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J Thorac Cardiovasc Surg 1994;107:394-0407
© 1994 Mosby, Inc.
Surgery for Acquired Heart Disease |
Browns Mills, N.J.
Supported in part by a grant from the St. Jude Medical S.C., Inc., St. Paul, Minn.
Address for reprints: Javier Fernandez, MD, Deborah Heart and Lung Center, 200 Trenton Rd., Browns Mills, NJ 08015.
Abstract
From May 1982 to August 1991, 1200 patients underwent valve replacement with the St. Jude Medical (St. Jude Medical, Inc., St. Paul, Minn.) valve: 615 men (51%) and 585 women, mean age 58 years. Preoperatively, 830 patients (69%) were in functional class III or IV. A total of 611 patients (51%) had the aortic valve replaced, 490 (41%) the mitral valve, 2 (0.2%) the tricuspid valve, and 97 (8%) multiple valves. There were 81 hospital deaths (6.8%). Risk factors included older age (p = 0.0001), female gender (p = 0.02), higher preoperative left ventricular end-diastolic pressure (p = 0.05), previous cardiac operation (p = 0.003), longer aortic crossclamp time (p = 0.0001), and longer cardiopulmonary bypass time (p = 0.0001). Follow-up was 98% complete (3153 patient-years). There were 152 late deaths; 32 (21%) were considered valve-related: six thromboembolism, four valve thrombosis, five anticoagulant-related hemorrhage, eight prosthetic valve endocarditis, one paravalvular leak, and seven sudden death. The 5-year actuarial survival was 75%. Risk factors for late death included older age (p = 0.03), lower preoperative ejection fraction (p = 0.005), longer aortic crossclamp time (p = 0.0001), longer cardiopulmonary bypass time (p = 0.0001), previous cardiac operation (p = 0.02), and higher preoperative functional class (p = 0.0001). Actuarial freedom at 5 years from major thromboembolic events and anticoagulant-related hemorrhage was 97% and 95%, respectively. This value for valve thrombosis was 99%, for reoperation 96%, for prosthetic valve endocarditis 98%, and for paravalvular leak 96%. Actuarial freedom from all valve-related events and valve-related death at 5 years was 74% and 94%, respectively. We conclude that the low incidence of valve-related events and low mortality supports the continued use of the St. Jude Medical valve. (J THORAC CARDIOVASC SURG 1994;107:394-407)
Numerous mechanical valve prostheses and biologic valves have been developed and introduced to clinical practice over the past three decades since the first successful implant of a silicone ball and cage prosthesis in the mitral position by Albert Starr in September 1960.
1
Despite refinements in materials and improved prosthetic valve design, valve failure continued to occur. The cloth-covered prostheses and the Björk-Shiley* low-profile tilting-disc valves, as well as biologic tissue valves such as the Hancock,
Carpentier-Edwards,
and Ionescu* pericardial valves, were introduced to reduce these events. Tissue valves demonstrated a lower incidence of thromboembolic complications and a reduced need for chronic anticoagulation. However, in the long term, these valves had serious durability problems that led to replacement at an early interval. Mechanical valves were plagued with structural problems such as strut fracture or unacceptable hemodynamics that made them undesirable.
In an effort to reduce the incidence of thromboembolic events and structural dysfunction, the St. Jude Medical (St. Jude Medical, Inc., St. Paul, Minn.) bileaflet Pyrolite valve was introduced in 1977 and received approval by the Food and Drug Administration in 1982. The purpose of this review was to evaluate the overall rate of valve-related events and valve-related mortality after valve replacement with the St. Jude Medical valve.
METHODS
The patient population consisted of 1200 consecutive patients who underwent valve replacement with the St. Jude Medical valve prosthesis between May 17, 1982, and Aug. 31, 1991, at the Deborah Heart and Lung Center. A total of 611 patients (51%) underwent isolated aortic valve replacement, 490 (41%) mitral valve replacement, and 2 (0.2%) tricuspid valve replacement; 87 (7.2%) had combined aortic and mitral valve implants, 6 combined mitral and tricuspid valves, 2 aortic and tricuspid valves, and 2 aortic, mitral, and tricuspid valves.
