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Ann Thorac Surg 2001;71:S318-S322
© 2001 The Society of Thoracic Surgeons

Bioprosthetic valves and conduits: new developments

A new aortic root prosthesis with compliant sinuses for valve-sparing operations

Mano J. Thubrikar, PhDa, Francis Robicsek, MD, PhDa, Geoffrey G. Gong, MDa, Brett L. Fowler, BSa

a Heineman Medical Research Laboratory and the Department of Thoracic and Cardiovascular Surgery, Carolinas Medical Center, Charlotte, North Carolina, USA

Address reprint requests to Dr Thubrikar, Heineman Medical Research Laboratory, Carolinas Medical Center, 1000 Blythe Blvd, Charlotte, NC 28203
e-mail: mthubrikar{at}carolinas.org

Presented at the VIII International Symposium on Cardiac Bioprostheses, Cancun, Mexico, Nov 3–5, 2000.


   Abstract
Top
 Footnotes
 Abstract
Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
 References
 
Background. We designed and tested a novel aortic root prosthesis with compliant sinuses for valve-sparing operations.

Methods. In eight human aortic roots, the aorta was trimmed 2 mm above the leaflet attachment. The aortic portion of the graft was made by scalloping the Dacron tube. Three sinuses were made individually after turning z-folds in the fabric 90 degrees. Three rectangular pieces were cut and purse strings sewn in each to form the sinuses. The graft was sutured to the aortic root and studied in a left heart simulator. The leaflet motion was recorded (500 frames/second), commissural movement was measured with ultrasound, and the shape of the root was determined from a mold. Seven intact aortic roots were also studied.

Results. In the aortic graft roots, the valves were competent and leaflets opened rapidly into a circular orifice, not touching the sinus wall. Commissural diameter increased by 22% when pressure increased from 0 to 80 mm Hg, and increased by a further 6.6% when pressure increased to 120 mm Hg. The sinuses had a teardrop shape.

Conclusions. The dynamics of the aortic graft root and the leaflets were comparable to that of the intact aortic root. This prosthesis is being introduced in clinical practice.


   Introduction
Top
 Footnotes
 Abstract
 Introduction
Material and methods
 Results
 Comment
 Acknowledgments
 References
 
In a significant number of patients, aortic regurgitation develops secondary to the dilation of the aortic root while the valve leaflets remain anatomically normal. Although aortic regurgitation from rheumatic valve disease has been declining in western countries, its occurrence secondary to aortic root dilation is on the rise [1]. The standard treatment for these patients is surgical replacement of the complete aortic root with a tubular graft and a prosthetic valve. Because of the disadvantages of prosthetic valves, attempts are being made to spare the native valve and replace only the aorta, usually with a Dacron tube. In patients with dilated aortic roots, both of Marfan and non-Marfan origin, the valve-sparing operation has gained increasing popularity over the last 10 to 15 years.

The pioneering work in this field was done by Yacoub and coworkers [2] and David and Feindel [3], among others. In this operation, normal or near normal aortic valve leaflets are preserved while the dilated aorta is replaced with a tube graft. It has been recognized that the natural aortic root has the sinuses of Valsalva, which may play an important role in both valve closure [4, 5] and minimizing the stresses in the leaflets [6]. Because of this recognition, and because the tube graft does not have the sinuses, some surgeons have attempted to create pseudosinuses by using their own specialized surgical technique during graft implantation [7–9]. To what extent they are able to mimic the geometry of the natural sinuses has not been established. Creation of the proper sinuses in the graft is important because some studies have reported that the leaflets hit the wall of the tube graft and become pathologic [7, 10].

Besides the shape of the sinus, there is also an importance to the compliant nature of the sinus. Our own studies have shown that the compliance of the sinus is what allows commissural movement, which is critical in the mechanism of valve opening [11]. Addressing the compliant nature of the graft, therefore, is essential.

In the present study, we have described the creation of a new aortic root prosthesis with compliant sinuses and how the spared valve works within it.


