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Aortic valve replacement with stentless porcine aortic bioprosthesis
J
THORAC CARDIOVASC SURG
1990;99:113-8
Aortic valve replacement with stentless porcine aortic bioprosthesis Twenty-nine patients were entered in a clinical trial on aortic valve replacement with a stentless glutaraldehyde-fixed porcine aortic valve. This bioprosthesis is secured to the aortic root by the same technique used for aortic valve replacement with aortic valve homografts. The functional results obtained from this operation have been most satisfactory. To assess the hemodynamic benefit of eliminating the stent of a porcine aortic valve, we matched 22 patients with a stentless porcine bioprosthesis for age, sex, body surface area, valve lesion, and bioprosthesis size to 22 patients who had aortic valve replacement with a Hancock Il bioprosthesis. Mean and peak systolic gradients across the aortic bioprosthesis and effective aortic valve areas were obtained by Doppler studies. Gradients across the stentless bioprosthesis were significantly lower than gradients across the Hancock Il valve for every bioprosthesis size. Effective aortic valve areas of the stentless bioprosthesis were significantly larger thaR the valve areas of the Hancock Il valve. Our data demonstrate that the hemodynamic characteristics of a glutaraldehyde-fixed porcine aortic bioprosthesis are greatly improved when the aortic root is used as a stent for the valve. This technique of implantation is expected to enhance the durability of the bioprosthesis, because the aortic root may dampen the mechanical stress to which the leaflets are subjected during the cardiac cycle.
Tirone E. David, MD,Charles Pollick, MD (by invitation), and Joanne Bos, RN (by invitation), Toronto, Ontario, Canada
Currently availablemechanicalor biologic heart valves used for aortic valvereplacement cause differentdegrees of obstruction to blood flow because the effective orifice of a prostheticvalveis alwayssmaller than the crosssection of the left ventricular outflowtract. Aortic valvereplacement with porcine bioprostheses may leave unacceptablegradientswhenthe sizeof the bioprosthesis isnot properly matched to the sizeof the patient. 1-3 During the past decade,severalmodifications have been made in the method of fixation of the porcine aortic valveand in the design and composition of the stents to improvetheir hemodynamic performanceand their durability.v 5 Despite these changes, the hemodynamic characteristics have improved only slightly." From the Division of Cardiovascular Surgery of the Toronto Western Hospital and the University of Toronto, Toronto, Ontario, Canada. Supported by a grant from the Heart and Stroke Foundation of Ontario. Read at the Sixty-ninth Annual Meeting of The American Association for Thoracic Surgery, Boston, Mass., May 8-10,1989. Address for reprints: T. E. David, MD, 200 Elizabeth St., Toronto, Ontario M5G 2C4, Canada.
12/6/16326
In the quest for a better bioprosthesis, wei have replaced the aortic valve of sheep with a stentless glutaraldehyde-fixed porcine aortic valve. Because the functional results have been satisfactory, we believed it was reasonable to begin a clinical trial. This article describesour experiencewith aortic valve replacement with a stentless porcine aortic valve and comparesits hemodynamicperformance to that of a new generationof commerciallyavailable porcinebioprostheses. Material Stentless porcine aortic valve. The stentless porcine aortic valve used in this study was manufactured by Johnson & Johnson Cardiovascular Products (presently owned by Medtronic Inc., Minneapolis, Minn.) according to our specifications. The porcine aortic valve was fixed with glutaraldehyde under low pressure (1.5 to 2.0 mm Hg) and treated with sodium dodecyl sulfate to retard calcification.Sf The coronary sinuses and subannular tissues of the valve were trimmed down to approximately 1.5 to 2.0 mm from the base of the leaflets, and the outside arterial wall was thinned slightly and covered with a Dacron cloth. Three colored stitches were placed in the inflow of the valve at 120 degrees equidistant from one another to facilitate the distribution of sutures during implantation (Fig. 1). Hancock II bioprosthesis. The Hancock II bioprosthesis
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by the eth icscommittee of our institution. Informed consent was obtained from everyone of the 29 patients who have received this bioprosthesis. There were 15 men and 14 women whose mean age was 57.7 years, with a range from 26 to 72. The preoperative electrocardiogram revealed sinus rh ythm in 24 patients, atrial fibrillation in four, and complete heart block with a permanent transvenou s pacemaker in one pat ient. Only two patients were in New York Heart Associat ion functional class I, six were in class II, 11 were in class III, and 10 were in class IV. The predominant aortic valve lesion was stenosis in 18 patients, insufficiency in 10, and failed aortic bioprosthesis in one. Six patients also had mitral valve disease and 10 patients had coronary artery disease. All 29 patients had aortic valve replacement with a stentless porcine aortic valve. In addition, four patients had mitral valve repair, two patients had mitral valve replacement, and 10 patients had coronary artery bypass. One patient also had repair of a large abdominal aortic aneurysm at the same operation for aortic valve replacement and coronary artery bypass. The stentless porcine aortic valve was secured in the subcoronary position by the same techn ique as the one used for aortic valve homografts. The inflow area of the valve was sutured with interrupted 4-0 multifilament polyester suture in patients with a small aortic anulus and with a continuous running 3-0 polypropylene suture in the others. The second layer of sutures was always done with runn ing 3-0 or 4-0 polypropylene. The outside diameter ofthe stentless porcine aortic valve was 19 mm in one patient, 21 mm in three, 22 mm in one, 23 mm in five,25 mm in nine, 27 mm in four, and 29 mm in six patients . As part of the study protocol, all patients are interviewed and examined 3 and 6 months postoperati vely and a nnually thereafter. A Doppler echocardiographic stud y is obtained at every postoperative visit. Echocardiographic analysis of the leaflets of the valve and pulse, continuous-wave, and color Doppler studies are used for hemodynamic assessment of its function. Mean aortic valve gradient is obtained by planimetry. Peak systolic gradient across the bioprosthesis is calculated by the modified Bernoulli equation: Gradient = 4 V.V., where v is the maximum velocity across the aortic valve.? The aortic valve area is calculated by the continuity equation.'?
Results
Fig. 1. Stentless glutaraldehyde-fixed porcine aortic valve.
(Hancock Extracorporeal Inc., Anaheim, Calif.) differs from its older models in several aspects: It is fixed under low pressure, it is treated with sodium dodecyl sulfate, it is mounted in a Delrin stent (in the original Hancock valve the stent is made of polypropylene), a nd the sewing ring is supraannular in the prosthesis used for aortic valve replacement (Fig . 2).
