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J Thorac Cardiovasc Surg 1994;108:1021-1029
© 1994 Mosby, Inc.
SURGERY FOR ACQUIRED HEART DISEASE |
Kurume, Japan
From the Second Department of Surgery, Kurume University School of Medicine, Kurume, Japan.
Received for publication April 1, 1994. Accepted for publication July 28, 1994. Address for reprints: Shigeaki Aoyagi, MD, Second Department of Surgery, Kurume University School of Medicine, 67 Asahi-machi, Kurume, 830 Japan.
Abstract
Between 1980 and 1992, 908 patients underwent single aortic (n = 178), single mitral (n = 577), or double aortic and mitral (n = 153) valve replacement with the St. Jude Medical valve at our hospital. There were 392 male patients and 516 female patients whose ages ranged from 1.2 to 74 years (mean, 52 years). The early mortality rate was 5.0% (45 patients). A 94% complete follow-up was accomplished for 863 patients who were discharged from the hospital (4682.3 patient-years). Sixty-nine of these patients died, for a late mortality rate of 8.0%. Fifty-two patients, including four patients with valve thrombosis, had thromboembolic episodes (1.1%/100 patient-years). Sixteen patients (0.3%/100 patient-years) had anticoagulant-related hemorrhage, 4 (0.1%/100 patient-years) had prosthetic valve endocarditis, 11 (0.2%/100 patient-years) had nonstructural valve dysfunction, and 16 (0.3%/100 patient-years) underwent reoperation. There were no structural valve failures in this series. The total number of valve-related deaths was 22. Of those patients who survived, 98% were in New York Heart Association functional class I or II at the date of the last follow-up. The probabilities of freedom from thromboembolism and anticoagulant-related hemorrhage at 10 years were 94% ± 2% and 97% ± 2% in aortic valve replacement, 89% ± 2% and 98% ± 4% in mitral valve replacement, and 89% ± 6% and 92% ± 6% in double valve replacement, respectively. Significant hemolysis related to the St. Jude Medical valve occurred in 8 of the 577 patients who received mitral valve replacement in our early experience, and modifying the valve orientation appeared to play an important role in reducing hemolysis. The event-free rate, including all complications and late deaths, at 10 years was 75% ± 7%, 74% ± 3%, and 81% ± 6% in aortic valve replacement, mitral valve replacement, and double valve replacement, respectively. On the basis of these results, the St. Jude Medical valve seems to be an excellent mechanical valve in terms of durability and low thrombogenicity and remains our prosthetic valve of choice when valve replacement with a mechanical valve is indicated. (J THORAC CARDIOVASC SURG 1994;108:1021-9)
The St. Jude Medical (St. Jude Medical, Inc., St. Paul, Minn.) valve is now one of the most widely used cardiac valve prostheses in the world. Since 1980 we have used the St. Jude Medical valve as our first choice of prosthetic valves for valve replacement.
This report summarizes our long-term (14-year) experience with cardiac valve replacement, including aortic, mitral, and aortic and mitral valve replacement, with particular regard to valve-related complications and survival.
PATIENTS AND METHODS
Patients
Between May 1980 and December 1992, 908 patients underwent single aortic valve replacement (AVR; n = 178), single mitral valve replacement (MVR; n = 577), or double aortic and mitral valve replacement (DVR; n = 153) with the St. Jude Medical valve at our hospital. There were 392 male patients and 516 female patients whose ages ranged from 1.2 to 74 years (mean, 52 years). The cause of the valve disease was rheumatic heart disease in the majority of patients. Two hundred eight (23%) patients had had previous valve operations once or twice, and 28 (3%) patients underwent concomitant coronary artery bypass procedures. The preoperative New York Heart Association (NYHA) functional class was II in 34.6% (314 patients) of the cases, III in 57.9% (526 patients), and IV in 7.5% (68 patients). 
Table I summarizes the characteristics of the patients who underwent valve replacement with the St. Jude Medical valve.
