Results of mitral valve replacement with the Beall prosthesis in 209 patients

Results of mitral valve replacement with the Beall prosthesis in 209 patients In this 3 year study of 209 patients who underwest mitral valve replacement with the newer Beall prostheses (Models 104 and 105) the operative mortality rate was 5.2 per cent. None of these deaths was related to the valve. This prosthesis features a larger frustrum area and a "turtle-neck" sewing ring which permits its rapid insertion with a continuous suture technique. Of the 20 (9.5 per cent) late deaths, two were due to thrombosis of the valve. Among the 178 survivors, 17 developed thromboembolic complications; however, 10 of these patients recovered. Late clinical results have been quite satisfactory in over 90 per cent of the survivors. In the 15 patients who underwent hemodynamic studies postoperatively, the cardiac index and pulmonary artery pressure showed significant improvement; however, they still had transvalvular gradients at rest. The improvement in the design of this prosthesis has been an important factor in lowering the operative risk and improving the late results of mitral valve replacement.

Javier Fernandez, M.D., Dryden Morse, M.D., Paschal Spagna, M.D., Gerald Lemole, M.D., Alden Gooch, M.D., Sing Sang Yang, M.D., and Vladir Maranhao, M.D., Browns Mills, N. J., and Philadelphia, Pa.

A he low-profile Teflon-disc mitral Beall prosthesis, introduced for clinical use in 1967,1, 2 was designed primarily to decrease the incidence of thromboembolism by totally covering the valve ring with Dacron velour. Our clinical experience with the early model of this valve indicated a significant decrease of thromboemboli as compared with our ball valve experience.3 In this report we analyze the long-term results with the later models (104 and 105). In these the frustrum area was increased 20 per cent. In Model 105 both the occluder disc and the struts were coated with Pyrolite carbon.4 Clinical material A total of 209 patients underwent isolated mitral valve replacement between September, 1971, and December, 1973; 109 had Model 104 implanted and 100 had Model 105. There were a total of 212 valves implanted (three re-replacements). The period of From the Department of Cardiology and Cardiothoracic Surgery at Deborah Heart and Lung Center, Browns Mills, N. J., and the Department of Cardiothoracic Surgery at Temple University Hospital, Philadelphia, Pa. Received for publication April 29, 1975. Address for reprints: Javier Fernandez, M.D., Deborah Heart and Lung Center, Trenton Rd., Browns Mills, N. J. 08015.

2 18

observation extended until December, 1974, and it ranged from 1 to over 3 years. A 100 per cent follow-up was achieved. There were 70 male and 139 female patients with an age range of 20 to 75 years; most of the patients were in the fourth, fifth, and sixth decades of life. Rheumatic valvulitis was the operative indication in 185 (88.5 per cent) of the patients. Various etiologic factors were present in the remaining 24 patients. Atrial fibrillation was present in 174 (83 per cent) and preoperative embolism was present in 34 (16 per cent) patients (Table I). There were 39 (18.6 per cent) patients with predominant mitral stenosis, 58 (27.8 per cent) with mitral regurgitation, and 107 (51 per cent) had combined stenosis and regurgitation. Malfunctioning of a previously inserted mitral valve prosthesis was present in five (2.4 per cent) patients. There were 134 (64 per cent) patients who had associated heart lesions; however, in only 32 (15 per cent) was a concomitant procedure required (Table II). Patients requiring multiple valve replacements were excluded from this study. There were 46 (22 per cent) patients who had a history of previous heart operations (Table III). The approach was through a median sternotomy incision, although reoperation was occasionally done through a right thoracotomy. Total cardiopulmonary

Volume 71 Number 2 February, 1976

Mitral valve replacement with Beall prosthesis

Table I. Operative indications

Table III. Previous heart operations

Rheumatic heart disease Bacterial endocarditis Papillary muscle dysfunction Malfunctioning prosthesis Undetermined Other findings Atrial fibrillation Previous embolism or atrial thrombus

No. of patients

Per cent

185 4 8 5 7 209

88.5 1.9 3.8 2.4 3.3

174 34

83.0 16.0

219

No.

