The Complete Supraannular Concept
In Vivo Hemodynamics of Bovine and Porcine Aortic Bioprostheses
Background— Complete supraannular placement of an aortic bioprosthesis is one approach to optimize the hemodynamic result of an aortic valve replacement. It is achieved with the combination of a special valve design and the supraannular sewing technique with noneverted mattress sutures. We evaluated 5 bioprostheses designed for complete supraannular placement to assess potential hemodynamic differences caused by factors (eg, valve material) other than implantation position.
Methods and Results— In 336 patients (mean age, 72.0±7.1 years; 143 women), hemodynamics including mean pressure gradients, effective orifice areas, and indices and incidence of patient-prosthesis mismatch were evaluated 6 months after surgery. Annulus diameter was measured during surgery. Patients received the Carpentier Edwards Perimount Magna (Magna, n=169), the Medtronic Mosaic (Mosaic, n=46), the Mosaic Ultra (Ultra, n=17), the SJM Epic Supra (Epic, n=46), and the Sorin Soprano (Soprano, n=58). For small annulus sizes (<23 mm), the mean pressure gradients of the Magna (11.82±4.8 mm Hg) were significantly lower than the Mosaic (16.04±6.1 mm Hg) and the Ultra (22.0±4.1 mm Hg), and the Soprano (13.3±5.2 mm Hg) was hemodynamically superior to the Ultra. For medium (23 to 24 mm) and large (>24 mm) annulus sizes, the mean pressure gradients of the Magna were lower than the Epic (10.0±3.5 mm Hg versus 14.9±6.4 mm Hg; 9.9±4.0 mm Hg versus 18.6±12.7 mm Hg). Furthermore, in patients with large annulus size, the mean pressure gradients of the Soprano (11.4±3.8 mm Hg) were lower compared with the Epic (18.5±12.7 mm Hg). Severe patient-prosthesis mismatch was observed more frequently in patients with the Mosaic (12/46; 26.1%) and the Ultra (3/17; 17.6%) prostheses.
Conclusions— Complete supraannular placement cannot prevent high pressure gradients or patient-prosthesis mismatch thoroughly, but the choice of a bovine prosthesis can optimize hemodynamic performance.
The complete supraannular design of stented aortic bioprostheses combined with the supraannular sewing technique is one approach to optimize the hemodynamic result after aortic valve replacement. In prostheses with this design, the stent is placed on top of the sewing ring and not beside it. Therefore, the entire valve is positioned above the annulus, and no parts of the stent or sewing ring impair the blood stream. With this concept, the internal valve diameter should theoretically be equal to the tissue annulus diameter and thus achieve an optimal hemodynamic performance with no obstruction of the blood flow.1 In fact, the effective orifice area of a valve prosthesis is in the order of 35% to 48% of the geometric annulus area that is theoretically available2; thus, the aim of the supraannular concept can only be to gain as much effective orifice area as possible in relation to the patient’s annulus size.
There are several prostheses for complete supraannular placement available from different manufacturers, all following the same concept but with different design implementations. To evaluate factors other than prosthesis position, which might influence the hemodynamic performance (eg, valve material), we evaluated 5 commercially available bioprostheses for complete supraannular placement (Carpentier Edwards Perimount Magna,1,3 Medtronic Mosaic,1,4–9 Medtronic Mosaic Ultra,10,11 St Jude Medical Epic Supra,4,7,12 and Sorin Soprano1,7,8,13).
In this retrospective study, our focus lies on the hemodynamic in vivo performance (mean pressure gradients, effective orifice area, patient-prosthesis mismatch), geometric parameters, and a literature review concerning hemodynamic data to evaluate differences between prostheses designed according to the complete supraannular concept.
The discrepancy between valve size labeling by different companies makes comparisons of valves on the basis of labeled valve size meaningless. Therefore, we use as a basis for comparisons—as in previous studies—the patient’s aortic annulus, which is measured with a standardized sizer during surgery.1,4,8,13,14
The Carpentier Edwards (CE) Perimount Magna (Magna) valve is a stented bovine pericardial bioprosthesis. It is a modification of the CE Perimount valve and is characterized by glutaraldehyde fixation and a modified stent and sewing-ring design to permit complete supraannular placement. It has been in clinical use since September 20021 (Figure 1A).
The Medtronic Mosaic (Mosaic) valve is a stented porcine bioprosthesis. The prosthetic tissue is treated with glutaraldehyde, and fixation is done by combining zero-pressure and root-pressure techniques. Amino-oleic acid was applied as an anticalcification treatment.1,4,5,15 It has been in clinical use in Europe since 1994 (Figure 1B).