Patients and methods A clinical trial on aortic valve replacement with stentless porcine aortic valves was initiated in October 1987 after approval
One patient had a cardiac arrest a few hours 'a fter the operation and could not be resuscitated. This patient had isolated aortic valve replacement and received a 23 mm stentless porcine aortic bioprosthesis. Autopsy findings suggested papillary muscle infarction as the cause of death. Two patients had low cardiac output syndrome after the operation and required inotropic and intraaortic balloon pump support. In one of these two patients, ischemia of the leg necessitated removal of the balloon pump and arterial thrombectomy. Anterior compartment syndrome and permanent foot drop further developed in this patient. The remaining patients had an uneventful postoperative course. All patients have been observed from 7 to 22 months (mean 12). No patient has had evidence of thromboembolic events or infective endocarditis. All patients had symptomatic improvement-25 patients to class I and three to class II.
Volume 99 Number 1 January 1990
Although an aortic diastolic murmur was audible in only one patient, Doppler studies indicate trivial or mild aortic insufficiency in five. Table I summarizes the Doppler hemodynamic assessment of the stentless bioprostheses of sizes 21 through 29 mm performed 3 months postoperatively. Because only one patient had a 19 mm valve (Doppler area of 1.56 cm-) and one a 22 mm valve (Doppler area of 1.1 cm-), they were not included in Table I. Comparative studies. To compare the hemodynamic performance of this stentless porcine aortic valve, we matched 22 patients for age, sex, predominant valve lesion, body surface area, and bioprosthesis size to patients who had had aortic valve replacement with the Hancock II bioprosthesis. The operation in this cohort of 22 patients was performed at our institution during the 2 most recent years. Six patients had undergone aortic valve replacement with enlargement of the aortic anulus, two had also had mitral valve repair, and eight had had myocardial revascularization. Most were asymptomatic after aortic valve replacement after a mean follow-up period of 11 months. None of these patients has Doppler echocardiographic evidence of aortic insufficiency. Because the majority of patients with a stentless porcine aortic bioprosthesis had at least two postoperative Doppler echocardiographic studies and most patients with a Hancock II valve had only one, we chose those studies done at approximately the same length of time from the operation. Each Doppler study was carefully reviewed by an experienced echocardiographer, and mean and peak gradients and aortic valve areas were calculated and recorded" 10Doppler cardiac outputs were measured in each patient by the formula: CO = HR X CSA X FVI, where CO is cardiac output, HR is heart rate, CSA is cross section of the aorta, and FYI is flow velocity integral.'! Although the values obtained by this formula were high, the mean cardiac outputs of patients with stentless and stented porcine bioprostheses were similar and correlated well with body surface areas. Table II summarizes the Doppler hemodynamic data of these two groups of patients. The body surface areas and the hemodynamic data of the two groups were compared by paired t tests. The mean gradients and the peak systolic gradients across the aortic valve of patients with the stentless bioprosthesis were significantly lower than the gradients in patients with the Hancock II valve for every bioprosthesis size. The effective aortic valve areas in patients with a stentless bioprosthesis were significantly larger than the valve areas in patients with the Hancock II valve. Although the valve area of stentless porcine valves of 21 mm was larger than the valve area of the Hancock II bioprosthesis, the difference did not reach
Stentless porcine aortic bioprosthesis 1 1 5
Fig. 2. Hancock II bioprosthesis for aortic valve replacement.
statistical significance because of the small sample size (only three patients in each group). Discussion It is not surprising that a stentless porcine aortic valve has better hemodynamic performance than a stented bioprosthesis. The elimination of the stent allows for insertion of a larger porcine valve in a given patient. For instance, in a patient with an aortic anulus of precisely 26 mm, we can easily implant a stentless porcine aortic valve
The Journal of Thoracic and Cardiovascular
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Surgery
Table I. Summary of the Doppler echocardiographic studies in 26 patients with a stentless porcine aortic valve Valve size (mm) 21 23 25 27 29
No. of patients
Mean gradient (mmHg)*
3
1.54 1.64 1.80 1.93 1.88
4 9 4 6
± ± ± ± ±
0.11 0.14 0.18 0.09 0.11
1.6 5.7 4.7 2.5 2.3
± ± ± ± ±
2.8 0.9 0.2 0.3 2.7
Peak gradient (mmHg)*
Aortic valve area (em2)*
± ± ± ± ±
1.63 ± 0.15 1.71 ± 0.15 1.73 ± 0.21 1.87 ± 010 2.1 ± 0.38
7.0 13.7 12.2 8.0 6.0
5.1 2.0 5.0 3.9 1.5
BSA, Body surface area. 'Values are expressed as mean ± standard deviation.
Table II. Comparison of hemodynamic data of 22 patients with stentless porcine aortic valve and a cohort of 22 patients with a Hancock II bioprosthesis Bioprosthesis
No. of patients
Stentless 21 mm Hancock II 21 mm Stentless 23 mm Hancock II 23 mm Stentless 25 mm Hancock II 25 mm Stentless 27 mm Hancock II 27 mm Stentless 29 mm Hancock II 29 mm
3 3 4 4 6 6 4 4 5 5
BSA (m 2) 1.59 1.56 1.64 1.68 1.73 1.73 1.93 1.92 1.88 1.90
± 0.14 ± 0.08 ± 0.14 ± 0.15 ± 0.07 ± 0.13 ± 0.09 ± 0.17 ± 0.41 ± 0.27
Mean gradient (mmHg)*
Peak gradient (mmHg)*
1.6 11.6 5.7 12.0 5.0 11.0 2.5 7.7
2.8 } t 1.5 0.9 } t 3.1 3.2 } t 2.5 ± 0.3 ± 2.7
7.0 ± 5.1 } t 20.6 ± 4.0 13.7±2.0}t 24.5 ± 5.9
1.63 1.20 1.71 1.35
11.3 ± 4.1 } t 22.0 ± 5.3 8.2 ± 3.9 15.7 ± 1.8
ft
1.71 ± 0.15 1.43 ± 0.15
1.87 ± 0.10} t 1.52 ± 0.17
2.3 ± 2.7 } t 8.2 ± 1.7
6.0 ± 1.5 } t 16.2 ± 1.5
2.10 ± 0.38} t 1.57 ± 0.17
± ± ± ± ± ±
Aortic valve area (em2)* ± 0.15
± 0.21 ± 0.15}t
± 0.12
ft
'Values are expressed as mean ± standard deviation. tIndicates statistically significant difference by paired t tests.