A total of 1299 St. Jude Medical valves were implanted. Of the 702 aortic prostheses, 130 (18%) were size 19. Of the 585 mitral implants, 87 (15%) were sizes from 21 to 25 and 498 (85%) were sizes from 27 to 33. Among the 12 tricuspid valve implants, the sizes ranged from 27 to 33.
There were 615 men (51%) and 585 women (49%). The mean age was 58 ± 18 years, range 2 to 89 years. Fifty-seven patients (4.75%) were 16 years or younger, and 44 (3.7%) were octogenarians.
Before operation, 830 patients (69%) were in New York Heart Association (NYHA) functional class III or IV. Atrial fibrillation was present in 366 patients (31%). Three hundred and fifty-nine patients (30%) had undergone previous cardiac operation. Fifty-one of these patients had previous coronary artery bypass grafting. The average aortic valve systolic gradient (n = 229) was 69 ± 24 mm Hg, the mitral valve diastolic gradient (n = 221) was 19 ± 8 mm Hg, and the left ventricular ejection fraction (n = 356) was 57% ± 14%.
The valve etiology, valve pathophysiologic condition, and other clinical data are shown in
Table I.
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Follow-up
Patient follow-up was accomplished by mail or telephone contact with the patient, family, or the referring physician. Of the 1119 hospital survivors, 1099 (98.2%) were followed up at a mean of 2.9 years, range 1 to 10 years (3153 patient-years). Follow-up was continued to August 1992.
On hospital dismissal, the referring physician was responsible for warfarin dosage and prothrombin regulation. Of the 947 late survivors who were followed up, 944 (99.6%) were receiving warfarin or antiplatelet therapy, or both, at the time of follow-up, 3 (0.3%) were receiving no medications at all, and 50 (4.1%) reported some interruption of anticoagulant therapy.
Surgical techniques
Cardiopulmonary bypass was conducted with a disposable bubble or membrane oxygenator. The mean aortic crossclamp time was 61 minutes (0 to 224 minutes) and the mean cardiopulmonary bypass time was 100 minutes (38 to 592 minutes). The systemic temperature was maintained at a mean 28.5° C during bypass. Myocardial protection was accomplished by the use of antegrade cold potassium crystalloid cardioplegia in 43% of patients and cold blood cardioplegia in 57% of patients. The cardioplegia was delivered through a standard cannula in the aortic root in most patients. In cases of aortic valve replacement, the cardioplegic solution was accomplished by direct coronary infusion or by retrograde perfusion of the coronary sinus.
The heart was approached through a midline sternotomy incision in the majority of cases except in a few patients with mitral valve disease and a history of multiple previous cardiac operations who were at high risk of operative bleeding. In these patients, a right thoracotomy approach was used to avoid the extensive pericardial adhesions.
Previously described standard surgical techniques of valve replacement were used. The prostheses were anchored to the valve anulus either by continuous (42%) or interrupted (58%) suture techniques.
2-4
Standard guidelines to define hospital and late mortality and valve-related events were followed.
5 Patients who died at reoperation were considered to have died of valve-related causes. Thromboembolic and hemorrhagic complications of anticoagulants were classified as major if they resulted in death or disability or necessitated transfusions or surgical intervention. Thromboembolic events were considered early if they occurred after the patient had fully recovered from anesthesia. Hemorrhagic events were identified as valve-related if they occurred in a patient who was receiving warfarin or heparin to prevent thrombus formation on the valve after operation.
Statistical methods
Because of the complexity of the database, the numbers reported may refer to number of patients, number of valves, or number of events, as indicated in the text. Rates of hospital events or of events in patients were given as percent of the total patients. Univariate analysis, including Wilcoxon's test, Fisher's exact test, and
2 test were done to identify the risk factors for the event hospital death. Rates of late events were expressed in linearized format and actuarially by Kaplan-Meier estimator with 70% confidence limits. Whenever it was applicable, the log-rank test was used to identify the risk factors of late events. If multiple events occurred in one patient, only the first occurrence was counted. However, different types of events occurring in one patient were counted separately. The actuarial curves show patients at risk at specified intervals.
A total of 45 preoperative and perioperative risk factors were analyzed for early and late death, late thromboembolic events, prosthetic valve endocarditis, and paravalvular leak late deaths (see appendix tables).
