Eur J Cardiothorac Surg 2005;28:845-849
© 2005 Elsevier Science NL
The ideal theoretical graft oversizing in valve-sparing aortic operations with a standard tubular or a Valsalva graft
Daniele Maselli
a
,
*
,
Gabriele Borelli
b
,
Andrea Amerini
a
,
Pietro Bajona
a
,
Luca Bellieni
a
,
Mariagrazia Croccia
a
,
Gaetano Minzioni
a
a Department of Cardiothoracic Surgery, Azienda Ospedaliera Pisana, 56124 Pisa, Italy
b Department of Cardiology, Azienda Ospedaliera Pisana, 56124 Pisa, Italy
Received 11 August 2005;
received in revised form 21 September 2005;
accepted 22 September 2005.
* Corresponding author. Tel.: +39 050 995261; fax: +39 050 995271. (Email: dmaselli{at}tiscali.it).
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Abstract
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Objective: We sought to determine, by a mathematical model, the ideal theoretical degree of ascending aortic graft oversizing needed to obtain normal sinuses dimension in the reimplantation type of valve-sparing aortic operations. Methods: To define a normal-range value, size of sinuses of Valsalva was conventionally expressed as the area surrounding fully opened aortic cusps, the so-called beyond leaflets area (BLA), and measured in 50 healthy subjects. A mathematical relationship between aortic annulus diameter, aortic sinuses diameter and resulting BLA was defined. By simulating intra-operative scenarios, the effect of different degrees of a standard or Valsalva graft oversizing on BLA extension was tested. Results: The same degree of graft oversizing resulted in a bigger beyond leaflets area for the Valsalva graft than for a standard graft. Oversizing degrees exceeding +7 mm for a standard graft and +3 mm for the Valsalva graft resulted in a beyond leaflets area over normal limits. Results were expressed in a visual form as two different normograms, one for the standard graft and one for the Valsalva graft. Conclusions: A less pronounced graft oversizing is needed to achieve normal-range sinuses size when using a Valsalva graft, the ideal theoretical graft oversizing was +7 mm for a standard graft and +3 mm for the Valsalva graft, our normograms can be helpful in selecting a proper graft size when performing a valve-sparing aortic procedure.
Key Words: Aortic valve-sparing operation • Sinuses of Valsalva • Aortic valve reimplantation • Aortic root sizing
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1. Introduction
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Since the original description of the reimplantation technique by David and Feindel [1], this type of aortic valve-sparing operation has gained widespread consent for surgical treatment of aortic regurgitation due to aortic root dilatation with preserved aortic leaflets.
Physiologic reconstruction of the aortic root including creation of neo-sinuses of Valsalva [2] is based on historical studies which emphasized the role of sinuses in driving a correct function and durability of aortic cusps [3,4].
De Paulis recently proposed the Valsalva graft (Gelweave Valsalva; Sulzer Vascutek, Renfrewshire, Scotland) incorporating a self-expandable region, obtained by 90° rotation of the Dacron fabric corrugations, which has been demonstrated to produce neo-sinuses of Valsalva and physiologic aortic leaflets movement [5].
Many methods have been suggested to select the appropriate graft size in David operations [6–9], none of them analyzed the effect of graft sizing methods on dimensions of sinuses of Valsalva.
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2. Materials and methods
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Data about normal size of sinuses of Valsalva were obtained from a previous study [10]. Fifty healthy subjects (22 male, age 38.5 ± 10.9, BSA 1.76 ± 0.18 m2) underwent transthoracic echocardiography, using a Hewlett-Packard Sonos 5500 system (Hewlett-Packard, Andover, MA, USA) with a 2.5 MHz ultrasound transducer, to define aortic root dimensions in a normal population. Data were acquired in parasternal long axis and short axis views. The following measures were recorded in diastole and in systole: aortic annulus diameter (AD), sinuses diameter (SD), and sino-tubular junction diameter (STJD). Normal sinuses dimension was expressed as the difference between maximal aortic root cross-section area at sinuses level and trans-valvular systolic aortic flow cross-section area, the so-called maximal systolic beyond leaflets area (BLA, Fig. 1
). The ratio between aortic annulus diameter and sino-tubular junction diameter was expressed as a percentage.
