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Influence of amount of exposed fabric on thrombotic complications of aortic ball valves in the calf
Influence of Amount of Exposed Fabric on Thrombotic
Complications
of Aortic
Ball Valves in the Calf* LESTER R. SAUVAGE, M.D.,KNUTE E. BERGER,M.D.,~TEPHEN J. WOOD, M.D., ABBASA. SAMEH,M.D.,MARK P. DEDOMENICO, M.D.,AND ROBERT F. VIGGERS, M.s., Seattle, Washington
From The ReconstructGe Cardiovascular Research Laboratory, Providence Hosfiital, The Department of Surgery, University of Washington and The School of Engineering, Seattle University, Seattle, Washington. This research was supportedby The John A. Hartford Foundation, Inc., New York, New York.
HROMBOSIS and thromboembolism remain problems associated with the use of prosthetic aortic valves. Possible solutions have been studied in many research laboratories. In general, approaches have involved variations of design, materials, and amount of exposed fabric. The latter has recently received much attention and has led to the development of aortic valve prostheses whose stationary parts are completely covered by fabric. However, the experimental work on which this development is based has been primarily with mitral [1,2] and tricuspid valve replacements [3] in the calf. In contrast, our observations on aortic ball valve replacements in fifty-two calves have suggested that less exposed fabric, rather than more, is superior in the control of thrombus formation and in the prevention of embolism with ball valves for use in the aortic site. In this paper we are reporting the results of these experiments.
T
1000 with substitute small sewing ring, eight; (3) Starr-Edwards model 1200, seven; (4) Starr-Edwards model 2300 (cloth-covered), six; (5) Edwards guided-flow valve (Viggers) , four. The metal component of all valves was stellite 21. All had a mirror finish except model 2300. In this model the ball is a hollow sphere of mirror-finished stellite 21 whereas in the others the ball is solid Silastic@. The fabric is knitted Teflon@in groups 1 and 3 acd knitted Dacron@in groups 2 and 5; in group 4 both knitted Dacron and Teflon are used. The pertinent configurations of the valves and the amount of exposed fabric are shown in Figure 1. Additional details of the guided-flow valve are shown in Figure 2. Its hydraulic characteristics and dimensions have already been reported [P61. Implantation. Calves of both sexes, most of which
were of the Holstein breed, weighing between 100 and 160 pounds were employed. Anesthesia was induced by ether and maintained by Fluothane@. The aortic valve was approached through a midline sternotomy. A disk oxygenator was used for extracorporeal circulation with complete blood prime. A single venous line from the right atrium and a double arterial line (internal mammary and femoral arteries) were employed for bypass. The transverse aortic arch and brachiocephalic trunk were both clamped to provide access to the short ascending aorta of the calf. Both coronary arteries were perfused for the greater part of the period of valve replacement. The valve cusps were excised and the sewing ring of the prosthesis was attached to the annulus with No. 2-O Dacron. The suture technic described by Wood and Sauvage [7] was found useful during the latter part of the series.
MATERIAL AND METHODS Valves. The valves were all manufactured by Edwards Laboratories and were employed in five different groups of experiments: (1) Starr-Edwards model 1000, twenty-seven; (2) Starr-Edwards model * Presented
at the Thirty-Ninth Annual Meeting of the Pacific Coast Surgical Association, Honolulu, Hawaii, February 18-22, 1968. 260
The American Journal of Surgery
Thrombotic
--+
Complications
0
D
5
S 8-E
of Aortic
“Ii1
Ball Valve
1OC N
SSR
G-F
(Vigger SSR
‘S
.J
1
FIG. 1. Development of guided-flow valve with small sewing ring. Tllcr Starr~Edwards concepts 1x1~~.illi IVLYI111the direction 1, B, and C to total cloth coverage of the stationary parts. On the basis of experimental WWLW u-in< tlw Starr-Edwards valve but replacing the cloth with a small sewing ring, as at D, the guide&flow valve t 1, (Ic=.iq:n~~lby Viggers is also fitted with a small sewing ring. The metal configuration has ~olv~~tl as shown here.
guided-How (Viggers) valve with small sewing ring is shown at A .L tlelnonstrnted in B. the cuff is yieldable when sutures are placed and tied. Mattress sutures that catch both leaves (rolls) of the fabric arc tied on the top, thereby securing the ring as it is fixed to the tissues. C shows construction of the cuff. There is 110 sewn circular seam; instead, the material holding the cuff in place is kept to a minimum, while the fabric itself is very pervious. The “lumen” of the sewing ring is highly accessible to tissue ingrowth. The rounded metal Iills extend out a millimeter from the struts so as to decrease the likelihood of tissue overlapping into the ball path. FIG. 2. Edwards
Posioperuhe Cure cd Collecfiox of Specimens. used postoperatively Anticoagulation was not whereas antibiotics were administered for the first two days. Most animals were sent to a farm after the second day, and those dying at the farm were brought to the laboratory for autopsy. Animals slaughtered were handled in the usual commercial way without the administration of anticoagulants. .4t the time of slaughter the heart was quickly obtained, the ascending aorta opened, and the valve gently flushed with a 0 per cent solution of glucose. The gross findings were assessed and photographed, and the specimens were then placed in formalin for later sectioning and histologic study.
