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Ann Thorac Surg 1998;66:762-767
© 1998 The Society of Thoracic Surgeons

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Original articles: Cardiovascular

Mitral valve replacement with the St. Jude medical prosthesis: a 15-year follow-up

^a Cardiovascular Surgery Unit and Department of Anesthesiology, The G and R Laënnec University Hospital, Nantes, France

Accepted for publication March 25, 1998.

Address reprint requests to Dr Remadi, Cardiovascular Surgery Unit, The G and R Laënnec Hospital, 44035 St Herblain, Nantes, France

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. A retrospective study was conducted to analyze the results of St. Jude Medical mitral valve replacement.

Methods. From January 1979 to December 1989, 870 patients (54% women, 46% men; mean age, 55.8 ± 6.2 years) underwent mitral valve replacement with the St. Jude Medical prosthesis. Of these operations 616 were isolated mitral valve replacements and 254 were double valve replacements. Coronary artery bypass grafting was performed concomitantly in 55 patients (6.3%).

Results. Overall, early mortality was 5.05%, with 4.2% for the isolated mitral valve procedure and 7.08% for the double valve replacement. Follow-up at 15 years was complete in 859 patients (98.74%). Mean follow-up time was 93.5 months, for a total of 6,436 years. Actuarial survival at 15 years was 59.5% ± 5%, 60.5% ± 6%, and 56.9% ± 9%, for the entire group, the isolated mitral valve and double valve procedures, respectively. Multivariate analysis identified age, sex, hospital stay, and preoperative mitral regurgitation as independent prognosis factors for overall mortality. Of 606 patients alive at the latest follow-up, the New York Heart Association class improved significantly (from 67% class III/IV before the operation to 88% class I/II after the operation). All patients received warfarin to maintain an international normalized ratio between 3.5 and 4. The linearized rates (% per patient-year) of thrombosis, thromboembolism, and major hemorrhage were, respectively, 0.21, 0.75, and 0.94 for the entire group; 0.18, 0.67, and 0.88 for the isolated mitral valve operation; and 0.15, 0.92, and 1.08 for the double valve replacement. For the entire group the freedom from thrombosis and thromboembolism at 15 years was 98.1% ± 1% and 88% ± 4%, respectively. No case of structural dysfunction occurred. The freedom from paravalvular leak and endocarditis at 15 years was 95.3% ± 2% and 97.3% ± 2.4%, respectively. The probability of remaining free from reoperation at 15 years was therefore 95.6% ± 2.5%.

Conclusions. These results confirm that the St. Jude Medical valve is a reliable prosthesis with very low thrombosis and thromboembolism rates, allowing the use of a low dose of anticoagulation with an international normalized ratio of about 3.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
The St. Jude Medical (SJM) prosthesis is a central-flow, low-profile, bileaflet pyrolytic carbon heart valve. Since the first clinical implantation in October 1977 [1], the excellent performance of the SJM valve has been reported by many authors [2–11]. We started our clinical use of it in March 1979. Before this date, we used Björk-Shiley valves, but the thromboembolic and valvular thrombosis rates were high, leading us to adopt another mechanical prosthesis [12]. Thus, our intermediate results in 1984, with 330 SJM implantations, already showed better results in terms of morbidity and early mortality [13]. This article therefore retrospectively analyzes 870 consecutive patients undergoing SJM mitral valve replacement.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
Between February 1979 and December 1989, 870 patients underwent mitral valve replacement (MVR) with SJM prostheses at our institution. The main subgroups were isolated mitral replacement (iMVR, 616 patients) and double valve replacement (AVR-MVR, 254 patients). Fifty-five coronary artery bypass grafting procedures were performed in the iMVR subgroup. Mean age was 55.9 ± 11.6 years (range, 7 to 80 years) (Table 1), with a female predominance (54%). Mean age increased during this study from 53 years in 1979 to 59 years in 1989. The patients in the coronary artery bypass grafting subgroup were older (mean age, 60 years).

Preoperatively, 80% of the patients were in New York Heart Association (NYHA) functional class III or IV. Twenty percent of the patients had undergone a previous cardiac surgery (commissurotomy in 18%). Four hundred fifty-two patients (52%) were in atrial fibrillation. Eighty-three percent and 82% of patients were in sinus rhythm, in the ischemic and endocarditis subgroups, respectively.