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Fig. 1. Schematic drawing of a longitudinal (A) and transverse (B) section of the aortic root. Beyond leaflets area (gray area) was calculated as the difference between systolic aortic root cross-section area (ARCSA) and systolic aortic annulus cross-section area (AAA). Aortic root cross-section area was derived by systolic sinuses diameter in healthy people, by graft diameter in standard graft group, and by diameter of the expandable region of the graft in Valsalva graft group (see text). BLA = beyond leaflets area.
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Systolic BLA was calculated by the following formula:
where SDS is the sinuses diameter systolic and ADS is the aortic annulus diameter systolic.
The theoretical BLA resulting from a certain aortic annulus and a certain standard tubular aortic graft used to reimplant the aortic valve can be calculated by the following formula:
where GD = graft diameter and AD = annulus diameter.
According to the declared measures of the Valsalva graft (Sulzer Vascutek), the fully expanded sinuses portion is 32 mm for a 24 mm graft, 34 mm for a 26 mm graft, 36 mm for a 28 mm graft, 38 mm for a 30 mm graft, 42 mm for a 32 mm graft, and 44 mm for a 34 mm graft. The theoretical BLA resulting from a certain aortic annulus and a certain Valsalva graft used to reimplant the aortic valve can be calculated by the following formula:
where ER = expandable region diameter, and AD = annulus diameter. Valsalva graft size is expressed by the manufacturer as size of the tubular portion of the graft not as size of the expandable region, and any Valsalva graft size has a fixed ER.
We tested any possible combination between aortic annulus diameter ranging 19–31 mm with a step-by-step increase of 0.1 mm and amount of graft oversizing ranging +0 to +13 mm with a step-by-step increase of 1 mm. Theoretical combinations between any aortic annulus diameter bigger than the neo-ascending aortic prosthesis were censored in order to avoid negative BLA values.
Results are given as mean ± standard deviation. Student's t-test, Mann–Whitney, or Wilcoxon rank-sum tests were applied as appropriate to compare mean BLA extension in Valsalva graft population and standard graft population. The effect on BLA extension of combination between graft diameter and graft type was tested by the ANOVA test for repeated measures. Statistical analysis was performed by NCSS-PASS 2004 statistical package.
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3. Results
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Normal diastolic and systolic aortic root dimension and BLA values are reported in Table 1
. Simulated BLA was always higher for the Valsalva graft than for the standard graft; mean values and results of statistical analysis are reported in Table 2 . In order to allow a fast and easy visualization of the effect of graft oversizing on BLA, results were expressed as normograms for standard graft (Fig. 2
) or Valsalva graft (Fig. 3
): theoretical annular diameters were plotted against different grades of theoretical oversizing of the graft. Four different BLA ranges of 250 mm2 each were defined as diagram areas. According to our "healthy population" data, the white area represents normal BLA range. A normal-range BLA was achieved, for aortic annulus diameter ranging 21–29 mm, by an oversizing of +7 mm for standard graft simulations and +1 mm for Valsalva graft simulations.
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Fig. 2. Theoretical BLA resulting from any possible combination between aortic annulus size and STANDARD ascending aortic tubular graft. Size of the graft is reported as amount of oversizing, in millimeters, in respect to aortic annulus diameter. The white area represents normal BLA range in healthy people.
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Fig. 3. Theoretical BLA resulting from any possible combination between aortic annulus size and VALSALVA ascending aortic graft. Size of the graft is reported as amount of oversizing, in millimeters, in respect to aortic annulus diameter. The white area represents normal BLA range in healthy people.
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In normal subjects, aortic annulus diameter to sino-tubular junction diameter ratio was 95.5 ± 11.8%. In both Valsalva graft and standard grafts, this ratio was 96 ± 1% for a +1 mm oversizing, 89 ± 2% for a +3 mm oversizing, 83 ± 2% for a +5 mm oversizing, 78 ± 3% for a +7 mm oversizing, and 73 ± 3% for a +9 mm oversizing.
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4. Discussion
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In native aortic root, sinuses of Valsalva, by accommodating eddy currents generated by sino-tubular junction ridge, drive a correct opening and closure of aortic leaflets sharing with them the stress of aortic valve closure and promoting coronary blood flow [11,12]. The purpose of reconstruction or recreation of sinuses of Valsalva and sino-tubular junction is to obtain a neo-aortic root closely mimicking nature, in the hope that anatomic presence of sino-tubular junction and sinuses can prelude to preserved function.
In the reimplantation type of valve-sparing aortic procedure, shape of sinuses, when a standard graft is used, depends on surgical technique and every step of the operation can have a big impact on final result. Moreover, the new sino-tubular junction has to be re-created by reducing the graft diameter, at proper level, with additional sutures.
