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Eur J Cardiothorac Surg 2005;28:850-855
© 2005 Elsevier Science NL

Aortic root dilatation may alter the dimensions of the valve leaflets

Mano J. Thubrikar a , Michel R. Labrosse a , * , Kenton J. Zehr b , Francis Robicsek a , Geoffrey G. Gong a , Brett L. Fowler a

a Heineman Medical Research Laboratory, Department of Thoracic and Cardiovascular Surgery, Carolinas Medical Center, Charlotte, NC, USA
b Division of Cardiovascular Surgery, Mayo Clinic, Rochester, MN, USA

Received 22 June 2005; received in revised form 20 August 2005; accepted 18 September 2005.

* Corresponding author at: Department of Mechanical Engineering, University of Ottawa, Ottawa, Ont., Canada K1N 6N5. Tel.: +1 613 562 5800x6284; fax: +1 613 562 5177. (Email: labrosse{at}eng.uottawa.ca).


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 
Objective: Valve-sparing surgery can be used in patients with dilated aortic roots and aortic insufficiency (AI) but has not become a common practice, in part because the spared valve may be incompetent. Our goal was to study how the dimensions of the aortic root and leaflets have changed in such patients. Methods: Fourteen patients with dilated aortic root and AI were examined by transesophageal echocardiography. The annulus diameter, sinotubular junction (STJ) diameter, sinus height, leaflet free-edge length, and leaflet height were measured. Correlations among these dimensions and with the AI grades were explored. Measurements were also made in 19 normal human aortic valves from silicone molds. Results: There was no evident change in the average diameter of the annulus between the normal valves and those in the dilated aortic roots. The STJ diameter was obviously increased in the dilated aortic roots; the aortic sinuses also appeared to be taller and the leaflets larger than normal. The leaflet free-edge length, the leaflet height, and the sinus height were found to increase with the dilated STJ diameter. The degree of AI was not found to correlate well with any of the dimensions measured. Conclusions: The dimensions of the leaflets may change parallel to aortic root dilatation with AI. Therefore, during valve sparing, it may be necessary to correct both the dilatation of the root and the leaflet free-edge length to achieve a competent valve.

Key Words: Aortic valve • Aortic root • Leaflets • Dimensions • Aneurysm • Insufficiency


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 References
 
Aortic root dilatation may present itself as an aneurysm of the ascending aorta, aneurysm of the sinuses of Valsalva, or annuloaortic ectasia. It has been recognized as the primary cause of aortic insufficiency (AI) [1]. Aortic insufficiency was shown to occur when the distance between the commissures increases beyond a certain limit so that the coaptation of the leaflets is no longer possible [2]. The result is a central hole in the valve and regurgitation during diastole. Over time, the condition of the patient may deteriorate and require surgical intervention. The standard surgical repair procedure consists of replacing the ascending aorta with a tubular Dacron graft and the aortic valve with a mechanical heart valve.

Prompted by the observation that many patients with AI seem to have anatomically normal leaflets, Yacoub and associates [3] pioneered aortic valve-sparing operations in the early 1980s. Different procedures, including remodeling and reimplantation are currently in practice. Early and short-term results have been good [4–8]. Regardless of the technique used, the advantages of valve sparing over valve replacement with a mechanical prosthesis are significant. There are no complications associated with anticoagulation therapy required in case of mechanical valves, and native valves are alive, which essentially protects them from the structural degeneration that impairs the long-term performance of bioprosthetic valves. However, the valve-sparing procedure has had limited success, in part because the valve may not be completely competent after the procedure. There are several reports that describe the residual AI present immediately after the procedure or leaflet prolapse and AI requiring correction in the leaflet length during the procedure, or progression of AI over time in some cases [7,9–14].

To obtain a competent valve during valve-sparing surgery, a good match between the various dimensions of the valve must be achieved [15,16]. This could be made difficult if the process of aortic root dilatation were to alter the dimensions of the valve leaflets. It is therefore necessary to understand how various dimensions of the valve may have changed in order to successfully approach valve-sparing surgery.

The objective of the present study was to investigate dimensional changes in the aortic valves of selected patients with dilated aortic roots who may be candidates for the valve-sparing surgery. Measurements of various dimensions of the aortic valve were made using transesophageal echocardiography (TEE). Similar measurements were also made from silicone molds of normal aortic valves. The results were analyzed to determine to what extent aortic root dilatation affects the dimensions of the aortic root and valve leaflets.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 References
 
