Asian Cardiovasc Thorac Ann 1998;6:162-165
© 1998 Asia Publishing EXchange Pte Ltd
In Vitro Self-Training in the Surgical Technique of Aortic Valve Repair and Reconstruction
Luo Hong He, MD,
Choo Suk Jung, MD,
James H Oury, MD,
Carlos MG Duran, MD, PhD
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The International Heart Institute of Montana Foundation Missoula, MT, USA
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For reprint information contact: Carlos MG Duran, MD, PhD The International Heart Institute of Montana Foundation 554 West Broadway Avenue Missoula, MT 59802, USA Tel:1 406 329 5668 Fax:1 406 329 5880 Email: duran{at}montana.com
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ABSTRACT
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A simple device for in vitro assessment of aortic surgery on an isolated heart or aortic root specimen is described. This device was designed as a simple tool to provide surgeons with immediate and direct visual feedback on the results of a procedure performed on the aortic valve in an isolated cardiac specimen. The objectives were to assess the duration of learning new aortic surgical procedures and to instill a greater sense of confidence to the surgeon prior to operating on a patient. Free-hand pericardial aortic valve reconstructions were performed on 9 pig hearts and 5 human homografts, which were tested with this device. In the pig, valve reconstruction was tested using the whole heart as well as the isolated aortic root. Detailed qualitative and quantitative assessments of the performance of the reconstructed aortic valve were possible using this device.
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INTRODUCTION
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Aortic valve repairs and reconstructions are technically more demanding than valve replacement, which is the main drawback to their widespread application. The traditional learning method of watching surgery performed by an expert is not only limited by economic and geo-graphic factors but also lacks the personal hands-on experience. We have found that teaching workshops where the surgery is performed individually on isolated animal hearts have been useful but a method is required to evaluate the results of the procedures. We describe a simple method for visually checking the results of aortic valve surgery performed on isolated hearts, especially the results of free-hand pericardial reconstruction of the aortic valve.
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MATERIALS AND METHODS
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The study was undertaken on 2 groups of hearts. Group 1 comprised 9 whole porcine hearts and their free aortic roots. Group 2 consisted of 5 human aortic root homografts (Cryolife Inc., Atlanta, GA, USA) from donors between the ages of 17 and 47 years. The base diameters of the roots ranged from 19 to 25 mm. The aortic valves were devoid of structural or anatomic abnormalities. The cryopreserved aortic homografts were thawed in warm water according to the standard protocol. After rinsing in saline, the aortic root was truncated just proximal to the brachiocephalic trunk, well above the sino-tubular junc-tion. Measurement of the aortic diameter was made with standard Duran ball-valve obturators (Pilling Weck Inc., Fort Washington, PA, USA).
Fresh whole pig hearts were obtained from the slaughter-house and stored in a freezer at –20°C. The pig hearts were individually placed in plastic bags and thawed in a water bath at 40°C. The aorta was trimmed by transecting the ascending aorta at the level of its bifurcation into the brachiocephalic trunk and arch. Both coronary arteries were subsequently tied. The aortic valve was exposed by a transverse aortotomy after which the respective coronary orifices and sinuses were identified. After proper exposure, the cusps were excised and the aortic diameter was measured with the Duran ball-valve obturators. A piece of bovine pericardium was then fixed in 0.625% (v/v) glutaraldehyde for 10 minutes after being placed over a template for constructing a shaped pericardial tricuspid valve.1,2 Selection of the appropriate mold size was determined by the aortic valve diameter. Details of the surgical implantation technique have been published elsewhere.3 After completion of the procedure, the recon-struction was evaluated by gross overall appearance and the degree of redundancy of the pericardial tissue. Each pig aortic root was checked twice: as a whole heart and after excising an isolated free root. The whole heart or free root was then connected to a specially designed viewer and circuit to assess the closing function of the aortic valve under constant pressure (Figure 1
). The viewer was a hollow chamber constructed of translucent acrylic plastic with two confluent side-branches.4 Silicone tubing of the desired length was interposed between a pressure-regulated faucet and the proximal side-branch of the viewer. The distal limb was tied to the distal ascending aorta with polyester tapes. The viewing surface of the acrylic chamber opposite the aortic valve was flat so that the morphology of the aortic leaflets could be observed. Intra-aortic pressure was maintained at a constant level above 100 mm Hg.
Gross assessment was made for: (1) leaflet coaptation; (2) the presence of a central defect; (3) bending of the leaflet free-edge towards the corresponding sinuses; (4) leakage; (5) a regurgitant jet; (6) a pressure decrease. Aortic roots were evaluated from both aortic and ventri-cular aspects (Figures 2 and 3). Qualitative assessment of valve regurgitation was performed in both groups using the following criteria. None: no detectable fluid leakage and no pressure decrease. Trace: fluid dripping between valve leaflets but a minimal pressure decrease. Mild: steady leakage through the valve but pressure drop could be prevented with increased inflow. Moderate: almost unhindered leakage of fluid through the valve and the degree of regurgitation was such that even with increased inflow, pressure continued to drop. Severe: unhindered leakage of fluid through the valve leaflets and the implanted valve was unable to maintain pressure regardless of inflow. Quantitative assessment of valve regurgitation was performed only in group 2 (human aortic roots) by measuring the regurgitant volume during 1 minute.
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Figure 2. Appearance in the aortic aspect of a free-hand pericardial total aortic valve reconstruction in a human aortic root as seen through the viewer.
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Figure 3. Free-hand pericardial total valve reconstruction in a human aortic root specimen shown from the left ventricular aspect.
