Ann Thorac Surg 2001;72:33-38
© 2001 The Society of Thoracic Surgeons
Original article: cardiovascular
Hemodynamic performance of stented and stentless aortic bioprostheses
Aldo D. Milano, MDa,
Claudio Blanzola, MDa,
Gianclaudio Mecozzi, MDa,
Alessandro D’Alfonso, MDa,
Marco De Carlo, MDb,
Carmela Nardi, MDb,
Uberto Bortolotti, MDa
a Division of Cardiac Surgery, Cardiac and Thoracic Department, University of Pisa Medical School, Pisa, Italy
b Division of Cardiology, Cardiac and Thoracic Department, University of Pisa Medical School, Pisa, Italy
Accepted for publication March 27, 2001.
Address reprint requests to Dr Bortolotti, U.O. Cardiochirurgia, Ospedale Cisanello, Via Paradisa 2, 56124 Pisa, Italy
e-mail: u.bortolotti{at}cardchir.med.unipi.it
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Abstract
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Background. This study compares the hemodynamic performance of stented and stentless bioprostheses used for aortic valve replacement in patients with aortic stenosis and small aortic root.
Methods. Between 1995 and 1998, 37 patients with a 21-mm aortic annulus (group 1) underwent aortic valve replacement with either a 21-mm Edwards Perimount or a 23-mm St. Jude Toronto bioprosthesis whereas 47 patients with a 23-mm aortic annulus (group 2) received either a 23-mm Medtronic Mosaic or a 25-mm Edwards Prima bioprosthesis. In each group mean and peak gradients, effective orifice area index, and left ventricular mass index were compared during follow-up.
Results. Group 1 patients showed a significant reduction of mean (p < 0.001) and peak gradients (p = 0.001) during follow-up, more evident for St. Jude Toronto versus Edwards Perimount (p = 0.02 and p = 0.05, respectively). Group 2 patients showed a significant reduction of mean and peak gradients (p < 0.001), more evident for Edwards Prima versus Medtronic Mosaic (p < 0.001 and p = 0.07, respectively). Effective orifice area index significantly increased only in group 1 (p = 0.005). Left ventricular mass index significantly decreased in all patients regardless of the type of valve (p < 0.001). Patients with Edwards Prima showed a trend to a higher regression of left ventricular mass index versus Medtronic Mosaic recipients (p = 0.07).
Conclusions. After aortic valve replacement, stented and stentless bioprostheses exhibited similar results with a more evident hemodynamic improvement during follow-up in the stentless valves. Stented bioprostheses of new generation, however, may parallel the hemodynamic performance of stentless valves and appear to be a valid alternative for aortic valve replacement in elderly patients with a small aortic annulus.
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Introduction
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Stented porcine bioprostheses have been widely used as cardiac valve substitutes in the past with substantially acceptable long-term results [1]. Limited durability because of progressive structural deterioration and suboptimal hemodynamic performance in the small sizes have been considered as the major weak points of such prostheses [1–3]. In recent years a variety of new models of both stented and stentless tissue valves, which should provide better hemodynamics and theoretically longer durability, have been available for clinical use. In this report we evaluated and compared the hemodynamic performance of four bioprostheses of new generation implanted in patients with small aortic roots. Comparison was performed between patients with the same measured aortic annulus size and not between patients with the same prosthesis size, inasmuch as the labeled valve size may differ from the actual dimensions of the valve or its sizer [4, 5].
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Material and methods
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Patient profile
We reviewed preoperative, perioperative, and postoperative data of all patients who underwent isolated aortic valve replacement (AVR) and received a bioprosthesis, the main indication being patient age (> 70 years), between January 1995 and December 1998. Among these patients a series of 84 patients with small aortic roots were selected. Inclusion criteria for this study were the following: severe or prevalent aortic valve stenosis; a native aortic annulus of 21 or 23 mm, and a minimum follow-up after AVR of 1 year. In patients with a 21-mm aortic annulus (group 1) a 21-mm Edwards Perimount (n = 22) or an oversized 23-mm St. Jude Toronto (n = 15) bioprosthesis was used, whereas in those with a 23-mm aortic annulus (group 2) a 23-mm Medtronic Mosaic (n = 26) or an oversized 25-mm Edwards Prima (n = 21) valve was implanted. Comparison of the hemodynamic performance of stented and stentless valves was performed between patients with the same aortic annulus diameter, thus stented valves were compared with stentless prostheses one size larger. Main preoperative characteristics of groups 1 and 2 patients are summarized in Table 1.