of 27 mm external diameter. We cannot, however, implant a 27 mm Hancock II valve. Even a Hancock II valve of 25 mm may be difficult to implant because of its design and the possibility of obstructing a coronary artery orifice. In addition, the size of a glutaraldehyde-fixed porcine aortic valve in a Hancock II bioprosthesis is always smaller than the size of its sewing ring. Thus, in a 21 mm Hancock II valve, the porcine valve in it corresponds to a stentless 19 mm valve; in a 23 mm Hancock II valve;the porcine valve correspondes to a stentless valve of 21 mm, and the difference becomes greater in larger bioprostheses: In a Hancock II valve of 29 mm external diameter, the porcine valve corresponds to a stentless valve of 25 mm external diameter. It is considerably more difficult to implant a stentless porcine aortic valve than a stented one. It is easier, however, to implant a stentless porcine aortic valve than an aortic valve homograft. The firmness of the fixed tissue coupled with the covering cloth on its outside wall facilitates the suturing of the valve and the alignment of the commissures in the aortic root. Thus one may argue that the hemodynamic advantage of this stentless valvemaybe outweighed by the potential clinical problems related to its implantation. Indeed, we believe that, as with aortic valve homografts, there is a learning curve and the first
few patients of a series may be left with an incompetent aortic valve bioprosthesis. Five of our 28 patients had evidence of mild aortic insufficiency by Doppler echocardiography. This may reflect inappropriate coaptation of the leaflets resulting from incorrect alignment of the commissures or inadequate leaflet tissue to cover the aortic orifice. We have learned that oversizing the aortic valve heterograft usually corrects this problem. The durability of bioprostheses is perhaps a more important issue than their hemodynamic performance. At 10 years, approximately 20% to 30% of the porcine aortic bioprostheses implanted in the aortic position will have failed. I2, 13 Infection, calcification, and leaflet disruption are the most common causes of bioprosthetic valve failure. 14 Although the biologic reactions of the host may adversely affect the durability of the bioprosthesis,I5, 16 mechanical stress is an important determinant in bioprosthetic valve failure.F'!" The stress is greatest along the leaflet attachments and it decreases from the commissures to the base of the leaflets.'? Leaflet calcification, perforation, and disruption occur predominantly along the attachments to the commissural regions. 14, 19 Several factors affect the magnitude of the mechanical stress on the leaflets of a bioprosthesis.P: 21 A flexiblestent is believed to decrease the mechanical stress on the
Volume 99 Number 1 January 1990
leaflets.P The material and the design of the stent also appear to be important factors." At the present time, there is no perfect stent for bioprostheses. The clinical experience with bioprostheses far exceeds our knowledge of the complex relationships of tissue properties, stents, and valve design. The aortic root is probably the best stent for the aortic valve. The anatomy and function of the aortic anulus and coronary sinuses are such that they may dampen the mechanical stress to which the leaflets ofthe aortic valve are subjected during the cardiac cycle. This hypothesis is supported by clinical experience with aortic valve homografts. Hand-sewn aortic valve homografts in the aortic root are significantly more durable than stent-mounted aortic valve homografts used for aortic valve replacement.Pv" The average time for aortic valve homograft failure is approximately 12 years when they are hand-sewn and 8 years when they are mounted in a stent.? Interestingly, the average time for failure of a stented porcine aortic valve used in the aortic position is also 8 years. 12,13,22 Aortic valve replacement with stentless aortic valve heterografts is by no means a new idea. Binet and associatese' first reported their experience with five patients who underwent aortic valve replacement with stentless pig and calf aortic valves in an article titled "Heterologous Aortic Valve Transplantation," published in 1965. O'Brien and Clarebrough-' began to replace the aortic valve with stentless formaldehyde-preserved porcine and bovine aortic valves in 1966. With the development of tissue fixation with glutaraldehyde, porcine aortic valves became commercially available already mounted in a frame and the interest in stentless aortic valve heterografts vanished. The renewed interest in aortic valve homografts and the associated problems in procurement prompted us to begin to search for ways to improve the hemodynamic characteristics and durability of the glutaraldehyde-fixed porcine aortic valve. We believe that securing a bioprosthetic aortic valve directly to the aortic root without a stent prolongs its durability. This technique has merit and warrants-further investigation. It is reasonable to assume that the anatomy of the normal aortic valve represents the optimal adaptation for its function and, therefore, any operative procedure that closely mimics anatomic and functional principles should provide better clinical results. We are thankful to Dr. A. Kerwin for his assistance in the preparation of this manuscript.
REFERENCES 1. Pelletier C, Chaitman BR, Baillot R, Val PG, Bonan R, Dyrda I. Clinical and hemodynamic results with Carpenti-
Stentless porcine aortic bioprosthesis 1 1 7
er-Edwards porcine bioprosthesis. Ann Thorac Surg 1982;34:612-24. 2. Jones EL, Craver JM, Morris DC, eta!. Hemodynamic and clinical evaluation of the Hancock xenograft bioprosthesis for aortic valve replacement (with emphasis on management of the small aortic root). J THORAC CARDIOVASC SURG 1978;75:300-8. 3. David TE, Uden DE. Aortic valve replacement in adult patients with small aortic annuli. Ann Thorac Surg 1983;36:577-83. 4. Carpentier A, Dubost C, Lane E, et a!. Continuing improvement in valvular prostheses. J THORAC CARDIOVASC SURG 1982;83:27-42. 5. Wright JTM, Eberhardt CE, Gibbs ML, Saul T, Gilpin CB. Hancock II-an improved bioprosthesis. In: Cohn LH, Gallucci V, eds. Cardiac bioprostheses: proceedings of the Second International Symposium. New York: Yorke Medical Books, 1982:425-44. 6. Cosgrove DM, Lytle BW, Gill CC, et a!. In vivo hemodynamic comparison of porcine and pericardial valves. J THORAC CARDIOVASC SURG 1985;89:358-68. 7. David TE, Ropchan GC, Butany JW. Aortic valve replacement with stentless porcine bioprostheses. J Cardiac Surg 1988;3:501-5. 8. JonesM, Eidbo EE, Walters SM, Ferrans VJ, Clark RE. Effects of 2 types of preimplantation processes on calcification of bioprosthetic valves. In: Bodnar E, Yacoub M, eds. Biologic bioprosthetic valves-proceedings of the Third International Symposium. New York: Yorke Medical Books, 1986:451-9. 9. Currie PJ, Seward JB, Reeder GS, Vlietstra RE, et a!. Continuous-wave Doppler echocardiographic assessment of severity of calcific aortic stenosis: a simultaneous Doppler-catheter correlative study in 100 adult patients. Circulation 1985;71:1162-9. 10. Skjaerpe T, Hegrenaes L, Hade L. Non-invasive estimation of valve area in patients with aortic stenosis by Doppler ultrasound and two-dimensional echocardiography. Circulation 1985;72:810-8. II. Labovitz AJ, Buckingham TA, Habermehl K, et a!. The effects of sampling site on the two-dimensional echo-Doppler determination of cardiac output. Am Heart J 1985;109:327-32. 12. Magilligan DJ Jr, Kemp SR, Stein PP, Peterson E. Asynchronous primary valve failure in patients with porcine bioprosthetis aortic and mitral valves. Circulation 1987;76(Pt 2):IIII41-5. 13. Cohn LH, Allred EN, DiSesa VJ, Sawtelle K, Shermin RJ, Collins JJ Jr. Early and late risk of aortic valve replacement. J THORAC CARDIOVASC SURG 1984;88:695-705. 14. Ishihara T, Ferrans VS, BoyceSW,Jones M, Roberts We. Structure and classification of cuspal tears and perforations in porcine bioprosthetic cardiac valves implanted in patients. Am J Cardiol 1981;48:665-78. 15. Rocchini AP, Weesner KM, Heildelberger K, Keren D, Behrendt D, Rosenthal A. Porcine xenograft valve failure in children: an immunologic response. Circulation 1981;64(Pt 2):11162-72.
