The vanishing tricuspid annuloplasty

The vanishing tricuspid annuloplasty A new concept A tricuspid De Vega anmiloplasty with absorbable 2-0 polydioxanone sutures was performed on 16 sheep supported by cardiopulmonary bypass. The anulus diameter was reduced by 2 to 6 0101. Four sheep died perioperatively. The 12 survivors were electively killed at 2-week intervals during a period of 6 months. Infective endocarditis was not observed. At the time of death no gradient was found on simultaneous pressure measurements of the right atrium and ventricle. Epicardial echocardiography did not reveal tricuspid stenosis or regurgitation. Macroscopically there was no thrombus and the tricuspid leaflets were of a normal appearance. A thin white cord was observed at the anulus in all animals killed after 12 weeks. The annular size remained as surgically induced until the fourth month, but it reverted to its preoperative size after 5 months. Histologically there was granulation tissue initially only around the foreign material, but then progressively it appeared also between the foreign filaments, with the development of multinucleated foreign body giant cells. At approximately 5 months most of the foreign material had been disrupted or absorbed, leaving a tenuous ring of granulation tissue, which allowed expansion of the tricuspid ring to its original circumference. By 6 months most of the foreign material had disappeared and was replaced by loose collagenous tissue. The concept of a "vanishing annuloplasty" is advanced, with particular application in children and in patients with functional tricuspid insufficiency. (J THORAC CARDIOVASC SURG 1992;104:796-801)

Carlos M. G. Duran, MD, PhD,a Sengoda G. Balasundaram, MBBS, FRCS,a Stephen Bianchi, MBBS, FFARACS, FRCP(C),b and Peter Herdson, MB, ChB, PhD, FRCPA, FRACR,c Riyadh, Saudi Arabia

Enctional tricuspid regurgitation often disappears spontaneously after the correction ofleft-sided lesions. I In the presence of significant insufficiency, however, an annuloplasty is usually recommended to avoid its deleterious effect during the early postoperative period.? In an earlier study we' investigated the original concept of a time-controlled reabsorbable annuloplasty that would avoid the presence of a permanent prosthetic ring. At that time a biodegradable ring was used experimentally with unconvincing results. The present experimental study was From the Departments of Cardiovascular Diseases; Anesthesiology, b and Pathology and Laboratory Medicine," King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia. Supported in part by external grant AT-II-12 from the KingAbdulaziz City for Science and Technology, Riyadh, Saudi Arabia. Received for publication March 5, 1991. Accepted for publication Aug. 6, 1991. Address for reprints: C. M. G. Duran, MD, PhD, Department of Cardiovascular Diseases, King Faisal Specialist Hospital, P.O. Box 3354, Riyadh 11211, Saudi Arabia. 12/1/32923

796

undertaken to determine the behavior, in sheep, of a De Vega type annuloplasty created with a polydioxanone suture, which has been shown to remain intact longer. Materials and methods Sixteen sheep weighing between 30 and 45 kg were used. Under general anesthesia, with endotracheal intubation, the right internal jugular vein and the left superficial femoral artery were cannulated for pressure monitoring. The electrocardiogram and both pressures were continuously monitored throughout the procedure. Anesthesia was maintained with a mixture of oxygen, nitrous oxide, and 1% halothane. After a right thoracotomy through the fourth intercostal space, the lung was retracted. The pericardium was excised and used for a different study. Heparin was given at a dose of 2.5 rug/kg body weight. The two venae cavae were cannulated separately through pursestring sutures in the right atrial wall. Arterial return was achieved through a right common femoral artery cannula. The priming volume was 1000 ml of Ringer's lactate solution, 100 ml of albumin 25%, and 25 mg of sodium bicarbonate and heparin. Total cardiopulmonary bypass was established by snaring both venae cavae with tape. Normothermic bypass was maintained without aortic crossclamping.

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Fig. 1. Epicardial echocardiogram of the tricuspid valve 22 weeks after polydioxanone De Vega annuloplasty. Observe the changes in diameter between systole and diastole.

Fig. 2. Simultaneous pressure tracings of the right atrium and ventricle, 22 weeks after polydioxanone De Vega annuloplasty. No transvalvular gradient is detected.

