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Interact CardioVasc Thorac Surg 2007;6:345-349. doi:10.1510/icvts.2006.144196 © 2007 European Association of Cardio-Thoracic Surgery
One year hemodynamic performance of the Perimount Magna pericardial xenograft and the Medtronic Mosaic bioprosthesis in the aortic position: a prospective randomized study
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| Abstract |
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Key Words: Aortic valve replacement; Biological prosthesis; Hemodynamic performance
| 1. Introduction |
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| 2. Patients and methods |
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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.
| 3. Results |
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0.85 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).
| 4. Discussion |
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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 2223 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.
| 5. Conclusion |
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| Conference discussion |
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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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