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16. Magilligan DJ Jr, Lewis JW, Tilley B, Peterson E. The porcine bioprosthetic valve: twelve years later. J THORAC CARDIOVASC SURG 1985;89:499c507. 17. Thurbrikar M, Deck JD, Aouad J, Nolan SP. Role of mechanical stress in calcification of aortic bioprosthetic valves. J THORAC CARDIOVASC SURG 1983;86:115-25. 18. Broom ND. Fatigue-induced damage in glutaraldehydepreserved heart valve tissue. J THORAC CARDIOVASC SURG 1978;76:202-11. 19. Pomar JL, Bosch X, Chaitman BR, Pelletier C, Grondin CM. Late tears in leaflets of porcine bioprostheses in adults. Ann Thorac Surg 1984;37:78-83. 20. Reis RL, Hancock WD, Yarbrough JW, Glancy DL, Morrow AG. The flexible stent: a new concept in the fabrication of tissue heart valve prostheses. J THORAC CARDIOVASC SURG 1971;62:683-9. 21. Druxy PJ, Dobrin J, Bodnar E, Black MM. Distribution of flexibility in the porcine aortic root and in cardiac suppot frames. In: Bodnar E, Yacoub M, eds. Biologic prosthetic valves-proceedings of the Third International Symposium. New York: Yorke Medical Books, 1986:580-7. 22. Angell WW, Angell JD, Oury JH, Lamberti JJ, Grehl TM. Long-term follow-up of viable.frozen aortic homografts: a viable homograft valve bank. J THORAC CARDIOVASC SURG 1987;93:815-22. 23. Angell WW, Oury JH, Lamberti JJ, Koziol J. Durability of the viable aortic allograft. J THORAC CARDIOVASC SURG 1989;98:48-56. 24. Binet JP, Duran CG, Carpentier A, Langlois J. Heterologous aortic valve transplantation. Lancet 1965;2:1275. 25. O'Brien MF, Clarebrough JK. Heterograft aortic valve transplantation for human valve disease. Med J Aust 1966;2:228-30.
Discussion Dr. Alain F. Carpentier (Paris, France). Dr. David's paper takes me back to 1968, when I implanted the first glutaraldehyde-preserved valve. It was a stentless bovine aortic valve bioprosthesis that was inserted with a double-row suture technique to secure the lower edge and the upper edge of the valve. The patient survived 17 years with the original valve. An angiogram taken at 15 years showed normal function with a trivial and stable residual insufficiency. The use of a stentless bioprosthetic valve has one important advantage: The full flexibility of the orifice reduces the turbulence and probably also the risk of calcification because, as we have shown in the past, turbulence and shear stress are important factors in calcification. This advantage, however, is compensated by the increased difficulty of implantation. There are a number of possible technical mistakes: Improper fixation of the lower edge of the valve may lead to valve dissection; improper sizing or improper cusp orientation (or both) may lead to residual leak. As shown by Dr. David, refinement in valve mounting and technique of insertion may reduce those risks, but they cannot eliminate them. Thus the stentless valves cannot be considered usable by everyone for everyone. For this reason, in past years, we have developed the "supraannular valve concept,"
The Journal of Thoracic and Cardiovascular Surgery
which aims at adding the advantages ofstentless valves (reduced turbulence) to those of stented valves (easier implantation). I have only one question: Will the theoretical advantage of reduced turbulence compensate for the inconvenience of residualleaks after implantation? Only time can answer this question, but Dr. David should be congratulated for having raised it. Dr. Randas J. V. Batista (Curitiba, Parana, Brazil). Dr. David, I share your opinion regarding the hemodynamics and durability of the stentless aortic biologic prosthesis. For the past 6 years I have been sewing a sheath of glutaraldehyde-tanned bovine pericardium directly to the patient's aortic anulus in such a way as to form a tricuspid aortic prosthesis. I have operated on 216 patients (seven deaths). One of the last 150 patients was in septic and cardiogenic shock because of infective endocarditis and died in the intensive care unit (mortality rate 0.6%). So far, none of these prostheses has calcified. I am very much concerned about the children in whom I purposely make a larger sheath to allow further annular growth. Consequently, I have been doing experiments in young calves, and in these animals all prostheses calcified between 2 and 3 months after implantation. According to the veterinarians, 3 months in a calfs life is equivalent to 15 years in a human's. If that is true, I expect these prostheses to calcify within 15 years. You told me that in your experiments, also in calves, you do not have any calcification up to 6 months postoperatively, when the animals are put to death. What are you doing to your prostheses to have this significant difference in the rate of calcification? Dr. David. The stentless porcine aortic valve was prepared in the same manner as the Hancock II bioprosthesis. The valve is treated with sodium dodecyl sulfate, and there is evidence that this substance retards calcification in glutaraldehyde-fixed porcine aortic bioprostheses. In addition, our experimental work had to be done in 5-month to 6-month-old sheep because of the difficulty in implanting a stentless porcine aortic valve in younger animals. Thus the combination of the anticalcification treatment of the valve and the age of the animals may explain why our valves did not calcify after implantation times of 6 to 9 months. Dr. Robert W. M. Frater (Bronx, N.Y.). I have no doubt that Dr. David is moving in the right direction. I would like to show two slides indicating that there is a profound difference between glutaraldehyde-tanned tissue when it is "protected," as Dr. Carpentier calls it, by a stent, and when it is not protected. [Slide] This slide shows degenerated collagen and lipid insudation 7 years after implantation. [Slide] This slide shows an experimental animal Zva years after the tanned material was directly sutured to the aortic wall. The original material is disappearing and on each side of it is host tissue, both fibrosa and intima, which is essentially replacing the original material. I am not sure this is going to happen with your valve, Dr. David, and I am not sure you want this to happen, because you have given yourself some protection by putting it into a sheath. But I would ask if you would hope that your valve would one day be a new living valve rather than a piece of high-class leather. Dr. David. I do not believe that the glutaraldehyde-fixed porcine aortic valve will ever be replaced by the host tissues and thus become a living valve. The Dacron fabric was sewn to the outside wall of the porcine tissue to facilitate implantation and, eventually, explantation of the heterograft from the aortic root of the patient.
