quality of life. Interestingly, this rate was very similar to what we have reported after modified Bentall procedures using a mechanical valved conduit [2]. This observation suggests that these minor thromboembolic events are not so much related to the heart valve substitute as to the replacement of the ascending aorta by a tubular Dacron graft. When in contact with blood, Dacron grafts are rapidly coated by albumin, immunoglobulins, and fibrinogen from circulating plasma, providing a fibrinogen-coated foreign surface that creates low shear stress conditions mediating platelet aggregation. However, the adhesion of platelets to fibrinogen on this surface is not as irreversible as to von Willebrand factor of damaged blood vessels and may account for an increased risk of embolism of platelet–fibrin aggregates [18]. In addition, introduction of an inelastic graft in the natural aorta results in increased pulse pressure, which modulates propagation of pressure waves, causing wave reflection and eddy currents that promote thrombi formation [19, 20]. For these reasons, we recommend prolonged administration of antiplatelet drugs in the postoperative period.
Although long-term results using this technique are not available yet, xenograft replacement of the ascending aorta exposes patients to structural valve deterioration with its associated risk of reoperation. Reoperative procedures on the aortic root are challenging and high-risk procedures [21]. Some authors have suggested the creation of a Dacron skirt below the stented or stentless valves allowing isolated valve replacement within the Dacron tube in case of reoperation [22, 23]. The only reoperation we had to perform was performed for prosthetic valve endocarditis, and all prosthetic material had to be removed and replaced. In other situations, the possibility of implanting a new stented valve within the previous Freestyle valve after resection of its damaged cusps has been proposed [8]. However, the new prosthesis will have to be undersized with respect to the previous one. Furthermore, late bioprosthetic aortic wall calcification might complicate this type of procedure. Indeed, Akpinar and Guden [24] have reported two reoperations with Edwards Prima valve. They had to perform the entire root re-replacement because the extremely calcified suture line between the valve and the left ventricular outflow tract made it impossible to put stitches through it. Even though the Freestyle may be more resistant to calcification than homografts and other stentless bioprostheses because of its anticalcification treatment [25], some calcification of its aortic wall is to be expected. Percutaneous or transapical valve implantation could be an interesting alternative for patients in whom reoperation is estimated to be at very high risk. However, the Freestyle has no rigid proximal sewing ring, and the prosthetic valve annulus was found in all controls to be elliptic rather than strictly circular. This could cause a nonperfect application of the valved stent exposing it to paravalvular leaks [26].
In conclusion, the composite Freestyle stentless xenograft with Dacron tube extension offers a safe alternative in patients requiring aortic valve, root, and tubular ascending aorta replacement and in whom anticoagulation is contraindicated or undesirable. However, long-term results of this technique will have to be evaluated and compared with those of other surgical strategies used to perform a bioprosthetic replacement of the ascending aorta.
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References
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Abstract
Introduction
