Interact CardioVasc Thorac Surg 2007;6:345-349. doi:10.1510/icvts.2006.144196
© 2007 European Association of Cardio-Thoracic Surgery
Institutional report - Valves |
One year hemodynamic performance of the Perimount Magna pericardial xenograft and the Medtronic Mosaic bioprosthesis in the aortic position: a prospective randomized study
María José Dalmaua,*,
José María González-Santosa,
Javier López-Rodrígueza,
María Buenoa,
Antonio Arribasb and
Félix Nietob
a Department of Cardiac Surgery, Salamanca University Hospital, Paseo de San Vicente 58-182, 37007 Salamanca, Spain
b Department of Cardiology, Salamanca University Hospital, Paseo de San Vicente 58-182, 37007 Salamanca, Spain
Received 8 September 2006;
received in revised form 3 February 2007;
accepted 7 February 2007
 Presented at the joint 20th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 14th Annual Meeting of the European Society of Thoracic Surgeons, Stockholm, Sweden, September 10–13, 2006.
*Corresponding author. Tel.: +34-923291383; fax: +34-923291383.
E-mail address: dalmau_mjo{at}gva.es (M.J. Dalmau).
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Abstract
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We compared the hemodynamic performance of the Edwards Perimount Magna (EPM) and the Medtronic Mosaic (MM) bioprostheses according to the patient aortic annulus diameter (AAD). Eighty-six patients undergoing aortic valve replacement were prospectively assigned to receive either an EPM-valve (n=43) or an MM-bioprosthesis (n=43). Randomization was performed after measuring the AAD and patients were grouped according to their AAD: <22 mm (n=12), 22–23 mm (n=31) and >23 mm (n=43). Echocardiographic assessment was performed one year postoperatively. The mean AAD (EPM 23.9±2.1 mm vs. MM 23.6±2.3 mm) and mean valve size implanted (EPM 22.6±2.1 mm vs. MM 23.3±2.1 mm) were comparable in both groups. The EPM-group showed significantly lower mean gradient (EPM 10.2±3.2 mmHg vs. MM 17.1±8.2 mmHg) and larger effective orifice area (EOA) (EPM 1.99±0.4 cm2 vs. MM 1.69±0.4 cm2, P<0.0001). The EPM-valve was superior with respect to mean pressure gradient and EOA in all AAD. This difference was statistically significant in AAD of 22–23 mm (EPM 9.6±3.0 mmHg vs. MM 18.2±8.6 mmHg; EPM 1.82±0.3 cm 2 vs. MM 1.51±0.2 cm 2) and >23 mm (EPM 9.9±3.1 mmHg vs. MM 14.2±5.6 mmHg; EPM 2.18±0.4 cm2 vs. MM 1.94±0.5 cm2). Patient-prosthesis mismatch was present in 26.8% (MM) vs. 6.9% (EPM) of the patients (P=0.01). When the same AAD is taken as a reference, the EPM-valve was hemodynamically superior to the MM-bioprosthesis. The EPM-prosthesis significantly reduced the incidence of PPM.
Key Words: Aortic valve replacement; Biological prosthesis; Hemodynamic performance
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1. Introduction
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An accurate hemodynamic comparison between the different biological prostheses is difficult because of the differences existing between industry-labeled valve sizes, diameters of sizers and real size of the prosthesis [1]. Therefore, the value of hemodynamic comparisons between different prostheses based on labeled valve-size, are questionable. To allow a methodically correct comparison between different valve prostheses, it is necessary to use a parameter which will be independent of valve-size. Accordingly, comparisons performed in relation to the dimensions of the native aortic annulus appear to offer more objective data [2]. As such, in this prospective randomized study two supra-annular aortic valve prostheses, the Edwards Perimount Magna (EPM) pericardial xenograft and the Medtronic Mosaic porcine bioprosthesis (MM), were compared taking the diameter of the patient's aortic annulus as a reference and also compared on the basis of industry-labeled valve size.
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2. Patients and methods
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Eighty-eight consecutive patients selected for elective bioprosthetic aortic valve replacement (AVR), were prospectively assigned to receive either an EPM-valve or an MM-bioprosthesis. The medical records of 86 hospital survivors (EPM n=43, MM n=43) and the echocardiographic studies of 84 patients were analyzed. Patients undergoing an isolated AVR or those requiring AVR associated to aortocoronary bypass grafting, ascending aortic surgery or tricuspid annuloplasty were included in the study.