THORAC CARDIOVASC SURG
1990;99:113-8
Aortic valve replacement with stentless porcine aortic bioprosthesis Twenty-nine patients were entered in a clinical trial on aortic valve replacement with a stentless glutaraldehyde-fixed porcine aortic valve. This bioprosthesis is secured to the aortic root by the same technique used for aortic valve replacement with aortic valve homografts. The functional results obtained from this operation have been most satisfactory. To assess the hemodynamic benefit of eliminating the stent of a porcine aortic valve, we matched 22 patients with a stentless porcine bioprosthesis for age, sex, body surface area, valve lesion, and bioprosthesis size to 22 patients who had aortic valve replacement with a Hancock Il bioprosthesis. Mean and peak systolic gradients across the aortic bioprosthesis and effective aortic valve areas were obtained by Doppler studies. Gradients across the stentless bioprosthesis were significantly lower than gradients across the Hancock Il valve for every bioprosthesis size. Effective aortic valve areas of the stentless bioprosthesis were significantly larger thaR the valve areas of the Hancock Il valve. Our data demonstrate that the hemodynamic characteristics of a glutaraldehyde-fixed porcine aortic bioprosthesis are greatly improved when the aortic root is used as a stent for the valve. This technique of implantation is expected to enhance the durability of the bioprosthesis, because the aortic root may dampen the mechanical stress to which the leaflets are subjected during the cardiac cycle.
Tirone E. David, MD,Charles Pollick, MD (by invitation), and Joanne Bos, RN (by invitation), Toronto, Ontario, Canada
Currently availablemechanicalor biologic heart valves used for aortic valvereplacement cause differentdegrees of obstruction to blood flow because the effective orifice of a prostheticvalveis alwayssmaller than the crosssection of the left ventricular outflowtract. Aortic valvereplacement with porcine bioprostheses may leave unacceptablegradientswhenthe sizeof the bioprosthesis isnot properly matched to the sizeof the patient. 1-3 During the past decade,severalmodifications have been made in the method of fixation of the porcine aortic valveand in the design and composition of the stents to improvetheir hemodynamic performanceand their durability.v 5 Despite these changes, the hemodynamic characteristics have improved only slightly." From the Division of Cardiovascular Surgery of the Toronto Western Hospital and the University of Toronto, Toronto, Ontario, Canada. Supported by a grant from the Heart and Stroke Foundation of Ontario. Read at the Sixty-ninth Annual Meeting of The American Association for Thoracic Surgery, Boston, Mass., May 8-10,1989. Address for reprints: T. E. David, MD, 200 Elizabeth St., Toronto, Ontario M5G 2C4, Canada.
12/6/16326
In the quest for a better bioprosthesis, wei have replaced the aortic valve of sheep with a stentless glutaraldehyde-fixed porcine aortic valve. Because the functional results have been satisfactory, we believed it was reasonable to begin a clinical trial. This article describesour experiencewith aortic valve replacement with a stentless porcine aortic valve and comparesits hemodynamicperformance to that of a new generationof commerciallyavailable porcinebioprostheses. Material Stentless porcine aortic valve. The stentless porcine aortic valve used in this study was manufactured by Johnson & Johnson Cardiovascular Products (presently owned by Medtronic Inc., Minneapolis, Minn.) according to our specifications. The porcine aortic valve was fixed with glutaraldehyde under low pressure (1.5 to 2.0 mm Hg) and treated with sodium dodecyl sulfate to retard calcification.Sf The coronary sinuses and subannular tissues of the valve were trimmed down to approximately 1.5 to 2.0 mm from the base of the leaflets, and the outside arterial wall was thinned slightly and covered with a Dacron cloth. Three colored stitches were placed in the inflow of the valve at 120 degrees equidistant from one another to facilitate the distribution of sutures during implantation (Fig. 1). Hancock II bioprosthesis. The Hancock II bioprosthesis
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David. Pollick. Bos
Thoracic and Cardiovascular Surgery
by the eth icscommittee of our institution. Informed consent was obtained from everyone of the 29 patients who have received this bioprosthesis. There were 15 men and 14 women whose mean age was 57.7 years, with a range from 26 to 72. The preoperative electrocardiogram revealed sinus rh ythm in 24 patients, atrial fibrillation in four, and complete heart block with a permanent transvenou s pacemaker in one pat ient. Only two patients were in New York Heart Associat ion functional class I, six were in class II, 11 were in class III, and 10 were in class IV. The predominant aortic valve lesion was stenosis in 18 patients, insufficiency in 10, and failed aortic bioprosthesis in one. Six patients also had mitral valve disease and 10 patients had coronary artery disease. All 29 patients had aortic valve replacement with a stentless porcine aortic valve. In addition, four patients had mitral valve repair, two patients had mitral valve replacement, and 10 patients had coronary artery bypass. One patient also had repair of a large abdominal aortic aneurysm at the same operation for aortic valve replacement and coronary artery bypass. The stentless porcine aortic valve was secured in the subcoronary position by the same techn ique as the one used for aortic valve homografts. The inflow area of the valve was sutured with interrupted 4-0 multifilament polyester suture in patients with a small aortic anulus and with a continuous running 3-0 polypropylene suture in the others. The second layer of sutures was always done with runn ing 3-0 or 4-0 polypropylene. The outside diameter ofthe stentless porcine aortic valve was 19 mm in one patient, 21 mm in three, 22 mm in one, 23 mm in five,25 mm in nine, 27 mm in four, and 29 mm in six patients . As part of the study protocol, all patients are interviewed and examined 3 and 6 months postoperati vely and a nnually thereafter. A Doppler echocardiographic stud y is obtained at every postoperative visit. Echocardiographic analysis of the leaflets of the valve and pulse, continuous-wave, and color Doppler studies are used for hemodynamic assessment of its function. Mean aortic valve gradient is obtained by planimetry. Peak systolic gradient across the bioprosthesis is calculated by the modified Bernoulli equation: Gradient = 4 V.V., where v is the maximum velocity across the aortic valve.? The aortic valve area is calculated by the continuity equation.'?
Results
Fig. 1. Stentless glutaraldehyde-fixed porcine aortic valve.
(Hancock Extracorporeal Inc., Anaheim, Calif.) differs from its older models in several aspects: It is fixed under low pressure, it is treated with sodium dodecyl sulfate, it is mounted in a Delrin stent (in the original Hancock valve the stent is made of polypropylene), a nd the sewing ring is supraannular in the prosthesis used for aortic valve replacement (Fig . 2).