38 2 4 1 1 46 (22%)

Mitral commissurotomy Aortic prosthesis Cross-Jones mitral valve Beall valve Jump graft Total

T n h i n i\r

/<„■„(,.,.,•.. „t „ „ - / , ,

A„„t Un „f*„r *>nQ

mitral valve replacements Table II. Associated cardiac and procedures procedures Concomitant procedure

Lesion Aortic Coronary Tricuspid ASD*

73 20 38 3 134 (64%)

Aortic commissurotomy "Jump" graft Tricuspid plication ASD closure

3 10 16 3 32 (15%)

Myocardial failure Pulmonary embolism Acute aortic dissection Uncontrolled bleeding Upper gastrointestinal hemorrhage Mesenteric thrombosis Acute thrombosis—carotid artery Total

No. of patients

Time postop.

4 2

1 day 3, 6 days Intraoperative Intraoperative 1 day 2 days 12 days

11 (5.2%)

* Atrial septal defect.

bypass with hemodilution was used. The "turtle-neck" prosthesis was fastened in place with a continuous suture in 90 per cent of the cases. Interrupted sutures were used in cases with severe calcification or weak annular tissue. Results There was a 5.2 per cent operative mortality rate. None of the 11 early deaths was related to the prosthesis (Table IV). During the follow-up period (one to three years) there were 20 deaths (Table V). Seven of these were related to the prosthesis: three patients developed bacterial endocarditis at 2, 11, and 13 months after operation. In one of these patients a second Beall valve was inserted as a replacement after an intensive course of antibiotic therapy. Subsequently, however, the infection recurred and the patient developed congestive failure and died after 2 months. Thrombosis of the valve occurred at 24 months after operation in a drug addict who had discontinued anticoagulant medication. She was admitted in a moribund state and died following replacement of her prosthesis. Another patient died 2 days after reoperation to extract valve thrombi, evidenced by repeated emboli. Another died after reoperation to correct a paravalvular leak. One

further patient died of a cerebellar hemorrhage due to excessive doses of anticoagulants. The remaining 13 late deaths were unrelated to the prosthesis. The various causes of death were common to other types of open-heart operations. Four patients in this group died of progressive myocardial failure. There were a total of 178 (85.5 per cent) survivors at the end of the study period. Fig. 1 represents the survival of the total group in actuarial fashion. The survivorship curve shows that most nonoperative deaths occurred during the first year after operation. At the end of the first year the curve tends to reach a slowly declining plateau, following closely the pattern of the general population curve. Complications Nonfatal late thromboemboli occurred in 17 (9.5 per cent) of the survivors between 2 and 18 months after operation (Table VI). Of this group, 10 had minor and transient episodes with complete recovery. Seven others had signs of neurologic deficit at the time of their most recent follow-up visit, but none was incapacitated. Anticoagulant therapy with Coumadin is given to every patient. An effort is made to maintain their prothrombin times between 20 and 30 seconds. After discharge from the hospital the patient is referred to his

The Journal of Thoracic and Cardiovascular Surgery

2 2 0 Fernandez et al.

M«+« _

80-

I (178 Pts.)

70 -

60 -

^

_i i i

■ ■ ! ■ ■ ■ ■

_i

12 Months Postoperative

i

! ' ■ ■ ' ■

24

I

36

Fig. 1. Actuarial survival curve after isolated mitral valve replacement with the Beall prosthesis in 209 patients. Table V. Analysis of late deaths after 209 mitral valve replacements No. of patients Related to prosthesis: Endocarditis Thrombosed valve Reoperation for valve thrombi Reoperation for leak Anticoagulants Total Other causes of late deaths: Heart failure Myocardial infarction Pneumonia Renal failure Arrhythmia Unknown Total

Months post op.