Operative technique
Myocardial protection was achieved with mild systemic hypothermia (28°C), topical cooling, and anterograde cristalloid cardioplegia (St. Thomas and Breitschneider solutions). The prostheses were inserted using interrupted sutures of braided suture material or continuous rolling sutures of polypropylene suture material. In this study the mitral subvalvular apparatus was never preserved, and the prosthesis was implanted in an intraannular antianatomical position. The prosthesis diameter most frequently implanted was 29 mm. Aortic replacement was performed with Björk-Shiley valve (121 cases), SJM prosthesis (123 cases), and bioprostheses (10 cases). Seventy-three associated tricuspid annuloplasty operations (De Vega) were performed. Intravenous heparin administration was started at the sixth postoperative hour and coumadin treatment was introduced on the fourth postoperative day, to obtain a prothrombin time level between 25% and 35% and an international normalized ratio between 3 and 4.

Follow-up
Eight hundred twenty-six patients (94.9%) were discharged from the hospital (590 MVR [95.75%]). A questionnaire was sent to the patient, referring physician, and cardiologist. Follow-up ended in December 1995. Eleven patients were lost to follow-up. Follow-up was therefore 98.74% complete. Mean follow-up time was 93.5 months (7.79 years), for a total of 6,436 patient-years.

Statistical methods
Continuous variables were expressed as mean ± standard deviation and compared using Student’s t test or Mann-Whitney test where appropriate. Qualitative variables were expressed as a percentage and compared by ² test or Fischer’s exact test where appropriate. A p value less than 0.05 was considered significant. Multivariate analysis was performed to determine which factors were associated with deaths or events. As a first step, the preoperative, intraoperative, and postoperative variables were studied by factorial analysis (multiple correspondence analysis). The variables were extracted from the model when their contribution to the formation extracted from the factorial axis was greater than 80%. In the second stage, these extracted variables were submitted to logistic regression analysis. A variable was identified as a significant independent factor when the p value was less than 0.05.

Actuarial analysis of events were calculated using the Kaplan-Meier method. All late mortality and morbidity rates were expressed as linearized rates and by actuarial analysis. Linearized occurrence rates were calculated by dividing the observed number of occurrences of a particular event (death or complication) by the total number of years of patient follow-up. All operative deaths were included in the actuarial survival analysis. For the comparison of two event-free curves, the log-rank was given, which is ² distributed with one degree of freedom.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Early mortality
The overall hospital mortality rate (0 to 30 days) was 5.05% (44 of 870 patients), whereas hospital mortality rate was 4.2% (26 of 616 patients) in the iMVR subgroup and 7.08% (18 of 254 patients) in AVR-MVR procedures. Urgent procedure and ischemic disease were associated with very high mortality (13% and 17%, respectively). The main cause or early postoperative morbidity and death was low cardiac output syndrome. The causes of mortality were as follows:

Low cardiac output syndrome 15 Left ventricular free wall rupture 4 Ventricular dysrythmia 5 Infection 5 Thrombosis 2 Myocardial infarction 3 Stroke 2 Renal failure 3 Other 5

Univariate analysis showed a significant correlation between operative mortality and the following variables: advanced age (> 70 years; p < 0.05), NYHA class III/IV (p < 0.01), urgent operative procedure (p < 0.02), difficult weaning from cardiopulmonary bypass (p < 0.001), low cardiac output syndrome (p < 0.001), ischemic cause (p < 0.01), and acute endocarditis cause (p < 0.01) (Table 2).

View larger version (40K): [in this window] [in a new window]   Fig 1. New York Heart Association class improvement (dark bars = postoperative; light bars = preoperative).

Late mortality
Two hundred-twenty late deaths occurred, with an overall actuarial survival (including operative mortality) or 59.5% ± 5% at 15 years (60.5% ± 6% in the isolated MVR population and 56.9% ± 9% in the AVR-MVR population) (Figs 2, 3) . One hundred fifty-nine deaths (72%) were not related to valve problems (50 progressive heart failures). Sixty-one deaths (28%) were related to the valve (Table 3).

View larger version (16K): [in this window] [in a new window]   Fig 2. Actuarial curves of deaths for the entire group (n = 870) (including operative deaths). (VRD = valve-related deaths).

View larger version (22K): [in this window] [in a new window]   Fig 3. Actuarial curves of deaths for two subgroups (including operative deaths). (AVR-MVR = aortic valve replacement; iMVR = isolated mitral valve replacement; VRD = valve-related deaths.)

Univariate analysis showed a significant association between late deaths and advanced age (>70 years, p < 0.001), male sex (p < 0.001), NYHA class III/IV (p < 0.001), mitral regurgitation (p < 0.01), degenerative disease (p < 0.01), emergency operation (p < 0.001), coronary disease (p < 0.01), ischemic disease (p < 0.001), associated coronary artery bypass grafting (p < 0.001), and ejection fraction less than 0.50 (p < 0.001) (Table 4).