RESULTS VALVE
INCtDESCE
OF
HALL VAI,VE
SIGSIFICANT
.I‘ABLE VALVE
THROMBOSIS
REPLACEMEST
AFTER
IN FIFTY-TWO
\VITt-tOcJT ANTICOAGULANTS
(1~504
AORTIC
CRITERIA
OF SALUTARY REPLACEMEST
WtTHOKT
II
HEALING IN
AFTER
Edwards guided-flow (Viggers) Starr-Edwards 1000, small sewing ring Starr-Edwards 1000 Starr-Edwards 1200 Starr-Edwards 2300 (cloth-covered)
Vol.
116.
August
196X
Days
ANTICOAGULANTS
(SO-SIN
DAYS)
DAYS)
Salutary Hrulitli:
K\;o.
Per cent
18.-11’1
0
0
x 2; 7
5-183 l-504 9 -2 73
1 11 5
1” 40 71
6
100
30 hr.-111
BALI.
CALVES
CALVES
1
6
AOR’IIC
TWENTY-THREE
Significant Thrombosis Total
01:
ASSESSMENT
The results are summarized in Tables I and II, with additional detail in Figures 2 through 5. Generally the results of ball valve replacement of the aortic valve in the calf were improved by decreasing the amount of exposed fabric to a practical minimum. In Table I the judgment call of “significant thrombosis” was based on the thickness or bulk, position, and nature of the deposit. For
INCIDESCE
TABLE I
.\NU
Yalvc Edwards guided-tlow (Viggers) Starr-Edwards 1000, small sewing ring Starr-Edwards 1000 Starr-Edwards 130 Starr-Edwards 300 (cloth-covered)
2 3 11 1
101,121 01 -183 113--50-l 9,5-2;:3
o*
* X11 anirnnls died prior to 60 days.
2
100
:i !I 2
100 til 50
262
Sauvage
et al.
FIG. 3. Ventricular aspects of the valves across top and their respective aortic aspects across bottom. A, model 1000 Starr-Edwards valve (8A), 504 days after implantation in the calf. Sote thin tissue on much of the sewing ring,
absence of thrombus, and benign nature of cloth-metal junction. This valve was judged to show salutary healing. B, same type of valve 180 days after inplantation in the calf. Thick tissue has extended to cover the presenting surface of most of the metal and much of the orifice is occluded by thrombus. Histologic studies of this specimen (8) revealed the thrombus to originate from thick tissue subject to ball contact. C, 8A model 1000 Starr-Edwards valve at 183 days in the calf. The large Teflon sewing ring of the original prosthesis was removed and replaced with a very small Dacron cuff kept well within the confines of the lateral aspect of the body of the valve. With this small ring the top and bottom of the valve body were in direct contact with the tissues. The tissue-metal iunction appears benign-good healing; no thrombus present. example, a thrombus of 2 mm. in thickness or more tended to be slow to organize and was judged significant. (Fig. 4.) Thrombus, whether thick or thin and of a highly friable nature, was likely to embolize and was judged significant. The small thrombotic deposit seen in Figure 4B was highly friable (the kidneys
showed evidence of emboli), and was judged as significant thrombus. Thrombus along the struts, projecting into the ball path or inlet orifice, was judged significant. With regard to “salutary healing” noted in Table II, although the outflow aspect of the valve in Figure 4B was well healed, it could not be judged healthy at ninety-five days because of thrombus on the inflow aspect. However, the same type of valve at 273 days (Fig. 4Bb) showed good healing on both the inflow and outflow sides and was judged salutary. In summary, salutary healing had the
following attributes: the valve was securely fixed by tissue ingrowth; tissue did not interfere with occluder function; generally the tissue was less than 1 mm. thick except adjacent to the annulus; no significant thrombus, either residual or new, was present; and the ball did not touch tissue. Sixty days or more was the point in time chosen for judging healing although earlier specimens, particularly with the small cuff, showed salutary healing prior to sixty days. (Fig. 5A.) COMMENTS
The results reported indicate that ball valve replacements of the aortic valve in the calf have fewer thrombotic complications when, by the design of the valve, the amount of fabric exposed to the blood is small and the fabric is kept close to the suture line and well away The American Journal of Surgevy
Thrombotic
Complications
of Aortic Ball Valve
FIG. 4. A, 8il model 1200 Starr-Edwards aortic valve nine days after inplantation in the calf. Note the ertension of thrombus across the cloth-metal junction with protrusion into the flow channel on both aspects of the valve. B, ventricular aspect of model 1200 Starr-Edwards valve (8.11 ninety-five days after implantation. Sate the granular. friable thromhus along about 1-O per ccut of the valve rim. We classify this type and extent of thrombus as significant. Bh, aortic aspect of an 8A model 1200 at 273 days in the calf. Sate that the tissue is thin in some areas and quite thick in others. \%‘c helicve the thick tissue results from the organization of considerable quantities of thronbus. C. model 2300 Starr-Edwards aortic valve (XX) fifteen days after implantation in the calf. Note the build-up of thrombus (gray, granular, and friable) at the inlet orifice with marked reduction in the area of the flow path. There is a seam at this point (junction of Teflon inside and Dacron outside) which may he related to this localization, This finding has been uniform in all valves of this type studied in this tiaboratory. iTlrhlc I.) The nortic aspect of the valve is comparatively free of thromhus.