Table VI. Late thromboemboli (2 to 18 months) With complete recovery With residual deficit

No. of patients

Per cent

10

5.6 3.9 9.5

2

17*

3 I 1 1 1 7 (3.3%)

2, 11, 23 24 2 5 3

4 3 1 1 1 3 13 (6.2%)

4, 3, 9, 10 2, 2, 2 2 2 11 12, 16, 16

private physician for continuation of the anticoagulation program. As mentioned in the discussion of mortality rates, there was also one patient who developed a thrombosed prosthesis and another who died after reoperation to extract valve thrombi. The total incidence of thromboembolic phenomena in the survivors is represented actuarially in Fig. 2. It can be noted that the greatest incidence of thromboembolism occurred within the first 15 months after operation. No embolic episodes have thus far occurred in patients whose follow-up has exceeded this length of time. At the end of the study

*Seven not on anticoagulants or poorly controlled.

period 90 per cent of the surviving patients were free of emboli or a history of emboli. Other late complications. In addition to the patient who died following correction of a paravalvular leak, there were two others who are surviving with a significant paravalvular leak. Both will require correction in the near future since they are symptomatic and have hemolytic anemia. As mentioned above, none of our patients with bacterial endocarditis survived. No instance of malfunction of the disc of the prosthesis owing to wear occurred in this series. We did not see any case of fracture of the struts in patients who received the Model 105 with the disc and struts coated with Pyrolite. With the exception of the two patients mentioned who had paravalvular leak, we have not seen significant hemolytic anemia in this series; however, many of our patients receive prophylactic iron therapy. Functional results. Most of the 178 late survivors reported symptomatic improvement with resumption of normal or near normal activities, as shown in their New York Heart Association functional classification (Table VII). Most patients were in Class III or IV before operation and improved to Class I or II after mitral replacement. Surgery was necessary in 8 Class I

Volume 71 Number 2 February, 1976

Mitral valve replacement with Beall prosthesis

22 1

Percent 100

i088Pts.)

T

-O

%

E w |

i

« §

■ &

85

'>

03

*-N—*

90-

80-

1

i i ■ ■

'

12

_l_l

■ ■ ■ ■

24

■ ■ '

36

Months Postoperative

Fig. 2 Actuarial curve showing the percentage of survivors free of embolic complications after mitral valve replacement with the Beall prosthesis in 209 patients.

Table VII. Results: Functional class (NYHA) Preoperative

Class

No. of patients

I II III IV Total

8 42 122 37 209

Per cent 4 20 59 17

Postoperative No. of patients 101 65 10 2 178

Table VIII. Hemodynamic data in 15 patients after mitral valve replacements Parameters

Per cent* 56.7 36.5 5.6 1.1

*Per cent of the survivors.

and 42 Class II patients who had either embolic episodes and/or a malfunctioning (mitral) prosthetic valve. Objective evidence of the degree of improvement was obtained in 32 patients through treadmill exercise testing preoperatively and between 12 and 36 months postoperatively. As shown in Fig. 3, in most cases there was a definite objective improvement with the exception of three patients who performed at the same level and one who did not do as well. Hemodynamic studies were performed in 15 patients postoperatively 12 and 36 months following operation (Table VIII). The mean transvalvular gradient was 15 mm. Hg preoperatively and 10 mm. Hg postoperatively. This gradient occurred at rest. All of these patients had the Model 105 valve. There were 10 large, four medium, and one small prostheses in this group. The frustrum areas for this prosthesis, according to the manufacturer (Surgitool, Inc., Pittsburgh, Pa.), are 5.4 sq. cm. for the large, 4.3 sq. cm. for the medium, and 3.4 sq. cm. for the small valve. Among the 15 patients

Mean

Mitral valve gradient (mm. Hg): Preop. Postop.

15 10*

Peak pulmonary artery pressure (mm. Hg): Preop. Postop.

36t

Cardiac index Preop. Postop.

57

(L./m./M.2): 1.95 2.90t

*Not significantly different from preop. value (p < 0.05). tSignificantly different from preop. value (p < 0.01).

catheterized, in 13 the calculated functioned valve area postoperatively for each size prosthesis was 1.7, 1.5, and 1.6 sq. cm., respectively. In each case the mean systolic pulmonary artery pressure showed a significant drop; the average went from 57 mm. Hg preoperatively to 36 mm. Hg postoperatively (p < 0.01). Similarly, there was a significant increase in the mean cardiac index from 1.95 L. per minute per square meter before operation to 2.9 L. per minute per square meter postoperatively (p < 0.01). Discussion Previous experimental and clinical work by Braunwald,5 Bonchek,6 and Davila7 and their co-workers suggested that cloth covering of the nonmoving parts of a rigid prosthetic heart valve would decrease the

The Journal of Thoracic and Cardiovascular Surgery

2 2 2 Fernandez et al.