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Early valve-related events
There were 85 valve-related events in 76 patients (6.3%), which are listed in
Table II. Forty-four neurologic thromboembolic events (3.6%) occurred on the fourth or fifth postoperative day, in the presence of warfarin therapy with the exception of one patient who was receiving heparin. Of the 44 events, 19 were minor. One valve thrombosis (0.08%) occurred 2 days after isolated aortic valve replacement. This patient died on the fourth postoperative day. Autopsy findings revealed an organized thrombus on the St. Jude Medical valve.
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Prosthetic valve endocarditis was diagnosed in 8 patients (0.7%), and two of these cases were fatal. Five patients had mitral and three had aortic valve replacement. Four patients (50%) had previous cardiac operation or remote history of infective endocarditis, or both. In all cases, there were positive blood cultures. All patients were started on a 6-week course of antibiotic therapy.
Paravalvular leak was detected in nine patients between postoperative days 6 and 19. Seven had mitral valve replacement and two had aortic valve replacement. Of the nine patients, five required reoperation. Four of these had early repair and one had late repair. At follow-up, all were doing well.
Hemolysis was demonstrated in 6 patients (5%) in the early postoperative period. In three cases, the hemolysis was clearly related to a paravalvular leak that required repair in two cases (6 weeks and 4 months).
An interesting operative finding was a leaflet defect noticed after insertion of an aortic prosthesis. The valve was immediately replaced. Examination of the valve by the manufacturer showed surface scratches on the leaflet and an intact carbon coating by scanning electron microscopy.
Hospital deaths
Eighty-one hospital deaths (6.8%) occurred of which three (4%) were valve-related. Two of these patients died of prosthetic valve endocarditis and one of a thrombosed valve. Analysis of the causes of hospital deaths is shown in
Table III. Most deaths occurred as a result of nonvalvular causes. The mortality rate in the aortic valve replacement group was 5.4%, in the mitral valve replacement group 8.2%, and in the multiple valve group 8.3%.
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Late valve-related events
During the period of follow-up, 195 patients had 217 valve-related events (linearized rate: 6.8% per patient-year). Some patients had more than one complication.
Table IV lists the specific valve-related events and linear rates with corresponding mortality rates of each event. The actuarial freedom from late events at 5 years and at the end of the study period is given in
Table V.
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Of the 39 patients who had minor thromboembolic events (1.2% per patient-year: mitral valve replacement, 23; aortic valve replacement, 13; double valve, 3), sixteen (41%) were in atrial fibrillation at hospital discharge. Risk factors for thromboembolic events identified by log-rank test were atrial fibrillation (p = 0.014) and interruption of anticoagulation (p = 0.0001). The actuarial freedom from major and total thromboembolic events is shown in Fig. 1. Patients with late thromboembolic events represented 33% of the total patients who had late valve-related events.
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Minor anticoagulant-related hemorrhage consisted primarily of 59 episodes that occurred in 58 patients (1.8% per patient-year) at 3 ± 0.3 years after operation. All the patients were treated medically. Fig. 3 depicts the total and major actual freedom these complications.
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Twenty-seven paravalvular leaks developed in 24 patients (0.76% per patient-year). Three patients (12%) of the 24 had moderate leak, which was treated medically. The remaining 21 patients were treated surgically (mitral, 14; aortic, 7) with one death at reoperation. Of the 14 patients with mitral valve replacement, 11 underwent repair of the paravalvular leak and two underwent replacement of the St. Jude Medical valve. One patient who initially had a repair subsequently required a replacement of the mitral prosthesis. Of the seven patients with aortic valve replacement, three underwent repair of the paravalvular leak, one had repair twice, two underwent aortic valve replacement once, and one had repair first followed by replacement. Fig. 5 shows the actuarial freedom from this complication. Log-rank test identified mitral valve replacement versus aortic (p = 0.03) and history of previous infective endocarditis (p = 0.0001) as significant risk factors for development of late paravalvular leak. The use of continuous suture versus interrupted suture for valve implantation was not a significant risk factor (p = 0.78) for late development of paravalvular leak.
