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Ann Thorac Surg 2002;73:1117-1121
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

Aortic root remodeling operation: how do we tailor a tube graft?

^a Department of Thoracic and Cardiovascular Surgery and Second Department of Anatomy, Sapporo Medical University School of Medicine, Sapporo, Japan

Accepted for publication December 18, 2001.

* Address reprint requests to Dr Morishita, Department of Thoracic and Cardiovascular Surgery, Sapporo Medical University School of Medicine, South 1 West 16, Chuo-ku, Sapporo 060-8556, Japan
e-mail: kmori{at}sapmed.ac.jp

	Abstract

Top Abstract Introduction Material and methods Results Comment Conclusions Acknowledgments References

 
Background. In aortic root remodeling operation, it is difficult to perform graft sizing and tailor a graft appropriately. Thus the aim of this study was to create guidelines for sizing and tailoring that would help to standardize the operation.

Methods. We studied the anatomy of the aortic root and assessed the reliability of three equations reported to assist in graft sizing with aortic root casts obtained from 127 cadavers.

Results. Yacoub’s equation and ours accurately predicted the diameter at the sinotubular junction. Three cusps of the aortic valve were not equal in size. Sinus height of the aortic root was unpredictable.

Conclusions. Based on these results, we recommend that aortic root remodeling operation should be performed as follows: (1) graft sizing should be performed using Yacoub’s way or our way; (2) the tube graft should be cut into three parts in proportion to the size of each cusp; and (3) the position of the commissures in the tube graft should be secured with sutures first, and the depth of the sinuses should be determined later.

	Introduction

Top Abstract Introduction Material and methods Results Comment Conclusions Acknowledgments References

 
Yacoub and Sarsam [1] developed an aortic root remodeling operation to preserve the native aortic valve, and Yacoub and associates [2] recently reported satisfactory long-term results by using this procedure. David and colleagues [3] also reported excellent clinical outcomes from using their aortic valve-sparing operations. Despite these results, concern remains over the risk of recurrent aortic insufficiency. This consideration has prevented the general acceptance of these operations. Aortic root remodeling is a very complex procedure, and an inexperienced surgeon cannot adapt the procedure to the pathology of each individual. Thus guidelines for the procedure would help to standardize the aortic root remodeling operation.

For editorial comment see page 1029

The primary mechanism of aortic regurgitation secondary to aortic wall disease is outward displacement of three commissures. Theoretically, in order to make the aortic valve competent the surgeon must normalize the spatial relationship among the three commissures (Fig 1). For this purpose the surgeon selects a tube graft corresponding to the diameter of the normal or near-normal sinotubular (ST) junction, makes three cuts in the graft, and fixes the top of each of the three commissures to the upper part of each cut.

View larger version (39K): [in this window] [in a new window]   Fig 1. Schema of the aortic root: the level of the sinotubular (ST) junction (1 star); the bottom of the aorto-ventricular junction (2 stars); view of transection of the aorta at the level of the ST junction (3 stars).

Various methods for determining the appropriate size of a graft have been reported [4, 5, 6]. Pepper and Yacoub [4] determined the appropriate size of a graft, while keeping the three commissures positioned normally, with the geometric principle that the distance between the commissures approximately equals the circumference of the desired ST junction. Similarly, we determined the appropriate graft size by using another geometrical equation [5]. David [6] predicted the appropriate diameter of a graft from the aortic leaflet that remained normal or near-normal in candidates for aortic root remodeling operation. These methods, however, have not been validated scientifically.

The appropriate method for tailoring a tube graft for the aortic sinuses, which comprises another important part of the aortic root remodeling operation, also remains controversial [7]. The existence of various techniques is no doubt confusing for surgeons.

The aim of the present study was to establish guidelines for sizing and tailoring in aortic root remodeling. For this purpose, we studied the anatomy of the aortic root and assessed the reliability of each of the three above-mentioned methods.

	Material and methods

Top Abstract Introduction Material and methods Results Comment Conclusions Acknowledgments References

 
Anatomic measurements were performed on casts of aortic roots obtained from cadavers. The hearts consisted of 80 formol-fixed specimens donated by Japanese (47 men and 33 women) aged 44 to 97 years (mean age 79 ± 10) and 47 formol-fixed specimens donated by Caucasians (24 men and 23 women) aged 51 to 95 years (mean age 72 ± 11). Specimens had no evidence of aortic valvular disease or aneurysm.

Cast preparation
The heart was removed from the cadaver by dividing the ascending aorta 4 to 5 cm above the ST junction, the main pulmonary artery, the venae cavae, and the pulmonary veins. Any intracavital clot was removed completely before the injection of dental impression material into the aortic root. Casts were obtained by cutting the aortic root longitudinally 20 minutes after the injection.