Patients and methods A clinical trial on aortic valve replacement with stentless porcine aortic valves was initiated in October 1987 after approval
One patient had a cardiac arrest a few hours 'a fter the operation and could not be resuscitated. This patient had isolated aortic valve replacement and received a 23 mm stentless porcine aortic bioprosthesis. Autopsy findings suggested papillary muscle infarction as the cause of death. Two patients had low cardiac output syndrome after the operation and required inotropic and intraaortic balloon pump support. In one of these two patients, ischemia of the leg necessitated removal of the balloon pump and arterial thrombectomy. Anterior compartment syndrome and permanent foot drop further developed in this patient. The remaining patients had an uneventful postoperative course. All patients have been observed from 7 to 22 months (mean 12). No patient has had evidence of thromboembolic events or infective endocarditis. All patients had symptomatic improvement-25 patients to class I and three to class II.
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Although an aortic diastolic murmur was audible in only one patient, Doppler studies indicate trivial or mild aortic insufficiency in five. Table I summarizes the Doppler hemodynamic assessment of the stentless bioprostheses of sizes 21 through 29 mm performed 3 months postoperatively. Because only one patient had a 19 mm valve (Doppler area of 1.56 cm-) and one a 22 mm valve (Doppler area of 1.1 cm-), they were not included in Table I. Comparative studies. To compare the hemodynamic performance of this stentless porcine aortic valve, we matched 22 patients for age, sex, predominant valve lesion, body surface area, and bioprosthesis size to patients who had had aortic valve replacement with the Hancock II bioprosthesis. The operation in this cohort of 22 patients was performed at our institution during the 2 most recent years. Six patients had undergone aortic valve replacement with enlargement of the aortic anulus, two had also had mitral valve repair, and eight had had myocardial revascularization. Most were asymptomatic after aortic valve replacement after a mean follow-up period of 11 months. None of these patients has Doppler echocardiographic evidence of aortic insufficiency. Because the majority of patients with a stentless porcine aortic bioprosthesis had at least two postoperative Doppler echocardiographic studies and most patients with a Hancock II valve had only one, we chose those studies done at approximately the same length of time from the operation. Each Doppler study was carefully reviewed by an experienced echocardiographer, and mean and peak gradients and aortic valve areas were calculated and recorded" 10Doppler cardiac outputs were measured in each patient by the formula: CO = HR X CSA X FVI, where CO is cardiac output, HR is heart rate, CSA is cross section of the aorta, and FYI is flow velocity integral.'! Although the values obtained by this formula were high, the mean cardiac outputs of patients with stentless and stented porcine bioprostheses were similar and correlated well with body surface areas. Table II summarizes the Doppler hemodynamic data of these two groups of patients. The body surface areas and the hemodynamic data of the two groups were compared by paired t tests. The mean gradients and the peak systolic gradients across the aortic valve of patients with the stentless bioprosthesis were significantly lower than the gradients in patients with the Hancock II valve for every bioprosthesis size. The effective aortic valve areas in patients with a stentless bioprosthesis were significantly larger than the valve areas in patients with the Hancock II valve. Although the valve area of stentless porcine valves of 21 mm was larger than the valve area of the Hancock II bioprosthesis, the difference did not reach
Stentless porcine aortic bioprosthesis 1 1 5
Fig. 2. Hancock II bioprosthesis for aortic valve replacement.
statistical significance because of the small sample size (only three patients in each group). Discussion It is not surprising that a stentless porcine aortic valve has better hemodynamic performance than a stented bioprosthesis. The elimination of the stent allows for insertion of a larger porcine valve in a given patient. For instance, in a patient with an aortic anulus of precisely 26 mm, we can easily implant a stentless porcine aortic valve
The Journal of Thoracic and Cardiovascular
1 1 6 David, Pollick, Bos
Surgery
Table I. Summary of the Doppler echocardiographic studies in 26 patients with a stentless porcine aortic valve Valve size (mm) 21 23 25 27 29
No. of patients
Mean gradient (mmHg)*
3
1.54 1.64 1.80 1.93 1.88
4 9 4 6
± ± ± ± ±
0.11 0.14 0.18 0.09 0.11
1.6 5.7 4.7 2.5 2.3
± ± ± ± ±
2.8 0.9 0.2 0.3 2.7
Peak gradient (mmHg)*
Aortic valve area (em2)*
± ± ± ± ±
1.63 ± 0.15 1.71 ± 0.15 1.73 ± 0.21 1.87 ± 010 2.1 ± 0.38
7.0 13.7 12.2 8.0 6.0
5.1 2.0 5.0 3.9 1.5
BSA, Body surface area. 'Values are expressed as mean ± standard deviation.
Table II. Comparison of hemodynamic data of 22 patients with stentless porcine aortic valve and a cohort of 22 patients with a Hancock II bioprosthesis Bioprosthesis
No. of patients
Stentless 21 mm Hancock II 21 mm Stentless 23 mm Hancock II 23 mm Stentless 25 mm Hancock II 25 mm Stentless 27 mm Hancock II 27 mm Stentless 29 mm Hancock II 29 mm
3 3 4 4 6 6 4 4 5 5
BSA (m 2) 1.59 1.56 1.64 1.68 1.73 1.73 1.93 1.92 1.88 1.90
± 0.14 ± 0.08 ± 0.14 ± 0.15 ± 0.07 ± 0.13 ± 0.09 ± 0.17 ± 0.41 ± 0.27
Mean gradient (mmHg)*
Peak gradient (mmHg)*
1.6 11.6 5.7 12.0 5.0 11.0 2.5 7.7
2.8 } t 1.5 0.9 } t 3.1 3.2 } t 2.5 ± 0.3 ± 2.7
7.0 ± 5.1 } t 20.6 ± 4.0 13.7±2.0}t 24.5 ± 5.9
1.63 1.20 1.71 1.35
11.3 ± 4.1 } t 22.0 ± 5.3 8.2 ± 3.9 15.7 ± 1.8
ft
1.71 ± 0.15 1.43 ± 0.15
1.87 ± 0.10} t 1.52 ± 0.17
2.3 ± 2.7 } t 8.2 ± 1.7
6.0 ± 1.5 } t 16.2 ± 1.5
2.10 ± 0.38} t 1.57 ± 0.17
± ± ± ± ± ±
Aortic valve area (em2)* ± 0.15
± 0.21 ± 0.15}t
± 0.12
ft
'Values are expressed as mean ± standard deviation. tIndicates statistically significant difference by paired t tests.