3 2

c ,t

7

(>8m)

IS

rformance

7

S. F

12

3 3 i

7

10

!

3

•5 (3-«m)

I

3

P

(2m)

VP ■ w

3 No.Pts.

Pre-op

No Pts.

Post-op

Treadmill Exercise Test in 32 Patients

Fig. 3. Treadmill exercise testing in 32 patients after isolated mitral valve replacement with the Beall prosthesis. E, Excellent. G, good. F, Fair. P, Poor, m, Minutes on the treadmill at 5 miles per hour.

incidence of postoperative thromboemboli by vitue of the elimination of the metal-to-tissue interface, and by allowing for the natural process of healing "to encapsulate" or endothelialize the valve seat. These investigators suggested that the thrombus in a prosthetic valve originated at that junction. The application of this principle resulted in the design and improvement of various types of prosthetic valves in which the nonmoving parts were either partially or totally cloth covered. The introduction of low-profile prostheses8"11 did much in the way of eliminating some of the problems related to the more bulky ball valves, such as obstruction of the left ventricular outflow tract by the cage and the ball, and arrhythmias due to irritation of the septum from the protrusions of the cage into the left ventricle. In 1968 we adopted the low-profile Dacron-velourcovered mitral Beall valve. Our initial results with this prosthesis indicated a substantial decrease in the incidence of postoperative emboli and a significant clinical improvement in the survivors.3, 12 Others have reported similar results. 13-16 Our present over-all operative mortality rate of 5 per cent compares favorably with the 8.6 per cent in our previous (1973) series.3 This reflects improvements in the preoperative care, in the design of the valve, and in our surgical technique. The main modification in technique in the present series has been the use of a

continuous suture for valve fixation17 in most cases, which allows us to cut down bypass time. Improvements in the design of this valve have centered on increasing its frustrum area without changing its mounting diameter, and on making the materials more durable. In the Models 104 and 105 used in this series the increase in the frustrum area was 20 per cent over the previous models. The occluder disc in the Model 104 was made of a more highly compressed and durable Teflon. In the 105 the disc and struts were covered by Pyrolite (carbon). After strut breakage was reported, the struts were made stronger and new packaging adopted. The late mortality rate of 9.5 per cent was similar to the rate in our first series. The most common cause of death, congestive heart failure, was related to the degree of underlying myocardial or coronary disease. Seven late deaths occurred from causes related to the prosthesis but common to other prosthetic valves. Postoperative emboli occurred in 19 (9 per cent) of the cases. This represents a substantial decrease from our experience with the uncovered ball valves and about the same as with the earlier models of the Beall valve. Beall4' 18 himself has reported only four thromboembolic complications in 175 patients who had the Model 105 valve. Although 2 of our patients died because of thrombosis of the valve, both died at the reoperation in an attempt to replace the prosthesis. Most of the 17 patients who experienced emboli and survived had minor episodes that left no neurological sequelae. One of these patients was reoperated upon 16 months after the initial surgery and the valve re-replaced sucessfully with another Beall valve. Clots were found attached to the struts of the valve on the ventricular side. He is alive and well at present, 3 years after his reoperation. It is interesting to note that the embolic actuarial curve showed that the incidence of embolic episodes was greatest during the first postoperative year and decreased precipitously during the subsequent years of follow-up, just as observed in our first series.3 Rossi and Ehrenhaft19 reported a similar observation using various models of the Beall valve, including the Model 104, although in one of their patients cases one embolic episode occurred at 54 months after operation. In our present series, among those patients who have a follow-up of more than 18 months, no embolic episodes have occurred so far. This observation probably indicates a decreased tendency to local thrombus formation as the cloth-covered valve seat becomes endothelialized. Some of the older Beall valves that we have excised