The Medtronic Mosaic Ultra (Ultra) valve is a modification of the Mosaic valve. The sewing ring of the Mosaic was reduced to adapt to the small aortic root and to maximize the valve-to-annulus ratio. Fixation and anticalcification process are similar to that of the Mosaic valve. It was introduced in our institution in February 200710,11 (Figure 1C).
The SJM Epic Supra (Epic) is a stented porcine tissue valve based on the design of the SJM Epic valve. Modification of the SJM Epic allows a complete supraannular implantation of the Epic Supra. The SJM Epic and the Epic Supra are both based on the design of the Biocor valve, which has a documented 20-year long-term durability.16 Its design consists of a triple composite construction with matched individual leaflets. The leaflet tissue is fixed under low pressure in glutaraldehyde to promote retention of collagen crimp and elasticity, before applying the Linx anticalcification treatment. The Epic Supra was introduced to the European market in October 20034 (Figure 1D).
The Sorin Soprano (Soprano) is a stented bovine pericardial bioprosthesis. The tissue is fixed at low pressure with glutaraldehyde and then detoxified using homocysteic acid to neutralize residues of unbound aldehyde groups. The Soprano is based on the Sorin Pericarbon More, which has been in clinical use for more than 15 years. New features of the Soprano are the stent design, allowing complete supraannular implantation, the prosthetic dimensions, and the valve size labeling1,13 (Figure 1E).
Aortic valve replacement was performed using standard cardiopulmonary bypass with moderate hypothermia at 32°C with cold crystalloid cardioplegic cardiac arrest. After removal of the native aortic valve and decalcification of the aortic annulus and root, the internal diameter of the aortic annulus was routinely measured by inserting a probe (Hegar dilator) into the annulus (unit: 1 mm). With the assumption that the aortic annulus approaches a circular shape, the annulus orifice area was calculated as follows: (Hegar dilator diameter (cm)×0.5)2×π. The prosthetic valve size was determined by using the original sizer provided by each manufacturer. All bioprostheses were implanted with pledgeted, interrupted, noneverting mattress sutures.
By using ventriculoarterial mattress sutures combined with the special valve design, complete supraannular placement is achieved (Figure 2).
Patient Enrollment and Follow-Up
Inclusion criteria were aortic valve replacement because of degenerative aortic valve disease with aortic stenosis or a combined aortic lesion, a completed 6-month follow-up examination including echocardiography, and a valid intraoperative annulus measurement. Concomitant procedures were allowed, except of valve replacement in other positions. Patients with aortic valve replacement due to acute endocarditis or isolated aortic regurgitation were excluded as well as patients requiring emergency operations.
In total, 336 patients (143 women) were included in this retrospective, nonrandomized study. One hundred sixty-nine patients received the Magna, 46 the Mosaic, 17 the Ultra, 46 the Epic, and 58 the Soprano. The 5 tested valves were not all available at the same time during the whole period of the study. The Mosaic has been used since August 2000. The Magna was introduced in January 2001 and the Soprano in September 2003. The Epic was used since June 2004 and the Ultra was introduced in February 2007; therefore this is the smallest group. Patients were included consecutively to avoid bias by patient selection. Valves were chosen by the surgeon’s preference. All patients gave informed consent, and this study was approved by the local ethics committee (No. 2234/08).
Patient demographic data are summarized in online supplemental Table 2. There is no significant difference between the groups concerning aortic cross clamp time and annulus dimension.
All echocardiographic examinations were performed transthoracally by 3 experienced echocardiographers. Transvalvular flow velocity, pressure gradient, and velocity time integral (VTI) were measured using continuous-wave Doppler. Pulsed-wave Doppler was used for the measurements in the left ventricular outflow tract (LVOT).
We used following calculations for the parameters:
MPG (mm Hg)=mean aortic pressure gradient−mean LVOT pressure gradient
EOA (cm2)=(LVOT diameter [cm]×0.5)2×π×VTILVOT/VTIValve (continuity equation)
where MPG is mean pressure gradient, EOA is effective orifice area, and BSA is body surface area.
Patient-prosthesis mismatch was defined by Blais et al17 as severe for an EOAi of ≤0.65 cm2/m2, as moderate for an EOAi >0.65 cm2 and <0.85 cm2/m2, and as clinically not significant if EOAi was >0.85 cm2/m2. For the calculation of the EOAi we only used EOAs that were measured 6 months after surgery.
