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Ann Thorac Surg 1996;62:40-47
© 1996 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

The Spanish Monostrut Study Group: A Ten-Year Experience With 8,599 Implants

Cardiac Surgery Centers in Barcelona, Madrid, Santander, Pamplona, and Córdoba, Spain

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 
Background. The Monostrut valve is a pyrolytic carbon, tilting-disc prosthesis with no welds. After the first implantation in Spain in May 1983, the Spanish Monostrut Study Group was established to evaluate prospectively the performance of the valve using uniform protocols.

Methods. During a 10-year period, 8,599 Monostrut valves were implanted in 7,317 patients in 22 centers. Mean age was 53.3 ± 11 years. Of the total group, 3,229 underwent aortic valve replacement, 2,806 had mitral valve replacement, and 1,282 had double valve replacement. Follow-up was 96% complete, with a mean period of 4.3 years and a total of 29,155 patient-years.

Results. The operative mortality rate was 7.2%. The 10-year probability of freedom from valve-related complications and linearized rates (event/100 patient-years in parentheses) were as follows: structural deterioration, 100% (0); nonstructural dysfunction, 96% ± 0.5% (0.51); thromboembolism, 82.9% ± 1.5% (1.32); anticoagulant-related hemorrhage, 87.6% ± 1.4% (0.98); and prosthetic valve endocarditis, 96.1% ± 0.5% (0.48). There were five obstructive valve thromboses (0.017/100 patient-years). Actuarial freedom from reoperation was 95% ± 0.5% at 10 years. Actuarial freedom from all valve-related morbidity was 70.2% ± 1.6%; freedom from all valve-related morbidity and mortality (including operative and sudden deaths) was 62.6% ± 2% (70.1% ± 2% for aortic valve replacement, 56.9% ± 2% for mitral valve replacement, and 59.8% ± 3% for double valve replacement; p < 0.0001). Clinically, 5,988 patients (94%) are in New York Heart Association class I-II.

Conclusions. The Monostrut valve has shown no structural failures and a low rate of valve-related complications over a 10-year period in a large patient population.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 
The Monostrut valve was first implanted in Spain in May 1983. Shortly thereafter, a multicenter Spanish Monostrut Study Group (Appendix A) was created to evaluate the performance of the valve using prospective uniform data collection and analysis protocols. Five-year results with 3,199 valves implanted in 2,726 patients in 14 centers have been reported previously [1]. We now report the combined experience of 22 centers, with 8,599 valves implanted in 7,317 patients during a 10-year period.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 
The Valve
The Monostrut cardiac valve (Sorin Biomedical, Irvine, CA) is a tilting-disc prosthesis with no welds [2]. The struts and ring are manufactured from a single block of a chromium and cobalt-based alloy. The outlet strut has a hook shape that holds the disc in place. The disc, with a convex-concave shape, is made of pyrolytic carbon and opens to 70 degrees. No mechanical failures have been reported in more than 110,000 implantations. To date, the Food and Drug Administration has not approved its use in the United States.

Patient Population
The Spanish Monostrut Study Group was initially created to collect data from patients using uniform protocols. The original 14 centers were joined on a later date by eight more in which a large number of valves were implanted. From May 1983 to April 1993, a total of 8,599 valves were implanted in 7,317 patients. The average number of prostheses implanted in each center was 391 (range, 47 to 1,337). The follow-up protocols were modified slightly in 1988 to conform to the guidelines of the Ad Hoc Committee for Standardizing Definitions of Prosthetic Heart Valve Morbidity of The American Association for Thoracic Surgery and The Society of Thoracic Surgeons [3]. To increase the reliability of data analysis in the study group, some patients were excluded: those younger than 15 years old, those undergoing a double valve replacement (DVR) in whom a prosthesis other than the Monostrut was also employed, and those who had a prosthesis in a tricuspid position. All the remaining patients with a Monostrut valve implanted at the participating hospitals were included, regardless of age, previous operation, or emergency operation.

