Results of valve replacement with the Omniscience prosthesis

J

THoRAc CARDIOVASC SURG

86:621-625, 1983

Results of valve replacement with the Omniscience prosthesis Clinical experience with the Omniscience prosthesis from two regional cardiac units in England is presented. Actuarial analysis suggests a prohibitive incidence of prosthetic thrombosis of the mitral valve, this complication occurring in 14 of a total of 96 (/5%) patients studied over a mean period of approximately 10 years. Aortic valve implantations were frequently complicated by prosthetic dehiscence, which occurred in nine of a total of 88 (10%) patients who received this valve. Our results with this prosthesis contrasts markedly with our favorable experience with other types of prostheses and lead us to question the suitability of the Omniscience valve for further clinical use.

Lameh Fananapazir, M.R.C.P., David B. Clarke, F.R.C.S.,* John F. Dark, F.R.C.S., Robert A. M. Lawson, F.R.C.S., and Henri Moussalli, F.R.C.S., Manchester and Birmingham, United Kingdom

he

Omniscience prosthesis (Medical Incorporated, Inver Grove Heights, Minn.) is a low-profilevalve with a pivoting disc and central flow, designed to reduce transvalvular gradients and thrombus formation. The disc, concavo-convex in section, is manufactured from silicon-alloyed Pyrolite and is free floating within a titanium frame. It was developed from the LilleheiKaster valve but differs from it most notably in the replacement of the long curved retaining prongs by low finlike projections on the outflow aspect of the valve frame (Fig. 1). This report deals with the results of aortic and mitral valve replacement in 196 patients, treated in two regional cardiac surgical units in Manchester and Birmingham, United Kingdom. Clinical experience with this valve is compared 'with that of other types of prostheses, also implanted over the period of study. Patients and methods

A total of 196 patients underwent valve replacement with the Omniscience prosthesis at the Regional CardiFrom the Regional Cardiac Center, Wythenshawe Hospital, Manchester. and the Queen Elizabeth Hospital, Birmingham, United Kingdom. Received for publication Dec. 7, 1982. Accepted for publication Feb. 12, 1983. Address for reprints: Dr. L. Fananapazir, M.R.C.P., Regional Cardiac Center, Wythenshawe Hospital, Manchester M23 9LT, United Kingdom. "Queen Elizabeth Hospital.

ac Center, Wythenshawe Hospital, Manchester, and the Queen Elizabeth Hospital, Birmingham, during the period June, 1979, to June, 1981. Their details are as follows: Regional Cardiac Center, Wythenshawe Hospital, Manchester. Mitral valve replacement. This group comprised 48 patients, of whom nine were men. Their ages ranged from 35 to 66 years (mean 54). All were symptomatic (Class III or IV, New York Heart Association). Sinus rhythm was present in 26 and atrial fibrillation in 22 patients. Rheumatic heart disease was the indication for operation in 38, valve prolapse in four, postinfarction mitral regurgitation in four, and malfunction of another type of prosthesis in two. The majority of the valves inserted were 27 or 29 mm in external diameter. A continuous or interrupted suture was used and the valve was oriented with its large orifice facing posteriorly. Additionally, five patients underwent De Vega tricuspid annuloplasty and six patients coronary artery bypass grafting at the same operation. Hospital survivors were followed up for a mean of 19 months (range 3 to 37). Aortic valve replacement. This group comprised 54 patients, of whom 39 were men. Their ages ranged from 34 to 68 years (mean 52). The indication for operation was calcific aortic valve disease in 50, infective endocarditis in two, and replacement of a malfunctioning prosthesis of another type in two patients. The Queen Elizabeth Hospital, Birmingham. Mitral valve replacement. This group was composed 621

The Journal of Thoracic and Cardiovascular Surgery

622 Fananapazir et al.

Anderson and associates,' were used to analyze survival and thromboembolic complication rates. Statistical differences between cumulative survival porportions or complication rates were estimated by X2 and Poisson's tests. The calculations were made using Version 8 of the Statistical Package for the Social Sciences (SPSS). Results