Volume 71 Number 2 February, 1976

(usually for disc wear) after several years of implantation confirm the impression that the valve seat becomes well encapsulated without excessive tissue build-up between 1 and 2 years after operation in most cases. Based on these observations, we feel that anticoagulation is important, particularly during the first 18 months, although this question has not been completely settled.13, 15 We made an effort to maintain the prothrombin time at therapeutic levels (between 20 and 30 per cent of the control). Our follow-up experience to date with anticoagulants indicates that about one third of the patients stop or have stopped the Coumadin at some time, or are very poorly controlled. This may be one factor explaining why we still see embolic episodes during the first 2 years after mitral valve replacement. When the prosthesis becomes encapsulated after this time perhaps anticoagulant therapy is not so essential. We feel that the risk of emoblism during the first 2 years of implantation is higher than the risk of anticoagulants. Further study and longer follow-up are necessary to determine if it would be advisable to discontinue anticoagulants after 2 years of mitral valve implantation. Paravalvular leak is a complication common to the use of all types of prosthetic valve replacements. In our 3 cases it appeared unrelated to the method of valve fixation with the continuous suture technique, since it has been seen also with the interrupted method. 3 ' 20 " 22 We feel that the subannular position of this "turtleneck" valve tends to decrease any possible suture leak,17 since the flanged edge of the valve abuts against the ventricular side of the mitral annulus, especially during systole. Regardless of the method of valve fixation, attention to surgical details—the delicate handling of tissues, the placement of the suture "bites" close together, adequate exposure, and the judicious use of ichemic arrest to improve operative conditions during implantation—makes the difference between a high or a low incidence of this complication. As pointed out by Fishman, Hutchinson, and Roe,20 factors such as the friability of the annulus in cases of floppy mitral valve or of pure mitral regurgitation, and unequal tension of sutures, are to be considered as other underlying causes of paravalvular leak. Despite reports of early and late hemolysis occurring with the Beall valve and other cloth-covered prostheses23-25 we have not seen significant hemolytic anemia in our patients in the normally functioning valve without a paravalvular leak. (Routine hematocrit and hemoglobin determinations are done during the follow-up visits, and red cell counts have been maintained within a normal range.)

Mitral valve replacement with Beall prosthesis

223

Since we have not seen serious hemolysis in this series except with paravalvular leak, no specific studies were made to investigate the state of compensated hemolytic anemia that occurs in some patients. In most cases iron therapy has been given for varying periods of time. Theoretically, if the hemolytic effect of the valve is due to the Dacron covering of the valve, this effect would tend to decrease as the valve becomes endothelialized. Prosthetic endocarditis, however, was a particularly lethal complication. All three patients who developed this complication died despite desperate efforts to control the infection with antibiotic coverage and surgical excision of the infected prosthesis in two of them. It is worth noting that no patient developed complications related to mechanical malfunction of the valve. It seemed that the new compressed Teflon disc in the Model 104 valve did not show the wearing characteristics that were seen in the early model of the Beall valve,26 although we did remove for emboli one Model 104 prosthesis after 18 months that did show beginning notching of the disc. In the case of the Model 105 with the Pyrolite carbon disc and struts, there were no cases of malfunction due to strut fracture or disc wear. Nathan27 reported four cases of strut fracture, which he suggested were due to either damage in shipping or some intrinsic defect of the prosthesis. The Pyrolite carbon, although more durable than Teflon, is more brittle and can break easily. Because of this serious complication the Pyrolite valve was withdrawn from the market temporarily in 1974. The modified new Pyrolite valve (Model 106) has stronger struts and comes in a new packing device with rigid instructions to protect the valve from traumatic handling. The great majority of the patients in this series improved markedly clinically and are leading nearly normal lives. Comparative treadmill testing, in the few patients subjected to it, also showed objective improvement. Despite the manufacturer's prediction that the Model 104 and 105 valves with the larger frustrum areas would improve the hemodynamic characteristics of the valve, however, in the 15 patients who underwent hemodynamic studies after operation a resting mean transprosthetic diastolic gradient of 10 mm. Hg was found. Linhart,28 Ramsey,29 and Reid30 and their co-workers reported similar gradients with the early models of the Beall valve. This persistent postoperative gradient perhaps can partly be explained by the fact that those patients whom we studied were the ones who

2 24

The Journal of Thoracic and Cardiovascular Surgery

Fernandez et al.