   Material and methods
Top
 Footnotes
 Abstract
 Introduction
 Material and methods
Results
 Comment
 Acknowledgments
 References
 
Preparing the aortic root
Eight human aortic roots of 17 to 21 mm diameter at the sinotubular junction obtained from Lifenet (Virginia Beach, VA) were used. The aortic wall was trimmed approximately 2 mm above the commissures and scalloped parallel to the leaflet attachment.

Preparing the graft
The aortic root graft was constructed as follows: The ascending aorta portion of the graft, up to the sinotubular junction, was made by slightly scalloping one end of the tubular Dacron graft (Hemashield Gold, Meadox Medical, Inc, Oakland, NJ). The three sinuses were made individually, using the same fabric after turning the z-folds of the fabric 90 degrees. A rectangular piece of appropriate dimensions was cut. Two purse strings were sewn in the fabric to form a teardrop shape of the sinus. The formed sinuses were then sutured to the scalloped aorta graft to form a sinotubular junction. The excess fabric was trimmed to produce a scalloped line similar to that created previously in the natural valve. This completed the preparation of the aortic root graft having the three compliant sinuses (Fig 1).



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  		Fig 1. Aortic root prosthesis with compliant sinuses. The prosthesis is made by attaching three sinus-shaped flaps to the tubular Dacron graft. Three flaps used for creation of the three sinuses can be seen (patent pending).

 
Attaching the graft to the valve
First, three alignment sutures were placed in the valve above the commissures. These sutures were inserted, then pulled through the graft at the corresponding locations in the graft, and then tied. This attachment placed the tissue on the inside and the graft on the outside. Then, stitching of the sinuses to the aortic wall was started in the middle of the bottom of the sinuses near the base of the leaflets. Using a double-armed suture, each sinus flap was attached to the aortic wall placing the tissue on the inside and the graft on the outside. The attachment was continued with a running stitch until first one half and then the other half of the sinus flap was completely attached to the aortic wall. These sutures were tied at the ends in the commissural location of the graft. All three sinus flaps were attached in this manner. In the in vitro experiments, the coronary artery attachments were not necessary. This completed the attachment of the aortic root graft to the valve. Most often, the graft chosen was 3 mm larger than the valve.

Testing the spared valve
The aortic graft root having the natural valve was mounted and tested in a left heart simulator (ViVitro System, Vancouver, Canada) over the aortic pressure range of 80/40 to 150/100 mm Hg, a heart rate of 72 beats/min, and a cardiac output of 4 L/min. The apparatus was filled with 38% glycerol to simulate blood viscosity. The leaflet movement was recorded with a high-speed video camera (500 frames/second) and from these images the orifice area and the leaflet topography was analyzed during a cardiac cycle. The outside view of the aortic graft root was also recorded to detect the movement of the commissures and the sinuses. The commissural movement was measured using an intravascular ultrasound technique (Cardiovascular Imaging System Inc, Insight, CA) in which a catheter was inserted through the valve and the echo images were recorded. To determine the overall shape of the aortic graft root, a silicone rubber mold of the valve in the closed position was made at a pressure of 80 mm Hg. For comparison, seven intact (human) aortic roots were also studied.


   Results
Top
 Footnotes
 Abstract
 Introduction
 Material and methods
 Results
Comment
 Acknowledgments
 References
 
The intact root
In the natural (human) aortic roots, all of the valves were competent and had no valvular gradient. The commissural diameter increased on average by 25% as the aortic pressure increased from 0 to 80 mm Hg and another 7% as the pressure increased further to 120 mm Hg.

The aortic graft root
In the aortic graft roots under systemic pressure, the sinuses bulged outwardly into a teardrop shape (Fig 2). The overall shape of the aortic graft root appeared similar to that of the intact natural root.



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  		Fig 2. Photographs of the aortic graft root with the valve in a left heart simulator. (Left) Under the aortic pressure the teardrop shape of the sinus in the graft root can be clearly appreciated. (Right top) Complete and symmetric valve closure. (Right bottom) Fully open valve in the graft.

 
Valve dynamics of the graft root
In the graft roots also, the valves were competent and there was no transvalvular pressure gradient. The valve opened rapidly, first in a triangular shape and then in a circular shape. This activity was followed by a stable opening phase during which the orifice area remained relatively unchanged. During the closing phase, the orifice area decreased and the configuration changed from circular to stellate to a complete closure. In the aortic graft roots, as in the intact aortic roots, the leaflets opened symmetrically and synchronously without any wrinkles in the free edge and they also closed symmetrically (Fig 2).