FIG. 5. Edwards guided-flow (I’iggers) ball valves. All specimens recovered at slaughter. A, as early as fifty-one days after implantation in the calf healing appears to be complete and no thrombus is present. B, specimen 101 days after implantation; salutary healing and no significant thrombus. C, specimen at 121 days; salutary healing and no thrombus.
264
Sauvage
from the ball path. Despite the excellent results obtained with the guided-flow valves, the small number (four) makes definitive interpretation premature. The performance of the StarrEdwards valve model 1000 was improved in terms of both thrombus reduction and salutary healing by removal of the valve’s large sewing ring and substituting a small one. Further studies of the guided-flow, small-cuffed valve are in progress. The hydraulic characteristics of this design have been shown by Viggers et al. [&6] to be favorable and may contribute to an environment conducive to salutary healing. The appearance of this valve and cuff is shown in Figure 2. In man, more is known about the healing of arterial prostheses than about the healing of valvular prostheses. Since the aortic valve, at least on the outflow side, is subjected to pressures similar to the inside of an arterial graft, information drawn from the healing patterns of the inner wall of arterial prostheses in man may be useful. In adult man, and especially elderly man, the luminal aspect of porous arterial fabric grafts remains covered for the most part by nonorganized fibrinous material, even years after implantation. Although the grafts may remain useful for extended periods of time, they remain nonhealed for the most part as regards the inner surface, except for the areas within a few millimeters of the suture lines. We believe that the frequency of incomplete healing or lack of healing of the inner wall of prosthetic arterial conduits is pertinent to the healing of prosthetic aortic valves. There are three potential avenues for healing of the inner wall of porous prosthetic arterial conduits in man and experimental animals : (1) pannus extending from the ends of the host artery across anastomoses, (2) transinterstice ingrowth from the perivascular tissues, and (3) deposition of organizing cells from the blood stream, that is, “fallout” healing. Pannus, although limited to a few millimeters, reaches its potential in both man and experimental animals and remains quite stable. However, the potential of the other two avenues, especially of “fallout” healing, is more limited in adult man than in the mature dog or growing pig. Hence, the relative importance of the three healing avenues appears to vary among species. In addition, it may be influenced by age [8]. Reducing the cloth sewing ring of an aortic
et al. valve prosthesis to a practical minimum enables pannus healing to function as the principal healing mechanism. The amount of thrombus is and about the valve requiring organization is reduced by “hiding” the cloth. AS to the success of complete tissue coverage of the static components of aortic heart valves, we have pointed out that this may work better in valve sites other than the aortic [9]. One must view the experimental results reported in this paper against the background of the excellent clinical results of Starr [IO] and Morrow [II] with cloth-covered aortic ball valves in man. Yet we suggest that neither short-term data in man nor experimental data such as herein reported are adequate to support a dogmatic position at this time. SUMMARY
The results of ball valve replacement of the aortic valve in fifty-two calves are reported. These observations indicate that the less fabric exposed to the blood and the closer the fabric cuff to the suture line, the lower the incidence of thrombotic complications in this species. Acknowledgment: We wish to thank the following for their help and cooperation: Jay H. Miller, D.v.M., President, Miller Packing Co., Renton, Washington and the Seattle Packing Co., Seattle, Washington. The following contributions to the research program of this laboratory are gratefully acknowledged : American Silk sutures, Dacron sutures; Ayerst Laboratories, Fluothane; Cutter Laboratories, intravenous fluids; Edwards Laboratories, Starr-Edwards aortic valves and guided-flow aortic valves (Viggers); Ethicon, Inc., Mersilene sutures; Eli Lilly 8.~Co., Keflin. REFERENCES
1. DAVILA, J. C., AMONGERO, F., SETHI, R. S., RINCON, L. L., PALMER, T. E., and LAUTSCH, E. V. The prevention of thrombosis in artificial cardiac valves. Ann. Thoracic Surg., 2: 714, 1966. 2. PALMER, T. E., LAUTSCH, E. V., SANMARCO,M. E., and DAVILA, J. C. A nonthrombogenic, nonanticoagulant-dependent mitral valve prosthesis. Circulation (suppl. l), 35: 42, 1967. 3. BRAUNWALD, N. S. and BONCHEK, L. I. Prevention of thrombus on rigid prosthetic cardiac valves by an autogenous tissue covering. J. Th.oracic & Cardiovasc. Surg., 54: 630, 1967. 4. VIGGERS, R. F., ROBEL, S. B., and SAUVAGE, L. R. A hydraulic figure-of-merit for heart valve prostheses. J. Biomed. Mater. Res., 1: 103, 1967. 5. VIGGERS, R. F., ROBEL, S. B., WOOD, S. J., SAWThe American
Journal
of Surgery
Thrombotic
6.
i.