failed to improve. In 2 patients this was due to paravalvular leak. In this group we also included the patient who underwent reoperation for extraction of valve thrombi. The asymptomatic patients refused to be subjected to catheterization and our staff was hesitant to bring into the hospital patients who were doing well and subject them to the discomfort and risk of recatheterization. Therefore, it is possible that the general hemodynamic results are much better than they appear from this study. Behrendt and Austen 31 suggested that obstruction at the tertiary orifice (that is, the opening between the perimeter of the disc and the surrounding tissue when the valve is open) is what determines the main obstruction to forward flow. With this point in mind, and in the light of the average 10 mm. gradient, we now make sure that the size of the inserted prosthesis is no larger than necessary to avoid reducing the "tertiary orifice." It is worth noting, nevertheless, that in all cases the mean pulmonary artery pressure and mean cardiac index improved significantly after mitral replacement. Beall and associates 4 reported a similar increase in the cardiac index and smaller mean diastolic gradients (2 to 7 mm. Hg) across the prosthesis (105) in 17 patients. The clinical improvement manifested by the majority of the survivors speaks in favor of the continued use of this prosthesis for mitral valve replacement. It seems, however, that patients with the Beall valve are still subject to embolic complications and postoperative gradients. It is hoped that further improvements in anticoagulation methods and valve design will improve still more the clinical results of prosthetic mitral valve replacement. REFERENCES 1 Beall, A. C , Jr., Bloodwell, R. D., Liotta, D., et al.: Elimination of the Sewing Ring-Metal Seat Interface in Mitral Valve Prosthesis, Circulation 38 (Suppl. I): 184, 1968. 2 Beall, A. C , Jr., Bloodwell, R. D., Liotta, D., et al.: Clinical Experience With a Dacron Velour-Covered Teflon-Disc Mitral Valve Prosthesis, Ann. Thorac. Surg. 5: 402, 1968. 3 Nichols, H. T., Fernandez, J., Morse, D., and Gooch, A. S.: Improved Results in 336 Patients With the Isolated Mitral Beall Valve Replacement, Chest 62: 266, 1972. 4 Beall, A. C , Jr., Morris, G. C , Jr., Noon, G. P., et al.: Clinical Experience With an Improved Mitral Valve Prosthesis, Ann. Thorac. Surg. 15: 601, 1973. 5 Braunwald, N. S., and Bonchek, L. I.: Prevention of Thrombus Formation on Rigid Prosthetic Heart Valves by Ingrowth of Autogenous Tissue, J. THORAC. CARDIOVAS. SURG. 54: 630,

1967.

6 Bonchek, L. I., and Braunwald, N. S.: Thrombus Resistant Rigid Prosthetic Heart Valves Covered With Porous Synthetic Fabric, Trans. Am. Soc. Artif. Intern. Organs 13: 101, 1967. 7 Davila, J. C , Amongero, F., Sethi, R. S., et al.: Prevention of Thrombosis in Artifical Heart Valves, Ann. Thorac. Surg. 2: 714, 1966. 8 Cooley, D. A., Bloodwell, R. D., and Hallman, G. L.: Mitral Valve Replacement With a Discoid Prosthesis, Ann. Thorac. Surg. 3: 487, 1967. 9 Cross, F. S., and Jones, R. D.: A Caged-Lens Prosthesis for Replacement of the Aortic and Mitral Valves, Ann. Thorac. Surg. 2: 499, 1966. 10 Kay, J. H., Kawashima, Y., Kagawa, Y., Tsuji, H. K., and Redington, V. V.: Experimental Mitral Valve Replacement With a New Disc Valve, Ann. Thorac. Surg. 2: 485, 1966. 11 Vaidya, M. P., Cohen, L. H., and Collins, J. J.: Valve Replacement in Rheumatic Heart Disease, Chest 63: 807, 1973. 12 Morse, D. P., Nichols, H. T., Fernandez, J., and Gooch, A. S.: The Low Incidence of Systemic Emboli in Patients With the Beall Mitral Prosthesis, Presented at the Twentieth Annual Scientific Session of the American College of Cardiology, Washington, D. C , Feb. 5, 1971. 13 Javier, R. P., Hildner, F. J., Berry, W., Greenberg, J. J., and Samet, P.: Systemic Embolism and the Beall Mitral Valve Prosthesis, Ann. Thorac. Surg. 10: 20, 1970. 14 Messmer, B. J., Okies, J. E., Hallman, G. L., and Cooley, D. A.: Early and Late Thromboembolic Complications After Mitral Valve Replacement, J. Cardiovasc. Surg. 13: 281, 1972. 15 Stanford, W., Lindbert, E. F., and Armstrong, R. G.: Implantation of Heart Valve Prostheses Without Anticoagulants, J. Cardiovasc. Surg. 63: 648, 1972. 16 Vogel, J. H. K., Paton, B. C , Overy, H. R., Pappas, G., Davies, H., and Blount, S. G., Jr.: Advantages of the Beall Valve Prosthesis, Chest 59: 249, 1971. 17 Fernandez, J., Tesler, U. F., Morse, D., and Lemole, G. L.: Continuous Suture Technique for Fixation of Turtleneck Beall Mitral Prosthesis, J. Cardiovasc. Surg. 15: 411, 1974. 18 Beall, A. C , Jr.: In discussion of Cooley, D. A., Okies, J. E., Wukasch, D. C , et al.: Ten-Year Experience With Cardiac Replacement: Results With a New Mitral Prosthesis, Ann. Surg. 177: 818, 1973. 19 Rossi, N. P., and Enrenhaft, J. L.: Single Valve Replacement With the Beall Mitral Prosthesis, J. THORAC. CARDIOVASC. SURG. 67: 83,

