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Ann Thorac Surg 2005;80:495-501
© 2005 The Society of Thoracic Surgeons

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Original article: Cardiovascular

Long-Term Results After Aortic Valve Replacement With the Bravo 400 Stentless Xenograft

^a Department of Cardiac Surgery and Cardiology, University of Milan, Centro Cardiologico Monzino IRCCS, Milan, Italy
^b Department of Cardiac Surgery, University of Insubria, Ospedale di Circolo "Fondazione Macchi," Varese, Italy

Accepted for publication March 3, 2005.

^_* Address reprint requests to Dr Barili, Department of Cardiac Surgery, University of Milan, Centro Cardiologico Monzino IRCCS, Via Parea 4, 20138 Milan, Italy (Email: fabarili{at}libero.it).

	Abstract

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BACKGROUND: This study was undertaken to evaluate the long-term clinical and echocardiographic outcome after aortic valve replacement with the Bravo Cardiovascular Model 400 stentless xenograft.

METHODS: Between February 1992 and January 1994, 67 patients underwent aortic valve replacement with the Bravo 400 bioprosthesis. The valvular pathology was aortic stenosis in 36 patients (53.7%), aortic insufficiency in 17 patients (25.4%), and mixed lesion in 14 patients (20.9%). Mean follow-up time was 9.8 ± 2.73 years and median follow-up time was 11 years. Cumulative follow-up time was 659 patients-years and was 94% complete.

RESULTS: No early deaths were observed. Overall survival estimates at 11 years were 74.71% ± 5.47%. The actuarial freedom from valve-related death at 11 years was 91.04% ± 3.84%; from cardiac-related death at 11 years it was 87.95% ± 4.29%; and from noncardiac death at 11 years it was 85.14% ± 4.58%. Eleven-year Kaplan-Meier survival of patients younger than 65 years was 90.91% ± 6.13% versus 66.08% ± 7.38% for older patients (p = 0.0307, log-rank test). The actuarial freedom from all valve-related morbidity and mortality at 11 years was 80.3% ± 5.4%. The mean transvalvular gradient decreased significantly after aortic valve replacement with a corresponding increase in effective orifice area. Left ventricular mass index at 10-year follow-up was 68.5% of the preoperative value.

CONCLUSIONS: The Bravo Cardiovascular Model 400 stentless xenograft has provided good clinical and hemodynamic results up until 11 years of follow-up.

	Introduction

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Interest in stentless aortic bioprostheses has increased in the last 2 decades. New knowledge on aortic valve pathophysiology has pointed out the role of stent-related stresses in bioprosthesis degeneration [1] and leaflet abrasion. Aortic homografts have demonstrated better performances but their use is limited by poor availability of all valve sizes and higher degeneration rates. Therefore, new stentless aortic xenografts were developed to eliminate stented bioprostheses and homografts drawbacks. Many advantages of stentless prostheses have been reported, including good hemodynamic performance, a low risk of thromboembolism without the use of anticoagulation, a decreased risk of endocarditis, and good technical results in left ventricular outflow tract reconstruction [2–5]. Long-term valve durability and patient survival are the key issues that remain to be addressed.

In 1992, we started our clinical experience by implanting a stentless porcine bioprosthesis in aortic position, the Bravo Cardiovascular Model 400 Stentless Xenograft (manufactured by Bravo Cardiovascular, Irvine, California, acquired by Cryolife, Marietta, Georgia). It was an entire porcine aortic root characterized by low pressure fixation (less than 2 mm Hg in 0.35% glutaraldehyde), valve outflow portion reinforcement with zero pressure fixed equine pericardium, absence of synthetic materials, coronary arteries ligation, and long aortic root (4 to 5 cm).

This report evaluates the 10-year mean follow-up of patients who underwent aortic valve replacement with the Bravo Cardiovascular Model 400 stentless xenograft.