Fig. 1. Omniscience mitral valve prosthesis.

of 48 patients, of whom eight were men. Their ages ranged from 18 to 66 years (mean 52). All were in Functional Class III or IV. Rheumatic heart disease was the indication for operation in 42, valve prolapse in two, infective endocarditis in two, and replacement of a malfunctioning prosthesis of another type in two patients. Either a 29 or 31 mm (external diameter) prosthesis was inserted with continuous 2-0 Polydek suture, and the valve was oriented with its larger orifice facing posteriorly. Four patients underwent correction of tricuspid incompetence by a De Vega annuloplasty. Mean follow-up in the hospital survivors was 22 months (range 4 to 37). Aortic valve replacement. This group comprised 34 patients, of whom 28 were men. Their ages ranged from 20 to 69 years (mean 58). Rheumatic or congenital aortic valve disease was the indication for operation in 28, infective endocarditis in five, and replacement of a malfunctioning prosthesis in one patient. Interrupted 2-0 Polydek sutures were used. Five patients underwent additional coronary artery bypass grafting. Multiple valve replacement. Combined aortic and mitral valve replacements were performed in 11 patients. One patient underwent triple (aortic, mitral, and tricuspid) valve replacement. Statistical analysis. Actuarial methods, described by

Mitral valve replacement. . Operative mortality and late survival. There were nine hospital deaths, none directly related to the valve. Eight were from intractable left ventricular failure and one from massive pulmonary embolism. The long-term results of operation in the two series are shown in Fig. 2 and are compared with results in 294 patients who underwent valve replacement ~)Ver the same period of study by the same surgeons with other types of mitral prostheses-132 Starr-Edwards (Model 6120), 92 Bjork-Shiley, and 70 Lillehei-Kaster valves. There was no statistically significant difference (p > 0.05) between the operative mortality and survival rates of any of the patients having different types of valve replacement. The 2-year survival rate of the Omniscience mitral valve was 80%. Valve failure and thromboembolism. The incidence of thromboembolism and valve failure in patients with implanted Omniscience mitral valve prostheses in the two series are shown in Table I and compared with that in patients with other types of mitral prostheses implanted over the same period of time. Prosthetic obstruction occurred in 14 (16%) of the 87 hospital survivors. This complication occurred 3 to 31 months after implantation. One of these patients died at home and the remaining patients underwent urgent reoperation. Four died on the operating table but nine made uneventful recoveries. Actuarial analysis suggests a 31 month rate of approximately 50% for complications attributable to thrombus formation (systemic embolism plus prosthetic obstruction) (Fig. 3). Anticoagulation therapy was monitored regularly and the prothrombin index in all patients admitted with valvular thrombosis was within the therapeutic range (prothrombin ratio 1.9 to 3.1). Gradual impairment of exercise tolerance over the preceding 3 to 5 weeks was a feature of the history in 10 patients, but in 4 patients increasing dyspnea over a 6 month period had been noted. In 10 patients the thrombus was confined to the region of the pivotal mechanism and held the disc in the 20 degree open position. On the atrial aspect the clot extended onto the disc, but on the ventricular aspect it encased the finlike projection. Four of the valves were

Volume 86 Number 4 October, 1983

Omniscience valve prosthesis

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Fig. 2. Actuarial survival curves of the Omniscience mitral valve in the Manchester and Birmingham series and other mitral prostheses implanted during the same period of study.