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There were three pediatric (mean age 5.5 years) patients in whom extrinsic valve dysfunction developed (0.09% per patient-year). Operative findings in two patients (one aortic and one mitral) showed the presence of tissue ingrowth probably interfering with the hemodynamics of the aortic St. Jude Medical valve. Both patients survived the rereplacement of the prostheses, however, one died a year and a half later of a non-valve-related complication. The third child, who had undergone mitral valve replacement with a 21 mm St. Jude Medical valve at 4 years of age, had outgrown the valve and at 14 years of age required rereplacement with a 25 mm valve. The patient had an uneventful recovery and is a long-term survivor. Fig. 6 shows freedom from extrinsic valve dysfunction. There were no late intrinsic or structural failures of the St. Jude Medical valve recorded during the entire period of observation in this study.
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Results of these morbid events
Reoperation on the St. Jude Medical valve was done in 29 patients who underwent 32 operations (0.92% per patient-year). The actuarial freedom from reoperation at 5 years was 96% and at 9 years was 88% (Fig. 7). The most common indication for reoperation was the presence of clinically significant paravalvular leak in 21 patients. There was one valve-related death in a patient who underwent mitral valve repair for paravalvular leak 5.5 years after operation and died 6 days after repair.
Table VI lists the indications of valve-related events that necessitated reoperations. One elderly patient had recurrent anticoagulant-related gastrointestinal bleeding and underwent successful reoperation to replace the St. Jude Medical aortic valve with a Carpentier-Edwards tissue prosthesis.
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In patients with mitral valve replacement, univariate analysis identified as risk factors for late mortality advanced age (p = 0.004) and higher preoperative NYHA functional class (p = 0.0004). In the aortic valve replacement group, the risk factors were longer cardiopulmonary bypass time (p = 0.03) and preoperative infective endocarditis (p = 0.0001).
There was a significant improvement of the NYHA functional class at follow-up as shown in
Table VIII. Seventy-seven percent of the 947 long-term survivors were in NYHA functional class I or II.
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Despite refinements in the design of artificial cardiac prostheses over the past 30 years, mechanical or biologic valve replacement has been associated with a variety of valve-related complications often leading to serious disability or death.
During the past two decades, other prosthetic valves, mechanical and biologic, in addition to the St. Jude Medical valve, were in use at our center, particularly during the early phase of our investigation.
6 Some of the biologic valves showed a decreased durability earlier than expected because of premature tissue degeneration.
7, 8 Others were withdrawn from the market.
9 A similar situation occurred with mechanical valves. A significant number of patients with prostheses implanted in the 1970s have returned to our facility for reoperation because of structural failure, hemolysis, or hemodynamic dysfunction.
10-12 More recently, the Björk-Shiley prosthesis was withdrawn from the market because of numerous case reports of strut fractures.
12, 13
The present study was undertaken to evaluate the overall valve-related events and mortality of the St. Jude Medical valve, in regards to thromboemboli, anticoagulation, hemorrhagic events, reoperation, structural deterioration, and other complications. The hemodynamic characteristics of this valve have been reported by other authors and show low transvalvular gradients at rest and minimal increase during exercise.
14-17
Standard definitions of valve-related terms were used in this report.
5 In regard to hospital events, specific definitions of thromboembolic and anticoagulant-related hemorrhage were used to better differentiate events directly related to the valve from similar events that occurred as a result of the operation. Thromboembolic events were defined as those that occurred in patients who were completely awake and recovered from anesthesia. Anticoagulant-related hemorrhage was identified as events that occurred in patients taking warfarin. At our institution, warfarin administration is started when both the chest tubes and pacemaker wires have been removed from the patient (average fourth postoperative day).
Among the early valve-related events, only three patients (4%) had a valve-related death. No similar data for the St. Jude Medical valve were available in the literature for comparison. The total operative mortality rate of 6.8% compared favorably with that reported in the literature of 3.25% to 14.5%.
18-27 No significant difference in operative mortality according to valve position was noted by the univariate analysis.
Little has been written regarding early valve-related events with the St. Jude Medical valve. Most reports focus on the late valve-related complications and mortality. In our experience, the total percent of patients with valve-related events of 6.8% was probably not excessive.