8.
9.
10.
11.
Complications
YER, P. ?j., WESOI,OTVSKI,S. A., and SAUVAGE L. R. Improvement of aortic ball valve function by flow guidance. .%rger_v, 63: 5’2, 1968. SAWAGE, L. R., ~‘IGCERS, R. F., WOOD, S. J., BERGER, K. E., ROBEI,, S. B., and WESOLOWSKI, S A. Prosthetic heart valve replacement. i\luter. Biomed. Engyg. New York Acad. Sci., 146: 289, 1068. WOOD, S. J. and SAUVAGE. L. R. Single plane fisation for prosthetic aortic valves. J. Tho~acic & Cc~vdiouasc. Suvy., 54: 90. 1967. SAMEH. A. A., BERGER. K. E., WOOD, S. Jo, DEDOh!ENIco. M., and SAUVAGE, L. R. Arterial healing in the mature dog, growing pig and adult man. Unpublished data. BEKGER, K., SAUVAGE, L. R.. WOOD, S. J., and WESOLOWSKI, S. A. Sewing ring healing of cardiac valve prostheses. .%rgery, 61: 102, 1967. STARR. A. Clinical and laboratory experience with the ball valve prostheses. Presented at the American Heart Association Postgraduate Seminar, San Francisco, California, October 19, 1967. MORROW, A. G. Personal communication, January 16. 1968. DISCUSSION
ALBERT STARR (Portland, Ore.): Much of our knowledge on neointima formation on cloth surfaces of prostheses has come from Dr. Sauvage. It was quite a shattering experience to find that we had taken divergent pathways with regard to design of the aortic valve prostheses. He has shown that there is a lack of thrombogenicity in highly polished metallic surfaces placed in the arterial system. This coincides with the work of Vincent Gott, for example, who showed that GBH bonded rings in the inferior vena cava of dogs did not become occluded by clot; he believed this was related to the heparinized surface of this plastic material. He then studied stellite 21 highly polished rings, made in the same manner by Edwards Laboratory as the valves Dr. Sauvage described, and found they functioned as well as GBH rings in the inferior vena cava. Also. Dr. McGoon tested pins of various materials in the aorta of experimental animals and could find no material better than a highly polished metallic surface in terms of lack of thrombogenicity. How can we correlate these findings with our own attempt to have as little exposed metallic material as possible? Dr. Sauvage’s findings are an index of what can really be expected with the model 1000 valve in the calf. His results with the completely cloth-covered valve and the completely metallic valves have involved too few experiments to be conclusive. The \ralve employed by Dr. Mcgovern and intro-
Vol. 116, August
1968
of Aortic Ball Valve duced in 1Wi3 was a rc,mplcte!y metallic valve oi highly polished titanium. This particular prosthesis gave a significant incidence of thrombc~cmbcJic camplications after implantation in man. Autopsy examinations of patients dying late after aortic valve surgery suggest that thrcrmbt~sis arises from the metallic portion of the valve where neointima could not become adherent. The cloth of the prosthesis becomes completely healed and covered with a smooth neointitna. The incidence of embolic complications with the model 1001) valve or the valve with a considerable metallic surface, was 2;i per cent, and with the model 1200 or extended cloth valve the incidence dropped to about 9 per cent. Thus there has been a significant decrease in the incidence of thromboembolic complications in man, with a reduction in the amount of metallic material exposed to the circulation. The model 2300, which was used in six call,es and which was completely cloth-covered, has been implanted in about sixty patients thus far; however, it is too early to determine whether there will be a further decrease in late thromboembolic complications. These observations in man will be crucial in determining our direction from a clinical point of view. In a specimen obtained from a patient iour years after implantation using a model 1000 valve, a glistening neointima was seen firmly attached to the cloth portion of the prosthesis: however, four years later. there was considerable thrombus material which overlapped onto the metallic side of the valve and which had a completely different appearance from the material on the cloth. In another patient a specimen obtained three months after operation using a model 1200 valve showed that in some areas the cloth and metallic junction were completely clean, as Dr. Sauvage has shown in the past, but in other areas strands of neointima extended over onto the metallic material. On liiting these up, small strands of fibrin material were seen. In a dog six months after implantation of a model 2300 valve. the valve was completely encapsulated, thereby showing how. with the use ot cloth t.hroughout the extent of the sewing ring of the val:-e. conplete healing of the prosthesis can be obtained. LESTER K. SAUVACE (closing): Dr. Starr has pointed out that there are many factors we really do not know very much about. His comments help to give us perspective which is needed by those of us involved in a considerable amount of experimental work (and Dr. Starr certainly is involved in this despite the magnitude of his clinical load). il’c have onlv a partial glimpse of it at the prcceiit time.
