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Interact CardioVasc Thorac Surg 2009;8:206-210. doi:10.1510/icvts.2008.187666 © 2009 European Association of Cardio-Thoracic Surgery
Which valve and which size should we use in the valve-on-valve technique for re-do mitral valve surgery?
a Department of Cardiovascular Surgery, Osaka City General Hospital, 2-13-22, Miyakojima-hondori, Miyakojima, Osaka, 534-0021, Japan Received 7 July 2008; received in revised form 18 October 2008; accepted 23 October 2008
*Corresponding author. Tel.: +81-6-6929-1221; fax: +81-6-6929-1090.
The valve-on-valve (VOV) technique is that a mechanical valve is implanted on the sewing cuff of the previous bioprosthesis after removing degenerated leaflets. We conducted an in vitro study to determine the size-match of the valves for VOV technique. The Carpentier–Edwards pericardial (CEP) valve and Mosaic valve were used. We measured the inner diameter of the bioprosthesis after removing the leaflets. We investigated five mechanical mitral valves and two mechanical aortic valves (inverted use). The mitral valves used in this study were the ATS valve (ATS), the CarboMedics standard valve (CMS), the CarboMedics OptiForm valve (CMO), the On-X valve, and the St Jude valve (SJM). Two aortic mechanical valves, CarboMedics and St Jude Regent valves, were investigated for inverted use. After removing the tissue leaflets, the inner diameter of the Mosaic valve was 3 mm smaller than that of the CEP valve even in the same catalogue labeling size. The outer diameters of the housing of the ATS, CMS, CMO, On-X, and SJM valves of the same catalogue size (25 mm) were 25.7, 25.8, 22.0, 25.0, and 23.2 mm, respectively. SJM and CMO valves are the favorite mechanical valve for the VOV technique in terms of the profile and size-match.
Key Words: Valve-on-valve; Mitral valve replacement; Re-do; Bioprosthesis
Although current bioprosthetic models have significantly better durability than previous models, structural failure is inevitable in the long-term [1, 2]. Structural degeneration of bioprostheses occurs more frequently in the mitral position than in the aortic position. Re-do mitral valve surgery has high mortality and morbidity [3, 4]. Paterson et al. [5] and Stassano et al. [6] reported a new technique of re-do mitral valve surgery without explantation of the initially implanted bioprosthesis. They implanted a new mechanical valve on the sewing cuff of the previously implanted bioprosthesis after removing the degenerated leaflets. The advantage of this alternative technique is that there is no need to remove the initially implanted bioprosthesis. In addition, the aortic cross-clamping time is shorter. The disadvantage of this technique is that the newly implanted mechanical valve is smaller than the initially implanted bioprosthesis. Several reports about the valve-on-valve (VOV) technique have described the use of a mechanical bileaflet valve 6–8 mm smaller in diameter than the bioprosthetic valve [5–7]. A recent report by Geha et al. demonstrated that a bileaflet mechanical valve (St Jude valve or CarboMedics valve) with an external diameter only 2 mm smaller than that of the mitral bioprosthesis could be implanted [8]. As shown in Table 1 [5–15], there is a limited amount of information about the VOV technique, and no reports demonstrate systematically which valve and which size are available for the VOV technique. Therefore, we conducted an in vitro study to determine the optimal size-match between the mechanical valves and bioprosthetic valves for applying the VOV technique.