In the Valsalva graft, the shape of sinuses and the dimensions of the sino-tubular junction are fixed by design and inter-commissural length, and the height of the commissures within the graft will determine the correct matching of the native root with neo-sinuses and neo sino-tubular junction.
Results of our simulations suggest that the ideal theoretical graft oversizing, in respect to final aortic annulus diameter, is +7 mm for a standard graft and +1 mm for the Valsalva graft. The "common sense feeling" is that a 28 mm or 30 mm graft covers most of the need when performing a David operation. Recently, David himself has criticized this behavior [13]. Our normogram suggests that this approximation is not reliable for a standard graft and can be extremely misleading when using a Valsalva graft. A 30 mm standard graft is optimal for a final annulus size of 23 mm, it is too small for a 25 mm aortic annulus. For aortic annulus size included between 23 and 25 mm, a 30 mm Valsalva graft gives a BLA over 500 mm2. This is obvious and depends on the design of the Valsalva graft. Less obvious is how big can be the effect of oversizing on BLA in Valsalva graft. In their analysis of aortic root dynamics after valve-sparing procedure with the Valsalva graft, De Paulis et al. [5] measured a mean BLA of 800 ± 110 mm2 in remodeling group and of 680 ± 150 mm2 in reimplantation group.
If the ideal oversizing degree is measured on the "final" aortic annulus diameter, how can it be determined before selecting graft size? In pathological aortic roots, dimensions of aortic root components are spread on a wide range of values. Our attempts to realize an exhaustive mathematical model to predict graft size on the basis of aortic leaflets size failed. This step of the operation, in our opinion, has to be managed by what David calls "art" [14]. We use a qualitative method based on appraisal of aortic leaflets coaptation after initial reduction of the annulus with annular mattress sutures. After passing annular sutures and while the three commissures are suspended in an ideal cylinder, we look at the quality of coaptation of aortic leaflets. When a nice leaflets coaptation with no folds or tension is obtained, we size the aortic annulus and the sino-tubular junction. Then we select, on the basis of our normograms, the appropriate graft size and tie annular sutures on the same dilator used to size the annulus, as described by Svensson [15], in order to avoid annulus over-reduction. Obviously, final leaflets coaptation will depend on commissure positioning inside the graft and eventual leaflets remodelling more than on aortic annulus size; however, fixing the annular size corresponding to a nice coaptation, allows a reference point for graft size selection.
It has to be observed that surgical technique could affect the final result. Since graft corrugations in the Valsalva graft have a vertical array, sub-coronary sutures, especially behind commissures, can crimp the graft and reduce the space available for sinuses bulging. This is possible, but to a lesser extent with a standard graft. To minimize the effect of graft crimping, we use, for the Valsalva graft, a grade of oversizing that is one step over the theoretical ideal one. That is, for annuli measuring 23–27 mm, a +3mm of oversizing. We believe that a careful technique should avoid or reduce to a minimum prosthesis crimping behind commissural pillars because, in the pressurized Valsalva graft, tension develops laterally and consequent crimps distension could cause tension or tears at commissural level.
Size of sino-tubular ridge is pre-determined in the Valsalva graft; in the standard graft it is determined by the surgeon. In our in vivo measurements in healthy subjects sino-tubular junction was slightly bigger than the aortic annulus (Table 1) and the annulus to sino-tubular junction ratio was 95 ± 12%. Independently from the aortic annulus diameter, neo-aortic annulus size to neo sino-tubular junction size ratios of 96 ± 1% and 89 ± 2% are obtained with a +1 mm and a +3 mm Valsalva graft oversizing, respectively. When using a standard graft with a +7 mm oversizing, the corresponding annulus to sino-tubular junction ratio falls to 73%. A +1 mm to +3 mm Valsalva graft oversizing offers a further advantage in respect to a standard graft: there is no need for sino-tubular junction reduction. Higher degrees of Valsalva graft oversizing could result not only in oversized sinuses but also in an oversized sino-tubular junction which may need to be reduced.
A Valsalva graft oversizing of +3 mm is probably the ideal way to achieve a normal BLA with no need for sino-tubular junction correction compensating at the same time for the minimal crimping effect of sub-coronary sutures.