Prediction of diameter of the ST junction
To assess the accuracy of each of the three methods for sizing we compared the measured diameters of the ST junction and the predicted diameters. Predicted diameters were obtained as follows. Pepper and Yacoub [4] used the geometric guideline that the circumference of the ST junction is three times the diameter at the ST junction. Accordingly, the distance between the commissures corresponds to the diameter at the ST junction. The distance was measured by laying a suture along the ST junction. This value was defined as Yacoub’s predicted diameter.

Our method was reported previously [5]. In brief, our equation is based on the fact that when each commissure is considered as the apex of an equilateral triangle, the triangle is circumscribed by a circle of the ST junction. According to the Pythagorean theorem, the diameter of the ST junction is calculated as follows: , where SD is the diameter of the ST junction and ID is the intercommissural straight-line distance. We measured the intercommissural straight-line distance with calipers (Digimatic Caliper; Mitutoyo, Kawasaki, Japan) and calculated the diameter using this equation.

David [6] selected a tube graft whose diameter was 10% smaller than the length of the free margin of the aortic leaflet. We laid sutures along the free margins of the casts of the aortic leaflets and measured the lengths of the sutures. Ninety percent of the length represented the predicted diameter.

Measurement of the aortic root
Aortic root casts were sectioned at the level of the ST junction after sinus height, defined as the distance from the top of the commissures to the bottom of the cusp [8], was measured. The cut edge of the cross-section was digitally imaged using a MacIntosh 8600/250 computer and a color image scanner (GT-9600; Epson, Tokyo, Japan). The digitized image was stored using Adobe Photoshop 5.0 (Adobe System, San Jose, CA) and videotaped by Media 100 (Data Translation, Marlboro, MA). The orifice area was then determined by calibration with a 1-cm ruler using computed planimetry (Clearview Ultra, Boston Scientific, Tokyo). The measured diameter was calculated from the area of the cross-section based on the assumption that the shape of the root at the ST junction is perfectly round. This method corrected for the irregular shape of the aortic root [9].

Data analysis
When the sinuses were different in size, we measured all three sinuses and averaged the result. Data are expressed as mean ± SD. Differences in measurements were analyzed using a one-way analysis of variance (ANOVA), followed by Scheffe’s test when the F value permitted. Correlation was calculated with the Pearson test. A value of p less than 0.05 was considered statistically significant. These analyses were performed with the StatView J-5.0 software (SAS Institute, Cary, NC).

	Results

Top Abstract Introduction Material and methods Results Comment Conclusions Acknowledgments References

 
Predicted diameter versus measured diameter of the ST junction
The relationships between measured and calculated diameters obtained by using Yacoub’s method and our method were both linear and had high coefficients of correlation (r = 0.871 and r = 0.911, respectively). In contrast, the relationship between the measured diameter and the diameter calculated using David’s equation, although linear, had a poor correlation (r = 0.397; Fig 2). Findings were similar in casts of white hearts, with correlation coefficients of 0.956, 0.910, and 0.593, respectively (Fig 3).

View larger version (24K): [in this window] [in a new window]   Fig 2. Diameter values predicted by equations versus measured diameter from Japanese cadavers at sinus level: (A) Yacoub’s method; (B) our method; (C) David’s method.

View larger version (19K): [in this window] [in a new window]   Fig 3. Diameter values obtained from equations versus measured diameter at sinus level in white casts: (A) Yacoub’s method; (B) our method; (C) David’s method.

In casts of white hearts, the distance was 35.4% ± 3.0% (range 28% to 42%), 33.3% ± 3.2% (range 28% to 43%), and 31.3% ± 2.8% (range 25% to 36%) for the right, noncoronary, and left coronary sinus, respectively. The left coronary sinus was significantly smaller than the right coronary sinus or the noncoronary sinus (right versus left, p = 0.0002; right versus noncoronary, p = 0.0649; left versus noncoronary, p = 0.0466).

Sinus height
We plotted the sinus heights of the cusps against the circumferences of the ST junction. The relationship was nonlinear in the Japanese group and showed a low level of correlation in the white group (r = 0.507). These results implied that sinus height varies considerably from patient to patient.

	Comment

Top Abstract Introduction Material and methods Results Comment Conclusions Acknowledgments References

 
Aortic root remodeling operations consist of graft sizing and making pseudosinuses. To correct aortic regurgitation due to displacement of the ST junction, normalization of the dilated ST junction is first required. The selected graft acts as a normalized ST junction to which three aortic commissures are fixed so that the aortic leaflets can meet centrally. Therefore successful repositioning must require accurate graft sizing. However, it is difficult to achieve central coaptation of the aortic valve because determination of size is not simple [10]. The success of this surgery hinges on the surgeon’s ability to accurately size the graft.

