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Ann Thorac Surg 2002;73:474-479
© 2002 The Society of Thoracic Surgeons

Original article: cardiovascular

Up to 8-year follow-up of valve replacement with CarboMedics valve

Yoshiharu Soga, MD*a, Hitoshi Okabayashi, MD, PhDa, Takeshi Nishina, MDa, Sakae Enomoto, MD, PhDa, Ichiro Shimada, MDa, Tadaomi-Alfonso Miyamoto, MDb, Toshihiko Ban, MD, PhDa

a Department of Cardiovascular Surgery, Kokura Memorial Hospital, Kitakyushu, Japan
b Research Department, Kokura Memorial Hospital, Kitakyushu, Japan

Accepted for publication October 17, 2001.

* Address reprint requests to Dr Soga, Department of Cardiovascular Surgery, Kyoto University Graduate School of Medicine, 54 Kawaharacho, Shogoin, Sakyo-ku, Kyoto, Japan 606-8507
e-mail: sogakin{at}kuhp.kyoto-u.ac.jp


   Abstract
Top
 Abstract
Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
 References
 
Background. The aim of this study was to report midterm valve replacement (VR) results with the CarboMedics valve (Sulzer Carbomedics, Austin, TX).

Methods. From 1991 to 1999, 468 patients aged 13 to 76 years (mean 56 years) underwent VR with CarboMedics valve: 239 aortic (A), 167 mitral (M), and 62 A+M or double valve replacement (DVR). Mean follow-up time was 4.4 years; follow-up was 99.1% complete for 2,016 patient-years (PY). The anticoagulation level was targeted to an international normalized ratio of 1.47 to 2.8.

Results. The hospital mortality rate was 1.2%. Actuarial analysis for the entire group at 7 years for survival was 87% ± 2.3%. Freedom from valve-related death was 94% ± 1.9%. Freedom from thromboembolic and bleeding events, respectively, were as follows: for AVR, 82% ± 4.9% (2.4%/PY) and 88% ± 2.9% (1.6%/PY); for MVR, 95% ± 2.1% (0.8%/PY) and 91% ± 3.1% (1.3%/PY); and for DVR, 96% ± 3.2% (0.7%/PY) and 85% ± 9.7% (1.0%/PY). Actuarial freedom from reoperation was 98% ± 1.4%.

Conclusions. The CarboMedics valve can be implanted with satisfactory early mortality and a low incidence of valve-related events even under low-intensity anticoagulation, as shown in a Japanese population.


   Introduction
Top
 Abstract
 Introduction
Material and methods
 Results
 Comment
 Acknowledgments
 References
 
Since the first implantation in 1986, the CarboMedics valve (Sulzer Carbomedics, Austin, TX) has been implanted more than 220,000 times worldwide. We prefer mechanical valves for patients younger than 75 years, and the CarboMedics valve has been used since December 1991 at our institution. The required effective levels of anticoagulation for prevention of thromboembolic and bleeding complications in the Japanese population is of lower intensity [1] than the recommended optimal anticoagulation levels according to the guidelines in western countries [2, 3]. The aim of this study is to report our 8-year experience with CarboMedics valve implantation after low intensity anticoagulation therapy.


   Material and methods
Top
 Abstract
 Introduction
 Material and methods
Results
 Comment
 Acknowledgments
 References
 
Patients
Of 1,146 patients undergoing valve surgery between December 1991 and December 1999, 245 had bioprosthetic valve replacement and 325 had valve repair (including 294 mitral repair). Of 576 with mechanical valve replacement 530 consecutive patients received CarboMedics valves at Kokura Memorial Hospital, Japan. Patients were excluded if they had undergone double valve replacement including a valve other than a CarboMedics valve; who had another, previously implanted mechanical valve that did not require replacement simultaneously; or who had also undergone aortic arch replacement. Patients on whom the aortic root was reconstructed using CarboMedics (Sulzer Carbomedics) valve-bearing conduits were included (n = 35), yielding 468 patients who form the basis of this report. There were 251 male and 217 female patients, ranging in age from 13 to 76 years (mean 56 years). Of these, 239 had isolated aortic valve replacement (AVR), 167 had isolated mitral valve replacement (MVR), and 62 had double valve (aortic and mitral) replacement (DVR). In all, 25% of patients were in New York Heart Association (NYHA) functional class III or IV at the time of the admission for operation. Clinical and operative characteristics are summarized in Tables 1 and 2. Among those who underwent MVR, 24 (14%) did so because of pure nonrheumatic mitral regurgitation.


