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Interact CardioVasc Thorac Surg 2006;5:526-530. doi:10.1510/icvts.2006.132654 © 2006 European Association of Cardio-Thoracic Surgery
Quantitative approach to aortic valve-sparing surgery
a Department of Cardiac Surgery, University of Heidelberg, INF 326, Heidelberg, 69120, Germany Received 10 March 2006; received in revised form 8 June 2006; accepted 12 June 2006
*Corresponding author. Tel.: +49 6221 566246; fax: +48 6221 564571.
Our goal was to understand why it is difficult to achieve reliable valve competence after aortic valve-sparing surgery, and to propose quantitative data aimed at improving the outcome of the procedure. Valve-sparing procedures were performed in patients with dilated aortic roots and aortic regurgitation, and reproduced in physical models to explore what should be the restored dimensions of the aortic root and leaflets for valve sparing to be successful. In parallel, a three-dimensional geometric model of the aortic valve was tested to evaluate its capability to predict the annulus diameter, sinotubular junction diameter, valve height, and leaflet free-edge length and height in competent spared valves. Valve sparing resulted in more or less severe residual regurgitation in all the patients considered. Successful valve-sparing was achieved in vitro by making further changes to the annulus diameter, the leaflet free-edge length and/or graft size. The changes needed were effectively predicted by the geometric model. Tabulated valve dimensions allowing restoration of competence were generated for convenient use by surgeons. A quantitative approach to aortic valve sparing is proposed, putting emphasis on the functional characteristics of the restored valve geometry.
Key Words: Aortic valve sparing; Aortic aneurysm; Aortic regurgitation; Leaflet dimensions
Aortic valve-sparing surgery was pioneered 20 years ago by Dr. Yacoub [1]. The patient's aortic valve can be saved if the valve leaflets (or cusps) look morphologically intact [2], while the aortic root wall and the ascending aorta are replaced with a prosthetic graft. Aortic valve sparing has none of the shortcomings associated with valve replacement, namely anticoagulation treatment for mechanical valves, and structural degeneration for bioprosthetic valves. Different techniques are currently in practice [1,3], yet aortic valve sparing has not become common practice, possibly because it has remained more art than science [4]. In spite of good early and short-term results, several reports describe complications associated with the procedure, such as residual regurgitation immediately after operation, leaflet prolapse requiring leaflet correction during the procedure, and progression of regurgitation over time in some cases [5–7]. In a recent publication, we presented evidence that in patients with aortic regurgitation associated with aortic root dilatation, the aortic valve leaflets may look anatomically normal but may not be geometrically normal [8]. This prompted the present study, in which we analyzed the outcome of aortic valve sparing procedures carried out in patients, and went back to the laboratory to perform the same procedures in physical models replicating the patients' conditions. The experiments were designed to help determine what dimensions of the aortic root and leaflets should be achieved for valve sparing to be successful. In parallel, we tested our three-dimensional (3D) geometric model of the normal aortic valve [9] to evaluate its capability to predict the annulus diameter, sinotubular junction (STJ) diameter, valve height, and leaflet free-edge length and height in competent valves.
2.1. Valve sparing in patients Ten consecutive patients from three different centers (the Mayo Clinic, Rochester, Minnesota; the Carolinas Medical Center, Charlotte, North Carolina; and the University of Essen, Germany) were studied. The patients had aortic regurgitation ranging from mild to severe. Table 1 lists their preoperative valve dimensions obtained from tranesophageal echography (TEE). The dimensions are the average of at least three measurements. The annulus diameter (Fig. 1a), the STJ diameter, and the leaflet height were measured to within ±1 mm. The uncertainty on the leaflet free-edge length and the sinus height was higher because of the limitations inherent to TEE imaging. The patients underwent aortic valve sparing surgery and received 24–28 mm Robicsek-Thubrikar sinus graft prostheses [10]. The surgeons did not follow other groups' rules for graft sizing; they relied on their experience and expertise instead. The graft size was assessed by estimating the diameter of the circle encompassing the three commissures after the aortic root was scalloped and the commissures were gently pulled up and brought together until the leaflets coapted. The size was chosen closest to the Dacron tube graft diameter available (i.e. 24, 26, 28, 30 mm), knowing that for the Robicsek-Thubrikar graft, the postoperative STJ diameter is about 2 mm larger than the graft.