	Patients and Methods

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Patient Population
Between February 1992 and January 1994, 67 patients (37 male and 30 female; mean age 67.9 ± 7.2 years, range, 22 to 83) underwent aortic valve replacement with the Bravo Cardiovascular Model 400 stentless porcine bioprosthesis. Preoperative data are detailed in Table 1. The valvular pathology was aortic stenosis in 36 patients (53.7%), aortic insufficiency in 17 patients (25.4%), and mixed lesion in 14 patients (20.9%). Among patients with aortic regurgitation, 2 patients had aortic annuloectasia (3%), 2 patients had endocarditis (3%), and 1 patient had endocarditis on aortic mechanical prosthesis (1.5%). No patient had bicuspid aortic valve disease.

We performed cardiac catheterization and coronary angiography in all patients. There was no significant coronary artery stenosis, except in 2 cases. One patient had previously undergone double-valve replacement (aortic and mitral valves) with mechanical valves. Concomitant procedures included coronary artery bypass grafting (CABG) in 2 patients.

Surgical Technique
Median sternotomy, cardiopulmonary bypass, moderate hypothermia, and aortic crossclamping were used in all patients. Cardiac arrest was obtained by an initial bolus of anterograde cold crystalloid cardioplegia followed by a bolus of retrograde cold crystalloid cardioplegia, and was maintained by retrograde cardioplegia repeated at 20-minute intervals, with additional topical cooling. Aortic calcifications were found in 50 patients, and complete decalcification was achieved in all cases.

We performed a subcoronary technique in 30 patients (45%), a miniroot (root inclusion) procedure in 35 patients (52%), and total aortic root replacement in 2 patients (3% [patients with aortic annuloectasia]). Surgical techniques have been described previously [6]. Choice of surgical technique was based on aortic morphology and surgeon preference. Aortic prosthesis sizes were 21 mm in 10 patients (14.9%), 23 mm in 25 patients (37.3%), 25 mm in 22 patients (32.9%), and 27 mm in 10 patients (14.9%). When associated CABG was required, distal anastomoses were completed first.

The mean aortic cross-clamp time was 95 ± 20 minutes and the mean duration of cardiopulmonary bypass was 115 ± 26 minutes. Table 2 summarizes the surgical techniques employed and operative data. Patients with sinus rhythm received 100 mg acetylsalicylic acid (ASA). Patients with chronic atrial fibrillation received anticoagulation therapy indefinitely with acenocoumarol.

Follow-up of survivors was last collected between August 15 and September 15, 2004. Cumulative follow-up time was 659 patient-years and was 94% complete. Median follow-up time was 11 years and mean follow-up time was 9.8 ± 2.73 years (range, 1 to 12).

Statistical Analysis
Postoperative events were defined as previously published by Edmunds and colleagues [10, 11]. Continuous variables were expressed as mean ± SD; discrete variables were expressed as percentage. Actuarial life-table estimates were constructed with the Kaplan-Meier method, and comparison among curves was carried out with the log-rank test. Significant differences in mean transvalvular gradients across the aortic valve prosthesis and in other echocardiographic parameters were evaluated with repeated-measures analysis of variance (ANOVA). If statistically significant, Student’s paired t test was then performed, with Bonferroni’s method used to correct for multiple comparisons. A p value less than 0.05 was considered statistically significant.

	Results

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Postoperative and Perioperative Mortality and Morbidity
No early death (before hospital discharge or at less than 30 days) was observed. Four patients (6%) needed surgical exploration for perioperative bleeding. Two patients (3%) had postoperative complete heart block with pacemaker implant. One patient (1.5%) had a sternal wound infection (Staphylococcus aureus) treated with antibiotic therapy, and 1 patient had a pericardial effusion that required subxiphoid exploration and drainage. No thromboembolic events, no endocarditis, and no valve-related complications were observed.