Table I. Comparison of mitral prostheses No. of complications (incidence per 100 patient-years)

Prosthesis Omniscience Starr-Edwards

Bjork-Shiley Lillehei- Kasler

Hospital survivors

87 118 66 61

Follow-up (mo) (mean ± SD)

21 ± 17 ± 24 ± 21 ±

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9 12 12 10

5 (3.4) 8 (4.9) 3 (2.3)* 7 (6.3)*

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2 (1.3) I (0.6)

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3 (2.0) 4 (2.5) 1 (0.8) 2 (1.8)

14 (9.4)tt

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.p < 0.05 compared with the Starr-Edwards prosthesis. tp < 0.002 compared with the Starr-Edwards prosthesis. :j:p < 0.002 compared with the Bjork-Shiley prosthesis. §p < 0.01 compared with the Bjork-Shiley prosthesis.

totally encapsulated in thrombus on both their atrial and ventricular aspects with the disc trapped again in the 20 degree open position (Figs. 4 and 5). The thrombus was sectioned and the lines of stratification suggested that in these patients, too, the thrombotic process originated in the region of the pivotal mechanism. There were five paraprosthetic leaks. Three were -severe, necessitating further operation, and two of the patients requiring reoperation died on the table. The incidence of this complication with the Omniscience valve was similar to that with the other types of valves (Table I). There have been three late deaths unrelated to the prosthesis. The surviving patients have attained a satisfactory improvement in exercise tolerance. Aortic valve replacement. There were no hospital or

late deaths in either series. A common problem during the follow-up period has been suture line dehiscence, occurring in nine (10%) of the 88 patients. In three patients this resulted in minor para prosthetic leaks that have not necessitated further treatment. Major disruptions of the attachment of the valve involving 50% or more of the circumference occurred in seven patients. These occurred 1 to 6 months following implantation; all were successfully managed by further operation. The sewing rings of the valve were intact as were the sutures that had cut out of the aortic anulus. A further patient has required a second operation for prosthetic thrombosis 12 months following implantation. The results of aortic valve replacement with the Omniscience prosthesis have been satisfactory to date in the remaining patients. In a comparable series of 200

The Journal of Thoracic and Cardiovascular Surgery

Fananapazir et al.

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Fig. 3. Thrombotic incidence (systemic emboli and prosthetic thr ombosis) of the Omniscience valve. Cumulative numbers of patients affected in the two series are given in parenthe-

ses.

Fig. 5. Major thromboses on the Omni science mitral valve.

Fig. 4. Minor thromboses around the retaining projections of the va lve ring.

aortic valve replacements with the Bjork-Shiley prosthesis. only one patient has required further operation for significant paraprosthetic leak and no major dehiscence has occurred. Multiple valve replacement. There has been one hospital death from refractory ventricular fibrillation. The surviving 11 patients have remained well without complications . Discussion The concept of the Omniscience valve is attractive. The orifice is free from the disc-retaining mechanism

used in other tilting disc valves. and the reduction of the long retaining prongs of the Lillehei-Kaster valve to small finlike projections reduces the risk of entanglement of the sutures and perforation of the myocardium. 1n vitro studies':' suggest that the Omniscience valve equals or betters the performance of other tilting disc prostheses. There have been few reviews of clinical experience with this valve. In a series of 320 implants, Aschatzy and associates' recorded acceptable postoperative gradients of 12 ± 4 mm Hg across the aortic and 4 ± 1.5 mm Hg across the mitral prostheses. No complications were reported in a follow-up period spanning 3 years. Data collected by DeWall and Mikhail" on 278 implants followed up over a mean period of 9 months (maximum 30) also indicate that the in vivo hemodynamic performance of the valve is good. The incidence of thromboembolism and thrombosis in the mitral valve ranged from 0.8 to 4.2 per 100 patientyears, and actuarial analysis suggests a 5 year survival rate of 87% to 90%. Our experience contrasts sadly with these favorable reports. There are two main problems. The incidence of thrombus on the Omniscience valve in the mitral area has been a devastating complication in our experience, occurring with a frequency of 12.8 per 100 patientyears. This is similar to the thrombotic incidence of the Lillehei-Kaster valve (l0.8 per 100 patient-years) but compares poorly with the thrombotic incidence of the Starr-Edwards and Bjork-Shiley prostheses implanted over the same period of time (4.9 and 2.3 per 100