2.2. Valve sparing in physical models of the patients' valves Based on the preoperative dimensions, experimental models were built for seven representative patients. To approximate the dilated aortic root seen in each patient, a conduit with sinuses was built from Dacron graft material and assembled with a 4-0 polypropylene suture. The portion of the graft corresponding to the ascending aorta down to STJ was created by making a tapered cylinder out of Dacron graft fabric. The taper was designed to replicate the difference in diameter measured between STJ and the ascending aorta at about 1 cm above the commissures. The wider end was scalloped for attachment of the three aortic sinuses. The graft distal end was prepared for cannulation at 4–6 cm above the STJ. The graft was attached onto a porcine root chosen to match the annulus diameter found in the patient. At least 10 mm of tissue of the outflow tract below the leaflet attachment was preserved for cannulation. The aortic wall was trimmed 4–5 mm above the commissures and scalloped parallel to the leaflet attachment. The original porcine leaflets were cut away. Based on the leaflet height and free edge length found in the patient, three semi-lunar leaflets of corresponding dimensions were cut from porcine pericardium fixed in 10% formalin. The leaflets were sutured onto the trimmed porcine aortic root with a 5-0 polypropylene suture, following the original attachment line. The dynamics of each model (Fig. 1b, Video 1) were studied in a left-heart simulator (ViVitro System, Vancouver, Canada). The pump was operated at an aortic pressure range of 120/80 mmHg, a rate of 72 bpm, and an output of 4 l/min. The apparatus was filled with 38% glycerol to simulate blood viscosity. An endoscopic camera was used for visual inspection of the leaflets (Fig. 1c, Video 1) and an external ultrasound color Doppler probe was used to evaluate the regurgitant flow.
2.2.1. Valve sparing without altering the leaflets (conventional procedure) Each graft representing a dilated aortic root was removed by cutting the sutures holding it in place. A new graft was created with three sinuses and attached to the porcine aortic root base with the pericardium leaflets. The graft was sized as described above in the patients. The valve was checked for proper closure under 0 mmHg pressure. The dynamics of the valves were again studied in the left-heart simulator. Special attention was paid to any sign of valve incompetence, and the regurgitant volume was measured when present. 2.3. Testing the predictive models Parallel to the experimental work, we analyzed by computer the functionality of combinations of various annulus diameters, STJ diameters, valve heights, and leaflet free-edge lengths and heights, using our 3D geometric model of the aortic valve [9]. Tables with predicted dimensions for competent valves were established for annulus diameters between 24 and 30 mm.When conventional valve sparing was successful in the physical models of aortic root aneurysms with regurgitation, the effective valve dimensions were simply compared to those listed in the predictive tables; when valve sparing failed, the predicted dimensions were applied as follows. The aortic root graft was first detached from the porcine valve. If shortening of the leaflet free edge length was needed, the leaflets were plicated at each commissure. Finally, the graft was sutured back on, and the dynamics of the spared valves were studied in the left-heart simulator.
3.1. Valve sparing in patients In eight out of ten patients, the regurgitation was reduced after valve sparing, yet no valve was completely competent (Table 1). One valve sustained severe prolapse and had to be replaced with a mechanical valve. Six of ten patients received aortic grafts without any modification to their original leaflet dimensions. Four patients required shortening of the leaflet free edge to reduce the important regurgitation present upon graft placement. 3.2. Valve sparing in physical models of the patients' valves The seven physical models of aneurysmal aortic roots and valves mounted in the left-heart simulator exhibited central holes (Fig. 1c) and were found to have regurgitant characteristics similar to those in the patients. After conventional valve sparing, all the valves in the models showed residual regurgitation. The bottom part of Table 1 lists dimensions as they were applied to achieve valve competence. Depending on the case, changes (noted in brackets) affected the annulus diameter, the leaflet free-edge length and/or the graft size. Patient 13's model presents an especially interesting case where annuloplasty as well as leaflet shortening had to be carried out to eliminate regurgitation (Fig. 2).