1974.

20 Fishman, N. H., Hutchinson, J. E., and Roe, R. B.: Prevention of Prosthetic Cardiac Valve Detachment, Surgery 67: 867, 1970. 21 Kastor, J. A., Akbarian, M., Buckley, M. J., Dinsmore, R. E., Sanders, C. A., Scannel, J. G., and Austen, W. G.: Paravalvular Leaks and Hemolytic Anemia Following Insertion of Starr-Edwards Aortic and Mitral Valves, J. THORAC. CARDIOVASC. SURG. 56: 279,

1968.

Volume 71 Number 2 February, 1976

22 Favaloro, R. G., Effier, D. B., Groves, L. K., Suarez, E., and Shirey, E. K.: Surgical Repair or Leaking Prosthetic Heart Valves, Ann. Thorac. Surg. 3: 503, 1967. 23 Henderson, B. J., Mitha, A. S., le Roux, B. T., and Gotsman, M. S.: Hemolysis Related to Mitral Valve Replacement With the Beall Valve Prosthesis, Thorax 28: 488, 1973. 24 Editorial: Anemia With Artificial Heart Valves, Lancet 1: 1321, 1972. 25 Williams, J. C , Vernon, C. R., Daicoff, G. R., et al.: Hemolysis Following Mitral Valve Replacemnt With the Beall Valve Prosthesis, J. THORAC. CARDIOVASC. SURG.

61: 393, 1971. 26 Robinson, M. J., Hildner, F. J., and Greenberg, J. J.: Disc Variance of Beall Mitral Valve, Ann. Thorac. Surg. 11: 11, 1971. 27 Nathan, M. J.: Strut Fracture, Ann. Thorac. Surg. 16: 610, 1973.

Mitral valve replacement with Beall prosthesis

225

28 Linhart, J. W., Barold, S. S., Hilner, J. F., Samet, P., Piccinimi, J. C., Moosten, J. L., and Greenberg, J. J.: Clinical and Hemodynamic Findings Following Replacement of the Mitral Valve With Beall Prosthesis (Dacron Velour-Covered, Teflon-Disc Valve), Circulation 39 (Suppl. I): 127, 1969. 29 Ramsey, H. W., Williams, T. C , Vernon, C. R., Wheat, M. W., Daircoff, G. R., and Bartley, T. D.: Hemodynamic Findings Following Replacement of the Mitral Valve With the Beall Valve Prosthesis, J. THORAC. CARDIOVASC. SURG. 62: 624,

1971.

30 Reid, J. R., Stevens, T. W., Segwart, U., Fulweber, R. C , and Alexander, J. K.: Hemodynamic Evaluation of the Beall Mitral Valve Prosthesis, Circulation 45 (Suppl. I): 1, 1972. 31 Behrendt, D. M., and Austen, W. G.: Current Status of Prosthetics for Heart Valve Replacement, Prog. Cardiovasc. Dis. 15: 369, 1973.