We employed two kinds of bioprostheses; the Carpentier–Edwards PERIMOUNT pericardial valve (CEP model 6900, Edwards Lifesciences, Irvine, LA) and the Medtronic Mosaic porcine valve (Medtronic, Minneapolis, MN). We chose a pericardial valve and a porcine valve that are widely used throughout the world. The CEP (model 6900) was introduced into clinical use. The Mosaic valve is a current model of the porcine valve, however, the housing and structures of the sewing ring are the same as the previous model (Hancock II). We used two catalogue labeling sizes (27 mm and 29 mm) in each bioprosthetic valve. All leaflets of the bioprostheses were excised with a No.11 blade. We investigated five mechanical mitral valves and two mechanical aortic valves. The mechanical mitral valves that we used were the ATS standard valve (ATS) (ATS Medical, Minneapolis, MN), the CarboMedics standard valve (CMS), the CarboMedics OptiForm valve (CMO) (SulzerMedica, Austin, TX), the On-X valve (Medical Carbon Research Institute, Austin, TX), and the St Jude Master valve (SJM) (St Jude Medical, St Paul, MN). The aortic valves used in this study were CarboMedics (CMA-S) (Sulzer Medica) and St Jude Regent valves (Regent) (St Jude Medical, St Paul, MN). 2.1. Profile of the mechanical valves and definition of the housing The portion of the mechanical valve to be inserted into the sewing ring of the bioprosthetic valve depends on the individual design of the mechanical valve. According to the profile of the mechanical valve, we defined two types of housing to be inserted in the bioprosthesis. First, there was a carbon housing consisting of a frame made by pyrolitic carbon containing the leaflets. Secondly, there was a fabric housing consisting of fabric around the carbon housing. The schema of the profile of each mechanical valve is shown in Fig. 1. The carbon housing of the ATS and CMS valves was almost completely covered with the fabric. On the On-X valve, there was no fabric around the carbon housing to be inserted in the bioprosthetic valve. The carbon housing partially protruded from the sewing cuff and there was a fabric dip of the sewing cuff around the carbon housing on the SJM and CMO valves. From a technical view of the VOV technique, there is impingement of the leaflet if the carbon housing of the SJM, CMO, and On-X valves are completely seated inside the sewing ring of the bioprosthesis. The fabric housing of the ATS and CMS valves must be inserted in the bioprosthesis. According to the design of the mechanical valves as mentioned above, we measured only the fabric housing diameter on the ATS and CMS valves, and only the outer diameter of the carbon housing on the SJM, CMO, and On-X valves.
We measured the inner diameter (ID) of the orifice of the bioprosthesis after removing the leaflets using an electronic vernier caliper that can be measured to an accuracy of 0.01 mm. The mean diameter, which was measured by five different authors (TS, YM, YB, TI, and KI) individually, was used in this study. The outer diameters of the carbon housing and the fabric housing were measured in the same manner. We mounted each mechanical valve on the bioprosthesis after removing all the leaflets. We checked if each mechanical valve was completely seated inside the sewing ring of the bioprosthesis without disorder of the leaflet opening.
3.1. Inner diameters of the sewing ring of the bioprosthesis Fig. 2 shows the bioprosthetic valves after removing the tissue leaflet of the bioprosthesis. In the CEP valve, there is a remnant of the tissue leaflet on the stent, but no tissue leaflet remained surrounding the inner orifice of the sewing cuff. In the Mosaic valve, the remnant of the tissue leaflet surrounding the inner orifice of the sewing cuff could not be removed completely. The inner diameters of the bioprosthesis after removal of the tissue leaflet are shown in Table 2. The inner diameter of the Mosaic valve was approximately 3 mm smaller than that of the CEP valve, even though they had the same catalogue labeling size.
3.2. Outer diameter of the mechanical valves The OD of the carbon housing or fabric housing, which was measured by five authors, is shown in Table 3. The results of actual availability of the mechanical valves for the VOV technique are also shown in Table 3. If the OD of the housing is smaller than the ID of the bioprosthetic sewing ring, theoretically, the mechanical valve can be inserted. However, the mechanical valve could actually be inserted in the bioprosthetic valve only when the OD of the housing of the mechanical valve was about 0.5 mm smaller than the ID of the sewing ring of the bioprosthetic valve.
Inverted use of the CMS-A 25 mm and the Regent 21 mm can be used for the VOV technique on the Mosaic 27 mm valve. The sewing cuff of the aortic mechanical valve is narrower than that of the mitral mechanical valve, and some aortic valves are too small to apply the VOV technique.