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RESULTS
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The results of the findings in group 1 are summarized in Table 1. All the reconstructed valves had a good gross appearance before they were viewed under pressure. The pericardial mold in pig heart no. 2 was one size smaller than the measured aortic diameter because the maximum pericardial mold size available was 29 mm and the aortic diameter was 31 mm. The remaining pig hearts had pericardial aortic valve reconstruction using pericardial templates matched for size. On qualitative assessment, the coaptation looked good in all specimens with the exception of one valve (no. 5). Backward leaflet bending was observed in 7 hearts, occurring in the right cusp in 5 of them. Central defects in leaflet coaptation were present in 4 hearts that had a central jet of regurgitation. Only one heart showed a total absence of regurgitation. Regurgitation was classified as trace in 3 hearts, mild in 3, and moderate in 2.
The findings in group 2 are summarized in Table 2. In all cases, the size of the pericardial template matched with the aortic diameter. Gross appearances of the pericardial valve reconstructions before pressurization were good. Under pressure, coaptation was good in all specimens. Backward leaflet bending was observed in 3 roots involving the left cusp in 2 and the right cusp in the other. There were no significant central defects in any of the free-root specimens although one (no. 4) showed a pinpoint-sized central defect. On qualitative assessment, regurgitation was absent in 1 root, trace in 3, and mild in 1. The regurgitant volume was greatest in root no. 1 at 300 mL·min-1. This would be equivalent to 3.3 mL per stroke volume at a heart rate of 60 beats per minute. The amount of regurgitation in the other hearts was minute.
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DISCUSSION
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The art and craft of surgery is still learned by the method used in the middle ages. After a prolonged period of watching the master, the apprentice performs the proce-dure under supervision until considered safe to go solo. In the case of surgery on patients, errors have severe consequences. The problem is compounded in modern surgery by the continuous development of new techniques. New teaching methods are imperative. The use of animals for teaching new techniques is not morally acceptable nowadays, very expensive, and not available to most surgeons. Furthermore, some techniques require a degree of expertise that is difficult to achieve in animal models. Today, the practice of a particular technique on an isolated animal organ has become increasingly popular as reflected in the numerous workshops being held. A limitation of this system is the lack of methods to evaluate the results of the surgery in relation to the clinical situation. The method described in this study addresses surgery of the aortic valve, specifically reconstruction of the aortic valve with pericardium. This method has also been successfully applied to the techniques of homograft implantation, the Ross procedure, and the use of stentless bioprostheses.
A good appearance without pressure is not an accurate indicator of the performance of the valve under pressure. This was observed to be true for both the human and pig hearts in this study. Therefore, demonstrating the ability of the aortic valve implant to maintain pressure in a circuit such as the one described here, is essential for a more realistic evaluation of valve function.
This method provides not only an opportunity to safely learn the intricacies of a complex surgical technique, hence shortening the duration of the learning curve, but also provides visual feedback to the surgeon who can immediately appreciate his surgical skills and short-comings. The results obtained in this study highlight several points worth emphasizing. Firstly, there was a notable difference between the results of reconstructions performed in pig versus human hearts. This difference was due to the well-known presence in the pig of a muscular shelf at the base of the right coronary sinus, which affects the size of the right cusp and frequently causes bending of the free edge towards the corresponding sinus in a significantly more pronounced manner than in human specimens. Secondly, this study provided an opportunity to test the most recent design of mold for free-hand pericardial aortic valve reconstruction. The design and construction of an aortic cusp requires a balance between achieving the maximum coaptation area and avoiding excessive length that would cause it to bend towards the sinus. This problem occurred when simple cusp extensions were performed and could be detected by transesophageal echocardiography.1 This phenomenon gave rise to the development of total valve replacement, which is not easier to perform correctly but avoids the problem. Finally, the degree of regurgitation detected in vitro was minimal in this study, particularly in the human specimens. Clinically, this regurgitation would be of no consequence and similar in degree to that detected after bileaflet valve replacement or a Ross procedure.5 This in vitro self-assessment tool has the potential to significantly decrease the duration of the learning curve and give the surgeon a greater sense of confidence in performing a new surgical procedure. A limitation of the method is the static nature of the observation. Dynamic studies that are possible with more complex pulse duplicators, belong more to the field of research and are outside the scope of this teaching method. The fact that the method is tested in vitro although not a guarantee that it will perform similarly in a patient, is a limitation that applies to all prostheses and techniques tested on a rig. The aim of this device is not to test the durability of the technique but its feasibility. Furthermore, normal aortic roots have been tested in this rig and showed a total absence of regurgitation whereas other repair techniques under study have shown varying degrees of insufficiency.
The advantages of this tool are that it is simple, easy to make, inexpensive, and gives reproducible results. In addition, any modifications to the surgical technique can be immediately assessed and compared and the surgeon gains a direct visual feedback of his technical performance.
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Acknowledgments
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We are grateful to Cryolife Inc., Atlanta, GA, for their generous supply of the cryopreserved human aortic root homografts.
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REFERENCES
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Duran CMG, Gometza B, Kumar N, et al. From aortic cusp extension to valve replacement with stentless pericardium. Ann Thorac Surg
1995;60:S428–32.
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Duran CMG, Gometza B, Kumar N, et al. Aortic valve replacement with free hand autologous pericardium. J Thorac Cardiovasc Surg
1995;110:511–6.[Abstract/Free Full Text]
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Duran CMG. Aortic valve repair and reconstruction. Operative Techs Cardiac Thorac Surg
1996;1:15–29.
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Duran CMG, Gunning AJ, McMillan T. A simple versatile pulse duplicator. Thorax
1964;19:503–6.[Medline]
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Gometza B, Duran CMG. Alternatives in aortic valve surgery: a comparison of mechanical (CarboMedics), bioprosthesis (Hancock II), autografts and repair. In: D'Alessandro LC, editor. Surgery. Rome: Casa Scientifica Internationale, 1995:41–54.
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ABSTRACT
INTRODUCTION