Complications
of Aortic
Ball Valves in the Calf* LESTER R. SAUVAGE, M.D.,KNUTE E. BERGER,M.D.,~TEPHEN J. WOOD, M.D., ABBASA. SAMEH,M.D.,MARK P. DEDOMENICO, M.D.,AND ROBERT F. VIGGERS, M.s., Seattle, Washington
From The ReconstructGe Cardiovascular Research Laboratory, Providence Hosfiital, The Department of Surgery, University of Washington and The School of Engineering, Seattle University, Seattle, Washington. This research was supportedby The John A. Hartford Foundation, Inc., New York, New York.
HROMBOSIS and thromboembolism remain problems associated with the use of prosthetic aortic valves. Possible solutions have been studied in many research laboratories. In general, approaches have involved variations of design, materials, and amount of exposed fabric. The latter has recently received much attention and has led to the development of aortic valve prostheses whose stationary parts are completely covered by fabric. However, the experimental work on which this development is based has been primarily with mitral [1,2] and tricuspid valve replacements [3] in the calf. In contrast, our observations on aortic ball valve replacements in fifty-two calves have suggested that less exposed fabric, rather than more, is superior in the control of thrombus formation and in the prevention of embolism with ball valves for use in the aortic site. In this paper we are reporting the results of these experiments.
T
1000 with substitute small sewing ring, eight; (3) Starr-Edwards model 1200, seven; (4) Starr-Edwards model 2300 (cloth-covered), six; (5) Edwards guided-flow valve (Viggers) , four. The metal component of all valves was stellite 21. All had a mirror finish except model 2300. In this model the ball is a hollow sphere of mirror-finished stellite 21 whereas in the others the ball is solid Silastic@. The fabric is knitted Teflon@in groups 1 and 3 acd knitted Dacron@in groups 2 and 5; in group 4 both knitted Dacron and Teflon are used. The pertinent configurations of the valves and the amount of exposed fabric are shown in Figure 1. Additional details of the guided-flow valve are shown in Figure 2. Its hydraulic characteristics and dimensions have already been reported [P61. Implantation. Calves of both sexes, most of which
were of the Holstein breed, weighing between 100 and 160 pounds were employed. Anesthesia was induced by ether and maintained by Fluothane@. The aortic valve was approached through a midline sternotomy. A disk oxygenator was used for extracorporeal circulation with complete blood prime. A single venous line from the right atrium and a double arterial line (internal mammary and femoral arteries) were employed for bypass. The transverse aortic arch and brachiocephalic trunk were both clamped to provide access to the short ascending aorta of the calf. Both coronary arteries were perfused for the greater part of the period of valve replacement. The valve cusps were excised and the sewing ring of the prosthesis was attached to the annulus with No. 2-O Dacron. The suture technic described by Wood and Sauvage [7] was found useful during the latter part of the series.
MATERIAL AND METHODS Valves. The valves were all manufactured by Edwards Laboratories and were employed in five different groups of experiments: (1) Starr-Edwards model 1000, twenty-seven; (2) Starr-Edwards model * Presented
at the Thirty-Ninth Annual Meeting of the Pacific Coast Surgical Association, Honolulu, Hawaii, February 18-22, 1968. 260
The American Journal of Surgery
Thrombotic
--+
Complications
0
D
5
S 8-E
of Aortic
“Ii1
Ball Valve
1OC N
SSR
G-F
(Vigger SSR
‘S
.J
1
FIG. 1. Development of guided-flow valve with small sewing ring. Tllcr Starr~Edwards concepts 1x1~~.illi IVLYI111the direction 1, B, and C to total cloth coverage of the stationary parts. On the basis of experimental WWLW u-in< tlw Starr-Edwards valve but replacing the cloth with a small sewing ring, as at D, the guide&flow valve t 1, (Ic=.iq:n~~lby Viggers is also fitted with a small sewing ring. The metal configuration has ~olv~~tl as shown here.
guided-How (Viggers) valve with small sewing ring is shown at A .L tlelnonstrnted in B. the cuff is yieldable when sutures are placed and tied. Mattress sutures that catch both leaves (rolls) of the fabric arc tied on the top, thereby securing the ring as it is fixed to the tissues. C shows construction of the cuff. There is 110 sewn circular seam; instead, the material holding the cuff in place is kept to a minimum, while the fabric itself is very pervious. The “lumen” of the sewing ring is highly accessible to tissue ingrowth. The rounded metal Iills extend out a millimeter from the struts so as to decrease the likelihood of tissue overlapping into the ball path. FIG. 2. Edwards
Posioperuhe Cure cd Collecfiox of Specimens. used postoperatively Anticoagulation was not whereas antibiotics were administered for the first two days. Most animals were sent to a farm after the second day, and those dying at the farm were brought to the laboratory for autopsy. Animals slaughtered were handled in the usual commercial way without the administration of anticoagulants. .4t the time of slaughter the heart was quickly obtained, the ascending aorta opened, and the valve gently flushed with a 0 per cent solution of glucose. The gross findings were assessed and photographed, and the specimens were then placed in formalin for later sectioning and histologic study.