This study revealed that the most frequent valve-related events in the early and late postoperative period were thromboembolic, including valve thrombosis and hemorrhagic complications related to anticoagulants. The first two events combined represented 59% of the total early events and 36% of the late events. The hemorrhagic events represented 22% of the early events and 46% of the late events. Other authors have reported similar data.
18, 19, 24 These two types of complications vary more or less inversely depending on the level of anticoagulation and the time this drug is initiated in the postoperative period. When warfarin is administered very soon after the operation, postoperative bleeding may occur. When warfarin administration is delayed, the thromboembolic rate may increase. In our series, warfarin was started on the fourth postoperative day. Other authors have reported beginning administration of the drug within 72 hours of operation.
18, 22, 24, 26 However, there seems to be no consensus as to when to initiate warfarin anticoagulation. Armenti, Stephenson, and Edmunds
22 suggested the use of heparin if warfarin is delayed for any reason.
In regards to the optimum level of anticoagulation, it has been the policy of our cardiology department to maintain a therapeutic level of 1.2 to 1.5 times the control. Czer and associates
18 found a significant reduction of hemorrhagic complications as they reduced the target level of anticoagulation from a maximum of 2.5 to 1.5 times control, with only a minimal rise in thromboembolic events. There seems to be a unified consensus that the patient with a St. Jude Medical valve needs to receive long-term warfarin therapy, however, there is no agreement on the exact therapeutic level.
In this study, univariate analysis showed that atrial fibrillation was an important risk factor of late thromboemboli. In 31% of our patients who were in atrial fibrillation on hospital discharge, the rate of thromboemboli was higher than in patients in sinus rhythm. Myers and associates
25 and Nair and associates
26 have shown in large series of patients with a St. Jude Medical valve that long-term anticoagulation with warfarin is the best method to minimize late thromboembolic events. The same authors demonstrated that antiplatelet agents did not provide adequate protection in adults. In the pediatric population, our group has also shown poor results with antiplatelet agents.
28
Valve thrombosis is probably the most serious of the thromboembolic complications. It carried a high mortality in our series (68%). The only survivors were three patients (of seven) who underwent emergency reoperation. Burckhardt and colleagues
23 reported thrombotic obstruction in three patients: two were operated on successfully and another died before operation. This was similar to our results.
The reported incidence of prosthetic valve endocarditis in patients with the St. Jude Medical valve ranges from 0.16% per patient-year to 1.13% per patient year.
18-20,
23, 24 In our series, the incidence was well within this range. The complication carried a 40% mortality rate, despite antibiotic treatment and surgical intervention.
Paravalvular leak and prosthetic endocarditis are not specific for any type of prosthesis. Our incidence of paravalvular leak compares well with that of others, ranging from 0.2% per patient-year to 0.9% per patient-year. Surgical intervention either to repair or replace the prosthesis is the treatment of choice. Among patients with this event (9 early and 24 late), one death occurred.
The St. Jude Medical valve showed excellent durability in our patient population despite the wide range in ages. There were no instances of intrinsic valve failure as a result of malfunction of the moving parts. The damaged leaflet found in one case was probably from rough handling before or at operation. The valve never functioned in vivo inasmuch as it was immediately removed from the patient.
Reoperations in patients with the St. Jude Medical valve in 4 early cases and 29 late cases were indicated mainly to treat paravalvular leak complications. In most series, the mortality of reoperations has ranged from 0% to 2% per patient-year.
18, 19, 23, 24 Our reoperation mortality (one case) was 0.92% per patient-year.
Our overall actuarial patient survival and the freedom from all valve-related events at 5 and 9 years, including the actuarial freedom from thromboemboli and hemorrhagic complications, were similar to those in other reported series. The excellent durability of the St. Jude Medical valve with total absence of mechanical intrinsic valve failure is the basis for the continuing use of this prosthesis as a valve of choice when cardiac valve replacement is indicated.
Appendix: DISCUSSION
Dr. Robert A. Guyton (Atlanta, Ga.)
This is an outstanding series with a large number of valves. I have three questions. First, the authors report no structural valve failure and yet report three instances of extrinsic valve failure, and I would like to know the definition of extrinsic valve failure in that instance.