Valve-related complications
No case of structural dysfunction was observed. Perivalvular leak and hemolysis were more frequent at the beginning of this study. A thicker Dacron sewing ring with modification of the suture procedure and antianatomical prosthesis orientation contributed to the decrease rate of this complication. Thus, the freedom from perivalvular leak at 15 years was 95.3% ± 2%.

An acute valve endocarditis occurred in 9 patients (two deaths). The most frequent causative organisms were Staphylococcus epidermidis and Streptococcus. The linearized endocarditis rate was 0.14% per patient-years (Table 5) and the freedom from endocarditis at 15 years was 97.3% ± 2.4%.

View larger version (21K): [in this window] [in a new window]   Fig 4. Actuarial curves of freedom from major events.

Major anticoagulant-related hemorrhage was always associated with an inappropriate anticoagulation protocol (prothrombin time level, 15%). Cerebral hemorrhage occurred in 16 patients (12 deaths). The cumulative mortality rate caused by major hemorrhage was 22.2% (16 of 72 patients). Freedom from major hemorrhage at 15 years was 84.9% ± 4%.

Thirty-six patients were reoperated. Reoperation was indicated for endocarditis (3 patients), leak (25 patients), and valve thrombosis (8 patients). Freedom from reoperation at 15 years was 95.6% ± 2.5% (Fig 4).

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
All results were studied according to the international guidelines published by The Society of Thoracic Surgeons [14, 15]. However, some criteria of this classification must be discussed. For example, sudden deaths must always be classified as valve-related deaths (VRDs). Sudden deaths therefore represent the main cause of VRDs, with a rate higher than 10% in most series [2, 3, 7, 8]. Consequently, sudden deaths significantly increase the VRD rate. A number of authors have therefore analyzed the causes of VRD in autopsy studies [16, 17–19]. Burke and associates [16] and Rooney and colleagues [19] showed that 50% to 90% of VRDs were not related to the prosthesis itself. Myocardial infarction and ventricular arrhythmia are often found to be responsible for VRD (80%). The VRD rate is certainly overestimated in most series reported [16–19]. The anticoagulation protocols also have to be discussed. In our series the thromboembolism rate was 0.8% patient-years for the entire group and varied from 0.5% to 2% patient-years in the literature [2, 4, 7, 10]. The linearized rate of hemorrhage was 0.94% patient-years. Hemorrhage was always attributed to an inappropriate anticoagulation protocol (prothrombin time level <15% and international normalized ratio >5). A high mortality rate was related to these events (20%). Therefore, we and many other authors [15, 20–23] currently recommand lower anticoagulation levels after mitral valve replacement with the SJM prosthesis. This approach could lower the incidence of severe hemorrhage without increasing embolism or thrombosis incidence.

Operative mortality after mitral valve replacement has decreased over the last 20 years. A previously published series of Björk-Shiley prostheses implanted between 1971 and 1976 in our unit [13] showed an operative mortality rate of 20%. The 5% early mortality rate observed in our series is similar to the mortality rate reported in other studies [3, 5, 6, 8, 9, 11–13]. In the literature, some preoperative criteria are often found to be related to operative mortality, by univariate or multivariate analysis [2–4, 6, 7, 18]; these include NYHA class IV, advanced age, male sex, left ventricular ejection fraction less than 0.50, coronary disease, and mitral regurgitation. In our study multivariate analysis only showed urgent operative procedure to be an independent preoperative risk factor for an increased early mortality rate. The main causes of these urgent procedures were ischemic disease (35%), acute endocarditis (30%), and chordal rupture (25%).

The results of the present study concerning the late mortality rate were in agreement with those reported in European and American studies [2, 3, 7, 10]. However, Japanese series showed better results with longer survival rates [9–11], but their patient populations were different, ie, younger (mean age <50 years), with a predominance of rheumatic disease, and with less ischemic disease than in Europe [9–11]. Several preoperative factors were also found to be related to late mortality in the literature [3-5, 7, 18]: degenerative disease, mitral regurgitation, NYHA class IV, advanced age, coronary disease, and male sex. In our study mitral regurgitation was the essential independent risk factor of late mortality, as mitral insufficiency leads to ventricular dilatation and a delayed cardiac failure after MVR. Non–valve-related cause of late deaths were therefore dominated by congestive heart failure (50 patients). Hemodynamic performance could be increased by the preservation of the subvalvular apparatus [24, 25], resulting in a decreased incidence of late cardiac failure [24, 25].

The SJM prosthesis is a reliable valve with a low rate of thrombosis and thromboembolism, suggesting that low-dose anticoagulation treatment appears to be appropriate. The SJM prosthesis remains the mechanical prosthesis of choice, especially in the mitral position. The follow-up with the new bileaflet prostheses, still less than 20 years, has now proved the excellent durability of the SJM valve.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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