The right atrium was opened vertically and the tricuspid valve was exposed. The coronary sinus was continuously drained with a flexible cardiotomy sucker. The tricuspid anulus was measured in all the sheep with sized obturators. A 2-0 polydioxanone suture (PDS; Ethicon Ltd., Edinburgh, Scotland) was selected as the absorbable synthetic material. The De Vega annuloplasty was performed with a double row of continuous sutures along the base of the anterior and posterior leaflets and passed at each extremity through small squares of autologous pericardium. The sutures were then tied over an obturator, 2 to 6 mm smaller in diameter than the measured tricuspid anulus. During the procedure arterial blood gases, potassium concentration, and heparinization were checked at 30-minute intervals and corrected, if necessary. The right atrium was closed with a continuous 5-0 monofilament suture and the vena cava snares were released. The heart was contracting throughout the procedure and took over the circulation easily. The ani-

mal was weaned from cardiopulmonary bypass and decannulated. Protamine was given at a dose of 4 rug/kg body weight, and hemostasis was checked. The chest was closed, with one intercostal drain left in the right pleural cavity. When the sheep was fully awake and attempting to stand, the intercostal drain was removed. Bloodtransfusion was not required. From the first postoperative day the sheep were kept in a pen and attended to until put to death. Penicillin G benzathine (Bicillin, I megaunit) was given by deep intramuscular injection daily for 3 days. The survivors received humane care in compliance with the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Sciences and published by the National Institutes of Health (NIH Publication No. 85-23, revised 1985). One sheep was killed at each 2-week interval for a period of 6 months. At the time of killing, under general anesthesia, each animal was intubated and its lungs ventilated with a positive-

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7 9 8 Duran et al.

Fig. 3. Section through area of annuloplasty after 2 weeks.The foreign material has dropped out in processing, and there is a mild inflammatory reaction in the surrounding tissue. (Hematoxylin and eosin stain, original magnification XI50.)

Table I. Tricuspid valve diameter before and after annuloplasty and at time of killing Sheep No. I

2 3 4 5 6 7 8 9 10 II

12

Tricuspid anulus diameter (mm)

Weeks postop

Preop

lntraop

At killing

2 4 6 8 10 12 14 16 18 20 22 24

31 27 31 31 33 35 31 31 31 29 25 29

25 25 27 27 27 29

25 25 27 27

27 29

27

27

25 25 25 23 25

25 25 29 27

29

pressure respirator. The arterial pressure and electrocardiogram were continuously monitored. Transthoracic echocardiography was attempted but showed poor results. The right thoracotomy was reentered, and all the adhesions were released.The lung was retracted. Epicardial echocardiography was performed in six animals. Simultaneous right atrial and right ventricular pressures were recorded, on similar baselines and scales, through a 22F needle. Both venae cavae were ligated, and the right atrium was opened at the site of the previous atriotomy. The findings in the right atrium, the tricuspid anulus, and the valveleaflets were recorded. The tricuspid size was measured on the beating heart and recorded. The heart was then excisedand sent fresh to the pathology laboratory. The heart was examined as soon as it reached the laboratory, the site of the annuloplasty was identified, and sections across the anulus, together with routine sections of the left and right ventricles, were taken for histologicexamination. After forma-

lin fixation, dehydration, and embedding, sectionswere stained with hematoxylin and eosin, by the periodic acid-Schiff technique, and with Masson's trichrome stain.

Results A total of 16 sheep were operated on, with four perioperative deaths, all of which occurred on the day of operation. One sheep died of uncontrollable bleeding from the superior vena cava, one from heart block, one did not awaken from the anesthetic, and the other died of respiratory arrest. The total cardiopulmonary bypass time varied from 27 to 35 minutes. The epicardial Doppler study showed no evidence oftricuspid stenosis or tricuspid regurgitation in any of the six animals that underwent this procedure (Fig. 1). In the four animals that survived longest, simultaneous right atrial and right ventricular pressures revealed no gradient across the tricuspid valve (Fig. 2). There was no clot in the right atrium in any of the animals. The tricuspid leaflets were all of a normal appearance. Four weeks after operation, the polydioxanone sutures could be seen through the thin covering of endothelium. At 8 weeks the suture was perfectly and completely covered with the endothelium. A slight thickening could be visualized and felt and the anulus size remained as induced at operation. At 12 weeks' follow-up the polydioxanone suture could not be visualized through the endothelium. A well-marked fibrous ring was seen and felt at the level of the annuloplasty, and the annular diameter was maintained as on the day of operation. After 16 weeks the endothelium was smooth, there was no clot inside the right atrium, and the

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Fig. 4. By 14weeks the foreign suture material has been infiltratedby granulation tissue, includingmultinucleated foreign bodygiant cellswith separationof individual filaments. (Hematoxylinand eosinstain, originalmagnification X4S0.)