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  		Table 1. Preoperative Patient Demographics

 

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  		Table 2. Operative Characteristics of Study Patients

 
Operative technique
Standard cardiopulmonary bypass was instituted in all cases. Myocardial protection was achieved by moderate systemic hypothermia with intermittent antegrade cold blood cardioplegia in 184 patients and systemic normothermia with intermittent antegrade warm blood cardioplegia in 275. Deep hypothermic circulatory arrest was used for patients with severely calcified ascending aorta (8 AVR and 1 DVR) to avoid aortic cross clamping. More than 90% of the patients were operated upon by 1 surgeon (H.O.). Prostheses were implanted with 1-0 polyester pledgeted everting mattress sutures, preserving the mitral subvalvular apparatus whenever possible.

Operative characteristics
A total of 227 patients (49%) had simple valve replacement, whereas 241 (51%) had additional procedures, with tricuspid valve plasty and MAZE procedure being the most frequent (Table 2). The intraaortic balloon pump was used in 11 patients (2.4%).

Anticoagulant therapy
Postoperatively all patients received permanent anticoagulation with Coumadin (Du Pont Pharmaceuticals, Wilmington, DE). The target level of anticoagulation was a prothrombin time of 30% to 15% for AVR, and 25% to 10% for MVR or DVR, which equals an international normalized ratio (INR) of 1.47 to 2.1 and 1.6 to 2.8, respectively. Antiplatelet agents including both aspirin (81 mg) and dipyridamole (75 to 150 mg) were given if tolerated. In 348 (75%) surviving patients, both were used. Aspirin was used alone in 28 patients, dipyridamole alone in 14, ticlopidine hydrochloride alone in 3. Both aspirin and ticlopidine hydrochloride were used in 2 patients, and in 67 (15%) antiplatelet agents had to be discontinued because of overt bleeding events or excessive Coumadin effect.

Follow-up
All information was collected and categorized in accordance with the latest international guidelines published in 1996 [4]. From January 5 to March 23, 2000, a total of 397 patients were followed-up at our outpatient clinic, and the remaining patients by means of telephone interviews; when the information was unsatisfactory, we also contacted patients’ family physicians. The follow-up rate was 99.1% (458 of 462) complete. The cumulative follow-up was 2,016.4 patient-years (PY), with a mean observation time of 53 months and range of 0.2 to 98 months: 927.5 PY in AVR, 799.7 PY in MVR, and 289.2 PY in DVR.

Statistical analysis
All early and late events were included for calculation of the annualized rates and actuarial estimates. StatView version 5.0 software was used with the {chi}2 test to evaluate incidence rate differences, the Kaplan-Meier method for actuarial estimation of morbid events, and the Mantel-Cox log-rank test for evaluation of differences between groups. A p value of less than 0.05 was considered significant. Multiplicity of analysis was adjusted by the Bonferroni method, which required a p less than 0.016 to be significant. Continuous variables are presented as mean ± standard error.


   Results
Top
 Abstract
 Introduction
 Material and methods
 Results
Comment
 Acknowledgments
 References
 
Hospital mortality was 1.2% (6 of 468). Three patients died within 30 days postoperatively: 1 of intraoperative aortic dissection originating from the aortic cannulation site, 1 of aspiration pneumonia, and 1 of multiple organ failure after acute liver dysfunction. Three other patients died in the hospital: 1 of diffuse cerebral infarction likely to be secondary to inadequate venous drainage during cardiopulmonary bypass rather than embolic, 1 of multiple organ failure after sepsis, and 1 of sudden death 6 months after having recovered from early postoperative hemorrhagic shock.

There were 31 late deaths (1.5%/PY); the causes are shown in Table 3. A total of 17 patients died of cardiac causes (55%): 3 of congestive heart failure and 14 of valve-related causes (45%). The overall annualized rate of valve-related death including early hospital mortality was 0.7%/PY; for AVR 0.6%/PY, for MVR 1.0%/PY, and for DVR 0.3%/PY.