3.3. Predictive models Table 2 shows the dimensions predicted for normal valve function and can be read using measurements made during the operation: suppose the annulus diameter is 26 mm, and the average values of the leaflet height and free-edge length are about 19 mm and 33 mm, respectively. From the table, the associated commissural diameter is 28 mm (under pressure), which means that a size 26 sinus graft would give good results. If the free edge of the leaflets had lengthened out of proportion, Table 2 indicates that it should be brought down to about 33 mm.
How does the surgeon choose the graft size, how does he/she know when to shorten the leaflets, and how much leaflet correction is needed? A lot of decisions have to be made by surgeons based on their expertise, as there is currently no way to assess if the valve will work properly after valve sparing. Many studies report residual or progressing regurgitation after valve sparing, irrespective of the surgical technique used; the results in our patients follow the same lines (Table 1). These observations point to changes that must have occurred in the patients' valves, and indeed, we showed in a previous study that their leaflets may look anatomically normal but may not be geometrically normal [8]. Therefore, valve sparing should account for all the geometric changes that have happened in the patients' valves, and quantitative guidance for resizing is needed. The physical models of the patients' dilated roots and valves that were built for this study provided unique benchmarks to test different dimensional modifications to be made to incompetent valves according to our 3D geometric model [9]. Briefly, the values in Table 2 ensure that the spared valve offers little or no resistance to blood flow in open position, and proper sealing capabilities in closed position; also, safety margins were included to account for the idealized elastic behavior of the valve tissue. Consequently, three-dimensional modeling of the aortic valve offers a more comprehensive solution to dimensioning it than proportionality factors [11,12]. The physical models helped confirm that in some cases, there is no alternative to reducing the leaflet free-edge length for successful surgery. Most importantly, they demonstrated that the dimensions provided in Table 2 can be used to restore aortic valve competence. Obviously, resizing could be performed in all types of potential patients, whether Marfan or not, although the tissue degradation in Marfan patients is likely to entail distensions and require earlier re-operation. Fragile leaflets may also forbid valve sparing in the first place. These very problems may explain why in Patient 15, dimensions that succeeded in the lab, and found to be correct according to the geometric model, actually failed in the operating room. Nevertheless, we believe that restoration of proper valve dimensions is the crucial step that directly conditions the success of the valve sparing procedure. In the present study, the graft size was typically 2 mm smaller than the restored STJ diameter. The sizes of other grafts may differ in their relationship to the STJ diameter when pressurized and such information can be integrated easily. The measurement accuracy from TEE recordings in the patients was limited, but the good match between the original valves and the physical models demonstrated the models' ability to reproduce the dynamics and regurgitant characteristics of the patients' valves. It also validated the choice of pericardium – although stiffer than native tissue – to construct the valve leaflets in the physical models.While Table 2 can be used with valve dimensions assessed from TEE for surgical planning, it is meant to be used with intraoperative measurements, when the leaflets can be measured directly e.g. with a flexible ruler. However, their flimsiness and elasticity are a challenge. The leaflets in a real valve are also known to be unequal; therefore averaging is needed, as well as reliance on the safety margins built into Table 2 [9]. Although only seven physical models were studied, they were thoroughly investigated and confirmed the predicted results from the geometric models over a range of valve dimensions. Yet, as a next step, we would recommend multicenter trials to test our proposed quantitative approach in the clinical arena to establish a standardized technique for restoration of functional valve geometry and improve the outcome of aortic valve sparing.
The authors express their gratitude to Prof. Dr. med. H. Jakob, of the Clinic for Thoracic and Cardiovascular Surgery, University of Essen, Germany, and to Dr. K.J. Zehr, of the Mayo Clinic, Rochester, Minnesota, USA, for their collaboration with valve sparing in patients.
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Abstract
1. Introduction
