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Ann Thorac Surg 1998;65:1631-1633
© 1998 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Discrepancies Between Sizer and Valve Dimensions: Implications for Small Aortic Root

^a Department of Cardiac Surgery, Medical University of Lübeck, Lübeck, Germany

Accepted for publication January 23, 1998.

Address reprint requests to Dr Bartels, Klinik für Herzchirurgie, Medical University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany

	Abstract

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
Background. Precise labeling of sizer and valve diameters is crucial for optimal valve selection especially in the small aortic root. This study examines the accuracy of manufacturers’ markings on small aortic prostheses and sizers.

Methods. Sizer and valve dimensions of 22 different mechanical aortic prostheses (19 to 23 mm) were evaluated by caliper micrometer measurements.

Results. Nearly all sizers exceeded their marked dimensions by up to 1.0 mm. Measured tissue annulus diameters for 19-mm-labeled valves varied between 18.3 and 19.6 mm, for 21-mm valves from 20.5 to 21.6 mm, and for 23-mm valves from 22.4 to 23.5 mm, respectively. The orifice areas ranged from 1.5 to 2.06 cm² for 19-mm valves, from 2.0 to 2.55 cm² for 21-mm valves, and from 2.4 to 3.09 cm² for 23-mm valves, respectively.

Conclusions. Actual sizer dimensions and tissue annulus diameters of various small mechanical aortic prostheses varied considerably from their marked diameters. These differences should be considered to ensure the optimal prosthesis selection for each patient.

	Introduction

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
The use of small mechanical aortic prostheses raises concern about their potentially harmful effect on residual left ventricular outflow obstruction. Increased pressure gradients across small standard mechanical prostheses at high flow rates subjects the left ventricle to both unacceptable pressure and energy demands. These two factors are suspected to contribute to the worse prognosis of patients with small standard aortic prostheses compared with those with larger prostheses implanted [1, 2]. Therefore, an appropriate aortic prosthesis should be implanted such that the effective valve orifice area corresponds to the patients’ body surface area.

However, discrepancies between internal and tissue annulus diameters of different valves as well as diameter differences in sizing equipment make small mechanical aortic prostheses hardly comparable. Therefore, these frequently overlooked discrepancies might result in the selection of suboptimal prostheses or unnecessary aortic root enlargements.

The purpose of our study was to compare differences in sizer dimensions with tissue annulus diameters and orifice areas of various small mechanical aortic prostheses.

	Material and methods

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
Valves studied
Valves studied and abbreviations used are indicated in Table 1. All valves and corresponding sizers were of clinical quality, and supplied sterile and free of charge by the manufacturers. CarboMedics Standard prostheses are available in Europe, but not in the United States. On the American market, the available CarboMedics Reduced valve has to be sized with the sizer set of the CarboMedics Standard, as the sizer set for CarboMedics Reduced is not licensed in the United States. The CarboMedics Standard sizers are 1 mm larger than the corresponding CarboMedics Reduced sizers and tissue annulus diameters of CarboMedics Reduced valves.

View larger version (17K): [in this window] [in a new window]   Fig 1. Dimensions of mechanical heart valves.

	Results

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
Sizer equipment
Almost all sizers exceeded the stated dimension between 0.6 and 1 mm (Tables 2 to 4). Exceptions were represented by the Baxter Edwards Tekna, the CarboMedics Supra-Annular, and the CarboMedics Reduced sizers, the actual dimensions of which were identical to or even smaller than those marked by the manufacturers.

21-mm- to 23-mm-labeled valves
Results for 21-mm and 23-mm prostheses were similar to those obtained for 19-mm valves. Smaller tissue annulus diameters were found for the St. Jude Medical Standard valves. Identical tissue annulus diameters were assessed for all CarboMedics prostheses and St. Jude Medical HP 21-mm valve. The measured tissue annulus diameters for 21-mm and 23-mm Baxter Edwards Tekna, 23-mm St. Jude Medical HP and Medtronic Hall valves were larger than indicated (see Tables 3 and 4 for details).

Regarding the comparison of measured sizer diameters versus measured tissue annulus diameters, our data indicate that in most cases the measured tissue annulus diameter did not correspond to the appropriate sizers as stated by the manufacturer. Actual sizer dimensions were both larger and smaller than the tissue annulus diameters of the corresponding valves due to incorrect labeling.

Orifice area
Orifice areas also varied considerably among the different studied artificial aortic valves indicated to have the same size. Modification of the external valve design (eg, reduced sewing ring) resulted in reduced tissue annulus diameters by constant orifice areas (Carbomedics Standard versus Carbomedics Reduced; Medtronic Hall 20-mm and 22-mm versus Medtronic Hall 21-mm and 23-mm). The largest orifice area stated for each valve size could be assessed in the St. Jude Medical HP series.

For 19-mm prostheses the orifice areas varied between 1.5 and 2.06 cm². Orifice areas for 21-mm valves varied from 2.0 to 2.55 cm². For 23-mm mechanical valves, the orifice areas varied from 2.4 to 3.09 cm² (see Tables 2 to 4).

	Comment

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
Our data show that identically labeled sizers differ in their dimensions and that sizer dimensions frequently do not correspond to the tissue annulus diameters of the corresponding valves. These discrepancies between marked and actual dimensions of small mechanical aortic valves may prevent optimal prosthesis selection.