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Surgical technique
The standard technique of cardiopulmonary bypass with moderate hypothermia (28° to 30° C) was used, and cold potassium cardioplegia combined with topical hypothermia was routinely used for myocardial protection. When coronary artery bypass grafting was done with the saphenous vein, the distal anastomoses were done first, followed by valve replacement, and finally the proximal anastomoses were done. In our early operations, the pivot of the St. Jude Medical valve was implanted parallel to the ventricular septum in the aortic position and parallel to the native leaflets in the mitral position. Since 1983 the valve has been placed perpendicular to the leaflets in the mitral position and perpendicular to the septum in the aortic position. 1 The St. Jude Medical valve was implanted with interrupted mattress sutures with Teflon pledgets. Three patients required enlargement of the aortic anulus. 2 After 1988, when possible, the continuity between the mitral posterior leaflet and the left ventricle was preserved in patients who required MVR, 3 particularly in patients with mitral regurgitation.
The sizes of the St. Jude Medical valves used are listed in Table II, and additional operative procedures done at the same time as valve replacement are shown in Table III.
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Follow-up studies
Hospital survivors were followed up annually or biannually by cardiologists or cardiac surgeons in our hospital. In addition to blood chemistry tests, echocardiographic evaluation including Doppler studies was routinely done for all patients who visited our hospital. The survivors were also examined by their family physicians at least once a month to evaluate their cardiac states and the level of anticoagulation and to receive medications. At the time of this study, patients were contacted directly by questionnaire or telephone communication or through the referring physician, and additional data were collected from patients' charts. Fifty-one patients (5.6%) could not be located and were considered lost to follow-up. Therefore 94.4% of all the patients were included in this study. The average period of follow-up was 4.3 years, with a maximum of 13.9 years. Patient-years of follow-up were 698.8 for AVR, 3386.7 for MVR, and 596.8 for DVR. Total follow-up was 4682.3 patient-years.
Deaths and complications were stringently defined according to published guidelines of The Society of Thoracic Surgeons and The American Association for Thoracic Surgery. 4
Statistical methods
Values are reported as the mean ± 1 standard deviation. Actuarial curves were constructed to describe mortality and the incidence of valve-related complications. Individual event-free curves were calculated for valve-related mortality and overall mortality, as well as for the incidence of reoperation, endocarditis, thromboembolic events, and anticoagulant-related hemorrhage. Valve-related deaths were given precedence over nonfatal complications in cases in which both occurred. Actuarial estimates were calculated by the Kaplan-Meier technique 5 and are reported with the standard error of the estimate.
RESULTS
Mortality and causes of death
Forty-five of the 908 patients died either within 30 days after operation or during the hospitalization in which the operation was done, and the operative mortality rate was 5.0% overall.
The operative mortality rate for the patients having AVR, MVR, or DVR was 3.9% (7 patients), 4.7% (27 patients), and 7.2% (11 patients), respectively. Low cardiac output syndrome, resultant multiple organ failure, and technical error were the main causes in 29 (64.4%) of 45 early deaths. Five patients who under went MVR died of sequelae of significant hemolysis related to the St. Jude Medical valve. A paravalvular leak was found in one of the five patients at autopsy. There were no significant cases of hemolysis or deaths resulting from hemolysis in patients who received AVR or DVR.
Late mortality
Sixty-nine patients (8.0%, 1.5%/100 patient-years) had died by the date of the last follow-up. The mortality is shown in Table IV. The causes of late death were valve-related in 22 patients, cardiac-related in 20, and noncardiac-related in 15 patients. In the remaining 12 patients, the causes of death were unknown because we were unable to contact their families. Patients' deaths were confirmed by referring to government records.