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  		Table 3. Causes of Mortality in Study Patients

 
Actuarial freedom from death from all causes at 5 and 7 years was 91.6% and 87.2%, respectively (Fig 1). Actuarial freedom from valve-related death for all patients at 5 and 7 years was 96.7% and 94.0%, respectively (Fig 2).



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  		Fig 1. Actuarial freedom from death of all causes. (AVR = aortic valve replacement; DVR = double valve replacement; MVR = mitral valve replacement.)

 


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  		Fig 2. Actuarial freedom from valve-related deaths. (AVR = aortic valve replacement; DVR = double valve replacement; MVR = mitral valve replacement.)

 
Valve-related morbid events
The overall actuarial freedom from any valve-related event in all patients was 86.2% at 5 years and 77.5% at 7 years. The nature of the events is summarized in Table 4. Paravalvular leak with hemolysis occurred in 1 case of MVR requiring reoperation 7 years after initial surgery.


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  		Table 4. Valve-Related Morbid Events in Study Patients

 
Thromboembolic events
Valve thrombosis was not observed in our series. A total of 30 thromboembolic events, 73% of which were documented in AVR patients, occurred in 28 patients. Atrial fibrillation was present in 7 of 20 AVR patients, in 5 of 6 MVR, and in 1 of 2 DVR. In all, 90% of events were cerebral: in 3 patients the strokes were fatal, in 14 nonfatal, and in 10 transient cerebral ischemic attacks. One patient had discontinued medications for personal reasons. One post-AVR patient with atrial fibrillation had 3 episodes of transient cerebral ischemic attacks despite a supposedly therapeutic level of anticoagulation; the prothrombin time was 19% (INR 1.87) at one of the events.

The prothrombin time at the time of event was documented in 13 events: 9 were within the therapeutic range from 11% to 26% (INR 1.6 to 2.6), but 4 were off: 37%, 38%, 40%, and 55% (INR < 1.38). Actuarial freedom from thromboembolic events for all patients at 5 and 7 years was 93.5% and 89.0% (Fig 3). Differences in the annualized rates between AVR and MVR were significant (p = 0.014), but actuarial estimate differences were not after Bonferroni’s adjustment (p = 0.018).



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  		Fig 3. Actuarial freedom from thromboembolic events. (AVR = aortic valve replacement; DVR = double valve replacement; MVR = mitral valve replacement.)

 
Bleeding events
A total of 28 bleeding events occurred in 26 patients (1.4%/PY). Gastrointestinal events occurred most frequently in all three groups, but five of six fatal events were cerebral. Six patients were on aspirin, one with dipyridamole in addition, and one other was on dipyridamole without aspirin. The prothrombin time at the time of event was documented in 19 events: in 7 were less than 10% (INR > 3.0), in 7 within the therapeutic range, but in 5 were more than 35% (INR < 1.37). Actuarial freedom from bleeding events for all patients was 93.6% at 5 years and 88.9% at 7 years (Fig 4). There were no significant differences between the groups.



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  		Fig 4. Actuarial freedom from bleeding events. (AVR = aortic valve replacement; DVR = double valve replacement; MVR = mitral valve replacement.)

 
Prosthetic valve endocarditis
One patient who had had AVR with mitral and tricuspid annuloplasty developed prosthetic valve endocarditis 6 months postoperatively. This patient underwent Bentall’s operation subsequently using a stentless bioprosthetic valve.

Reoperation
Two patients required reoperation. Both patients are currently alive.

Functional status
At the time of last follow-up, 88.3% of survivors were in New York Heart Association class I, 11.5% were in class II, and 0.2% were in class III.


   Comment
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
Acknowledgments
 References
 
The CarboMedics valve was introduced as the first low-profile, bileaflet, rotatable mechanical valve that facilitated the preservation of the subvalvular apparatus in MVR. Moreover, following the domestic release of the "R" series for aortic position with a thinner sewing ring than the standard, we have preferred it for patients with small aortic root since January 1993.