Late Mortality
There were 16 late deaths at the time of follow-up. Overall survival estimates at 5 and 11 years were 93.79% ± 3.01% and 74.71% ± 5.47%, respectively (Fig 1). The mean age at death was 76.9 ± 5.2 years (range, 64 to 83). Two patients (12.5% of deaths) were younger than 65 years at surgery. Ten patients were male (62.5%). There were 5 valve-related deaths. The cause of death was stroke in 3 patients, prosthesis endocarditis in 1, and sudden death in 1. The actuarial freedom from valve-related death at 5 and 11 years was 98.48% ± 1.50% and 91.04% ± 3.84%, respectively.

View larger version (14K): [in this window] [in a new window]   Fig 1. Actuarial freedom from death for all patients (triangles), patients younger than 65 years (circles), and patients older than 65 years (squares) is shown. Freedom from death was significantly higher among patients younger than 65 years (p = 0.0307, log-rank test).

Eleven-year Kaplan-Meier survival of patients younger than 65 years was 90.91% ± 6.13% versus 66.08% ± 7.38% for older patients (p = 0.0307, log-rank test; Fig 1). Freedom from valve-related death and from cardiac-related death was not significantly different between patients younger and older than 65 years (p = 0.9690 and p = 0.5823, respectively, log-rank test). Freedom from noncardiac deaths was significantly better in patients younger than 65 years (p = 0.0172, log-rank test; Fig 2).

View larger version (12K): [in this window] [in a new window]   Fig 2. Actuarial freedom from noncardiac deaths for patients younger (circles) and older (squares) than 65 years is shown. Freedom from noncardiac death was significantly higher among patients younger than 65 years (p = 0.0172, log-rank test).

Bioprosthetic Valve Endocarditis
One patient had prosthetic valve endocarditis at 8 years postoperatively. Blood cultures were positive with coagulase-negative Staphylococcus epidermis. This patient was treated with antibiotics but died of multiorgan failure before surgery. The actuarial freedom from bioprosthetic valve endocarditis at 5 and 11 years was 100% and 98.04% ± 1.94%, respectively. The linearized rate was 0.15% per patient-year.

Structural Valve Deterioration and Reoperations
Structural valve deterioration occurred in 5 patients after 3, 8, 9, 9, and 11 years. In all cases, prosthesis replacement was necessary. The mean age was 69.8 ± 21.9 years (range, 31 to 83). One patient (20%) was younger than 65 years. Three patients were male (60%). Echocardiography showed degeneration and calcification of leaflets, aortic annulus, and aortic root. Doppler-derived data showed peak and mean transvalvular gradients across the aortic valve prosthesis of 88.6 ± 13.8 mm Hg and 63.6 ± 15.8 mm Hg. All patients survived reoperation uneventfully. The actuarial freedom from reoperation at 5 and 11 years was 98.4% ± 1.6% and 90.2% ± 4.2%, respectively.

All Valve-Related Morbidity and Mortality
This composite category includes all morbidity and mortality related to the prosthesis. The actuarial freedom from all valve-related morbidity and mortality at 5 and 11 years was 95.4% ± 2.6% and 80.3% ± 5.4%, respectively (Fig 3). The linearized rate was 1.7% per patient-year. Freedom from all valve-related morbidity and mortality was not significantly different between patients younger and older than 65 years (p = 0.3789, log-rank test).

View larger version (14K): [in this window] [in a new window]   Fig 3. Actuarial freedom from valve-related mortality and morbidity (VRMM) for all patients (triangles), patients younger than 65 years (circles), and patients older than 65 years (squares) is shown. Freedom from all valve-related mortality and morbidity was not significantly different between patients younger and older than 65 years (p = 0.3789, log-rank test).

Late NYHA Functional Classification
At late follow-up, New York Heart Association (NYHA) functional classification was determined in 47 survivors: 29 patients (61.7%) were in NYHA class I, 14 (29.8%) were in NYHA class II, and 4 (8.5%) were in NYHA class III. No patient was in NYHA class IV.