The third generation Medtronic Mosaic bioprosthesis is a stented porcine heart valve, it has been in clinical use since 1994 and its clinical and hemodynamic performance has been found to be highly satisfactory [3]. Introduced in 2002, the Carpentier-Edwards Perimount Magna aortic xenograft consists of stented bovine pericardium. Although its long-term hemodynamic results are still not available, its short-term hemodynamic performance has been proven to be superior to those of the Perimount standard model [4].
Patient randomization was performed intraoperatively after the native aortic valve was excised and the dimension of the annulus measured with three different sizers: a neutral sizer (Hegar dilator) and the corresponding sizer provided by each manufacturer (model 7305 for the MM and 1130 for the EPM). The selected prosthesis size was determined by the largest sizer whose lower cylindrical portion comfortably fitted into the patient annulus. No attempts to oversize the valves were made in any patient. All valves were implanted in the supra-annular position and no patients underwent annular enlargement.
Patients were followed up by transthoracic Doppler echocardiography one year (mean 12±1.5 months) postoperatively. Left ventricular (LV) dimensions were measured according to the recommendations of the American Society of Echocardiography (ASE). LV mass was calculated with the corrected ASE formula. Residual LV hypertrophy was defined as an LVM index >131 g/m2 in males and >100 g/m2 in females. The modified Bernoulli equation was used to calculate peak and mean pressure gradients across the prosthetic valve. Effective orifice area (EOA) was calculated by the continuity equation and indexed to body surface area to assess the presence of patient-prosthesis mismatch (PPM). Significant PPM was defined by IEOA 0.85 cm2/m2.
The continuous variables were expressed as mean values±S.D. and compared using a t-test and the Mann-Whitney U-test as indicated. Nominal data are presented as frequencies and percentages and compared by Pearson's  2 test. Statistical significance was defined as a P<0.05. Statistical analysis of the association of variables was performed with the Pearson correlation coefficient or the determination coefficient when the relation was linear or nonlinear, respectively. Because there were few patients in the size 19 groups, no statistical comparison was performed for them.
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3. Results
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Patient preoperative characteristics were comparable in the two groups (Table 1). Patients were grouped according to their AAD in three categories: <22 mm (n=12), 22–23 mm (n=31) and 23 mm (n=43). When comparing the EPM and MM-groups the mean AAD (EPM 23.9±2.1 mm vs. MM 23.7±2.3 mm) and mean valve-size implanted (EPM 22.7±2.1 mm vs. MM 23.4±2.1 mm) did not show any significant difference. In 20 (46%) of the EPM-patients, as compared to 5 (12%) of the MM-patients, the implanted labeled valve size was smaller than the assessed AAD (P=0.001). There was a correlation between the AAD and each one of the prosthesis sizers (Fig. 1). For the EPM-sizer this correlation was even more distinctive (EPM-sizer: r=0.925, R2=0.85, P<0.0001; MM-sizer: r=0.865, R2=0.75, P<0.0001). With the MM-sizer a trend toward overestimation the AAD could be observed.
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Fig. 1. Correlation between the aortic annulus diameter of the patients and the respective sizers provided by each manufacturer. EPM-sizer: r=0.925, R2=0.85, P<0.0001; MM-sizer: r=0.865, R2= 0.75, P<0.0001. Solid squares=observed; lines=linear regression lines.
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3.1. Hemodynamic measurements
Hemodynamic comparisons between the EPM and MM bioprostheses according to valve size are listed in Table 2. Mean pressure gradients were lower in the EPM-group for each valve size. This difference was statistically significant for the 21 mm (P<0.001), >23 mm (P=0.010) and 25 mm valves (P=0.016). The mean EOA was significantly larger in the EPM-group (P<0.0001) and also for each valve size. The average indexed EOA was significantly higher (P<0.001) in the EPM-group (EPM 1.13±0.21 cm2/m2 vs. MM 0.97±0.22 cm2/m2). The comparisons of the IEOA according to type and size of the prosthesis are illustrated in Fig. 2.