RESULTS VALVE
INCtDESCE
OF
HALL VAI,VE
SIGSIFICANT
.I‘ABLE VALVE
THROMBOSIS
REPLACEMEST
AFTER
IN FIFTY-TWO
\VITt-tOcJT ANTICOAGULANTS
(1~504
AORTIC
CRITERIA
OF SALUTARY REPLACEMEST
WtTHOKT
II
HEALING IN
AFTER
Edwards guided-flow (Viggers) Starr-Edwards 1000, small sewing ring Starr-Edwards 1000 Starr-Edwards 1200 Starr-Edwards 2300 (cloth-covered)
Vol.
116.
August
196X
Days
ANTICOAGULANTS
(SO-SIN
DAYS)
DAYS)
Salutary Hrulitli:
K\;o.
Per cent
18.-11’1
0
0
x 2; 7
5-183 l-504 9 -2 73
1 11 5
1” 40 71
6
100
30 hr.-111
BALI.
CALVES
CALVES
1
6
AOR’IIC
TWENTY-THREE
Significant Thrombosis Total
01:
ASSESSMENT
The results are summarized in Tables I and II, with additional detail in Figures 2 through 5. Generally the results of ball valve replacement of the aortic valve in the calf were improved by decreasing the amount of exposed fabric to a practical minimum. In Table I the judgment call of “significant thrombosis” was based on the thickness or bulk, position, and nature of the deposit. For
INCIDESCE
TABLE I
.\NU
Yalvc Edwards guided-tlow (Viggers) Starr-Edwards 1000, small sewing ring Starr-Edwards 1000 Starr-Edwards 130 Starr-Edwards 300 (cloth-covered)
2 3 11 1
101,121 01 -183 113--50-l 9,5-2;:3
o*
* X11 anirnnls died prior to 60 days.
2
100
:i !I 2
100 til 50
262
Sauvage
et al.
FIG. 3. Ventricular aspects of the valves across top and their respective aortic aspects across bottom. A, model 1000 Starr-Edwards valve (8A), 504 days after implantation in the calf. Sote thin tissue on much of the sewing ring,
absence of thrombus, and benign nature of cloth-metal junction. This valve was judged to show salutary healing. B, same type of valve 180 days after inplantation in the calf. Thick tissue has extended to cover the presenting surface of most of the metal and much of the orifice is occluded by thrombus. Histologic studies of this specimen (8) revealed the thrombus to originate from thick tissue subject to ball contact. C, 8A model 1000 Starr-Edwards valve at 183 days in the calf. The large Teflon sewing ring of the original prosthesis was removed and replaced with a very small Dacron cuff kept well within the confines of the lateral aspect of the body of the valve. With this small ring the top and bottom of the valve body were in direct contact with the tissues. The tissue-metal iunction appears benign-good healing; no thrombus present. example, a thrombus of 2 mm. in thickness or more tended to be slow to organize and was judged significant. (Fig. 4.) Thrombus, whether thick or thin and of a highly friable nature, was likely to embolize and was judged significant. The small thrombotic deposit seen in Figure 4B was highly friable (the kidneys
showed evidence of emboli), and was judged as significant thrombus. Thrombus along the struts, projecting into the ball path or inlet orifice, was judged significant. With regard to “salutary healing” noted in Table II, although the outflow aspect of the valve in Figure 4B was well healed, it could not be judged healthy at ninety-five days because of thrombus on the inflow aspect. However, the same type of valve at 273 days (Fig. 4Bb) showed good healing on both the inflow and outflow sides and was judged salutary. In summary, salutary healing had the
following attributes: the valve was securely fixed by tissue ingrowth; tissue did not interfere with occluder function; generally the tissue was less than 1 mm. thick except adjacent to the annulus; no significant thrombus, either residual or new, was present; and the ball did not touch tissue. Sixty days or more was the point in time chosen for judging healing although earlier specimens, particularly with the small cuff, showed salutary healing prior to sixty days. (Fig. 5A.) COMMENTS
The results reported indicate that ball valve replacements of the aortic valve in the calf have fewer thrombotic complications when, by the design of the valve, the amount of fabric exposed to the blood is small and the fabric is kept close to the suture line and well away The American Journal of Surgevy
Thrombotic
Complications
of Aortic Ball Valve
FIG. 4. A, 8il model 1200 Starr-Edwards aortic valve nine days after inplantation in the calf. Note the ertension of thrombus across the cloth-metal junction with protrusion into the flow channel on both aspects of the valve. B, ventricular aspect of model 1200 Starr-Edwards valve (8.11 ninety-five days after implantation. Sate the granular. friable thromhus along about 1-O per ccut of the valve rim. We classify this type and extent of thrombus as significant. Bh, aortic aspect of an 8A model 1200 at 273 days in the calf. Sate that the tissue is thin in some areas and quite thick in others. \%‘c helicve the thick tissue results from the organization of considerable quantities of thronbus. C. model 2300 Starr-Edwards aortic valve (XX) fifteen days after implantation in the calf. Note the build-up of thrombus (gray, granular, and friable) at the inlet orifice with marked reduction in the area of the flow path. There is a seam at this point (junction of Teflon inside and Dacron outside) which may he related to this localization, This finding has been uniform in all valves of this type studied in this tiaboratory. iTlrhlc I.) The nortic aspect of the valve is comparatively free of thromhus.