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Valve thrombosis developed in four patients: in the aortic position in one and in the mitral position in three. Anticoagulant therapy in two of the four patients was inadequate at the time of diagnosis of valve thrombosis, and all four of the patients underwent replacement the St. Jude Medical valve with a new St. Jude Medical or another prosthetic valve. As shown in Fig. 2, freedom from thromboembolism, including valve thrombosis, at 10 years was 93.9% ± 2.3% in patients with AVR, 89.4% ± 1.9% in patients with MVR, and 89.1% ± 5.8% in patients with DVR. The incidence of thromboembolism was 1.0%/100 patient-years in patients with AVR, 1.1%/100 patient-years in patients with MVR, and 1.3%/100 patient-years in patients with DVR.
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Nonstructural dysfunction.
In total 11 patients (0.2%/ 100 patient-years) had nonstructural valve dysfunction, paravalvular leak, or entrapment of leaflets in the St. Jude Medical valve by pannus formation. Nine patients (AVR 2; MVR 6; DVR 1) had paravalvular leaks to various degrees. The paravalvular leak in the patient with DVR occurred in the aortic position. The diagnosis of paravalvular leak was made by physical examination, angiography, and echocardiography, including Doppler study and color flow mapping. Four (AVR 1; MVR 3) of the nine patients had symptoms severe enough to necessitate reoperation to repair the leak.
Entrapment of the leaflets of the St. Jude Medical valve by pannus formation occurred in two patients (AVR 1; MVR 1). The entrapment was diagnosed during reoperation, and both patients underwent excision of pannus.
The probability of freedom from nonstructural valve dysfunction at 10 years was 97.3% ± 2.0% in patients with AVR, 98.3% ± 0.9% in patients with MVR, and 99.3% ± 0.7% in patients with DVR. The linearized incidence of nonstructural dysfunction was 0.4%, 0.2%, and 0.2%/100 patient-years in patients with AVR, MVR, and DVR, respectively.
Hemolysis.
Significant hemolysis related to the St. Jude Medical valve was defined as mechanical hemolysis that serially showed remarkable elevation of serum lactate dehydrogenase values (
1000 Wroblewski unit) with an increase of type I isozyme and that necessitated blood transfusion or replacement of the prosthetic valve. Blood transfusion was indicated when the hemoglobin level decreased to less than 8.0 gm/dl. Eight patients who had undergone MVR with the St. Jude Medical valve had significant hemolysis that began immediately after operation, and five of the eight patients died of the sequelae of severe hemolysis. Replacement of the mitral St. Jude Medical valve with a porcine bioprosthesis was done in two patients with unsuccessful results. No significant hemolysis, however, occurred late after operation among the operative survivors. Paravalvular leak was confirmed in two of the eight patients, including the one patient mentioned previously, by left ventriculography or at reoperation or autopsy. Significant hemolysis was not seen in any of the patients with AVR or DVR. The linearized incidence of significant hemolysis related to the prosthetic valve was 0.2%/100 patient-years in the mitral position.
Structural deterioration.
No change in valve function occurred as a result of an intrinsic abnormality or any structural failure such as wear or stress fracture of any part of the prosthetic valve in any of the three groups.
Consequences of morbid events
Reoperation.
Fourteen patients (AVR 4; MVR 8; DVR 2) underwent reoperation for the St. Jude Medical valve. The linearized incidence of reoperation for the three patient groups as a whole was 0.3%/100 patient-years. Causes of reoperation were valve thrombosis in four patients (AVR 1; MVR 3), paravalvular leak in four (AVR 1; MVR 3), prosthetic valve endocarditis in four (AVR 1; MVR 1; DVR 2), and entrapment by pannus in two (AVR 1; MVR 1). In addition, the mitral St. Jude Medical valve was replaced with a bioprosthesis early after operation in two patients because of persistent significant hemolysis, as mentioned previously. The probability of freedom from reoperation at 10 years was 96.7% ± 0.9% in patients with AVR, 98.4% ± 0.7% in patients with MVR, and 98.5% ± 1.0% in patients with DVR. The linearized incidence of reoperation was 0.6%, 0.2%, and 0.3%/100 patient-years for patients with AVR, MVR, and DVR, respectively.
Valve-related mortality.