Fig. 5. Twenty weeks after insertion, much of the foreign material has been disrupted or absorbed. (Hematoxylin and eosin stain, original magnification XSO.)

leaflets were normal. An n-shaped ring of fibrous tissue had formed over the part of the anulus corresponding to the anterior and posterior leaflets. The annular diameter was maintained as surgically induced. At 20 weeks the polydioxanone suture had been partially resorbed. There was no breakdown in the endothelial surface, and a fibrous tissue ring could be seen and felt. The anulus size had reverted to the size before the annuloplasty was performed. At 24 weeks' follow-up there was no gradient across the tricuspid valve on

echocardiographic examination and pressure monitoring (see Figs. I and 2). No clot was found in the right atrium, and the tricuspid leaflets were of normal appearance. The endothelial surface was smooth and no polydioxanone suture could be visualized or identified through the endothelium. At the level of the annuloplasty a fibrous tissue ring could be seen and felt. The anulus diameter reverted to its preoperative size in the animals that survived 20 weeks or more after operation (Table I). Histology. Sections taken at right angles to the anulus

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8 0 0 Duran et al.

Fig. 6. By 24 weeks the foreign material has been severely disrupted, largelyresorbed, and replaced by relatively loose connective tissue. (Hematoxylin and eosin stain, original magnification x480.)

Table II. Residual tricuspid stenosis after annuloplasty Stenosis Reference Haerten et al. 8 Hatle and

Method

Patients

%

Gradient (mm Hg)

De Vega De Vega

12/24 5/7

50 71

2-8 2-7

Carpentier Carpentier Duran

13/25 17/51 17/55

48

5 4± 1 3± 2

Angelsen? al. lO

Hanania et Lambertz et al.? Duran et aLI

33

31

were examined from sheep killed at 2-week intervals from 2 to 24 weeks after operation. After 2 weeks there was a mild tissue reaction around the foreign material that consisted of granulation tissue, including capillaries, fibroblasts, and a few inflammatory cells, chiefly Iymphocytes (Fig. 3). During the succeeding 10 weeks this periannular granulation tissue increased, with the foreign material remaining apparently intact. In tissue sections from animals up to 12 weeks after the operation the suture material frequently fell out of the section, whereas at later times this was not a problem. At 14 weeks there was an obvious invasion of the suture material by the surrounding granulation tissue (Fig. 4). At this time multinucleated foreign body giant cells were apparent around the suture material and between individual filaments of the suture. During the next month the disruption of suture filaments progressed and the granulation tissue became

denser. At 20 weeks much of the foreign material was either disrupted or absorbed (Fig. 5). By 24 weeks the foreign material was severely disrupted and largely resorbed, being replaced by relatively loose collagenous tissue (Fig. 6). Discussion Regurgitant lesions of the atrioventricular valves are nowadays successfully treated by annuloplasty performed with encircling sutures" or prosthetic rigid' or flexible" rings. Although the results have been shown to be superior to those achieved with valve replacement, adequate reconstruction cannot be achieved without a compromise between stenosis and regurgitation." Even in the tricuspid area, where gradients are difficult to detect, careful studies have shown postoperative stenosis in a significant number of patients after the different types of annulopiasties (Table II). At best, all annuloplasties have the inherent drawback of permanently splinting the valve anulus to its systolic size and, in the case of the rigid rings, to its systolic shape, which results in a relative stenosis during the diastolic period. This not often recognized problem becomes more clinically significant in children because the permanent fixation of the anulus does not allow for further growth. Furthermore, the introduction of prosthetic ring materials into the bloodstream is not without danger, such as the risk of thromboembolism and infection. In an attempt to avoid these disadvantages, it was thought that a biodegradable ring with controlled time-