Second, I am interested in the separation between the early and late time periods, particularly with regard to paravalvular leak. The authors reported that 24 patients had late paravalvular leaks, which was less than the prevalence of late endocarditis. What was the etiology of those late paravalvular leaks and, also, what suture technique is used, particularly for the aortic valve? I have found with the St. Jude Medical valve that not using pledgets in the aortic position results in occasional paravalvular leak, whereas with other valves in which I use pledgets in the aortic position paravalvular leaks essentially never occur.
Finally, on Tuesday morning one of the papers presented data relative to the St. Jude medical valve with regard to anticoagulation, claiming that the rate of thromboembolism was just as low with low levels of anticoagulation that produced an international normalized ratio of 1.8 to 2.7 as it was with higher levels of anticoagulation and that the rate of bleeding was much less. These investigators recommended using relatively low levels of anticoagulation for the St. Jude Medical valve compared with those used with the Björk-Shiley valve or the Medtronic Hall (Medtronic, Inc., Minneapolis, Minn.) valve. What level of anticoagulation do you use, and do you have any comment on the suggestion of this other group that it would be safe, safer in fact, to use lower levels of anticoagulation with the St. Jude Medical valve?
Dr. James L. Cox (St. Louis, Mo.)
I would like to ask one question. The authors mentioned in their data that there were seven patients who had sudden death, and I wondered if those patients had autopsies to rule out the possibility of sudden valve failure as a cause of death.
Dr. Joshua D. Salvador (Chicago, Ill.)
These results show the same complications as have occurred with the Björk-Shiley and other prosthetic valves. Do the authors find any difference or superiority in the St. Jude Medical valve when they compared it with their previous experience with other prosthetic valves?
Dr. Norman W. Thomas (Topeka, Kan.)
What happened to the 8% of patients who did not receive warfarin and the 50 patients who stopped taking warfarin in terms of the thromboembolic rate in those subgroups?
Dr. Fernandez
In response to Dr. Guyton's questions, early events were those that occurred during the first 30 postoperative days, but also included the event of death in any patient who was not discharged from the hospital. All other events were considered late events.
Paravalvular leak was treated by valve replacement or repair in five out of nine patients with an early leak and 21 out of 24 patients with a late leak. Although valve implantation with continuous suture was used in 42% of the patients and interrupted sutures in 58%, surgical technique was not a significant factor for paravalvular leak by univariate analysis.The level of anticoagulation was controlled by the private physician on discharge from the hospital. At present, warfarin dose is adjusted to maintain a prothrombin time between 1.2 and 1.5 times the control.Sudden death was defined as a valve-related death in patients who died outside the hospital and in whom the underlying cause of death could not be determined. Autopsies were not obtained in this particular group and the information was obtained from the death certificate.
Dr. Guyton
Eight percent of the patients were not receiving warfarin. Were these cases analyzed separately for thromboembolic events?
Dr. Fernandez
Yes, they were evaluated by univariate analysis. There were only three patients or 0.03% who were not receiving warfarin and 50 patients or 4.1% who had intermittently interrupted the anticoagulation regimen. A decrease in anticoagulation or the absence of anticoagulation even for short periods was a significant risk factor for thromboembolic complications (p = 0.0001). Finally, Dr. Salvador, you asked about the Björk-Shiley valve versus the St. Jude Medical valve. As you know, strut fracture has been reported with the Björk-Shiley valve but in our series there were no cases of structural valve failures with the St. Jude Medical valve.
Acknowledgments
We appreciate the work done by Ray Ellis, Vicky Bada, Michele Meinhart, RN, and Otto B. Brdlik, DO, from the Department of Surgery, as well as the entire staff of the Audio-Visual Department, and Douglas Joyce, DO, for reviewing the manuscript.