Gap between the graft and the leaflet
Figure 3 shows the intravascular ultrasound images of both the intact root and the aortic graft root. The cloverleaf shape of the sinuses was evident from these images, both in the intact root and in the aortic graft root. The circular opening of the valve and the symmetric closure was also evident in the roots. Notably, the open leaflet did not touch the sinus wall in the graft and there was a comfortable gap between the graft and the open leaflet.



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  		Fig 3. Intravascular ultrasound images of the aortic valve in the intact root and in the aortic graft root. The shape of the sinus appears comparable between the graft and the natural root. The open leaflet has a substantial gap between itself and the graft wall.

 
Flexibility of the graft root
In the aortic graft roots, the sinuses were flexible. Also, the commissural movement inward and outward was clearly visible during a cardiac cycle. The intravascular ultrasound measurements indicated that the commissural diameter was 22% larger at a pressure of 80 mm Hg than at 0 mm Hg, primarily because the graft chosen was 3 mm larger than the valve (Table 1). The commissural diameter increased an additional 6.6% from diastole to systole during a cardiac cycle when the pressure changed from 80 to 120 mm Hg (Table 1). Flexibility of the graft was evident, as the commissures were moving in and out and the sinuses could also be seen to change their circumferential curvature during a cardiac cycle.


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  		Table 1. Aortic Valve Dimensions in Compliant Aortic Grafts

 
Overall shape of the aortic graft root
Silicon molds of the aortic graft roots made at a diastolic pressure showed that the sinuses had a teardrop shape and they bulged outward by 2 to 3 mm (Fig 4). The mold of the graft resembled that of the natural aortic root. When the individual sinus-leaflet units were cut away from the mold of the root, the coaptation surface of the leaflet could be examined in detail. As can be noted in Figure 4, the valve leaflets had an excellent coaptation area, which would provide a complete and satisfactory competence of the spared valve.



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  		Fig 4. Silicone molds of the aortic graft root with the valve closed at 80 mm Hg pressure. (A) Bottom view, showing the sinus portion of the graft and load-bearing portion of the leaflet. Sinus bulge can be clearly seen. (B) and (C) Coaptation surface of the leaflet can be appreciated when the mold is cut and one sinus-leaflet assembly is separated. Portions of the mold are shaded to show coaptation area (nonshaded).

 

   Comment
Top
 Footnotes
 Abstract
 Introduction
 Material and methods
 Results
 Comment
Acknowledgments
 References
 
A number of published studies describe the valve-sparing procedure with short- and long-term follow-up results in patients [2, 3, 7, 8]. Discussion has ensued on how to choose the size of the graft [12] and on the "resuspension" versus "remodeling" techniques used in the valve-sparing operation [8]. Follow-up reports on Marfan and non-Marfan patients [2, 3, 7, 8] have compared the success of the valve-sparing procedure in different groups. Also, the issue of whether and when to do annuloplasty has been considered [8]. However, only a few studies have dealt with laboratory investigation of the graft [9] and consequently, basic information such as geometry of the root after valve sparing and dynamics of the functioning valve remain sketchy. In fact, lack of such basic information may be at the root of why in many valves aortic regurgitation may persist, though to a lesser degree, after the valve-sparing procedure. The present study has provided some of this most basic and essential information on a newly developed graft.

The most significant aspect of the study is that the newly designed graft has the teardrop shape of the sinus, reproducing the geometry of the natural aortic root. This shape provides a necessary gap between the open leaflet and the wall so that the leaflet will not hit the wall. The dynamics of the leaflet during a cardiac cycle is virtually indistinguishable between the graft root and the natural root. The leaflet position and the orifice area change in the graft root almost exactly the same way as they do in the intact root [11], thereby assuring that the mechanisms of the valve closure, involving eddy currents in the sinuses and so forth, are preserved.