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dependent reabsorption might be the answer. In 1986 we:' reported the experimental use of a ring made of ox fibrin (Biethium, Ethicon Ltd., Edinburgh, Scotland). At 3 weeks there was already surface erosion of the ring, with total disappearance by 5 weeks after implantation. Chondroid degeneration was apparent at 6 months in two animals. It was believed that although the concept might be useful the material was unsatisfactory. The availability of new synthetic reabsorbable sutures stimulated interest in this project again. Polydioxanone has been shown to remain practically intact during the first 3 months but to be rapidly destroyed at about 5 months. I I, 12 Its monofilament thread is unbraided and has a smooth surface that minimizes drag and reduces the chances of infection. Our results show that a tricuspid De Vega type annuloplasty in sheep, constructed with 2-0 polydioxanone sutures to reduce the anulus by 2 to 6 mm, holds for about 4 months. During this time the foreign material causes a tissue reaction consisting predominantly of granulation tissue that initially surrounds the suture. Gradually the granulation tissue infiltrates the suture, which becomes disrupted and absorbed. By about 5 months the disruption of suture material is so advanced that the orifice dilates to about its original size. By 6 months most of the suture material has disappeared so that there is no permanent intracardiac foreign body. No evidence of infection, thrombosis, or leaflet abnormality was detected in any animal. The reabsorption process of a biodegradable annuloplasty can follow two different paths probably related to the type and amount of synthetic material selected. It either induces such a tenuous fibrous reaction that, as in our case, the anulus becomes normal with capacity for growth or, as reported by Chachques and associates.l-' a fibrous ring is induced that prevents secondary dilatation. Ideally one should aim to induce an autologous fibrous, and therefore flexible, ring that, while permanently stenting the anulus, would allow for growth. The possibility of balancing these two opposing requirements needs further investigation. The present study shows that temporary stenting of the tricuspid anulus is possible with a controlled time frame of disappearance. The use of this "vanishing annuloplasty" could be applied in cases of functional tricuspid insufficiency, particularly in children.

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We wish to acknowledge the invaluable cooperation of Dr. Raafat M. EISayed, veterinary surgeon,and histechnicians and the secretarial assistance of Miss Alison Silkstone and Mrs. Angela Palacio. REFERENCES I. Duran CMG, Pomar JL, Colman T, Figueroa A, Revuelta JM, Ubago JL. Is tricuspid valverepair necessary? J THORAC CARDIOVASC SURG 1980;80:849-60. 2. Breyer RH, McClenathan lH, Michaelis LL, McIntosh CL, Morrow AG. Tricuspid regurgitation: a comparison of nonoperative management, tricuspid annuloplasty, and tricuspid valve replacement. J THORAC CARDIOVASC SURG 1976;72:867-70. 3. Duran CMG, Revuelta JM, Val Bernal F. A new absorbable annuloplasty ring in the tricuspid position: an experimental study. Thorac Cardiovasc Surg 1986;34:377-9. 4. De Vega N. La anuloplastia selectiva, regulable y permanente. Rev Esp Cardiol 1972;25:555-60. 5. Carpentier A, Deloche A, Dauptain J, et al. A new reconstructive operation for correction of mitral and tricuspid insufficiency. J THORAC CARDIOVASC SURG 1971;61:1-13. 6. Duran CMG, Ubago JL. Clinical and hemodynamic performance of a totally flexible prosthetic ring for atrioventricular valve reconstruction. Ann Thorac Surg 1976; 22:458-63. 7. Lambertz H, Minale C, Flachskampf FA, et al. Long-term follow-up after Carpentier tricuspid valvuloplasty. Am HeartJ 1989;117:615-22. 8. Haerten K, Seipel L, Loogen F, Herzer J. Hemodynamic studies after De Vega's tricuspid annuloplasty. Circulation 1978;58(Pt 2):128-33. 9. Hatle L, Angelsen B. Doppler ultrasound in cardiology. Physical principles and clinical applications. 2nd ed. Philadelphia: Lea & Febiger, 1985:97-205. 10. Hanania G, Sellier P, Deloche A, et al. Resultats a moyen terme de l'annuloplastie tricuspide reconstructitutive de Carpentier. A propos de 25 cas avec catheterisme postoperatoire. Arch Mal Coeur 1974;67:895-909. II. Chiu IS, Hung CR, Chao SF, Huang SH, How SW. Growth of the aortic anastomosis in pigs: comparison of continuous absorbable suture with nonabsorbable suture. J THORAC CARDIOVASC SURG 1988;95:112-8. 12. Ray JA, Doddi N, Regula 0, Williams JA, Melveger A. Polydioxanone (PDS), a novel monofilament synthetic absorbable suture. SurgGynecol Obstet 1981;153:497-507. 13. Chachques .IC, Acar C, LaTremouille C, et al. Absorbable rings for pediatric valvuloplasty: preliminary study. Circulation 1990;82(Pt 2):IV82-8.