of 27 mm external diameter. We cannot, however, implant a 27 mm Hancock II valve. Even a Hancock II valve of 25 mm may be difficult to implant because of its design and the possibility of obstructing a coronary artery orifice. In addition, the size of a glutaraldehyde-fixed porcine aortic valve in a Hancock II bioprosthesis is always smaller than the size of its sewing ring. Thus, in a 21 mm Hancock II valve, the porcine valve in it corresponds to a stentless 19 mm valve; in a 23 mm Hancock II valve;the porcine valve correspondes to a stentless valve of 21 mm, and the difference becomes greater in larger bioprostheses: In a Hancock II valve of 29 mm external diameter, the porcine valve corresponds to a stentless valve of 25 mm external diameter. It is considerably more difficult to implant a stentless porcine aortic valve than a stented one. It is easier, however, to implant a stentless porcine aortic valve than an aortic valve homograft. The firmness of the fixed tissue coupled with the covering cloth on its outside wall facilitates the suturing of the valve and the alignment of the commissures in the aortic root. Thus one may argue that the hemodynamic advantage of this stentless valvemaybe outweighed by the potential clinical problems related to its implantation. Indeed, we believe that, as with aortic valve homografts, there is a learning curve and the first
few patients of a series may be left with an incompetent aortic valve bioprosthesis. Five of our 28 patients had evidence of mild aortic insufficiency by Doppler echocardiography. This may reflect inappropriate coaptation of the leaflets resulting from incorrect alignment of the commissures or inadequate leaflet tissue to cover the aortic orifice. We have learned that oversizing the aortic valve heterograft usually corrects this problem. The durability of bioprostheses is perhaps a more important issue than their hemodynamic performance. At 10 years, approximately 20% to 30% of the porcine aortic bioprostheses implanted in the aortic position will have failed. I2, 13 Infection, calcification, and leaflet disruption are the most common causes of bioprosthetic valve failure. 14 Although the biologic reactions of the host may adversely affect the durability of the bioprosthesis,I5, 16 mechanical stress is an important determinant in bioprosthetic valve failure.F'!" The stress is greatest along the leaflet attachments and it decreases from the commissures to the base of the leaflets.'? Leaflet calcification, perforation, and disruption occur predominantly along the attachments to the commissural regions. 14, 19 Several factors affect the magnitude of the mechanical stress on the leaflets of a bioprosthesis.P: 21 A flexiblestent is believed to decrease the mechanical stress on the
Volume 99 Number 1 January 1990
leaflets.P The material and the design of the stent also appear to be important factors." At the present time, there is no perfect stent for bioprostheses. The clinical experience with bioprostheses far exceeds our knowledge of the complex relationships of tissue properties, stents, and valve design. The aortic root is probably the best stent for the aortic valve. The anatomy and function of the aortic anulus and coronary sinuses are such that they may dampen the mechanical stress to which the leaflets ofthe aortic valve are subjected during the cardiac cycle. This hypothesis is supported by clinical experience with aortic valve homografts. Hand-sewn aortic valve homografts in the aortic root are significantly more durable than stent-mounted aortic valve homografts used for aortic valve replacement.Pv" The average time for aortic valve homograft failure is approximately 12 years when they are hand-sewn and 8 years when they are mounted in a stent.? Interestingly, the average time for failure of a stented porcine aortic valve used in the aortic position is also 8 years. 12,13,22 Aortic valve replacement with stentless aortic valve heterografts is by no means a new idea. Binet and associatese' first reported their experience with five patients who underwent aortic valve replacement with stentless pig and calf aortic valves in an article titled "Heterologous Aortic Valve Transplantation," published in 1965. O'Brien and Clarebrough-' began to replace the aortic valve with stentless formaldehyde-preserved porcine and bovine aortic valves in 1966. With the development of tissue fixation with glutaraldehyde, porcine aortic valves became commercially available already mounted in a frame and the interest in stentless aortic valve heterografts vanished. The renewed interest in aortic valve homografts and the associated problems in procurement prompted us to begin to search for ways to improve the hemodynamic characteristics and durability of the glutaraldehyde-fixed porcine aortic valve. We believe that securing a bioprosthetic aortic valve directly to the aortic root without a stent prolongs its durability. This technique has merit and warrants-further investigation. It is reasonable to assume that the anatomy of the normal aortic valve represents the optimal adaptation for its function and, therefore, any operative procedure that closely mimics anatomic and functional principles should provide better clinical results. We are thankful to Dr. A. Kerwin for his assistance in the preparation of this manuscript.
REFERENCES 1. Pelletier C, Chaitman BR, Baillot R, Val PG, Bonan R, Dyrda I. Clinical and hemodynamic results with Carpenti-
Stentless porcine aortic bioprosthesis 1 1 7
er-Edwards porcine bioprosthesis. Ann Thorac Surg 1982;34:612-24. 2. Jones EL, Craver JM, Morris DC, eta!. Hemodynamic and clinical evaluation of the Hancock xenograft bioprosthesis for aortic valve replacement (with emphasis on management of the small aortic root). J THORAC CARDIOVASC SURG 1978;75:300-8. 3. David TE, Uden DE. Aortic valve replacement in adult patients with small aortic annuli. Ann Thorac Surg 1983;36:577-83. 4. Carpentier A, Dubost C, Lane E, et a!. Continuing improvement in valvular prostheses. J THORAC CARDIOVASC SURG 1982;83:27-42. 5. Wright JTM, Eberhardt CE, Gibbs ML, Saul T, Gilpin CB. Hancock II-an improved bioprosthesis. In: Cohn LH, Gallucci V, eds. Cardiac bioprostheses: proceedings of the Second International Symposium. New York: Yorke Medical Books, 1982:425-44. 6. Cosgrove DM, Lytle BW, Gill CC, et a!. In vivo hemodynamic comparison of porcine and pericardial valves. J THORAC CARDIOVASC SURG 1985;89:358-68. 7. David TE, Ropchan GC, Butany JW. Aortic valve replacement with stentless porcine bioprostheses. J Cardiac Surg 1988;3:501-5. 8. JonesM, Eidbo EE, Walters SM, Ferrans VJ, Clark RE. Effects of 2 types of preimplantation processes on calcification of bioprosthetic valves. In: Bodnar E, Yacoub M, eds. Biologic bioprosthetic valves-proceedings of the Third International Symposium. New York: Yorke Medical Books, 1986:451-9. 9. Currie PJ, Seward JB, Reeder GS, Vlietstra RE, et a!. Continuous-wave Doppler echocardiographic assessment of severity of calcific aortic stenosis: a simultaneous Doppler-catheter correlative study in 100 adult patients. Circulation 1985;71:1162-9. 10. Skjaerpe T, Hegrenaes L, Hade L. Non-invasive estimation of valve area in patients with aortic stenosis by Doppler ultrasound and two-dimensional echocardiography. Circulation 1985;72:810-8. II. Labovitz AJ, Buckingham TA, Habermehl K, et a!. The effects of sampling site on the two-dimensional echo-Doppler determination of cardiac output. Am Heart J 1985;109:327-32. 12. Magilligan DJ Jr, Kemp SR, Stein PP, Peterson E. Asynchronous primary valve failure in patients with porcine bioprosthetis aortic and mitral valves. Circulation 1987;76(Pt 2):IIII41-5. 13. Cohn LH, Allred EN, DiSesa VJ, Sawtelle K, Shermin RJ, Collins JJ Jr. Early and late risk of aortic valve replacement. J THORAC CARDIOVASC SURG 1984;88:695-705. 14. Ishihara T, Ferrans VS, BoyceSW,Jones M, Roberts We. Structure and classification of cuspal tears and perforations in porcine bioprosthetic cardiac valves implanted in patients. Am J Cardiol 1981;48:665-78. 15. Rocchini AP, Weesner KM, Heildelberger K, Keren D, Behrendt D, Rosenthal A. Porcine xenograft valve failure in children: an immunologic response. Circulation 1981;64(Pt 2):11162-72.