Echocardiography
The echocardiographic parameters are summarized in Tables 3 and 4. As shown, the mean transvalvular gradient decreased significantly after aortic valve replacement, but the most significant decrease was a reduction to 37.4% of the preoperative value shown by echocardiogram at 3 months. Correspondingly, a significant increase in EOA was determined after surgery, without further changes. After the first year, EOA and peak and mean gradients remained stable. Decrease of interventricular septal thickness was shown at 3 months, but was significant at 7 years, while posterior wall thickness was significantly lower at 1-year follow-up and remained stable after 7 years. Left ventricular mass index was significantly reduced by 20.7% at 3 months and continued to decrease, to 68.5% of the preoperative value at 10-year follow-up. These changes reflected mainly the reduction in septal and posterior wall thickness.

	Comment

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Stentless aortic prostheses were designed to resemble native aortic root anatomy, hypothetically reducing mechanical stresses on the leaflets and improving longer durability and hemodynamic pattern. We have presented long-term results of a single-center series of aortic valve replacement with the Bravo Model 400 stentless porcine bioprosthesis. Despite the relative greater complexity of implantation and longer aortic cross-clamp time compared with stented aortic valves, we have demonstrated that Bravo 400 bioprosthesis implantation can be performed safely and without perioperative mortality. The excellent perioperative results of our series can be explained by accurate patient selection (patients with concomitant diseases being excluded). Furthermore, we went through a previous learning curve for homograft valves, which are similar in implant techniques to the Bravo 400 bioprosthesis. Other studies have pointed out the relationship between the learning curve and incidence of nonstructural valve failure, in particular with some stentless prosthesis models [12], and one of the possible contraindications of aortic stentless valve usage may be the surgeon’s unfamiliarity with the technique [13]. However, the operative results of our series are in line with other series with low perioperative mortality unrelated to valve surgery [14, 15].

Long-term follow-up has shown good survival rates, good stability of the prosthesis in a selected group composed of relatively young patients without coronary disease, and the regression of myocardial hypertrophy despite relatively high transvalvular pressure gradients. Midterm and long-term survival rate results compare favorably with those previously reported in other large series involving the use of stentless aortic valves [13–16] and are similar to those of aortic homografts [17]. These results are significantly lower than the Toronto SPV valve survival rates reported by David and colleagues [18], but the two study groups are not homogeneous, as our patients were older (mean age 68 years versus 62 years in the Toronto SPV group) and received smaller valves (mean size 23.9 mm versus 26.5 mm in Toronto SPV group). Analysis of age effect on survival has pointed out the impact of noncardiac deaths in our group, with a freedom from cardiac death and valve-related death at 11 years of 87.9% and 91%, respectively.

Also, the freedom from any valve-related complication is favorably comparable with that of other stentless prostheses [13–16, 18]. Recommendations regarding early anticoagulation after aortic replacement with a stentless valve are not well established. We prefer to give 100 mg ASA, reserving anticoagulation therapy for patients with atrial fibrillation. This choice probably explains the absence of major hemorrhage episode in our series and does not increase the risk of thromboembolic complications, similar to what has been reported by David and colleagues [18] in another 10-year experience with stentless prostheses, and by Luciani and colleagues [19]. Only Dagenais and colleagues [20] reported a higher incidence of thromboembolism (freedom from thromboembolic events, 86% at 7 years) using the same antiaggregation and anticoagulation protocol, whereas Williams and colleagues [21] abandoned the use of early anticoagulation in the latter part of the study, without an increase in thromboembolic events.