The early mortality rate in this series (1.2%) is the lowest compared with those of 4.4% to 9% reported in other series for CarboMedics valves [5–8] and 4.6% to 10.3% for other existing valves [9–15]. The relatively small percentages of preoperative NYHA class III or IV (25%), concomitant coronary artery bypass (7%), and emergent operation (3%) are possible factors that might account for this difference. The relatively small percentage of NYHA class III and IV most likely resulted from the maximal benefits of medication achieving control of symptoms by the time of preoperative evaluation. The incidence of concomitant coronary artery bypass in our series (7%), although lower than that of western countries, was higher than that of other Japanese reports, which range from 3.1% [16] to 4.6% in patients more than 65 years of age [17]. The prevalence of coronary artery disease in the Japanese population in general is lower than that in western countries. However, our series included high-risk patients such as those undergoing hemodialysis or those with severely calcified aorta. Gillinov and associates [18] reported high hospital mortality (14%) for patients with severely atherosclerotic ascending aorta. To address this problem, we prefer to use deep hypothermic circulatory arrest for AVR or ventricular fibrillation with moderate hypothermia for MVR to avoid cross clamping of the aorta. All 9 such patients included in this study are alive and well.

The annualized rates of overall late death and valve-related death of 1.5%/PY and 0.7%/PY respectively, for an actuarial survival and freedom from valve-related death at 7 years of 88.3% and 94.2%, respectively, compare favorably with other reports.

Thromboembolic and bleeding events after mechanical valve implantation, mostly associated with anticoagulation, are the most frequently observed and dreadful complications. We have neither the evidence nor a clear explanation of a requirement for lower-intensity anticoagulation in the Japanese population, but we have adopted the recommendations of The Tokyo Area Anticoagulation Study Group. Accordingly, adequate anticoagulation control after bileaflet mechanical valve replacement can optimally be achieved with an INR between 1.2 and 3.0 [1]. The regimens followed by Aoyagi and colleagues [16] and by Kobayashi and associates [17] were also within this range. Although the annualized rate of thromboembolic events of 1.5%/PY in our series is acceptable, nevertheless such events occurred significantly more frequently in AVR than in MVR patients, as opposed to the rates generally reported. Thromboembolic events, even if they did not reach statistical significance for the different valves, have been reported more frequently in MVR or DVR than AVR with practically all valves including CarboMedics [5–7, 19], St. Jude Medical [9, 11, 19] and Medtronic-Hall valves [14]. Although at first glance the lower anticoagulation intensity for AVR than MVR in our series might account for the differences, the incidence of thromboembolism for AVR is not significantly different from the generally reported rate. It is noteworthy, however, that our incidence of MVR is lower than the generally accepted one, which makes the incidence of AVR relatively large. Comparing the CarboMedics and St. Jude valves with regard to low-intensity anticoagulation (target INR 1.5), Wang and associates [20] reported low thromboembolism and valve thrombosis with the St. Jude patient group, but differences between the positions of the valve were not analyzed. Excluding the early death patients, thromboembolism generally occurred more frequently (p < 0.05) in the older patients with postoperative atrial fibrillation than in the younger patients in sinus rhythm (62.3 ± 6.3 vs 55.8 ± 10.6 years, p < 0.005), especially in AVR patients (p < 0.001).

The annualized incidence rate of bleeding events as well as the rate of freedom from bleeding events at 7 years compared favorably with those of other reports. Gastrointestinal hemorrhage accounted for 57% and cerebral hemorrhage for 29% of bleeding events, which contrasts with 90% of thromboembolic events being cerebral. The type of antiplatelet agents made no difference with regard to bleeding events.

Reoperation was required in only 2 patients. We endorse the technique of using interrupted mattress sutures to reduce paravalvular leak, as advocated by Dalrymple-Hay and colleagues [8].

Despite the limitations of the study (ie, retrospective analysis of a relatively small number of patients and use of various antiplatelet agents), our midterm results demonstrate that the CarboMedics valve can be implanted with low early mortality and a low incidence of valve-related morbid events. Although the anticoagulation regimen in AVR patients, especially those with atrial fibrillation, may still need to be optimized, the study corroborates the efficacy of low-intensity anticoagulation in the Japanese population.


   Acknowledgments
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
References
 
The authors thank Dr Yuhei Saitoh, Dr Atsushi Nagasawa, and Dr Jota Nakano for their great help in collecting patient information.