FIG. 5. Edwards guided-flow (I’iggers) ball valves. All specimens recovered at slaughter. A, as early as fifty-one days after implantation in the calf healing appears to be complete and no thrombus is present. B, specimen 101 days after implantation; salutary healing and no significant thrombus. C, specimen at 121 days; salutary healing and no thrombus.
264
Sauvage
from the ball path. Despite the excellent results obtained with the guided-flow valves, the small number (four) makes definitive interpretation premature. The performance of the StarrEdwards valve model 1000 was improved in terms of both thrombus reduction and salutary healing by removal of the valve’s large sewing ring and substituting a small one. Further studies of the guided-flow, small-cuffed valve are in progress. The hydraulic characteristics of this design have been shown by Viggers et al. [&6] to be favorable and may contribute to an environment conducive to salutary healing. The appearance of this valve and cuff is shown in Figure 2. In man, more is known about the healing of arterial prostheses than about the healing of valvular prostheses. Since the aortic valve, at least on the outflow side, is subjected to pressures similar to the inside of an arterial graft, information drawn from the healing patterns of the inner wall of arterial prostheses in man may be useful. In adult man, and especially elderly man, the luminal aspect of porous arterial fabric grafts remains covered for the most part by nonorganized fibrinous material, even years after implantation. Although the grafts may remain useful for extended periods of time, they remain nonhealed for the most part as regards the inner surface, except for the areas within a few millimeters of the suture lines. We believe that the frequency of incomplete healing or lack of healing of the inner wall of prosthetic arterial conduits is pertinent to the healing of prosthetic aortic valves. There are three potential avenues for healing of the inner wall of porous prosthetic arterial conduits in man and experimental animals : (1) pannus extending from the ends of the host artery across anastomoses, (2) transinterstice ingrowth from the perivascular tissues, and (3) deposition of organizing cells from the blood stream, that is, “fallout” healing. Pannus, although limited to a few millimeters, reaches its potential in both man and experimental animals and remains quite stable. However, the potential of the other two avenues, especially of “fallout” healing, is more limited in adult man than in the mature dog or growing pig. Hence, the relative importance of the three healing avenues appears to vary among species. In addition, it may be influenced by age [8]. Reducing the cloth sewing ring of an aortic
et al. valve prosthesis to a practical minimum enables pannus healing to function as the principal healing mechanism. The amount of thrombus is and about the valve requiring organization is reduced by “hiding” the cloth. AS to the success of complete tissue coverage of the static components of aortic heart valves, we have pointed out that this may work better in valve sites other than the aortic [9]. One must view the experimental results reported in this paper against the background of the excellent clinical results of Starr [IO] and Morrow [II] with cloth-covered aortic ball valves in man. Yet we suggest that neither short-term data in man nor experimental data such as herein reported are adequate to support a dogmatic position at this time. SUMMARY
The results of ball valve replacement of the aortic valve in fifty-two calves are reported. These observations indicate that the less fabric exposed to the blood and the closer the fabric cuff to the suture line, the lower the incidence of thrombotic complications in this species. Acknowledgment: We wish to thank the following for their help and cooperation: Jay H. Miller, D.v.M., President, Miller Packing Co., Renton, Washington and the Seattle Packing Co., Seattle, Washington. The following contributions to the research program of this laboratory are gratefully acknowledged : American Silk sutures, Dacron sutures; Ayerst Laboratories, Fluothane; Cutter Laboratories, intravenous fluids; Edwards Laboratories, Starr-Edwards aortic valves and guided-flow aortic valves (Viggers); Ethicon, Inc., Mersilene sutures; Eli Lilly 8.~Co., Keflin. REFERENCES
1. DAVILA, J. C., AMONGERO, F., SETHI, R. S., RINCON, L. L., PALMER, T. E., and LAUTSCH, E. V. The prevention of thrombosis in artificial cardiac valves. Ann. Thoracic Surg., 2: 714, 1966. 2. PALMER, T. E., LAUTSCH, E. V., SANMARCO,M. E., and DAVILA, J. C. A nonthrombogenic, nonanticoagulant-dependent mitral valve prosthesis. Circulation (suppl. l), 35: 42, 1967. 3. BRAUNWALD, N. S. and BONCHEK, L. I. Prevention of thrombus on rigid prosthetic cardiac valves by an autogenous tissue covering. J. Th.oracic & Cardiovasc. Surg., 54: 630, 1967. 4. VIGGERS, R. F., ROBEL, S. B., and SAUVAGE, L. R. A hydraulic figure-of-merit for heart valve prostheses. J. Biomed. Mater. Res., 1: 103, 1967. 5. VIGGERS, R. F., ROBEL, S. B., WOOD, S. J., SAWThe American
Journal
of Surgery
Thrombotic
6.
i.