Pepper and Yacoub [4] emphasized the importance of restoring optimum coaptation of the aortic leaflets during assessment of the size of the aortic root. They achieved coaptation by stretching the three commissures in a vertical direction. In such a situation a circle including the three commissures corresponds to the neo-ST junction. Geometrically the diameter of the ST junction can be determined from measurements of the distance between the commissures [4]. Similarly, we determined the size of the ST junction while creating optimum coaptation of the aortic leaflets [5].

David [6] developed numerous different aortic valve-sparing operations according to the pathology of the aortic root. However, his way of choosing the diameter of the graft is constant, regardless of its pathology. He focused on the fact that aortic valve leaflets still remain normal or only mildly diseased in patients undergoing aortic valve-sparing operations. In the case of a normal aortic root the diameter of the ST junction is approximately 90% of the length of the free margin of the aortic leaflets. Using this relationship the diameter of the normal ST junction is predicted from measurements of the aortic leaflets [6].

The above-mentioned methods for sizing appear appropriate. However, none of these methods have been validated. This study was therefore designed to assess the accuracy of each of the methods used to calculate aortic root diameter. Yacoub’s method and our methods both generated high correlation coefficients between the predicted and measured diameters in Japanese and white hearts. Despite the poor correlation coefficient obtained by using David’s method, especially in Japanese hearts, David and associates [3] surprisingly achieved excellent clinical results. This discordance may partially be due to racial differences but may also represent age-related changes such as fusion of the commissures [11]. As this change shortens the length of the free margin of the aortic leaflet, David’s method may be inaccurate for hearts in older Japanese. From a clinical point of view, accurate prediction of appropriate size regardless of the patient’s condition is naturally ideal. Thus we recommend either Yacoub’s method or our method for graft sizing.

Another important issue is how to create the pseudosinus. Yacoub and associates [2] created pseudosinuses exactly 120 degrees apart and reported long-term durability. On the other hand, Elkins [7] was concerned about dividing a tube graft into thirds given the different sizes of sinuses. He warned that the procedure could cause late valve failure. In reply to his comment, David stated that the difference was so minimal that it was not of clinical significance. However, the results of the present study, together with the previous study [11], confirmed that the sizes of cusps are different. Only 6 hearts among our 127 specimens had three cusps of equal sizes. Moreover, sinus size if expressed as a percentage of the circumference of the ST junction varied from 25% to 40%. Although skilled surgeons can modify the surgical technique to accord with each patient’s pathology, this would be difficult for inexperienced surgeons. Therefore we propose that the tube graft be cut in a tripartite way according to the patient’s sinus size.

The appropriate depth of the cut of a tube graft remains to be determined, although theoretically it should correspond to the sinus height. Unfortunately it does not seem possible to create a reliable equation for predicting sinus height, because the heights of the aortic sinuses are so variable. The initial length of the cut should be greater than the depth of the patient’s aortic sinus, and the depth of the cut should be determined later so as to accord with the patient’s aortic sinus, en route to suturing the graft from the commissure to the bottom of the annulus. We believe that appropriately sized pseudosinuses can be made using this technique.

David emphasized the importance of additional annuloplasty, especially in a patient with annuloaortic ectasia. He reduced the prolonged fibrous component to the normal length, because the fibrous component of the ventriculoaortic junction is dilated in such a patient. In the normal ventriculoaortic junction, 55% of its circumference is fibrous and 45% is muscular tissue. As the diameter of the ventriculoaortic junction is 10% larger than the diameter of the ST junction in the normal aortic root, we can predict the normal length of the fibrous component from the normal diameter of the ST junction. In annuloplasty, as well as aortic root remodeling operation, it is important to predict the normal diameter of the ST junction.

Yacoub, however, has not mentioned the necessity and usefulness of annuloplasty. This difference poses an interesting question: Does annular dilatation occur so significantly as to require annuloplasty despite patients with normal or near-normal aortic leaflets? David performed aortic anuloplasty in two thirds of patients with aortic root aneurysms whereas no patients underwent the anuloplasty in Yacoub’s series. David and colleagues [3] reported that only 1% of patients required reoperations at 5 years. This excellent result may validate the aortic annuloplasty. However, the series of Yacoub without annuloplasty showed 89% freedom from reoperation at 5 years. As aortic remodeling operation itself is a time-consuming procedure, it is desirable to omit the annuloplasty if not needed. Further investigations will be needed to establish the surgical indication of additional annuloplasty.

Recently, Choo and Duran [12] warned of dangers inherent in current methods of graft sizing. They noted that size mismatch between the native aortic root and the graft was possible since sizing was based on measurements in a nonpressured heart. Certainly, dimensions of the arrested heart differ from those of the beating heart. Nevertheless this difference does not overly concern us, as the pseudosinuses do not distend with pressure due to hard graft material, unlike the native aortic root. In other words, once the aortic root is reconstructed with a tube graft so that the aortic valve can coapt centrally, the aortic valve should remain competent under any pressure. Should radial expansion of the pseudosinuses occur, the range would be so minimal that coaptation would not be affected.