Geometric data were provided by the manufacturers and are summarized for comparison in online supplemental Table 3.
We did a complete PubMed literature review and used the software “Endnote” (Thomson Reuters, New York, NY) for archiving the reviewed literature. The following key word combinations were used for our research: “Mosaic hemodynamic,” “Mosaic Ultra hemodynamic,” “Epic supra hemodynamic,” “Perimount Magna hemodynamic,” and “Sorin Soprano hemodynamic.”
Statistical analysis was performed with the Statistical Package for the Social Science 16 for Windows (SPSS, Inc, Chicago, Ill). Continuous data are presented as mean±standard deviation. To compare categorical data, the χ2 test was performed. Ordinal data in more than 2 groups were compared with the Kruskal-Wallis test. To detect differences between groups, 2-way ANOVA with Bonferroni correction for multiple testing was applied.
Mean Pressure Gradients
The Magna demonstrated the lowest MPGs and had statistically significant lower gradients than the Mosaic and the Ultra (for annulus diameters <23 mm) or the Epic (for annulus diameters >23 mm). Additionally, in small annulus diameters, the Soprano had significantly lower MPGs than the Ultra and for large annulus sizes it demonstrated lower MPGs than the Epic (Table).
Effective Orifice Area
The Soprano bioprosthesis showed significantly larger EOAs compared with the Mosaic valve in patients with an annulus size <23 mm and compared with the Epic valve in patients with annulus diameters >23 mm. In addition, the Magna demonstrated significantly larger EOAs than the Mosaic in patients with annulus diameters of 23 to 24 mm (Table). According to the 2-way ANOVA, there was no interaction effect between annulus size and valve type.
Indexed EOA and Patient-Prosthesis Mismatch
The indexed EOA was comparable in all groups (Table), and no interaction effect was seen between annulus size and valve type.
There was a significant difference concerning the occurrence of severe patient-prosthesis mismatch in the small annulus analysis between the different valve types. Severe patient-prosthesis mismatch occurred most frequently in the group with small annulus and Mosaic valve. No valve type avoided mismatch completely (Figure 3).
The 2-way ANOVA showed that annulus size has a significant main effect on MPG (F=3.70, P<0.05). Small annulus sizes had significantly higher MPG values. This was a moderate influence (partial ETA2=0.023). The valve type also had a significant main effect on MPG (F=16.072, P<0.001), and the influence was higher (partial ETA2=0.169), indicating that depending on the valve type MPG defers significantly. According to the 2-way ANOVA, there was no interaction effect between annulus size and valve type.
Annulus size and prosthesis type also had a significant influence on EOA (for annulus size: P<0.001; for prosthesis size: P<0.001), but no interaction effect could be shown (P=0.14, partial ETA2=0.038).
Only annulus size had significant influence on EOAi (P<0.001). There was also no interaction effect between annulus size and prosthesis type (P=0.287, partial ETA2=0.030).
Comparison of the different manufacturers’ data resulted in different geometric dimensions of internal diameters for prostheses with the same valve size label. Online supplemental Table 3 depicts the geometric data provided by the manufacturers.
We analyzed the hemodynamic data given in all previous publications. Ten publications (3 in vitro studies) examined the Magna, 16 studies (1 in vitro) the Mosaic (the Mosaic prosthesis was examined until 2004, as there are more than 40 studies available), 4 studies (4 in vitro) the Ultra, 3 studies (2 in vitro) the Epic, and 6 studies (1 in vitro) the Soprano valve.
Online supplemental Table 4 (online-only Data Supplement) gives a complete overview of the PubMed research.
In 51 patients (15%), a prosthesis with an internal orifice diameter (IOD) larger or equal to the annulus diameter could be implanted (online supplemental Table 6). The MPG in this group was significantly lower (10.7±4.0 mm Hg versus 13.1±6.0 mm Hg, P<0.001).
Comparing hemodynamic parameters of different heart valve prostheses on the basis of labeled valve size is always associated with the difficulty of nonnormalized valve-size labels. First, the Soprano valve labels do not correlate to other valve labels (even numbers instead of uneven numbers). Second, as shown in online supplemental Table 3, there are differences in geometric dimensions for valves of the same labeled valve size. We addressed this problem in a prior study.13 Therefore, hemodynamic comparison studies based on labeled valve size will end in misleading results. For example, a comparison of a 23 Magna with a 23 Ultra implies comparison of a prosthesis with an IOD of 22 mm (Magna) to a prosthesis with an internal diameter of 20.5 mm (Ultra). The diameter difference of 1.5 mm results in a different geometric orifice area of 50 mm2, which might lead to a lower pressure gradient for the valve with the larger IOD. In this study, the patient’s aortic annulus is used as a basis for comparisons.