The mean age was 53.4 ± 11.6 years (range, 16 to 85 years); 3,823 patients (52.2%) were males. Aortic valve replacement (AVR) was performed in 3,229 patients (44%), mitral valve replacement (MVR) in 2,806 (38%), and DVR in 1,282 (18%). Of the 8,599 prosthesis implanted, 4,511 were in the aortic position (53%) and 4,088 (47%) were in the mitral position. A history of congestive heart failure was the main indication for operation and was present in 82.3% of the total group. According to the New York Heart Association classification, 3,831 patients (52%) were in class III and 1,365 (19%) were in class IV. Atrial fibrillation was present in 72% of the MVR group, 62% of the DVR group, and 11% of the AVR group; and a history of thromboembolic episodes was present in 16.7%, 12.8%, and 4.6%, respectively. Associated procedures were performed in 1,203 patients (16.4%). These included coronary revascularization (6.2%) and repair of other valves during replacement: 283 mitral repairs and 623 tricuspid annuloplasties. Urgent operation was performed in 629 patients (8.6%), and 1,822 (25%) had had a previous cardiac operation, including closed mitral commissurotomy. Of them, 1,098 (60%) had a prosthesis implanted previously.

The valvular lesions were diagnosed by cardiac catheterization in 4,811 patients (67%) and by echocardiography alone in the remaining 2,436 patients. Concomitant stenosis and insufficiency was the most frequent pathologic process in the mitral valve (44%). In the aortic valve, pure stenosis was found in 1,196 patients (26.5%), mixed lesions in 1,571 (35%), and pure insufficiency in 1,744 (38.5%).

Operative Technique
Moderate hypothermia during extracorporeal circulation was used in almost all the cases. Only 117 patients (1.6%) had an operation under normothermic conditions. Mean pump time was 91 ± 38 minutes, and ischemic time was 59 ± 24 minutes. Suturing of the prostheses was carried out according to the preferred technique of each individual surgeon. Of the total group, 7,180 (83.4%) had implantation with double 2-0 polyester stitches mounted over felt pledgets; 989 (11.5%) with interrupted stitches, 206 (2.4%) with figure-of-8 sutures, and 224 (2.6%) with continuous 2-0 polypropylene suture. Myocardial protection included cold crystalloid cardioplegia in 5,644 operations (77%), cold blood cardioplegia in 1,588 (21.7%), and continuous warm blood cardioplegia in the remaining 85. In addition, topical hypothermia with iced saline was used in 47% of the procedures. Figure 1 shows the distribution of the prostheses by size.

View larger version (27K): [in this window] [in a new window]   Fig 1. . Distribution of the prostheses by size.

Follow-up
Follow-up was 96% complete, with only 271 hospital survivors lost to follow-up. Closing time was 6 months. The mean observation time was 4.3 years (range, 6 months to 10.5 years). The follow-up represents a total of 29,155 patient-years (12,929 for AVR, 11,549 for MVR, and 4,677 for DVR). Data of all patients receiving a Monostrut valve at the participating hospitals were entered prospectively into a computer. Fourteen centers had a follow-up at 5 years [1]. In addition, eight centers joined the study after 5 years. All the known valve-related complications were entered when they occurred. An update was done in 20% of the patients at 3 and 7 years. At the tenth year, 96% of the survivors were contacted again. Personal interviews were done in the reference hospital in 38.5% of the cases. Other follow-up methods included contact by telephone (36.8%), mail questionnaire (15%), and evaluation by the family physician or cardiologist (9.7%). Anticoagulation centers were also contacted for possible unnoticed thromboembolic and anticoagulant-related complications.

Report of Data and Statistical Analysis
Analysis of temporally related events was carried out using actuarial techniques [4]. Linearized rates also were calculated to allow comparison of the results with those reported on a linearized form only. The actuarial survival curves were complemented with hazard function curves (instantaneous risk of event at each moment in time after the operation), expressed as percentage of events per patient-year at risk (Appendix B). Actuarial estimations of accumulated probability of being free of events and risk factors are presented as ±standard error with a confidence interval of approximately 70%. Linearized rates include 95% confidence limits. Actuarial curves were compared by applying the Mantel-Haenszel test [5].

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 
Hospital Mortality
Of the total 7,317 patients, 529 (7.2%) died in the first 30 postoperative days or during the hospital stay. Of these, 137 (26%) died intraoperatively and the remaining 392 patients died within the first 30 postoperative days or during the hospital stay: 200 from myocardial failure; 96 from renal, respiratory, or multiorgan failure; and 44 from other complications. Fifty-two patients died of valve-related complications (9.8% of all hospital deaths): 20 from thromboembolism, 8 from anticoagulant-related hemorrhage, 7 from reoperation for nonstructural failure, and 17 because of sudden death after hospital discharge but within 30 days of operation. The hospital mortality rate was significantly higher in patients with DVR (11.7%) than in those with MVR (7.4%) and AVR (5.3%). In addition, mortality was more than twice as high in patients undergoing combined valve replacement and coronary artery operations (15.6%) than in patients with no coronary procedure (6.6%) (p < 0.001). In patients older than 65 years, hospital mortality was 14.5%, as opposed to 6% in younger patients (p < 0.001). Finally, reoperation had an impact on hospital survival. In patients undergoing their first valve operation, operative mortality was 5.7%, in contrast to 11.8% for patients undergoing reoperation (p < 0.001).