There were 5 cases of structural valve deterioration that required reoperation. The pattern of primary degeneration was quite different from the stented valve, as tissue calcification was more prevalent in the aortic wall and less in the cusps, similar to other stentless valves [13]. No case of severe regurgitation was registered. This figure is comparable the experience of David and coworkers [18], but differ substantially from that of Luciani and colleagues [19], who found leaflet tear at reoperation at the level of commissures in the absence of calcification. They have attributed this evidence to the progression of aortic root dilatation and subsequent increasing prosthesis insufficiency, which alter leaflet stresses and accelerate tissue degeneration. The different suite of aortic stentless prostheses probably accounts for these different degeneration patterns. The all-porcine aortic root availability, in particular, allows for changing the all-aortic root if there is an initial dilatation and prevents subsequent dilatation. We hypothesize that the valve outflow portion reinforcement with zero pressure fixed equine pericardium has blocked the prosthesis dilatation, acting as a flexible stent and conferring more stability to the aortic root.

Bravo 400 follow-up confirms the good late clinical outcome after aortic valve replacement with stentless prostheses, in contrast with stented prostheses [22, 23]. In a case-matched study, David and associates have shown greater overall survival for recipients of the Toronto SPV stentless when compared with recipients of the Hancock II stented valves, and a freedom from any valve-related complications of 81% versus 50% for stented valves [24]. Similar conclusions have been reached by other retrospective studies [13, 19, 25]. In all cases, the stentless prostheses have manifested an increased survival with lower incidence in valve-related and cardiac deaths and valve-related complications.

The echocardiographic follow-up pointed out a significant decrease in mean transvalvular gradient after surgery, with a further decrease at 3 months. This improvement was probably related to the resolution of tissue edema secondary to surgical trauma. The residual pressure gradients caused by Bravo 400 prostheses were higher than those reported for the Freestyle stentless bioprosthesis [14], the Toronto SPV stentless valve [15, 18,26], and the Prima stentless aortic valve [27], and were similar to the Biocor stentless prosthesis [28]. Postoperative pressure overload is considered one of the most important risk factors for left ventricular diastolic function failure, as it decreases myocardial hypertrophy regression. In our series, these significant residual gradients did not affect left ventricular hypertrophy regression. Wall thickness decreased continuously over time and normalized at 5 years. Left ventricular mass index was significantly reduced after 3 months, and at 10 years, it was decreased by 31.5%, as a positive long-term effect of reduction in wall thickness. This finding is in agreement with Ikonomidis and colleagues [29], who demonstrated that residual pressure gradient did not appear to inhibit ventricular remodeling after aortic valve replacement.

In conclusion, the Bravo Cardiovascular Model 400 stentless xenografts provided good clinical and hemodynamic results after 11 years of follow-up. Rates of patient survival and freedom from valve-related complications are high in comparison with other series of aortic bioprostheses. This xenograft has demonstrated a good stability with low rates of structural valve deterioration and no cases of severe regurgitation and leaflet tears in a selected, relatively young group without coronary disease. The postoperative transvalvular gradients ended up significantly higher when compared with other stentless xenografts, but they did not modify ventricular remodeling and left ventricular hypertrophy regression.

	Notice From the American Board of Thoracic Surgery

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The 2005 Part I (written) examination will be held on Monday, December 5, 2005. It is planned that the examination will be given at multiple sites throughout the United States using an electronic format. The closing date for registration is August 1, 2005. Those wishing to be considered for examination must apply online at www.abts.org.

To be admissible to the Part II (oral) examination, a candidate must have successfully completed the Part I (written) examination.

A candidate applying for admission to the certifying examination must fulfill all the requirements of the Board in force at the time the application is received.

Please address all communications to the American Board of Thoracic Surgery, 6333 N St. Clair St, Suite 2320, Chicago, IL 60611; telephone: (312) 202-5900; fax: (312) 202-5960; e-mail: mailto:info{at}abts.org.

	References

Top Abstract Introduction Patients and Methods Results Comment Notice From the American... References

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Fabio Barili Luca Dainese Massimo Porqueddu Andrea Sala Paolo Biglioli Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Polvani, G. Articles by Biglioli, P. Search for Related Content PubMed PubMed Citation Articles by Polvani, G. Articles by Biglioli, P.