Volume 86

Omniscience valve prosthesis

Number 4 October, 1983

patient-years, respectively). Examination of valves removed before total encapsulation had occurred points to the pivot mechanism as the area where thrombosis starts. This impression is reinforced by study of the lines of stratification in the thrombus. There is little clearance between the disc and the valve ring. The pivotal mechanism consists of two small projections that serve to retain the disc whilelimiting its opening to 80 degrees. Inspection of this mechanism suggests that there are small areas where washing of the surfaces by blood is restricted, and thrombosis may well be initiated in these pockets. If this hypothesis is correct, a major modification of the design of the valve will be necessary to overcome its propensity to allow thrombosis. The possibility remains, however, that the thrombotic incidence may have been different if the mitral prosthesis had been oriented anteriorly. The incidence of valve dehiscence in the aortic position in this series is very much higher than with other valves used at our centers. In our view the design of the sewing ring is a significant factor. The skirt of the valve is a seamlesssleeve of knitted Dacron, packed with threads. This packing resists the passage of needles in a fashion not encountered with the foam or felt packing used by other valve manufacturers. In order to drive needles through the sewing ring, the surgeon may take rather shallow bites toward the periphery of the skirt. Therefore, little prosthetic material is included within the suture to buttress the tension used when tying knots, to cushion the stresses imposedduring valveclosure, and to bed down against the tissues.The manufacturers have recognized this shortcoming and are introducing a revised, more floppy sewing ring with improved penetrability. We have not used this modification but anticipate that, in its new format, the Omnscience aortic valve will perform well in this respect. We were also impressed by the lack of tissue ingrowth into the cloth ring in valves removed for paraprosthetic leak. Excessive incidence of thrombosis associated with the Lillehei-Kaster mitral valve has been reported previousIy;' and problems with the Omniscience prosthesis have

625

also been reported by other workers. Ohlmeier, Mannebach, and Greiterneier" found that opening of the disc was significantly less than that predicted by in vitro studies. Three of four mitral prostheses had to be replaced. Our adverse experience with the Omniscience and Lillehei-Kaster prostheses has led us to discontinue their use and prompts us to suggest that they are unsuitable for clinical valve replacement. We are grateful to Mrs. Mary Rooney for preparing the manuscript.

2

3

4 5

REFERENCES Anderson RP, Bonchek LI,Grunkemeier GE, Lambert LE, Starr A: Theanalysis and presentation ofsurgical results by actuarial method. J Surg Res 16:224-230, 1974. Huffstutler MC: Scientific evaluation of in-vitro performance of the Omniscience cardiac valve, presented at the Thirty-fourth Annual Conference of Engineering in Medicine and Biology, Houston, September, 1981 Reif TM, Huffstutler MC: A preliminary flow study of a two dimensional model of a concavo-convex pivoting disc prosthetic heart valve. Proceedings of the Seventh New England Bioengineering Conference, 1979, pp 209-211 Scotten LN, Racca RG, Nugent AH, Walker OK, Brownlee RT: New tilting disc cardiac valve prosthesis. J THoRAc CARDIOVASC SURG 82:136-146, 1981 Aschatzy R, Jelesijevic Y, Anyanwu E, Klinke F, Dittrich H: A new prosthetic heart valve (Omniscience). A clinical trial proceedings of the Joint International Cardiovascular and Thoracic Surgical Conference, Stockholm, September, 1982, p 14

6 DeWall RA, Mikhail AA: Omniscience cardiac valve prostheses. Clinical review, I. Presented before the American College of Cardiology, Snowmass, Colo., January, 1982

7 Forman R, Beck W, Barnard CN: Results of valve replacement with the Lillehei-Kaster disc prosthesis. Am Heart J 94:282-286, 1977 8 Ohlmeier H, Mannebach H, Greitemeier A: Clinical follow-up of patients after valve replacement with Omniscience cardiac valves. Can this valve be recommended? Z Kardiol 71:350-356, 1982