The actual size of the housing and sewing ring is quite different among the individual artificial valves, even if they have the same catalogue labeling size. We need to recognize the individual characteristics of the designs and actual size of both bioprosthetic and mechanical valves. This in-vitro study described a guide for choosing mechanical valves when we apply the VOV technique to re-do mitral valve surgery. This study revealed that the actual size of the Mosaic valve is smaller than the CEP valve even with the same catalogue labeling size. The catalogue labeling size is derived from the diameter of inter-stent (diameter of wire-form) in the CEP valve, but from the outer diameter of the stent post in the Mosaic valve (Fig. 3). Therefore, the real size of the CEP valve is essentially different from that of the Mosaic valve even with the same labeling size. The manufacturing technique of mounting the tissue leaflets on the sewing ring and the stent is quite different between the CEP and Mosaic valves. The tissue leaflets of the CEP valve are attached to the stent alone, while the tissue leaflets of the Mosaic valve are sewn on both the inner orifice of the sewing ring and the stent (Fig. 2). This difference in the manufacturing process affected the inner orifice size of the bioprosthetic valves after removing the tissue leaflet. The tissue orifice of the sewing cuff of the Mosaic valve is 2 mm smaller than that of the CEP in the catalogue. After removing the leaflet, the internal orifice of the housing in the Mosaic valve is 3 mm smaller than that of the CEP valve, because the tissue leaflet of the Mosaic valve could not be removed completely on the structural aspect as mentioned above.
4.2. Size of the housing The location for the mechanical valve to be inserted in the sewing ring of the bioprosthetic valves depends on the individual design of the mechanical valve (Fig. 1). Therefore, we first defined the two types of housing of mechanical valves, the carbon housing and the fabric housing, according to the design of the housing, and then measured each part of the housing to be inserted. Needless to say, the OD of the housing of the mechanical valve must be smaller than the ID of the sewing ring of the bioprosthetic valve for applying the VOV technique. The mechanical valve can be theoretically mounted on the bioprosthetic valve if the OD of the mechanical valve housing is smaller than the ID of the sewing ring of the bioprosthetic valve. In actual surgery, however, it is very difficult to mount the mechanical valve in the center of the sewing ring of the bioprosthetic valve. Therefore, a difference between the OD of the housing of the mechanical valve and the ID of the sewing ring of the bioprosthetic valve would be required. We think that a clearance of more than 1 mm would be required between the two parameters in the clinical situation. The SJM and CMO valves are implantable if the carbon housing can be inserted inside the sewing ring of the bioprosthetic ring. This characteristic of the design is an advantage in terms of size compared to other mechanical valves. The only two mechanical mitral valves that can be mounted on the Mosaic 27 mm valve are the SJM 23 mm and CMO 25 mm valves (Table 3). From a technical point of view, the St Jude valves are preferred, owing to the fact that the leaflets are hinged on the atrial side and do not protrude into the ventricular side. This design of SJM valves would avoid impingement of the disks on the bioprosthetic valve. The carbon housing of the ATS and CMS valves are completely surrounded by the fabric. Therefore, the fabric housing must be inserted completely in the sewing ring of the bioprosthetic valve. This means that the size of the ATS and CMS valves must be one size smaller than the SJM and CMO valves. ATS and CMS valves have a disadvantage in terms of size; however, if the fabric housing is completely inserted in the sewing ring of the bioprosthetic valve, there is no impingement of the bileaflet disks. We believe that the ATS and CMS valves can be used only when the large size of CEP has been used in the previous operation. The On-X valve has a unique design, and the carbon housing protrudes to the left ventricular side. The bileaflet disks can open and close if the carbon housing is completely seated in the sewing ring of the bioprosthetic valve. 4.4. Limitations of this study The major limitation of this study is that it was conducted in vitro study. We investigated brand new bioprosthetic valves in this study. In the clinical situation, it would be more difficult to remove the tissue leaflet completely in vivo than in vitro. Moreover, the sewing cuff would be surrounded by pseudo-intima after initial implantation. The sewing cuff itself might have some time-dependent degeneration. Therefore, the ID of the sewing ring of the bioprosthetic ring at actual re-do surgery might be smaller than our in vitro data. We believe that our in vitro data could be helpful in the decision making process for the VOV technique.
SJM and CMO valves are the favorite mechanical valve for the VOV technique in terms of the profile and size-match.
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Abstract
1. Introduction