Late Mortality
Of the 6,788 hospital survivors, 617 (9.1%) died during follow-up: 242 with AVR, 258 with MVR, and 117 with DVR (7.9%, 9.3%, and 10.3%, respectively). Causes of late death are shown in Table 1. Two hundred sixty-eight (44%) died of valve-related complications, including 94 (15.2%) sudden, unexplained deaths. The most common cause of cardiac, nonvalve-related death was congestive heart failure; the most common causes of noncardiac deaths were neoplasm and trauma.

The linearized rate of nonstructural dysfunction was 0.51/100 patient-years (0.35 for AVR, 0.59 for MVR, and 0.75 for DVR), with probabilities of being free from this complication at 10 years of 97.3% ± 0.5% for AVR and 95% ± 1% for both MVR and DVR (p < 0.002).

THROMBOEMBOLISM.
Three hundred forty-six patients (5.5% of the survivors) had thromboembolic complications as defined by Edmunds and associates [3]. There were a total of 385 thromboembolic episodes, with 309 patients (89%) suffering only one and the remaining 38 experiencing two or more. Anticoagulation levels at the time of the event were available in almost half of the patients. In two thirds of them (110 cases), anticoagulation therapy was considered adequate, and it was inadequate in the remaining 55. Thromboembolism was cerebral in 302 patients (87%), leaving permanent neurologic consequences in 107 (35.4%). In 32 (9.2%), the episode was fatal. Forty-two percent (152 of 385) of the thromboembolic events occurred during the first 3 years of follow-up. Linearized rates of thromboembolism were 1.72/100 patient-years in MVR, 1.58 in DVR, and 0.89 in AVR. The actuarial probability of being free from thromboembolic events in the three groups at 10 years was 76.5% ± 2.6%, 83.6% ± 3.7%, and 88.8% ± 1.8%, respectively (p < 0.001) (Figure 2).

View larger version (29K): [in this window] [in a new window]   Fig 2. . Actuarial curves of freedom from thromboembolism. The differences between the three groups are statistically significant (p < 0.001). Numbers at bottom refer to patients entering each time interval. (AVR = aortic valve replacement; DVR = double valve replacement; MVR = mitral valve replacement.)

ANTICOAGULANT-RELATED HEMORRHAGE.
Two hundred fifty patients (3.7% of the survivors) sustained a major bleeding episode causing death or stroke, requiring hospitalization or blood transfusion. The hemorrhagic episode was lethal in 59 patients (23.5%). Most patients (89%) experienced only one bleeding episode. The linearized rate was 0.98/100 patient-years, with no significant differences among the three groups. The 10-year probability of being free from this complication was 84.6% ± 2.6% in MVR, 91.2% ± 1.5% in AVR, and 85.8% ± 3.7% in DVR (p = not significant).

PROSTHETIC VALVE ENDOCARDITIS.
A total of 141 patients (2.1% of the hospital survivors) experienced prosthetic valve endocarditis. In 38 cases (27%), active endocarditis of the native valve was present before replacement. Infection developed within the first year after operation in 73 patients (52%). Fifty-eight patients (41%) had had AVR, 40 (28%) MVR, and 43 (31%) DVR. Prosthetic valve endocarditis carried a high mortality rate; more than half of the patients (77 of 141) died as a result of this complication. Deaths included 32 of 55 patients who underwent reoperation (58% operative mortality). Most of the reoperations were done on an emergency basis. Of the 86 patients who received medical treatment, 45 (52%) died. The linearized rate was 0.48/100 patient-years (0.35 for MVR, 0.45 for AVR, and 0.92 for DVR), with a 10-year probability of being free from endocarditis of 96.4% ± 0.7% in AVR, 96.5% ± 1% in MVR (p = not significant), and 94.4% ± 1% in DVR (p < 0.0001 versus AVR and MVR).