Surgical data
All operations were performed through a standard median sternotomy under moderately hypothermic cardiopulmonary bypass. Myocardial protection was achieved with injection of cold blood cardioplegia into the aortic root. After aortic valve removal and debridement of calcifications, the annulus and the sino-tubular junction were measured. Stentless bioprostheses were not implanted in patients with a significant dilation of the sino-tubular junction (difference between sino-tubular junction and aortic annulus > 10%) and in patients with calcific aortic root. Use of a stented or stentless bioprosthesis was left to the surgeon’s discretion; however, no 21-mm Medtronic Mosaic valves were implanted, the preference being for the 21-mm Edwards Perimount as a stented valve for patients with a 21-mm aortic annulus. The size of stented bioprostheses was selected according to the size of the annulus, whereas for stentless valves oversizing was adopted [6, 7], thus allowing implantation of a valve one size larger. All stented valves were implanted in supraannular position using multiple single sutures reinforced by subannular polytetrafluoroethylene felts. Stentless bioprostheses were inserted, as described by Konertz and colleagues [8] for the Edwards Prima and by David and associates [6] for the St. Jude Toronto, in the subcoronary position with the annular sutures in the outflow tract. Administration of warfarin was started on the second postoperative day with a target international normalized ratio of 3 and suspended after 3 months unless specific indications for long-term anticoagulation were present.
Patient follow-up
All patients were periodically evaluated at our outpatient clinic at 1, 6, and 12 months, and yearly thereafter to assess the clinical status and type and frequency of postoperative complications, which were evaluated on the basis of the recently revised guidelines [9]. Mean follow-up was 23 ± 6 months, ranging from 14 to 47 months. At each postoperative interval, transthoracic two-dimensional color Doppler echocardiographic studies were also obtained. Color Doppler echocardiography was performed with a Vingmed CFM 800 system (Vingmed Sound A/S, Oslo, Norway) equipped with a 2.5-MHz transducer. Standard M-mode and two-dimensional measurements were collected according to the criteria of the American Society of Echocardiography [10]. The left ventricular outflow diameter was averaged from three parasternal long-axis zoomed frames frozen in early systole, from the trailing edge of the left septal echo to the leading edge of the anterior mitral leaflet echo. All Doppler measurements were averaged for more than three cycles in patients with sinus rhythm or more than five cycles in those with atrial fibrillation. Subaortic peak and mean velocity, mean pressure gradient, and velocity-time integral were measured from the pulsed-wave Doppler recordings in the five-chamber apical view with the sample volume placed just below the point of fast flow acceleration. Transprosthetic peak and mean velocity, mean pressure gradient, and velocity-time integral were measured from the continuous-wave Doppler recordings from the apical view or from the right intercostal and suprasternal views. From these data we calculated the peak and mean gradients across the prosthesis (from the long form of the modified Bernoulli equation), the effective orifice area, the effective orifice area index (EOAi), and the left ventricular mass index (LVMi) from the formula given by Devereux and Reichek [11].
Statistical analysis
Data are presented as mean ± standard deviation and as simple percentages. Mean values of mean and peak gradients and EOAi are given at 1 and 6 months and at last follow-up (> 1 year) and compared among different prostheses by means of Student’s t test or Mann-Whitney, as appropriate, considering p values less than 0.05 as statistically significant. Two-factor repeated measures analysis of variance (ANOVA) with Bonferroni’s multiple comparison test was used to assess the influence of time and prosthesis type on peak and mean gradient, EOAi, and LVMi. Alpha value for Bonferroni test was set at 0.05. Statistical analysis was performed with the NCSS 2000 software (Statistical Solutions Ltd, Cork, Ireland).
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Results
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Hemodynamic data
In group 1 mean left ventricular ejection fraction was 52% ± 9%, 52% ± 7%, 54% ± 7%, and 55% ± 6% preoperatively, at 1 and 6 months, and at last follow-up. No significant difference could be found with repeated measures ANOVA.
In patients with Edwards Perimount, mean and peak gradients were 14 ± 4 and 23 ± 6 mm Hg at 1 month, 13 ± 5 and 22 ± 7 mm Hg at 6 months, and 13 ± 4 and 22 ± 6 mm Hg at last follow-up; EOAi was 1.04 ± 0.2, 1.07 ± 0.3, and 1.10 ± 0.2 cm2/m2 at 1 and 6 months and at last follow-up. In patients with St. Jude Toronto, mean and peak gradients were 14 ± 5 and 24 ± 7 mm Hg at 1 month, 13 ± 4 and 23 ± 6 mm Hg at 6 months, and 10 ± 4 and 19 ± 6 mm Hg at last follow-up (Fig 1); EOAi was 1.05 ± 0.2, 1.08 ± 0.2, and 1.16 ± 0.2 cm2/m2 at 1 and 6 months and at last follow-up.