It is important to distinguish between the “geometric” and the “effective” orifice area of any type of valve prosthesis. The geometric orifice area is derived from the IOD. The kind of leaflet material (pericardial, porcine, or even carbon in mechanical valves) is completely irrelevant in this approach. In contrast, the effective orifice area is an echocardiographically obtained, functional in vivo measurement. Our group demonstrated that the geometric orifice area of a valve prosthesis has no impact on hemodynamic performance (eg, patient-prosthesis mismatch).1,8,14,18,19
In the present study, we focus on aortic bioprostheses designed for and implanted in a complete supraannular position. The design of a complete supraannular heart valve prosthesis aims to optimize the area available for the bloodstream through the aortic root orifice. Regular intraannular or intrasupraannular positioned prostheses are positioned inside the aortic annulus, which narrows the orifice. By positioning the prosthesis on top of the annulus (complete supraannular position), the stent of the prosthesis is meant not to protrude into the orifice and ideally does not impair the bloodstream (Figure 2).1,4,8,13 The advantage of complete supraannular placement is of special importance in patients with a small aortic annulus.1,7,8,20–23 In our collective, the focus was not set on a special annulus size but on a normal distribution of annulus sizes within the patient group. All valves have small differences in design (online supplemental Table 3 and Figure 2) and can be divided into 2 groups, either bovine or porcine tissue valves. Prior comparisons of bovine and porcine heart valves showed a superiority of bovine tissue prostheses, especially in small annulus sizes.14,24 Those studies only compared 2 different valves, whereas this study includes 2 bovine and 3 porcine prostheses and might help to stress the findings in those prior studies.
Discussion of Results
Mean Pressure Gradients
Our results imply a general tendency toward lower mean pressure gradients and larger effective orifice areas for bovine prostheses compared with porcine prostheses. The largest difference appears to be between the Magna and the Ultra prostheses in small annulus groups (MPG difference, 10 mm Hg).
The hemodynamic data show satisfactory pressure gradients for all valves in all annulus sizes, except for the Mosaic Ultra in small annulus sizes. Pressure gradients of the Magna, the Mosaic, and the Soprano are in accord with findings of other groups.1,3–6,8,13,14,20,22,25–31 There are preliminary in vivo hemodynamic data available regarding the Mosaic Ultra10 and only 1 in vivo evaluation of the Epic, which was published previously by our group.4 The in vitro data concerning hemodynamic gradients of the Epic and the Ultra correspond well with our results.7,11,12,32,33
As described in other studies, the bovine prostheses appear to be superior concerning pressure gradient and effective orifice areas.1,8,14,24 In this study, the Magna as well as the Soprano showed a clear tendency toward lower pressure gradients and larger EOAs throughout all annulus size groups when compared with porcine prostheses.
Patient-prosthesis mismatch is a hot topic in the valve surgery community, and there are still many controversies. In the past, we propagated the method of Blais et al.17 This might be an arbitrarily defined value to distinguish between mismatch and no mismatch and might lead to a loss of information because of changing the interval scaled data to categorical data. Nevertheless, to be comparable to former studies, we analyzed our data as described and could find patient-prosthesis mismatch in all different valve prostheses. Although the supraannular concept is meant to prevent patient-prosthesis mismatch, in this study patient-prosthesis mismatch was not completely avoidable.
The complete supraannular concept was realized in 15% of our patients. These patients benefit in terms of lower MPGs. Hence, we showed that the complete supraannular concept, if put into practice, results in a better hemodynamic performance of the bioprostheses. To our knowledge, there is no other study showing this result.