2.1 Measurements in patients
Fourteen adult patients, nine males and five females, all with dilated aortic roots and AI, were selected for the study as potential candidates for valve-sparing surgery with a customized prosthesis [15]. Patients with Marfan's syndrome were excluded. All the patients had their aortic root evaluated using TEE. The severity of AI was studied with color Doppler velocimetry, and graded from 0 (none or trace) to 4 (severe). For dimensional measurements of the aortic root, the videotapes of TEE were analyzed using Image-Pro software (Media Cybernetics, Silver Springs, MD). Still-frame images of the valves were chosen at various times during the cardiac cycle, and the main geometric parameters of the aortic valve were measured. These parameters were (i) the annulus diameter, (ii) the sinotubular junction (STJ) diameter, (iii) the sinus height, (iv) the leaflet free-edge (FE) length, and (v) the leaflet height (Fig. 1 ). The annulus diameter, the sinus height, and the leaflet height were measured in the long-axis views (Figs. 1–3 ). The sinus height was defined as the distance between the lowermost point of the leaflet attachment and the STJ (Figs. 1–3). The leaflet height was defined as the radial length of the leaflet. The STJ diameter was measured in the short-axis view by tracing a circle through the three commissures (Figs. 2 and 3). The free-edge length of the leaflet was also measured in this view by tracing the leaflet outline.



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  		Fig. 1. Drawing of the aortic valve showing the side view of one leaflet. The parameters are the annulus diameter (AN), the sinotubular junction diameter (STJ), the sinus height (SH), the leaflet free-edge length (FE), and the leaflet height (LH). These parameters were measured from images like those shown in Figs. 3 and 4.

 


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  		Fig. 2. Typical transesophageal echocardiography images of the dilated aortic root in a patient. The top pictures present long-axis views of the valve in open (left) and closed (right) positions. The bottom pictures show the short-axis views of the valve in open (left) and closed (right) positions. In some patients, the sinotubular junction may not be clearly defined as in the top left picture. Also, the free edge of the leaflet may not lie in the plane of the short-axis view. Both factors contribute in reducing the accuracy of the measurements.

 
The parameters were determined in the closed valve and in the open valve, and each parameter was measured several times successively by three different individuals. All the measurements were averaged to obtain the mean value for each parameter. The annulus diameter, STJ diameter, and the leaflet height were measured to within ±1 mm. The free-edge length and the sinus height were more difficult to determine. Extra care was taken knowing that the free-edge length measurements are usually underestimates because the true free-edge has a suspension curve to it, whereas the image of the free-edge is cut through the leaflet in a plane of the short-axis view. The sinus height was also difficult to determine in some cases because the boundary of the STJ was not clearly identifiable in the long-axis view image.

2.2 Measurements from molds of normal valves
It was desirable to have measurements in the normal, non-dilated aortic roots and valves so as to have a basis for comparisons with the patients’ valves. Therefore, silicone rubber molds were made at 80 mmHg pressure in 15 normal human aortic roots with the valves in closed position. These roots were provided by LifeNet (Virginia Beach, VA). The same parameters as described above were measured from the molds using calipers. To determine the STJ diameter, the actual distance between the commissures was measured and the diameter of the circle going through the three commissures was calculated. Furthermore, the dimensions measured in the same fashion by Swanson and Clark [17] in four silicone molds of closed normal human valves were added to the data set.

2.3 Statistical methods
Because of the grossly different measurement techniques utilized in the normal and dilated aortic roots, it was decided not to use statistics to compare the valve parameters. However, linear regression analyses were carried out between the STJ diameter and the other parameters of the patients’ valves to study the influence of aortic root dilatation.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 References
 
The measurements with their ranges and means obtained for the normal aortic valves are reported in Table 1 ; those for the incompetent valves are in Table 2 . The data are arranged by increasing STJ diameter as the focus of the study was aortic root dilatation.


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  		Table 1. Dimensions (mm) in normal human aortic valves at 80 mmHg pressure, measured from silicone molds
 

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  		Table 2. Dimensions (mm) and AI grades measured in patients with dilated aortic roots
 
In the normal valves, the average diameter of the annulus was 24.7 mm, and that of the STJ was 23.6 mm. The typical height of the sinuses of Valsalva was about 21.8 mm. The leaflets were on average 31.2 mm wide (free-edge length) and 14.4 mm in height.

There was no obvious change in the average diameter of the annulus in the patients with dilated aortic roots, at 26.6 mm. The annulus diameter values reported in both Tables 1 and 2 are representative of the normals in adults. By contrast, the STJ diameter was, as one expects, markedly increased to 37.2 mm. The sinuses of Valsalva showed signs of being taller than in the normal valves, at 26.2 mm on average. The leaflets also appeared to be larger, being on average 33.8 mm wide (free-edge length) and 19.6 mm in height.

All the dimensions in the patients with dilated aortic roots had wider ranges, and the maximum values were also higher than those in the normal valves, while some of the minimum values were not. This latter observation points to a geometric mismatch between the dimensions of the valve components, consistent with the AI observed in the patients. Yet, none of the individual valve dimensions was found to correlate well with the degree of AI.

Overall, the female patients had smaller valves than the males, but the trends observed in the dilated roots were the same in both the genders. Fig. 4 shows how the free-edge length, the leaflet height, and the sinus height increased with the dilated STJ diameter. For information, the figure includes additional data points corresponding to the average values of these parameters in the normal valve, so that one can appreciate how the parameters may have increased from normal. Only the three best correlations, as noted from the R 2 values, between the STJ diameter and the other valve dimensions are shown. Even though the correlations are not very strong, the data suggest that as the aortic root dilates beyond normal values and becomes taller, the leaflets elongate in the circumferential and radial directions, i.e., they become larger. Parallel to these changes, Fig. 5 shows that in the patients’ valves, the leaflet height also tends to increase as the annulus diameter increases.