By repeated measures ANOVA, group 1 patients showed a significant reduction of peak gradient during follow-up (F = 7.3, p = 0.001), with a statistically significant difference between 1 month versus last follow-up by Bonferroni test (p < 0.001). The reduction was more evident in patients with a St. Jude Toronto valve (F = 3.2, p = 0.05). Mean gradient also significantly decreased during follow-up (F = 12.6, p < 0.001), with statistically significant differences between 1 month versus last follow-up (p < 0.001) and 6 months versus last follow-up (p = 0.005) by Bonferroni test. Reduction was more evident in St. Jude Toronto versus Edwards Perimount recipients (F = 4.0, p = 0.02). Effective orifice area index significantly increased in group 1 patients during follow-up (F = 5.7, p = 0.005), with a significant difference between 1 month versus last follow-up by Bonferroni test (p = 0.003). No significant difference in EOAi variations between stented and stentless valves was found.
One patient with a St. Jude Toronto valve showed trivial aortic regurgitation.
In group 2 mean left ventricular ejection fraction was 50% ± 9%, 59% ± 8%, 50% ± 7%, and 51% ± 6% before, at 1 and 6 months, and at last follow-up. No significant difference could be found by repeated measures ANOVA.
In patients with Medtronic Mosaic, mean and peak gradients were 13 ± 4 and 23 ± 7 mm Hg at 1 month, 13 ± 4 and 22 ± 8 mm Hg at 6 months, and 12 ± 4 and 22 ± 8 mm Hg at last follow-up; EOAi was 1.07 ± 0.2, 1.04 ± 0.2, and 1.06 ± 0.3 cm2/m2 at 1 and 6 months and at last follow-up. In patients with Edwards Prima, mean and peak gradients were 15 ± 6 and 26 ± 9 mm Hg at 1 month, 13 ± 5 and 23 ± 8 mm Hg at 6 months, and 11 ± 5 and 21 ± 9 mm Hg at last follow-up (Fig 2); EOAi was 1.07 ± 0.2, 1.14 ± 0.2, and 1.18 ± 0.2 cm2/m2 at 1 and 6 months and at last follow-up.
By repeated measures ANOVA, group 2 patients showed a significant reduction of peak gradient during follow-up (F = 10.3, p < 0.001), with statistically significant differences between 1 month versus last follow-up (p < 0.001) and 1 month versus 6 months (p = 0.02) by Bonferroni test. A trend toward a more pronounced reduction in patients with an Edwards Prima valve was observed (F = 2.8, p = 0.07). Mean gradient significantly decreased during follow-up as well (F = 14.4, p < 0.001), with statistically significant differences between 1 month versus last follow-up (p < 0.001) and 1 month versus 6 months (p = 0.008) by Bonferroni test. Reduction was more pronounced in Edwards Prima versus Medtronic Mosaic recipients (F = 5.9, p = 0.004). Group 2 patients showed no significant changes in EOAi during follow-up. Two patients with an Edwards Prima valve showed trivial aortic regurgitation.
Regression of left ventricular hypertrophy
In patients with an Edwards Perimount valve, LVMi decreased from 187 ± 21 g/m2 preoperatively to 166 ± 18, 153 ± 19, and 150 ± 15 g/m2 at 1 and 6 months and last follow-up; in those with a St. Jude Toronto valve, LVMi decreased from 181 ± 25 g/m2 preoperatively to 164 ± 27, 151 ± 25, and 142 ± 24 g/m2 at 1 and 6 months and last follow-up (Fig 3). By repeated measures ANOVA, group 1 patients showed a significant reduction of preoperative LVMi during follow-up (F = 50.5, p < 0.001), with significant differences between preoperative versus 1 month, 6 months, and last follow-up (p < 0.001), 1 month versus last follow-up (p < 0.001), and 1 month versus 6 months (p = 0.006) by Bonferroni test. No significant differences between Edwards Perimount and St. Jude Toronto recipients were found.
In Medtronic Mosaic recipients, LVMi decreased from 188 ± 36 g/m2 preoperatively to 171 ± 33, 160 ± 30, and 149 ± 27 g/m2 at 1 and 6 months and last follow-up; in Edwards Prima recipients, LVMi decreased from 193 ± 48 g/m2 preoperatively to 166 ± 38, 157 ± 33, and 131 ± 32 g/m2 at 1 and 6 months and last follow-up (Fig 3). By repeated measures ANOVA, group 2 patients showed a significant reduction of LVMi during follow-up (F = 45.7, p < 0.001), with statistically significant differences between preoperative versus 1 month, 6 months, and last follow-up (p < 0.001), 1 month versus last follow-up (p < 0.001), and 6 months versus last follow-up (p < 0.001) by Bonferroni test. A trend toward a higher regression in Edwards Prima recipients was observed (F = 2.4, p = 0.07).