Footnotes
Read at the Seventy-third Annual Meeting of The American Association for Thoracic Surgery, Chicago, Ill., April 25-28, 1993. ![]()
Johnson & Johnson Cardiovascular, King of Prussia, Pa. ![]()
Baxter Healthcare Corp., Santa Ana, Calif. ![]()
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T. K. Rosengart, M. O'Hara, S. J. Lang, W. Ko, N. Altorki, K. H. Krieger, and O. W. Isom Outcome analysis of 245 CarboMedics and St. Jude valves implanted at the same institution Ann. Thorac. Surg., November 1, 1998; 66(5): 1684 - 1691. [Abstract] [Full Text] [PDF] |
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J.-P. Remadi, P. Bizouarn, O. Baron, O. Al Habash, P. Despins, J.-L. Michaud, and D. Duveau Mitral valve replacement with the St. Jude medical prosthesis: a 15-year follow-up Ann. Thorac. Surg., September 1, 1998; 66(3): 762 - 767. [Abstract] [Full Text] [PDF] |
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A. E. Fiane, O. R. Geiran, and J. L. Svennevig Up to eight years' follow-up of 997 patients receiving the CarboMedics prosthetic heart valve Ann. Thorac. Surg., August 1, 1998; 66(2): 443 - 448. [Abstract] [Full Text] [PDF] |
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S. R. Craig and W. S. Walker The "Annular Sandwich": A Simple Method of Reinforcing a Friable Mitral Valve Annulus Ann. Thorac. Surg., June 1, 1998; 65(6): 1805 - 1806. [Abstract] [Full Text] [PDF] |
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W.R. E. Jamieson, A. I. Munro, R. T. Miyagishima, G. L. Grunkemeier, L. H. Burr, S. V. Lichtenstein, and G. F. O. Tyers Multiple mechanical valve replacement surgery comparison of St. Jude Medical and CarboMedics prostheses Eur. J. Cardiothorac. Surg., February 1, 1998; 13(2): 151 - 159. [Abstract] [Full Text] [PDF] |
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J. M. Bernal, J. M. Rabasa, F. Gutierrez-Garcia, C. Morales, J. F. Nistal, and J. M. Revuelta The CarboMedics Valve: Experience With 1,049 Implants Ann. Thorac. Surg., January 1, 1998; 65(1): 137 - 143. [Abstract] [Full Text] [PDF] |
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J. Hasegawa, S. Kitamura, S. Taniguchi, T. Kawata, K. Niwaya, K. Mizuguchi, H. Nishioka, and Y. Kameda Comparative Rest and Exercise Hemodynamics of Allograft and Prosthetic Valves in the Aortic Position Ann. Thorac. Surg., December 1, 1997; 64(6): 1753 - 1756. [Abstract] [Full Text] |
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T. A. Orszulak, H. V. Schaff, F. J. Puga, G. K. Danielson, C. J. Mullany, B. J. Anderson, and D. M. Ilstrup Event Status of the Starr-Edwards Aortic Valve to 20 Years: A Benchmark for Comparison Ann. Thorac. Surg., March 1, 1997; 63(3): 620 - 626. [Abstract] [Full Text] |
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M. R. Aupart, P. H. Neville, S. Hammami, A. L. Sirinelli, Y. A. Meurisse, and M. A. Marchand CARPENTIER-EDWARDS PERICARDIAL VALVES IN THE MITRAL POSITION: TEN-YEAR FOLLOW-UP J. Thorac. Cardiovasc. Surg., March 1, 1997; 113(3): 492 - 498. [Abstract] [Full Text] |
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T. E. David, V. L. Gott, L. A. Harker, G. E. Miller Jr, D. C. Naftel, A. G. G. Turpie, and C. W. Akins Mechanical Valves Ann. Thorac. Surg., November 1, 1996; 62(5): 1567 - 1570. [Full Text] |
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C. W. Akins Results With Mechanical Cardiac Valvular Prostheses Ann. Thorac. Surg., December 1, 1995; 60(6): 1836 - 1844. [Abstract] [Full Text] |
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R. P. Cochran, K. S. Kunzelman, A. C. Eddy, B. O. Hofer, and E. D. Verrier Modified conduit preparation creates a pseudosinus in an aortic valve-sparing procedure for aneurysm of the ascending aorta J. Thorac. Cardiovasc. Surg., June 1, 1995; 109(6): 1049 - 1058. [Abstract] [Full Text] |
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J. Jaggers, P. M. Chetham, T. L. Kinnard, and D. A. Fullerton Intraoperative Prosthetic Valve Dysfunction: Detection by Transesophageal Echocardiography Ann. Thorac. Surg., March 1, 1995; 59(3): 755 - 757. [Abstract] [Full Text] |
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