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Fig. 2. Comparison of the Indexed Effective Orifice Area (IEOA) according to the type of the prosthesis (EPM vs. MM) and grouped by valve size. Solid line indicates an IEOA=0.85 cm2/m2, thus defining the presence of significant patient-prosthesis mismatch.
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Hemodynamic data for both valve types according to the AAD are listed in Table 3. When the AAD was taken as a reference, mean pressure gradients were slightly lower for the EPM-valve and this difference was statistically significant in patients with an AAD of 22–23 mm (P<0.001) and >23 mm (P=0.003). With the EPM-prostheses, a significantly larger EOA was obtained for each AAD, especially in AAD of 22–23 mm (P=0.003) and >23 mm (P=0.05). Accordingly, in all AAD the EPM-prosthesis showed slightly higher IEOA, reaching statistical significance in AAD of 22–23 mm (P=0.001) and >23 mm (P=0.05). No hemodynamic differences were demonstrated in patients with an AAD of <22 mm, although an obvious trend toward better hemodynamics was also seen in this group. There was a significant correlation between the indexed EOA and the mean transvalvular pressure gradient in both subgroups (EPM group, r=–0.478, P=0.001; MM group, r=–0.348, P=0.02) (Fig. 3).
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Fig. 3. Correlation between the mean transvalvular gradient and the indexed effective orifice of the prosthesis: EPM group: r=0.478, R2=0.23, P=0.001; MM group: r=0.348, R2= 0.12, P=0.02. Open circles=Edwards Perimount Magna prosthesis; closed circles=Medtronic Mosaic valve.
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The prevalence of significant PPM was different according to the type and size of the implanted bioprosthesis (Table 3). Overall, 26.8% of patients with an MM-valve had an IEOA0.85 cm2/m2 whereas this occurred only in 6.9% of those with an EPM-valve (P<0.01). A significant percentage of patients with small AAD (<22 mm) showed a mismatch in both groups (MM 33.3% vs. EPM 20%). In the EPM-group the incidence of significant PPM decreased as the AAD increased. Nonetheless, in the MM-group PPM was present constantly in all AAD.
Changes in LV mass index between preoperative echocardiographic measurement and follow-up represented by the LV mass regression is shown in Table 3. The LV mass and LV mass index significantly decreased in both groups. Overall, there was no significant difference between both valve types regarding the absolute amount of LV mass regression (EPM –70.7±50.5 vs. MM –72.5±54.4) and the absolute LV mass index reduction (EPM –44.16±29.8 vs. MM –44.4±30).
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4. Discussion
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Significant variability between the manufacturer's provided actual dimensions of the sizer and the prosthesis itself led to question the scientific value of comparisons based only on the industry-labeled valve size [1]. Comparisons performed in relation to the dimensions of the native aortic annulus, an independent parameter of valve-size, appear to offer more objective data [2]. For this reason, the hemodynamic results of the current study are depicted according to the patient AAD, which was measured intraoperatively with a neutral instrument, as well as referring to the industry-labeled valve size.
When labeled valve sizes were compared, our data clearly showed that the EPM-prosthesis does have a hemodynamic advantage, especially in valve sizes 21, 23 and 25 mm. This can be explained because the size-matched internal diameter of the EPM-prosthesis is between 1.5 and 2 mm larger than the respective manufacturer-reported internal diameter of the MM-valve [5]. Upon implanting valves with larger internal diameters, the current study demonstrated the resultant hemodynamic advantages of the EPM-prosthesis: lower mean pressure gradients and larger EOA. These findings correlated closely with those reported by other researchers into these bioprostheses [2, 6] and confirm the observed hemodynamic superiority of the EPM-prosthesis in vitro [7] and under stress conditions [8].
Comparisons related to the AAD demonstrated that the hemodynamic performance of the EPM-valve was superior to the MM-prosthesis. In patients with an AAD <22 mm, the implanted valve did not influence the hemodynamic outcome after AVR, although the number of patients in this group (EPM n=5, MM n=7) was too small to permit meaningful analysis. In contrast, in AAD of 22–23 mm and >23 mm, the EPM-prosthesis was significantly superior regarding mean pressure gradient, EOA and indexed EOA. This difference definitively demonstrates the hemodynamic advantage of the larger EOA to tissue annulus ratio of the EPM-prosthesis.