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Comment
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Lessons learned from clinical and pathologic experience have clearly indicated that most of the porcine bioprosthetic valves used in the past had a suboptimal hemodynamic performance and limited durability because of structural valve deterioration caused by tissue calcification [12]. Stented pericardial bioprostheses were introduced to provide a tissue valve with superior hemodynamics, but incorrect valve design has led to accelerated failures caused by mechanical cusp tears in most of them [13]. The increasing number of patients requiring replacement of a dysfunctioning bioprosthesis and the inherent risk of reoperation has therefore resulted in a larger use of mechanical valves. There appears to be at present a renewed interest in biologic prostheses for AVR, mainly because of the increasing number of elderly patients with aortic valve stenosis requiring AVR and the persistent risk of thromboembolic and bleeding complications in patients with mechanical prostheses treated with life-long anticoagulation. Indeed, durability of tissue valves has been reported to be excellent in patients older than 70 years of age [14]; furthermore, the use of tissue valves with adequate hemodynamic performance might be extended also to younger patients to allow a life without limitations and without the burden of anticoagulation, provided that durability may exceed at least two decades. Accordingly stentless bioprostheses and a new generation of stented porcine and pericardial valves, which have undergone major design and tissue manufacture modifications to meet such expectations, are currently available. Although the issue of durability needs the test of a longer follow-up to be addressed, there are currently data that indicate a superior hemodynamic performance of stentless versus stented bioprostheses [6]. To confirm this we have retrospectively evaluated four different models of tissue valves used for AVR in patients with pure or predominant aortic stenosis by comparing the results of echocardiographic studies aimed at assessing mean and peak gradient, EOAi, and regression of left ventricular hypertrophy. Recently a discrepancy between the industry-labeled valve size and the actual dimensions of the valve has been demonstrated [4, 5]. Thus, we chose to compare the hemodynamic performance of stented versus stentless valves on the basis of measured aortic annulus size rather than labeled valve size.
As advocated by David [7] and David and coworkers [6], insertion of a stentless valve has been performed by an oversizing technique using a valve one size larger than the aortic annulus on the basis of the measure of the native sino-tubular junction. Accordingly, in the two groups of this series, performance of stentless valves was compared with that of stented bioprostheses of a smaller size. When evaluating the 21-mm Edwards Perimount versus the 23-mm St. Jude Toronto in group 1, we have found similar postoperative gradients; however in St. Jude Toronto recipients both mean and peak gradients decreased during follow-up more than in Edwards Perimount recipients. Comparison between the 23-mm Medtronic Mosaic and the 25-mm Edwards Prima in group 2 showed similar findings, with a significant difference in the postoperative reduction of mean gradient in favor of the stentless Edwards Prima. Moreover, patients with an Edwards Prima valve showed a trend toward a more pronounced regression of left ventricular hypertrophy compared with patients receiving a Medtronic Mosaic valve. These results indicate an overall good hemodynamic performance of all models used for AVR without major differences between stented and stentless valves [5, 15]. This may be because of the limited number of patients considered in each group and, at least in part, differences in prosthetic design. Indeed, in our experience the Edwards Prima has shown initially high gradients, which were attributed to an inward bending of the polyethylene terephthalate fiber cloth [16]; such gradients seem to resolve after 1 year, most likely because of remodeling of the aortic root as it should occur with most stentless valves [16, 17]. However, even at 1 year follow-up, the hemodynamic performance of the 25-mm Edwards Prima valve in our experience is less optimal than that reported by Jin and associates [18]. This may be because of differences in the technique of implantation or occasional excessive oversizing. A significant reduction of left ventricular hypertrophy occurred in all patients, indicating that effective relief of left ventricular obstruction was obtained regardless of the size and type of valve implanted, an indirect sign that all valves provided adequate hemodynamic performance in each patient. However, because of residual gradients, in all groups LVMi remained slightly greater than the range of normality.
An obvious limitation of this study is represented by the fact that the hemodynamic studies were performed at rest. Stentless valves have been reported to have better hemodynamics than stented valves in conditions of increased flow, such as during physical exercise [19] or dobutamine stress [20]. However, most of these valves are implanted in elderly patients, and the residual gradients observed should not adversely affect their quality of life [21].
In conclusion, evaluation of four different stented and stentless bioprostheses after AVR has shown substantially similar results with a more pronounced hemodynamic improvement in patients with a stentless bioprosthesis during follow-up. Stented bioprostheses of new generation, however, may parallel the hemodynamic performance of stentless valves and appear to be a valid alternative for AVR in elderly patients with a small aortic annulus.
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Abstract
Introduction