Our results are in agreement with Cochran and Kunzelman [3], who reported on discrepancies between labeled and actual dimensions of various aortic and mitral prosthetic valves and sizers. A larger number of different prostheses than in the study by Cochran and Kunzelman, including two supraannular prostheses, were evaluated in the present study. The present investigation also indicates different orifice areas of the studied prostheses. However, the significance of different calculated orifice areas of various prostheses (bileaflet valves, tilting disk valves) on hydrodynamic performance has to be evaluated in vivo.

In the small aortic root, accurate measurement of annulus size is essential for optimal mechanical valve selection and to decide whether the aortic root has to be enlarged. More than 10 years ago cardiac surgeons indicated that sizers were labeled incorrectly [4]. However, to date manufacturers have not standardized sizing equipment dimensions.

We found that in some cases sizers exceed their indicated dimension (eg, a labeled 19-mm CarboMedics Standard sizer was measured to be 19.8 mm). This under-labeling seems to be necessary for CarboMedics Standard and Medtronic Hall 21-, 22-, and 23-mm prostheses to allow implantation, as the tissue annulus diameters of these valves are larger than the labeled prosthesis size. The sizer equipment for Baxter Edwards Tekna valves is correctly labeled; however, the tissue annulus diameter of these valves are larger (0.5 mm) than the sizer dimensions and the stated valve dimensions. The variation between the sizer and tissue annulus diameter with the Baxter Edwards Tekna prostheses should be considered when implanting Baxter Edwards Tekna aortic valves. Moreover, for other valves (St. Jude Medical Standard, Medtronic Hall 20 mm), sizers are larger than the tissue annulus diameters, thus preventing optimal prosthesis/aortic root relation. Our data confirm the results of Walther and colleagues [5] who studied sizer dimensions of conventional and stentless aortic prostheses and observed significant differences between marked and actual sizer dimensions.

The use of small mechanical aortic prostheses raises concern about their potentially harmful effect on residual left ventricular outflow obstruction. The pressure gradient at high flow rates across a small aortic prosthesis is mainly determined by its internal diameter and its orifice area. Recently, González-Juanatey and colleagues [2] studied the influence of the size of aortic prostheses on hemodynamics and change in left ventricular mass using echocardiography. They concluded that 19-mm aortic prostheses create significant left ventricular outflow obstruction. Butterfield and coworkers [6] demonstrated that the pressure drop at high flow across 19-mm standard mechanical and bioprosthetic aortic prostheses are twice as high as across 21-mm valves. Similar results have been obtained from in vitro studies examining the hydrodynamic function of small mechanical aortic prostheses [7]. In their study, lower forward flow pressure drops were observed for the high-performance St. Jude Medical prostheses as compared to standard mechanical valves [7]. This favorable hydrodynamic performance was attributable to the larger orifice areas of supraannular valves. However, even with advances in valve design (eg, supraannular positioning, reduced sewing rings) resulting in increased orifice areas the optimal mechanical valve cannot be selected unless the true valve dimensions are considered.

The following conclusions can be drawn from our findings: (1) actual sizer dimensions and tissue annulus diameters of various small mechanical aortic prostheses vary considerably from their marked diameters. (2) these differences should be considered to ensure the optimal prosthesis selection. (3) standardized sizer equipment and standardized tissue annulus diameters are hardly needed to optimize prosthesis/patient aortic ring relation.

	Footnotes

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
This article has been selected for the open discussion forum on the STS Web side: http:www.sts.org/annals

	References

Top Footnotes Abstract Introduction Material and methods Results Comment References

 

1. Kratz J.M., Sade R.M., Crawford F.A., Crumbley A.J., Stroud M.R. The risk of small St. Jude aortic valve prostheses. Ann Thorac Surg 1994;57:1114-1119.[Abstract]
2. González-Juanatey J.R., García-Acuña J.M., Fernandez M.V., et al. Influence of the size of aortic valve prostheses on hemodynamics and change on left ventricular mass: implications for the surgical management of aortic stenosis. J Thorac Cardiovasc Surg 1996;112:273-280.[Abstract/Free Full Text]
3. Cochran R.P., Kunzelman K.S. Discrepancies between labeled and actual dimensions of prosthetic valves and sizers. J Card Surg 1996;11:318-324.[Medline]
4. Bonchek L.I., Burlingame M.W., Vazales B.E. Accuracy of sizers for aortic valves prostheses. J Thorac Cardiovasc Surg 1987;94:632-638.[Abstract]
5. Walther T., Falk V., Diegeler A., Rauch T., Autschbach R., Mohr F.W. Discrepancy of sizers for conventional and stentless aortic valve implants. J Heart Valve Dis 1997;6:145-148.[Medline]
6. Butterfield M., Fisher J., Davies G.A., Spyt T.J. Comparative study of the hydrodynamic function of the CarboMedics valve. Ann Thorac Surg 1991;52:815-820.[Abstract]
7. Fisher J. Comparative study of the hydrodynamic function of the size 19mm and 21mm St. Jude medical hemodynamic plus bileaflet heart valves. J Heart Valve Dis 1994;3:75-80.[Medline]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Claus Bartels Rainer G. Leyh Hans-Hinrich Sievers Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bartels, C. Articles by Sievers, H.-H. Search for Related Content PubMed PubMed Citation Articles by Bartels, C. Articles by Sievers, H.-H.