   References
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Kitamura M., Koyanagi H., Kudo T., et al. The Tokyo Area Anticoagulation Study (TAS) Group. Optimum anticoagulation control after bileaflet mechanical valve replacement: a prospective multi-institutional study. Kyobu Geka 1999;52:1001-1004.[Medline]
  2. British Society of Haematology. British Committee for Standards in Haematology. Haemostasis and Thrombosis Task Force. Guidelines on oral anticoagulation, second edition. J Clin Pathol 1990;43:177-183.[Free Full Text]
  3. Poller L. Therapeutic ranges for oral anticoagulation in different thromboembolic disorders. Ann Hematol 1992;64:52-59.[Medline]
  4. Edmunds L.H., Clark R.E., Cohn L.H., Miller D.C., Weisel R.D. Guidelines for reporting morbidity and mortality after cardiac valvular operations. Ann Thorac Surg 1996;62:932-935.[Abstract/Free Full Text]
  5. Rödler S.M., Moritz A., Schreiner W., End A., Dubsky P., Wolner E. Five-year follow-up after heart valve replacement with the CarboMedics bileaflet prosthesis. Ann Thorac Surg 1997;63:1018-1025.[Abstract/Free Full Text]
  6. Fiane A.E., Geiran O.R., Svennevig J.L. Up to eight years’ follow-up of 997 patients receiving the CarboMedics prosthetic heart valve. Ann Thorac Surg 1998;66:443-448.[Abstract/Free Full Text]
  7. Bernal J.M., Rabasa J.M., Gutierrez-Garcia F., Morales C., Nistal J.F., Revuelta J.M. The CarboMedics Valve: experience with 1,049 implants. Ann Thorac Surg 1998;65:137-143.[Abstract/Free Full Text]
  8. Dalrymple-Hay M.J.R., Pearce R., Dawkins S., et al. A single-center experience with 1,378 Carbomedics mechanical valve implants. Ann Thorac Surg 2000;69:457-463.[Abstract/Free Full Text]
  9. Czer L.S.C., Chaux A., Matloff J.M., et al. Ten-year experience with the St. Jude valve for primary valve replacement. J Thorac Cardiovasc Surg 1990;100:44-55.[Abstract]
  10. Arom K.V., Nicoloff D.M., Kersten T.E., Northrup W.F., III, Lindsay W.G., Emery R.W. Ten years’ experience with the St. Jude Medical valve prosthesis. Ann Thorac Surg 1989;47:831-837.[Abstract]
  11. Kratz J.M., Crawford F.A., Jr, Sade R.M., Crumbley A.J., Stroud M.R. St. Jude prosthesis for aortic and mitral valve replacement: a ten-year experience. Ann Thorac Surg 1993;56:462-468.[Abstract]
  12. Fernandez J., Laub G.W., Adkins M.S., et al. Early and late-phase events after valve replacement with St. Jude Medical prosthesis in 1200 patients. J Thorac Cardiovasc Surg 1994;107:394-407.[Abstract/Free Full Text]
  13. Keenan R.J., Armitage J.M., Trento A., et al. Clinical experience with the Medtronic-Hall valve prosthesis. Ann Thorac Surg 1990;50:748-753.[Abstract]
  14. Vallejo J.L., Gonzalez-Santos J.M., Albertos J., et al. Eight years’ experience with the Medtronic-Hall valve prosthesis. Ann Thorac Surg 1990;50:429-436.[Abstract]
  15. Akins C.W. Long-term results with the Medtronic-Hall valvular prosthesis. Ann Thorac Surg 1996;61:806-813.[Abstract/Free Full Text]
  16. Aoyagi S., Oryoji A., Nishi Y., Tanaka K., Kosuga K., Oishi K. Long-term results of valve replacement with the St. Jude Medical valve. J Thorac Cardiovasc Surg 1994;108:1021-1029.[Abstract/Free Full Text]
  17. Kobayashi Y., Eishi K., Nagata S., et al. Choice of replacement valve in the elderly. J Heart Valve Dis 1997;6:404-409.[Medline]
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  19. Rosengart T.K., O’Hara M., Lang S.J., et al. Outcome analysis of 245 CarboMedics and St. Jude valves implanted at the same institution. Ann Thorac Surg 1998;66:1684-1691.[Abstract/Free Full Text]
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