Echocardiography is a reliable method for measuring dimensions in the beating heart and graft sizing can be performed easily using echocardiography when the aortic root is normal. Conversely, when the aortic root is enlarged it is difficult to predict what size the graft should be even with real-time measurements. We believe that it is best to measure cardiac dimensions in the arrested heart, with competence of the aortic valve restored. Despite measurements being made in arrested hearts, some surgeons obtained satisfactory results [2] [3]. Their results may imply the adequacy of graft sizing based on measurements in the nonpressured heart.

Limitations of this study
This study has several limitations. First, the ages of the cadavers were 20 to 30 years older than the average age of typical patients [2, 3]. Aging affects the shape of the aortic root. Thus, these measurements should be repeated using younger cadavers. However, the unavailability of a large number of young cadavers makes such a study difficult.

Second, it is doubtful whether the anatomical findings of the normal aortic root are applicable to patients with dilated aortic roots. Yacoub and associates restored a normal spatial relationship among the three commissures during determination of the desired diameter of the ST junction. We also created a normal spatial relationship of the ST junction so that the aortic valves met centrally. David predicted the diameter of the neo-ST junction from measurements of the normal aortic leaflet. Each graft sizing was performed on the basis of normal spatial relationship or measurements of normal tissue. Thus, the use of casts of normal aortic roots for assessment of each of the above methods used for determining aortic root diameter seems reasonable.

The third limitation of this study was the use of formol-fixed aortic roots. Unlike a native aortic root, a formaldehyde-fixed aortic root does not expand under pressure. Ideally, an anatomical study of dimensions and geometric relationships as a function of intraaortic pressure between 0 and 120 mm Hg should be performed using casts of fresh human hearts. However, most surgeons determine the size of the Dacron graft by measuring dimensions of arrested hearts. In addition, dimensions and geometric relationships of the neo-aortic root are constant during each cardiac cycle because the compliance of currently available graft material is as low as 1% to 2%. In other words, a study of dimensions and geometric relationships in dynamic functioning states has little meaning unless we use a graft material for which the compliance is about the same as that of a native aorta. Currently available graft material does not have extensibility similar to that of the aorta. Therefore, we believe that it is acceptable to perform anatomic study in the nondynamic state in order to assess the reliability of each of the methods for determining the size of the graft replacement.

	Conclusions

Top Abstract Introduction Material and methods Results Comment Conclusions Acknowledgments References

 
The results of our study suggest that use of Yacoub’s equation or our equation enables accurate prediction of the diameter at the neo-ST junction; the three cusps are not equal in size; and sinus height is unpredictable. Based on these findings, we recommend that aortic root remodeling be performed as follows: (1) graft sizing should be performed using Yacoub’s way or our way; (2) the tube graft should be cut into three parts in proportion to the size of each cusp; and (3) the position of the commissures in the tube graft should be secured with sutures first and the depth of the sinuses should be determined later.

	Acknowledgments

Top Abstract Introduction Material and methods Results Comment Conclusions Acknowledgments References

 
We are grateful to the following persons for use of materials: Professor Y. Inoue (Hokkaido University of Medicine), Professor H. Kiyama (Asahikawa Medical College), Professor J. Kodama (Hokkaido University School of Medicine), and Professor von Lüdinghausen (University of Würzburg).

	References

Top Abstract Introduction Material and methods Results Comment Conclusions Acknowledgments References

 

1. Sarsam M.A.I., Yacoub M. Remodeling of the aortic valve anulus. J Thorac Cardiovasc Surg 1993;105:435-438.[Abstract]
2. Yacoub M.H., Gehle P., Chandrasekaran V., Birks E.J., Child A., Radley-Smith R. Late results of a valve-preserving operation in patients with aneurysms of the ascending aorta and root. J Thorac Cardiovasc Surg 1998;115:1080-1090.[Abstract/Free Full Text]
3. David T.E., Armstrong S., Ivanov J., Feindel C.M., Omran A., Webb G.D. Results of aortic valve-sparing operations. J Thorac Cardiovasc Surg 2001;122:39-46.[Abstract/Free Full Text]
4. Pepper J., Yacoub M. Valve conserving operation for aortic regurgitation. J Card Surg 1997;12(Suppl):151-156.[Medline]
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6. David T.E. Aortic valve-sparing operations in patients with aortic root aneurysm. In: Piwnica A., Westaby S., eds. Surgery for acquired aortic valve disease. Oxford: Isis Medical Media, 1997:135-143.
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