Reoperation
In the 10-year follow-up, 103 patients (1.5% of the survivors) required a second operation because of valve-related complications. Fifty-five reoperations (44.4%) were due to prosthetic valve endocarditis, 40 (32%) were for periprosthetic leak (3 patients in each category required two reinterventions), 4 for pannus or disc entrapment, and 4 for valve thrombosis. The probability of being free from reoperation at 10 years was 95% ± 0.5%.

Survival and Event-Free Curves
Valve-related deaths included those due to valve-related complications (both in the hospital and at follow-up); sudden, unexplained deaths; and death at reoperation [3]. The probability of being free from valve-related death was 93.2% ± 0.6%. For MVR, it was 91.9% ± 1.2%; for DVR, 92.8% ± 1.2% (p = not significant); and for AVR, 94.7% ± 0.7% (p < 0.02).

Adding operative and cardiac, nonvalve-related deaths, the actuarial survival at 10 years was 79% ± 1%, and 73.3% ± 1% when all causes of death (including neoplasm and trauma) were taken into account (Fig 3). All valve-related morbidity and mortality is a combination of operative and valve-related mortality; all valve-related complications, both fatal and nonfatal; and reoperations. The actuarial probability of being free from these events at 10 years for the whole group was 62.6% ± 1.5%. There were differences among the three groups: 70.1% ± 2% in AVR, 56.9% ± 2% in MVR, and 59.8% ± 3% in DVR (p < 0.0001).

View larger version (25K): [in this window] [in a new window]   Fig 3. . Actuarial survival curves for valve-related mortality, cardiac deaths (including operative and cardiac, nonvalve-related deaths), and overall survival (includes all modes of death).

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 
The study analyzes the long-term results obtained with the Monostrut valve. This third-generation tilting-disc mechanical prosthesis was designed to eliminate the risk of structural dysfunction, to facilitate washing of prosthetic surfaces, and to provide optimal hemodynamic function [2]. This report contains data on enough patients over a long period to allow meaningful and useful evaluation of the efficacy of this valvular prosthesis. Although the sample represents heterogeneous population of patients operated on in 22 hospitals throughout Spain by more than 50 different surgeons, the implantation technique and the anticoagulation protocols were similar in all centers, and the same protocol was used to analyze all sets of data. All the evaluations at different times were entered into a computer using a Patient Analysis Tracking System program (Dendrite Systems, Inc, Sistemas Hospitalarios, Grupo Palex, Barcelona, Spain). At the end of the study, only 271 hospital survivors (4%) were lost to follow-up. Personal interview was the most common method of follow-up, followed by telephone interview, which has proven to be superior to mail questionnaires, especially in terms of patient preference [6]. Mail questionnaires accounted only for 15% of the follow-up.

This report tries to comply with the guidelines for reporting of postoperative mortality and morbidity developed by the Joint Ad Hoc Committee of the American Association for Thoracic Surgery and The Society of Thoracic Surgeons [3]. Recently, Bodnar and colleagues [7] proposed a new method for reporting thromboembolism and bleeding. We also have tried to comply with this. The number of cerebral emboli with differentiation between major strokes and fatal events and obstructive valve thrombosis has been detailed, although data on systemic (not intracranial) hemorrhage are limited. We also have included the breakdown of patient-years of follow-up for each valve position (see Appendix B) and included the valve-related complications occurring during hospitalization. Failure to include these numbers prompted criticism by Akins [8] concerning a recent mechanical valve study. Despite these concerns, we believe this study contains so many data on a large number of patients that valid conclusions can be drawn, not only on this particular prosthesis, but also on the epidemiology of valve-related complications in general.

The matter of sudden death has been questioned in a recent editorial by Butchart [9]. We included all sudden, unexplained deaths as valve related except in patients who died suddenly but with a nonvalve cause found at autopsy, in accordance with these revised guidelines. However, in a recent study by Rooney and associates [10] with the Medtronic Hall valve, 70% of the sudden deaths were followed by autopsy. Overall, 90% of sudden deaths were unrelated to the prosthesis. The authors concluded that there was no evidence to support the recommendation that all nonautopsied sudden deaths be attributed to the prosthesis. In our series, we had 17 sudden deaths before the 30th postoperative day, which accounted for 0.3% of the total operative mortality rate of 7.2%. During follow-up, an additional 98 patients died suddenly (see Table 1). Of these, only 4 were autopsied and excluded when it was shown that the death was not valve related. However, sudden death was the most frequent cause of valve-related death, accounting for 36% of the total 268 patients who died of valve-related complications. Excluding sudden death, the probability of being free from valve-related death at 10 years was 95.7% ± 0.5%. We concur with Butchart [9] that, in relation to sudden death, the existing guidelines need reappraisal and revision.