There were 22 valve-related deaths, as mentioned in the section on late mortality. Fourteen of these patients, including one patient who had thrombotic obstruction of the mitral St. Jude Medical valve, died of thromboembolism or anticoagulant-related bleeding. Two patients who required reoperation because of prosthetic valve endocarditis in the aortic position died of persistent endocarditis early after the second operation. The remaining six patients died of sudden, unexplained, and unexpected causes. The probability of freedom from valve-related death at 10 years was 88.0% ± 5.7% in patients with AVR, 90.5% ± 1.5% in patients with MVR, and 84.1% ± 5.4% in patients with DVR, as shown in Fig. 4. The linearized incidence of valve-related death was 0.5%/100 patient-years.
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Freedom from all complications.
The probability of freedom from all complications, including nonvalve-related deaths, at 10 years was 74.5% ± 7.1% in patients with AVR, 74.2% ± 2.7% in patients with MVR, and 80.9% ± 5.7% in patients with DVR, as shown in Fig. 5.
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DISCUSSION
The St. Jude Medical valve is now one of the most widely used cardiac valve prostheses in the world. More than 10 years have passed since it was first introduced for clinical use, and several investigators have reported their long-term experiences with this valve. 6-8
In this study, we have summarized our 14 years of experience with the St. Jude Medical valve to evaluate the long-term performance characteristics of the St. Jude Medical valves and patient survival.
Our overall operative mortality rate (AVR 3.9%; MVR 4.7%; DVR 7.2%) is not significantly different from that reported by Arom and associates 6 and Czer and colleagues. 7 It also compares favorably with other contemporary series in which porcine valves 9,10 and the other most commonly used mechanical prosthesis 11,12 were used. The most common causes of early death were low cardiac output syndrome, multiple organ failure, and technical errors. It should be noted, however, that five of the 45 early deaths resulted from sequelae of significant hemolysis related to the prosthetic valve. All of the cases of significant hemolysis reported in this study began immediately after operation only in the patients who underwent MVR and were seen during the initial 6 years of the study period. No patients had significant hemolysis after AVR or DVR.
Mechanical hemolysis related to prosthetic valves may be generally influenced by the extent of paravalvular leaks, valve orientation, asynchronous movements of leaflets, and leakage flow through a prosthetic valve. 13 Although paravalvular leaks have clearly caused significant hemolysis in patients with the St. Jude Medical valve, not all cases of hemolysis have necessarily resulted from paravalvular leaks. Significant hemolysis without paravalvular leak was reported in several studies. 14,15 We also found small paravalvular leaks in two of the eight patients in our series with hemolysis. In our experience, the orientation of the St. Jude Medical valve in the mitral position seems to be one of the important factors influencing hemolysis. Our previous study demonstrated that lactate dehydrogenase values were significantly higher in patients with anatomic valve orientation than in those with antianatomic valve orientation, when patients had trace or mild aortic regurgitation. 16 Collision of the regurgitant jet through the aortic valve against an anterior leaflet of a St. Jude Medical valve that is perpendicular to the direction of the jet may easily cause destruction of the red blood cells. The fact that significant hemolysis was not seen in patients with AVR or DVR appears to support our observation. Thus all St. Jude Medical valves are now implanted with an antianatomic valve orientation, regardless of the presence of aortic regurgitation. In addition, the antianatomic orientation has advantages for preventing valve thrombosis and maintaining excellent hemodynamic performance. 1 Fortunately, we have not had a case of clinically troublesome hemolysis related to the St. Jude Medical valve in the past 7 years.
Long-term survival is related to underlying cardiac function, age, and valve performance. Our 10-year survival in the three patient groups (AVR 81.1% ± 7.2%; MVR 80.0% ± 2.3%; DVR 80.9% ± 7.1%) were better than those reported by Arom and associates 6 and others. 7,8Arom and associates 6 analyzed long-term results of valve replacement with the St. Jude Medical valve in three large series and suggested that younger and healthier patients without coronary artery disease obtained the best long-term results when operation was undertaken earlier. In our experience, rheumatic valvular disease, mainly associated with mitral stenosis, necessitated valve replacement in the majority of the patients, and only 3.1% of the patients received concomitant coronary artery bypass grafting. This is in contrast to the 28% of patients operated on by Arom and colleagues 6 who received coronary artery bypass grafting. Our patients were also younger than their patients.