Compliance of the graft was also comparable to that of the natural valve (Table 1) during a cardiac cycle. This property is important for enhancing valve longevity. As reported previously by us [13], the commissural movement allows the valve to open in such a way that the leaflet surface remains smooth and free of wrinkles. When the compliance of the sinus is lost [13] or when there is a tube graft, we found that the timing for opening and closing of the valve is not altered but that the topography of the leaflet surface is significantly changed to its detriment, as it begins to develop creases and wrinkles in its surface [13]. In fact, those studies lead us to believe that the role of the sinuses is less critical in the valve-closing mechanism, but both the shape and the compliance of the sinus are more critical for minimizing stresses in the leaflet and thereby enhancing valve longevity [6].

We also found that selection of a 3-mm larger graft allows the valve diameter to be restored to that diameter, which the valve had in the intact root at 80 mm Hg luminal pressure. Matching the graft size with the valve size in this manner produces the best valve function.

The dynamics of the aortic graft root and the valve leaflets were comparable to that of the intact aortic root. Thus, a newly designed aortic root prosthesis with compliant sinuses is expected to enhance longevity of the spared valve. This prosthesis is being introduced in the clinical practice [14].


   Acknowledgments
Top
 Footnotes
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
References
 
We gratefully acknowledge the help of LifeNet (5809 Ward Court, Virginia Beach, VA 23455) for supplying fresh human aortic valves for this study.


   Footnotes
Top
 Footnotes
Abstract
 Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
 References
 
This work was supported by grants from the Minna-James Heineman Foundation.


   References
Top
 Footnotes
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Olson L.J., Subramanian R., Edwards W.D. Surgical pathology of pure aortic insufficiency: a study of 225 cases. Mayo Clin Proc 1984;59:835-841.[Medline]
  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., Feindel C.M. An aortic valve-sparing operation for patient with aortic incompetence and aneurysm of the ascending aorta. J Thorac Cardiovasc Surg 1992;103:617-622.[Abstract]
  4. Bellhouse B.J. The fluid mechanics of the aortic valve. In: Ionescu M.L., Ross D.N., Wooler G.H., eds. Biological tissue in heart valve replacement. London: Butterworth-Heinemann, 1972 Chapter 2.
  5. Van Steenhoven A.A., van Dongen M.E.H. Model studies of the closing behaviour of the aortic valve. J Fluid Mech 1979;90:21-36.
  6. Thubrikar M.J., Nolan S.P., Aouad J., Deck J.D. Stress sharing between the sinus and leaflets of canine aortic valve. Ann Thorac Surg 1986;42:434-440.[Abstract]
  7. Leyh R.G., Schmidtke C., Sievers H.H., Yacoub M.H. Opening and closing characteristics of the aortic valve after different types of valve preserving surgery. Circulation 1999;100:2153-2160.[Abstract/Free Full Text]
  8. David T.E. Aortic root aneurysms: remodeling or composite replacement?. Ann Thorac Surg 1997;64:1564-1568.[Abstract/Free Full Text]
  9. Cochran R.P., Kunzelman K.S., Eddy C., Hofer B.O., Verrier E.D. Modified conduit preparation creates a pseudosinus in an aortic valve-sparing procedure for aneurysm of the ascending aorta. J Thorac Cardiovasc Surg 1995;109:1049-1058.
  10. Kamohara K., Itoh T., Natsuaki M., Norita H., Naito K. Early valve failure after aortic valve-sparing root reconstruction. Ann Thorac Surg 1999;68:257-259.[Abstract/Free Full Text]
  11. Thubrikar M. The aortic valve. Boca Raton, FL: CRC Press, 1990:40-54.
  12. Doty D.B., Arcidi J.M., Jr Methods for graft size selection in aortic valve-sparing operations. Ann Thorac Surg 2000;69:648-650.[Abstract/Free Full Text]
  13. Robicsek F., Thubrikar M.J. Role of sinus wall compliance in aortic leaflet function. Am J Cardiol 1999;84:944-946.[Medline]
  14. Zehr K.J., Thubrikar M.J., Gong G.G., Headrick J.R., Robicsek F. Clinical introduction of a novel prosthesis for valve preserving aortic root reconstruction for annuloaortic ectasia. J Thorac Cardiovasc Surg 2000;120:692-698.[Abstract/Free Full Text]



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