Our results indicate that the Monostrut prosthesis is free of structural deterioration and that obstructive valve thrombosis, once a frequent and dreaded complication, occurs very seldom in the patient with adequate anticoagulation therapy. We had only 1 known case of obstructive valve thrombosis in a patient with a therapeutic level of anticoagulation at the time of thrombosis. However, as Bodnar and associates point out [7], the process may have started weeks or months earlier, when the International Normalized Ratio was not available and anticoagulation may have been inadequate. In general, regarding valve-related complications, the Monostrut valve is as good, if not better, than other mechanical valves approved by the Food and Drug Administration. Akins [11] reviewed the complications of four mechanical valves approved for use in the United States at the time of writing his article (St. Jude, Medtronic Hall, Omniscience, and Starr Edwards). Our results with the Monostrut valve show equal or lower composite linearized rates of every valve-related complication (including thrombosis and reoperation), both for the aortic and mitral positions, compared with the four prostheses studied.

Excellent hemodynamic performance of the Monostrut valve has been confirmed by both cardiac catheterization [12–14] and Doppler echocardiographic studies [15]. The most recent study comes from one of the participating hospitals of the Spanish Monostrut Study Group [16]. A total of 244 patients with 286 prostheses were examined prospectively at hospital discharge and at 3, 6, 12, 24, and 36 months thereafter. For mitral prostheses, the median mean gradients were 4 mm Hg for all sizes of prostheses. In the aortic position, the transprosthetic gradient increased with decreasing valve size, ranging from a median value of 7 mm Hg for a size of 29 mm to 19 mm Hg for a size of 21 mm. In both cases, the gradient had no significant variations during the 3-year follow-up. The same group has reported recently that for the 19-mm size, the gradients of the Monostrut valve are similar to those of the St. Jude valve [17].

The Monostrut valve has proved to have a durable design and excellent hemodynamic performance. For these reasons, the structural model has been used in a study on MVR with a microporous-surface valve without long-term anticoagulation therapy. Results in the animal model [18] prompted evaluation of the valve in children and young women in sinus rhythm. During the follow-up, currently extending to 10.5 years, there were no thromboembolic complications, and 4 women gave birth to 7 children [19]. These promising results need further studies, but they may represent a breakthrough in cardiac valve replacement with mechanical prostheses.

In summary, the Monostrut valve has proven to be an excellent mechanical prosthesis, with a durable design and a low rate of valve-related complications. The large volume of patients followed during a 10-year period allows us to draw valid conclusions about the performance of the valve.

	Appendix A

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 
The Spanish Monostrut Study Group is formed by the following institutions: Madrid-Hospital Ramón y Cajal, Hospital La Paz, Clinica Puerta de Hierro, Hospital Gregorio Marañón, Clínica La Luz, and Clínica Nuestra Señora de Loreto; Barcelona-Hospital de la Santa Creu i Sant Pau, Hospital Vall d'Hebron, Hospital de Bellvitge, and Centre Quirurgic Sant Jordi; Pamplona-Clínica Universitaria de Navarra and Hospital de Navarra; Sevilla-Hospital Virgen del Rocio and Hospital Virgen Macarena; Granada-Hospital Virgen del Rocio; Córdoba-Hospital Reina Sofía; Zaragoza-Hospital Miguel Servet; Bilbao-Hospital de Basurto; Valladolid-Hospital Universitario; La Coruña-Hospital Juan Canalejo; Santander-Hospital Marques de Valdecilla; and Valencia-Hospital La Fe.

	Appendix B

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 
We wish to give as much information as possible regarding the present study. To include all the data in the general manuscript would have made it cumbersome and confusing to read. Some additional data are presented in this Appendix to help anyone wishing to examine the results in closer detail. Table B1 summarizes the actuarial probability of freedom from valve-related complications (both in the hospital and at follow-up) for the total and the three groups at 3, 5, and 10 years; complemented by the number of patients at risk, the number of events, and the number of patient-years of follow-up. Linearized rates with 95% confidence limits are also shown.

View larger version (30K): [in this window] [in a new window]   Fig B1. . Hazard function of valve-related complications. There were significant differences (p < 0.05) in the risk of nonstructural dysfunction and endocarditis at the first year as compared with the following years.