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  		Fig. 4. The leaflet free-edge length, the leaflet height, and the sinus height in the dilated aortic roots versus the STJ diameter. The symbol (+) shows the normal values in adults. Starting form this normal point, one can appreciate how the free-edge length was larger in patients with dilated aortic roots. Similarly, both the leaflet height and the sinus height showed an increasing trend in the patients.

 


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  		Fig. 5. The leaflet height in the dilated aortic roots is plotted against the annulus diameter. The symbol (+) shows normal values in adults. The leaflet height appears to increase in patients with increasing annulus diameters.

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
References
 
The patients in this series had dilated aortic roots and AI and had anatomically normal leaflets. Our measurements suggest that these anatomically normal leaflets, however, were not geometrically normal. Their dimensions had changed along with the other dimensions of the valve. All the patients had been diagnosed with a dilated STJ, while the annulus was dilated in only some of them. Yet, the STJ diameter did not correlate well with the degree of AI, which may indicate that the degree of AI depends on multiple factors.

There are no reports in the literature with which to compare our data quantitatively. Therefore, one gauge of how dimensions have changed is the comparison between the normal valves and the patients’ valves. The results obtained in the normal valves demonstrate that the parameters vary by a few millimeters from one healthy individual to another (Table 1). In addition to these individual variations, it is important to recall that the annulus and the STJ diameters change within a cardiac cycle by 2–3 mm [18] and the other parameters may also vary by up to 2 mm. Therefore, the values presented in Table 1 should be seen as averages. The measurements made in the patients from TEE images and reported in Table 2 should also be seen as averages. Because the measurement techniques were too radically different to allow for statistical comparisons of their results, only qualitative comparisons could be made between the normal and dilated aortic roots and valves.

Another gauge of how dimensions have changed is the correlation between the patients’ valves dimensions and the dilated STJ diameter. Although the correlations between different parameters of the valve are not strong, the tendencies for correlation offer some indication of an adaptation mechanism. Indeed, the lengthening of the leaflet free edge seems to parallel the increase in the distance between the commissures, and may point to an attempt to maintain cuspal coaptation. Similarly, the leaflets tend to increase in height with increasing STJ diameter and increasing annulus diameter, again perhaps to maintain cuspal coaptation. The nature of the signals that may trigger adaptation remains to be determined, but may be associated with the regurgitant flow.

These observations are consistent with the recent finding that cuspal tissue contains nerves whose endings have active chemicals [19]. As the leaflets of the human aortic valve have also been shown to have contractile properties triggered by a wide range of vasoactive agents [20], their possible adaptation to prevent or reduce AI is plausible. It has been a common observation that AI does not begin at the start of the STJ dilatation. Some STJ dilatation can be accommodated by the redundant surface of the leaflet while some more STJ dilatation might be accommodated by the increase of the leaflet dimensions. Hence, AI may not begin until STJ has reached a certain critical value. The enlarged leaflets then indicate that just decreasing STJ will not be sufficient to obtain a competent valve, because the leaflets have become too large for the valve. These leaflets are likely to prolapse and cause regurgitation after the valve-sparing procedure. Nonetheless, adaptation of the leaflets may be different in different patients and may even not occur in some (e.g., Patient 3).

The findings of this study call for observations in more patients as well as longitudinal studies in the same patients. They also make us aware that choosing a correct graft size does not necessarily guarantee the restoration of a "normal" valve geometry after valve-sparing surgery. They point to other dimensions that must be restored to achieve a competent valve. An aortic root prosthesis can be used to restore the annulus diameter, the STJ diameter, and the sinus height. Then, restoring the free-edge length of the leaflet may be necessary and sufficient to obtain a well functioning and competent valve. We have recently published how we believe the dimensions of the leaflets and those of the root should be matched [16].

In conclusion, the dilatation of the aortic root appears to increase the length of the free edge and the height of the leaflets. Therefore, during valve-sparing surgery, it may be necessary in some cases to correct not only the dilatation of the aortic root but also the leaflet free-edge length in order to achieve a competent valve.



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  		Fig. 3. Typical transesophageal echocardiography images of the dilated aortic root in another patient. The top pictures show the long-axis view of the valve in open (left) and closed (right) positions. The bottom left picture shows a central jet (regurgitation) in the closed valve in the same view. The bottom right picture shows the closed valve in the short-axis view.

 


   Acknowledgments
 
The authors express their gratitude to LifeNet, Virginia Beach, VA, for providing human valves for the present study.


   Footnotes
 
{star} This work was presented in part at the American Heart Association – Scientific Sessions, November 2001, and at the Symposium on Aortic Valve Sparing Surgery, September 2003, Charlotte.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 

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