8.
9.
10.
11.
Complications
YER, P. ?j., WESOI,OTVSKI,S. A., and SAUVAGE L. R. Improvement of aortic ball valve function by flow guidance. .%rger_v, 63: 5’2, 1968. SAWAGE, L. R., ~‘IGCERS, R. F., WOOD, S. J., BERGER, K. E., ROBEI,, S. B., and WESOLOWSKI, S A. Prosthetic heart valve replacement. i\luter. Biomed. Engyg. New York Acad. Sci., 146: 289, 1068. WOOD, S. J. and SAUVAGE. L. R. Single plane fisation for prosthetic aortic valves. J. Tho~acic & Cc~vdiouasc. Suvy., 54: 90. 1967. SAMEH. A. A., BERGER. K. E., WOOD, S. Jo, DEDOh!ENIco. M., and SAUVAGE, L. R. Arterial healing in the mature dog, growing pig and adult man. Unpublished data. BEKGER, K., SAUVAGE, L. R.. WOOD, S. J., and WESOLOWSKI, S. A. Sewing ring healing of cardiac valve prostheses. .%rgery, 61: 102, 1967. STARR. A. Clinical and laboratory experience with the ball valve prostheses. Presented at the American Heart Association Postgraduate Seminar, San Francisco, California, October 19, 1967. MORROW, A. G. Personal communication, January 16. 1968. DISCUSSION
ALBERT STARR (Portland, Ore.): Much of our knowledge on neointima formation on cloth surfaces of prostheses has come from Dr. Sauvage. It was quite a shattering experience to find that we had taken divergent pathways with regard to design of the aortic valve prostheses. He has shown that there is a lack of thrombogenicity in highly polished metallic surfaces placed in the arterial system. This coincides with the work of Vincent Gott, for example, who showed that GBH bonded rings in the inferior vena cava of dogs did not become occluded by clot; he believed this was related to the heparinized surface of this plastic material. He then studied stellite 21 highly polished rings, made in the same manner by Edwards Laboratory as the valves Dr. Sauvage described, and found they functioned as well as GBH rings in the inferior vena cava. Also. Dr. McGoon tested pins of various materials in the aorta of experimental animals and could find no material better than a highly polished metallic surface in terms of lack of thrombogenicity. How can we correlate these findings with our own attempt to have as little exposed metallic material as possible? Dr. Sauvage’s findings are an index of what can really be expected with the model 1000 valve in the calf. His results with the completely cloth-covered valve and the completely metallic valves have involved too few experiments to be conclusive. The \ralve employed by Dr. Mcgovern and intro-
Vol. 116, August
1968
of Aortic Ball Valve duced in 1Wi3 was a rc,mplcte!y metallic valve oi highly polished titanium. This particular prosthesis gave a significant incidence of thrombc~cmbcJic camplications after implantation in man. Autopsy examinations of patients dying late after aortic valve surgery suggest that thrcrmbt~sis arises from the metallic portion of the valve where neointima could not become adherent. The cloth of the prosthesis becomes completely healed and covered with a smooth neointitna. The incidence of embolic complications with the model 1001) valve or the valve with a considerable metallic surface, was 2;i per cent, and with the model 1200 or extended cloth valve the incidence dropped to about 9 per cent. Thus there has been a significant decrease in the incidence of thromboembolic complications in man, with a reduction in the amount of metallic material exposed to the circulation. The model 2300, which was used in six call,es and which was completely cloth-covered, has been implanted in about sixty patients thus far; however, it is too early to determine whether there will be a further decrease in late thromboembolic complications. These observations in man will be crucial in determining our direction from a clinical point of view. In a specimen obtained from a patient iour years after implantation using a model 1000 valve, a glistening neointima was seen firmly attached to the cloth portion of the prosthesis: however, four years later. there was considerable thrombus material which overlapped onto the metallic side of the valve and which had a completely different appearance from the material on the cloth. In another patient a specimen obtained three months after operation using a model 1200 valve showed that in some areas the cloth and metallic junction were completely clean, as Dr. Sauvage has shown in the past, but in other areas strands of neointima extended over onto the metallic material. On liiting these up, small strands of fibrin material were seen. In a dog six months after implantation of a model 2300 valve. the valve was completely encapsulated, thereby showing how. with the use ot cloth t.hroughout the extent of the sewing ring of the val:-e. conplete healing of the prosthesis can be obtained. LESTER K. SAUVACE (closing): Dr. Starr has pointed out that there are many factors we really do not know very much about. His comments help to give us perspective which is needed by those of us involved in a considerable amount of experimental work (and Dr. Starr certainly is involved in this despite the magnitude of his clinical load). il’c have onlv a partial glimpse of it at the prcceiit time.