As it can be observed by comparing the extension of the interrupted vertical lines area in Figs. 2 and 3, the risk of creating too small sinuses is absent with the Valsalva graft. In fact, except for a 19 mm annulus, even no oversizing is enough to avoid systolic contact between aortic leaflets and neo-aortic wall. Note that the combination between a size 19 mm or 21 mm aortic annulus and +0 mm Valsalva graft is only theoretical since the smallest Valsalva graft size available is 24 mm.
The study has some limitations. Since aortic annulus diameter is determined on the basis of qualitative appraisal of aortic leaflets coaptation, our sizing method is not fully quantitative. Moreover, intra-operative measures are obtained on a flaccid annulus and are quite approximate because clinical use sizers do not measure millimeters fractions, and may be quite different from final, beating heart, annulus size. In our previous study [9], however, we found an excellent correlation between predicted and observed values. Since our BLA measurements are based on the assumption that the normally trifoliate cross-section of the aortic root has a circular shape, values are slightly overestimated. The same degree of overestimation should, however, apply to healthy population group as to standard or Valsalva graft groups.
In conclusion, our results suggest that in the reimplantation type of valve-sparing aortic procedures theoretical graft oversizing should be obviously less when using a Valsalva graft than when using a standard graft and that the ideal oversizing in respect to aortic annulus is +7 mm for a standard graft and +3 mm for a Valsalva graft.
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References
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- David TE, Feindel CM. An aortic valve-sparing operation for patients with aortic incompetence and aneurysm of the ascending aorta. J Thorac Cardiovasc Surg 1992;103:617-622.[Abstract]
- Hopkins RA. Aortic valve leaflet sparing and salvage surgery: evolution of techniques for aortic root reconstruction. Eur J Cardiothorac Surg 2003;24:886-897.[Abstract/Free Full Text]
- Kunzelmann KS, Grande J, David TE, Cochran RP, Verrier ED. Aortic root and valve relationships: impact on surgical repair. J Thorac Cardiovasc Surg 1994;107:162-170.[Abstract/Free Full Text]
- Grande-Allen J, Cochran RP, Reinhall PG, Kunzelman KS. Re-creation of sinuses is important for sparing the aortic valve: a finite element study. J Thoarc Cardiovasc Surg 2000;119:753-763.[Abstract/Free Full Text]
- De Paulis R, De Matteis GM, Nardi P, Scaffa R, Bassano C, Chiariello L. Analysis of valve motion after the reimplantation type of valve-sparing procedure (David I) with a new aortic root conduit. Ann Thorac Surg 2002;74:53-57.[Abstract/Free Full Text]
- Morishita K, Murakami G, Koshino T, Fukada J, Fujisawa Y, Mawatari T, Abe T. Aortic root remodelling operation: how do we tailor a tube graft?. Ann Thorac Surg 2002;73:1117-1121.[Abstract/Free Full Text]
- Svensson LG. Sizing for modified David's reimplantation procedure. Ann Thorac Surg 2003;76:1751-1753.[Abstract/Free Full Text]
- David TE, Ivanon J, Armstrong S, Feindel CM, Webb GD. Aortic valve-sparing operations in patients with aneurysm of the aortic root or ascending aorta. Ann Thorac Surg 2002;74:S1758-S1761.[Abstract/Free Full Text]
- Gleason TG. New graft formulation and modification of the David reimplantation technique. J Thorac Cardiovasc Surg 2005;130:601-603.[Free Full Text]
- Maselli D, Montalto A, Santise G, Minardi G, Manzara C, Musumeci F. A normogram to anticipate dimension of neo-sinuses of Valsalva in valve-sparing aortic operations. Eur J Cardiothorac Surg 2005;27:831-835.[Abstract/Free Full Text]
- Bellhouse BJ, Bellhouse FH. Mechanism of closure of the aortic valve. Nature 1968;217:86-87.[Medline]
- Bellhouse BJ, Bellhouse FH, Red KG. Fluid mechanics of the aortic root with application to coronary flow. Nature 1968;219:1059-1061.[CrossRef][Medline]
- David TE. Sizing and tailoring the Dacron graft for reimplantation of the aortic valve. J Thorac Cardiovasc Surg 2005;130:243-244.[Free Full Text]
- David TE. Aortic valve-sparing operations. Ann Thorac Surg 2002;73:1029-1030.[Free Full Text]
- Svensson LG. Sizing for modified David's reimplantation procedure. Ann Thorac Surg 2003;76:1751-1753.
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Abstract
1. Introduction