There are 3 in vitro studies11,32,33 and 7 in vivo studies of the Magna.1,3,6,8,25–27 The annulus diameter is used in 5 of the 7 in vivo studies as a comparing parameter (online supplemental Table 4). The hemodynamic gradients are low for all annulus sizes; the lowest gradients were described by Botzenhardt in patients with an annulus diameter of 22 to 23 mm (7.3 mm Hg)27and the highest in patients with an annulus diameter of 18 to 22 mm (13.2 mm Hg).8
The Mosaic valve is by far the prosthesis that was studied most (online supplemental Table 4). There are 33 studies listed in PubMed; we only added the latest 16 in our table.1,4,6–9,14,20–22,28–30,32,34–37 Most of the studies are in vivo evaluations, and the lowest pressure gradients were around 10 mm Hg in patients with an annulus of 27 mm.28 In patients with an annulus <22 mm, different hemodynamic gradients were reported, ranging from 13 mm Hg to >20 mm Hg.4,6,28
There are no published clinical data available for the Ultra bioprosthesis except for 1 poster presentation showing MPGs ≥20 mm Hg in 55% of the patients.10 These results correspond to our in vivo study demonstrating gradients >20 mm Hg for annulus sizes smaller than 23 mm. There are 4 in vitro studies, 3 of them published by the Frankfurt group11,32,33 and 1 published by Bottio et al12 regarding the Mosaic Ultra.
Six studies evaluated the Soprano.1,7,8,13,30,31 Five of these studies are in vivo studies,1,8,13,30,31 and only 2 study groups1,8 used annulus diameters to compare the prostheses instead of using the labeled valve size for comparisons. Our results showed satisfactory pressure gradients, and the results were comparable to findings by Botzenhardt.8 Pavoni31 found surprisingly low gradients, all <10 mm Hg (for labeled valve sizes between 20 and 24), but only labeled valve sizes were given by the authors.
We and other authors who demonstrated in vivo results focused on the systolic function of heart valve prostheses. Some authors who published in vitro studies focused on other aspects such as calcification and valve opening and closing characteristics. They identified a faster and more severe calcification in pericardial valves leading to a prolongation of closing time and higher closing volumes (altered diastolic function) but an almost undisturbed systolic function.11,32,33 If this has any influence on durability, further long-term studies must be done. Thus far, there are not any consistent data showing the superiority of any valve material as far as valve durability is concerned.
Even though there are many studies concerning hemodynamics of valve prostheses published, it is difficult to compare the data. Our literature overview shows 2 major factors that cause hampered comparisons of different valve prostheses: first, the use of the labeled valve size instead of the annulus diameter, and second, the different grouping of patients depending on size or annulus diameter.
A clear limitation of our study is the small number of patients. Especially in the Ultra group we had very few patients included because this valve was included in our institutional valve portfolio only recently. This might bias the results on the Ultra.
This was a nonrandomized study, and patients were included consecutively into the study. The surgeon chose the valve by his or her preferences, which might also bias the results of our study. All surgeons used the same implantation technique for complete supraannular valves. The only difference between various surgeons could be the perseveration in choosing the largest valve possible for a patient with a given anatomy. Thus, we did an analysis of the relation of annulus diameter and implanted valve size label (online supplemental Table 5) and could demonstrate that most patients had annulus sizes around 23 mm and received prostheses with a valve size label around 23. A further analysis, namely a comparison of annulus diameter and “real” internal valve diameter (online supplemental Table 6) revealed that the bovine prostheses led to a more frequent implantation of prostheses with larger internal diameter than the annulus diameter, which, we assume, will lead to a beneficial hemodynamic performance.
In a prior study, we emphasized our patient-centered view not only to compare valve hemodynamics but to answer the question of what should be the ideal prosthesis for a patient with a certain annulus diameter.8 In a cardiothoracic surgery clinic, the surgeon has the possibility to choose between different prostheses and is confronted with a special situation: Some parameters (such as prosthesis type and implantation position) are changeable and some are given and not changeable (patient’s annulus diameter, body surface area), and the patient’s preferences according to his or her lifestyle must also be considered.38 The surgeon must identify the prosthesis that will be the most promising one for the patient (in means of hemodynamics and long-term performance).
Keeping this in mind, the implantation of a complete supraannular prosthesis is a good approach to optimize the blood flow through the aortic annulus. Nevertheless, in this study, we showed that even with this concept, high pressure gradients and patient-prosthesis mismatch cannot be prevented completely. The choice of a bovine prosthesis will optimize the systolic hemodynamic performance.
Dr Bauernschmitt received honoraria for consulting and lectures from Sorin above US$10,000. Dr Bleiziffer received honoraria for lectures from Datascope below US$10,000. Dr Eichinger received lecture fees from St Jude Medical, Inc and Medtronic, Inc both below US$10,000.
Presented in part at American Heart Association Scientific Sessions 2008, November 8–12, 2008, New Orleans, La.
The online-only Data Supplement is available with this article at http://circ.ahajournals.org/cgi/content/full/120/11_suppl_1/S139/DC1.
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