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16. Magilligan DJ Jr, Lewis JW, Tilley B, Peterson E. The porcine bioprosthetic valve: twelve years later. J THORAC CARDIOVASC SURG 1985;89:499c507. 17. Thurbrikar M, Deck JD, Aouad J, Nolan SP. Role of mechanical stress in calcification of aortic bioprosthetic valves. J THORAC CARDIOVASC SURG 1983;86:115-25. 18. Broom ND. Fatigue-induced damage in glutaraldehydepreserved heart valve tissue. J THORAC CARDIOVASC SURG 1978;76:202-11. 19. Pomar JL, Bosch X, Chaitman BR, Pelletier C, Grondin CM. Late tears in leaflets of porcine bioprostheses in adults. Ann Thorac Surg 1984;37:78-83. 20. Reis RL, Hancock WD, Yarbrough JW, Glancy DL, Morrow AG. The flexible stent: a new concept in the fabrication of tissue heart valve prostheses. J THORAC CARDIOVASC SURG 1971;62:683-9. 21. Druxy PJ, Dobrin J, Bodnar E, Black MM. Distribution of flexibility in the porcine aortic root and in cardiac suppot frames. In: Bodnar E, Yacoub M, eds. Biologic prosthetic valves-proceedings of the Third International Symposium. New York: Yorke Medical Books, 1986:580-7. 22. Angell WW, Angell JD, Oury JH, Lamberti JJ, Grehl TM. Long-term follow-up of viable.frozen aortic homografts: a viable homograft valve bank. J THORAC CARDIOVASC SURG 1987;93:815-22. 23. Angell WW, Oury JH, Lamberti JJ, Koziol J. Durability of the viable aortic allograft. J THORAC CARDIOVASC SURG 1989;98:48-56. 24. Binet JP, Duran CG, Carpentier A, Langlois J. Heterologous aortic valve transplantation. Lancet 1965;2:1275. 25. O'Brien MF, Clarebrough JK. Heterograft aortic valve transplantation for human valve disease. Med J Aust 1966;2:228-30.
Discussion Dr. Alain F. Carpentier (Paris, France). Dr. David's paper takes me back to 1968, when I implanted the first glutaraldehyde-preserved valve. It was a stentless bovine aortic valve bioprosthesis that was inserted with a double-row suture technique to secure the lower edge and the upper edge of the valve. The patient survived 17 years with the original valve. An angiogram taken at 15 years showed normal function with a trivial and stable residual insufficiency. The use of a stentless bioprosthetic valve has one important advantage: The full flexibility of the orifice reduces the turbulence and probably also the risk of calcification because, as we have shown in the past, turbulence and shear stress are important factors in calcification. This advantage, however, is compensated by the increased difficulty of implantation. There are a number of possible technical mistakes: Improper fixation of the lower edge of the valve may lead to valve dissection; improper sizing or improper cusp orientation (or both) may lead to residual leak. As shown by Dr. David, refinement in valve mounting and technique of insertion may reduce those risks, but they cannot eliminate them. Thus the stentless valves cannot be considered usable by everyone for everyone. For this reason, in past years, we have developed the "supraannular valve concept,"
The Journal of Thoracic and Cardiovascular Surgery
which aims at adding the advantages ofstentless valves (reduced turbulence) to those of stented valves (easier implantation). I have only one question: Will the theoretical advantage of reduced turbulence compensate for the inconvenience of residualleaks after implantation? Only time can answer this question, but Dr. David should be congratulated for having raised it. Dr. Randas J. V. Batista (Curitiba, Parana, Brazil). Dr. David, I share your opinion regarding the hemodynamics and durability of the stentless aortic biologic prosthesis. For the past 6 years I have been sewing a sheath of glutaraldehyde-tanned bovine pericardium directly to the patient's aortic anulus in such a way as to form a tricuspid aortic prosthesis. I have operated on 216 patients (seven deaths). One of the last 150 patients was in septic and cardiogenic shock because of infective endocarditis and died in the intensive care unit (mortality rate 0.6%). So far, none of these prostheses has calcified. I am very much concerned about the children in whom I purposely make a larger sheath to allow further annular growth. Consequently, I have been doing experiments in young calves, and in these animals all prostheses calcified between 2 and 3 months after implantation. According to the veterinarians, 3 months in a calfs life is equivalent to 15 years in a human's. If that is true, I expect these prostheses to calcify within 15 years. You told me that in your experiments, also in calves, you do not have any calcification up to 6 months postoperatively, when the animals are put to death. What are you doing to your prostheses to have this significant difference in the rate of calcification? Dr. David. The stentless porcine aortic valve was prepared in the same manner as the Hancock II bioprosthesis. The valve is treated with sodium dodecyl sulfate, and there is evidence that this substance retards calcification in glutaraldehyde-fixed porcine aortic bioprostheses. In addition, our experimental work had to be done in 5-month to 6-month-old sheep because of the difficulty in implanting a stentless porcine aortic valve in younger animals. Thus the combination of the anticalcification treatment of the valve and the age of the animals may explain why our valves did not calcify after implantation times of 6 to 9 months. Dr. Robert W. M. Frater (Bronx, N.Y.). I have no doubt that Dr. David is moving in the right direction. I would like to show two slides indicating that there is a profound difference between glutaraldehyde-tanned tissue when it is "protected," as Dr. Carpentier calls it, by a stent, and when it is not protected. [Slide] This slide shows degenerated collagen and lipid insudation 7 years after implantation. [Slide] This slide shows an experimental animal Zva years after the tanned material was directly sutured to the aortic wall. The original material is disappearing and on each side of it is host tissue, both fibrosa and intima, which is essentially replacing the original material. I am not sure this is going to happen with your valve, Dr. David, and I am not sure you want this to happen, because you have given yourself some protection by putting it into a sheath. But I would ask if you would hope that your valve would one day be a new living valve rather than a piece of high-class leather. Dr. David. I do not believe that the glutaraldehyde-fixed porcine aortic valve will ever be replaced by the host tissues and thus become a living valve. The Dacron fabric was sewn to the outside wall of the porcine tissue to facilitate implantation and, eventually, explantation of the heterograft from the aortic root of the patient.