	Acknowledgments

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 
We express our appreciation to Anthony L. Moulton, MD, for reviewing the manuscript.

This study was supported in part by Cormedica S.A. and Dideco s.p.A.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 
Presented at the Poster Session of the Thirty-second Annual Meeting of The Society of Thoracic Surgeons, Orlando, FL, Jan 29–31, 1996.

Address reprint requests to Dr Aris, Cardiac Surgery Service, Hospital de la Santa Creu i Sant Pau, San Antonio M. Claret 167, 08025 Barcelona, Spain.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment Appendix A Appendix B Acknowledgments References

 

1. The Spanish Monostrut Study Group: Castillón L, Pareja JG, Ruiz MC, Jimenez MAG, Infantes C, Duarte EP. Five years experience with the Björk-Shiley Monostrut valve in 2726 patients: a Spanish multicentre study. In: Bodnar E, ed. Surgery for heart valve disease. London: ICR Publishers, 1990:268–84.
2. Björk VO, Lindblom D. The Monostrut Björk-Shiley heart valve. J Am Coll Cardiol 1985;6:1142–8.[Abstract]
3. Edmunds LH, Clark RE, Cohn LH, Miller C, Weisel RD. Guidelines for reporting morbidity and mortality after cardiac valvular operations. Ann Thorac Surg 1988;46:257–9.[Medline]
4. Grunkemeier GL, Starr A. Actuarial analysis of surgical results: rationale and method. Ann Thorac Surg 1977;24:404–8.[Abstract]
5. Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 1959;22:719–48.
6. Amstrong CS, Sun Z, David TE. Follow up of patients after valvular surgery: mail vs. telephone. J Heart Valve Dis 1995;4:346–9.[Medline]
7. Bodnar E, Butchart EG, Bamford J, et al. Proposal for reporting thrombosis, embolism and bleeding after heart valve replacement. J Heart Valve Dis 1994;3:120–3.[Medline]
8. Akins CW. An international experience with the CarboMedics prosthetic heart valve [Letter]. J Heart Valve Dis 1995;4:321–3.[Medline]
9. Butchart EG. The significance of sudden and unwitnessed death after heart valve replacement. J Heart Valve Dis 1994;3:1–4.[Medline]
10. Rooney SJ, Moreno de la Santa P, Lewis PA, Butchart EG. Sudden death in a large prosthetic valve series based on a single prosthesis: experience with the Medtronic Hall valve. J Heart Valve Dis 1994;3:5–9.[Medline]
11. Akins CW. Mechanical cardiac valvular prostheses. Ann Thorac Surg 1991;52:161–72.[Abstract]
12. Aris A, Crexells C, Augé JM, Oriol A, Caralps JM. Hemodynamic evaluation of the Integral Monostrut Björk-Shiley prosthesis in the aortic position. Ann Thorac Surg 1985;40:234–40.[Abstract]
13. Aris A, Padró JM, Cámara ML, Crexells C, Augé JM, Caralps JM. Clinical and hemodynamic results of cardiac valve replacement with the Monostrut Björk-Shiley prosthesis. J Thorac Cardiovasc Surg 1988;95:423–31.[Abstract]
14. Nakamo A, Kawashima Y, Matsuda H, et al. A five-year appraisal and hemodynamic evaluation of the Björk-Shiley Monostrut valve. J Thorac Cardiovasc Surg 1991;101:881–7.[Abstract]
15. Aris A, Padró A, Cámara ML, et al. The Monostrut Björk Shiley valve. Seven years' experience. J Thorac Cardiovasc Surg 1992;103:1074–82.[Abstract]
16. Pons-Lladó G, Carreras F, Borrás X, et al. Doppler-derived gradients in normally functioning Monostrut Björk-Shiley prostheses. Am J Cardiol 1995;76:100–3.[Medline]
17. Aris A, Ramirez I, Cámara ML, Borrás X, Carreras F. Hemodynamic evaluation of small-size aortic prostheses [Abstract]. Cardiovasc Surg 1995;3(Suppl 1):11.
18. Björk VO, Kaminsky DB. The five-year evaluation of a mechanical heart valve without anticoagulation in goats. J Thorac Cardiovasc Surg 1992;104:22–5.[Abstract]
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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Alejandro Aris Rafael Llorens Jaime Casares Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Aris, A. Articles by Casares, J. Search for Related Content PubMed PubMed Citation Articles by Aris, A. Articles by Casares, J.