As expected, in this series, the mean AAD was similar in both groups (MM 23.6 mm vs. EPM 23.9 mm). However, a tendency to implant smaller EPM than MM-valves in relation to the AAD was observed (mean valve size implanted: Mosaic, 23.3 mm; Magna, 22.6 mm). This can be explained because the outer diameter of the EPM-sizer is almost 1.5 mm larger than the size-matched MM-sizer. Moreover, our findings demonstrated a trend toward overestimation of the AAD with the MM-sizer (Fig. 1).
In the current study, echocardiographic quantification of indexed EOA, the only valid parameter that identifies mismatch [9], has been employed to define PPM. The hemodynamic consequence of PPM is to generate high residual transvalvular gradients which are responsible for an incomplete LV mass regression [10], a phenomenon associated with a negative effect on intermediate and long-term survival [11]. In this study there was a significant difference in the incidence of PPM between groups. Overall, 27% of patients with an MM-valve had an indexed EOA 0.85 cm2/m2 while this occurred in only 6.9% of those with an EPM-valve (P<0.01), this difference was also statistically significant in patients with an AAD of 22 mm or more. Our data confirm the outcomes reported in other studies [12] and showed that the use of an EPM-valve may contribute to reduce the incidence of PPM, even in patients with a small AAD.
When analyzing the effect of PPM on the hemodynamic results, the transprosthetic pressure gradient is expected to decrease with increasing indexed EOA, a correlation that could be demonstrated in both groups (Fig. 3). Nevertheless, the effect of this benefit on LVM mass regression was less evident. All of our patients showed a significant regression in LVM and LVM index, irrespective of prosthesis type or AAD. Although patients in the EPM-group showed a higher indexed EOA and lower incidence of PPM, no statistical difference was found concerning absolute regression in LV mass. Our results confirm those of other studies showing that prosthesis size, indexed EOA, prosthesis type, and Doppler gradient do not negatively affect LV mass regression [13, 14]. The absence of differences in early LV mass regression seen in our series makes questionable the importance of PPM in this patient population (aged >70 years). Although relationship between LV mass and PPM has been largely identified, as long as the true incidence of PPM and its significance in terms of survival and quality of life is still controversial [15], long-term clinical outcomes are necessary.
The study has a number of limitations. Firstly, the overall population sizes were small, thereby inevitably limiting us to draw strong conclusions. Moreover the limited number of patients in each group did not allow a complete size-by-size analysis, especially in 19 mm valve sizes. Secondly, the hemodynamic measurements were performed at rest and not under stress conditions. During exercise the differences seen in this study could be more distinctive showing additional advantages of the EPM-prosthesis. Finally, though LV hypertrophy regression largely occurs within the first two postoperative years, it could continue more slowly for several years thereafter. As such, a longer follow-up of our patients would, therefore, be necessary to determine whether the difference between these prostheses increases over time.
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5. Conclusion
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Our study demonstrates that the hemodynamic outcomes of the EPM-prosthesis are substantially better than those of the MM, thus achieving lower gradients and larger indexed EOA when compared on the basis of industry-labeled valve sizes. When comparisons were related to the inner diameter of the AAD, patients clearly benefit from the implantation of the EPM-prosthesis, thus resulting in a significantly superior hemodynamic performance and a minimized risk of PPM.
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Conference discussion
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Dr. S. Bleiziffer (Munich, Germany): I wondered why you showed a linear relation between gradient and effective orifice area, because it was already shown in the early '90s that there is an exponential and not a linear correlation between effective orifice area and pressure gradients. You showed a linear correlation, but I think this must be an exponential correlation between gradients and orifice area.
Dr. Dalmau: This is simply a linear regression analysis and this is the correlation that we found.
Dr. P. Kleine (Frankfurt, Germany): How do you explain that the mass regression is not different between the groups? Does it maybe mean that the difference in gradients that has been shown by you is not sufficient to lead to an accelerated mass regression?
Dr. Dalmau: No. I think left ventricular mass regression largely occurs within the two first postoperative years, but it can also continue more slowly for several years thereafter. So perhaps with a longer follow-up of our patients there will be some difference between both bioprostheses. And moreover, not only residual transvalvular gradients could affect left ventricular mass regression. I think so many other factors as persistent high blood pressure, physical activity or genetic factors may influence also left ventricular mass regression.
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Abstract
1. Introduction