Thromboembolic complications are major problems in all mechanical valves. We observed excellent thromboembolism-free rates in all three patient groups. Low incidences of thromboembolism at 10 years have also been reported in other studies, 6-8 and their incidences were not significantly different from those in this series. Hemodynamic characteristics of blood flow across the St. Jude Medical valve and the structural characteristics of the St. Jude Medical valve are considered to be the main reason for its low thrombogenicity. 6 Because of its low thrombogenicity, some have suggested that postoperative anticoagulant therapy was not necessary for patients who received the St. Jude Medical valve, whereas Chaux and colleagues 17 and Baudet and associates 1 have shown that without the administration of anticoagulants the incidence of valve thrombosis and systemic embolism was significantly higher and that a low incidence of thromboembolism could be achieved only when anticoagulants were administered. As with the patients treated by Arom and colleagues 6 and others, 7,8 all of our patients received oral anticoagulant therapy with warfarin. These facts imply that the low incidence of this complication may be achieved with long-term anticoagulation.
Czer and colleagues 7 reported that anticoagulant-related hemorrhage was the most frequent valve-related complication (2.6%/100 patient-years) and the major contributor to valve-related morbidity and mortality in their series. Thus they have lowered the upper limit of their target prothrombin time ratio from 2.5 to 2.0 since 1987. In our experience, the incidence of anticoagulant-related hemorrhage was less than 1%/100 patient-years. This incidence was similar to that of Arom and colleagues 6 and others. 18 Frequent monitoring of the level of anticoagulation, which has generally been done once a month, may help explain the low incidence of thromboembolic and anticoagulant-related complications in our experience. However, because it is difficult to recognize all transient anticoagulant-related hemorrhages or transient peripheral embolic events by our method of follow-up, there is a slight possibility that incidences of these events have been underestimated in this study.
Although occasional reports of structural failure of the St. Jude Medical valve have appeared, 19 these incidents have been extremely rare. 6-8 In this series there was no prosthetic dysfunction resulting from structural failures such as wear or fracture. The fact that no structural failure occurred demonstrates the excellent durability of the St. Jude Medical valve, as compared with that of porcine and pericardial xenografts or earlier mechanical valves.
A paravalvular leak occasionally develops in patients with either residual calcification or poor native tissue of the anulus. Use of interrupted everted mattress stitches may allow better approximation between the sewing ring and anulus tissue.
The incidence of prosthetic valve endocarditis in our series was quite low and is similar to that of previous reports. 6,7 In this series, four patients had prosthetic valve endocarditis. Prosthetic valve endocarditis occurred early after valve replacement in two patients and late after operation in the remaining two. However, we have never had prosthetic valve endocarditis after the second year for aortic or mitral valves. Kratz and colleagues 8 reported a similar experience, and they presumed that the cloth sewing ring underwent complete tissue ingrowth by this time and was protected to some extent from bacterial invasion. Because prosthetic valve endocarditis is an extremely serious complication in patients who receive prosthetic valves, prophylaxis of infection with various invasive procedures, including dental and genitourinary procedures, is important.
In conclusion, long-term follow-up of the 908 patients who were discharged from the hospital after receiving the St. Jude Medical valve revealed that the incidence of valve-related complications and deaths was extremely low, with no incidence of structural valve failure. Significant hemolysis that occurred immediately after operation was a serious complication related to the St. Jude Medical valve in the mitral position, and changing the valve orientation appeared to play an important role in reducing mechanical hemolysis. On the basis of these results, the St. Jude Medical valve seems to be an excellent mechanical valve in terms of durability and low thrombogenicity, and it remains our prosthetic valve of choice when valve replacement with a mechanical valve is indicated.
References
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