Asian Cardiovasc Thorac Ann 1998;6:260-264
© 1998 Asia Publishing EXchange Pte Ltd
Ten-Year Results With Liotta Porcine Bioprostheses in the Mitral Position
Birol Yamak, MD,
Binali Mavita
, MD,
Ahmet Sarita, MD,
S Fehmi Katircioglu, MD,
A Tulga Ulus, MD,
Levent Birincioglu, MD,
Y Haldun Karagöz, MD1,
Erol Sener, MD,
Oguz Tademir, MD,
Kemal Bayazit, MD1
Department of Cardiovascular Surgery Türkiye Yüksek I·htisas Hospital Ankara, Turkey
1 Güven Hospital Ankara, Turkey
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For reprint information contact: Birol Yamak, MD Department of Cardiovascular Surgery Türkiye Yüksek I·htisas Hospital Sihhiye, Ankara 06100, Turkey Tel:90 312 310 3080 Ext. 1247 Fax:90 312 312 4120 Email: ulus{at}escortnet.com
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ABSTRACT
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The Liotta porcine bioprosthesis is a third generation bioprosthesis with a very low profile supraannular configuration with low-pressure glutaraldehyde-fixed tissue. Between May 1986 and December 1990, 670 patients underwent isolated mitral valve replacement with Liotta porcine bioprosthesis. There were 403 (60%) females and 267 (40%) males; the mean age was 39.03 ± 4.57 years (range, 16 to 75 years). The predominant lesion was combined mitral stenosis and mitral insufficiency in 46% of the patients. The operative mortality rate was 5.9% and the most frequent cause of the mortality was low cardiac output. Total follow-up was 3193.5 patient-years. The average follow-up period was 6.1 ± 2.5 years (range, 1 to 10 years). During the late period, 44 patients (1.4% per patient-year) died. The long-term survival estimate at 10 years was 84.8% ± 2.7%. Structural valve deterioration developed in 198 patients (6.2% per patient-year). Actuarial estimates of freedom from structural valve deterioration at 5 and 10 years were 87.6% ± 1.5% and 28.5% ± 4.5% and it was unrelated to sex or age. Most patients (88%) who developed bioprosthesis dysfunction underwent repeat valve replacement. The period between the implantation and development of structural valve deterioration was 5.9 ± 1.8 years for female patients and 6.2 ± 1.8 years for males (no statistically significant difference). We concluded from the early and high rates of structural valve deterioration in this young age group that the Liotta porcine bioprosthesis has limited long-term durability for mitral valve replacement.
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INTRODUCTION
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The Liotta porcine bioprosthesis (BioImplant Canada, Inc., Quebec, Canada) is a third generation bioprosthesis. The valve has a very low profile supraannular configuration with low-pressure glutaraldehyde-fixed tissue. Supraannular porcine bioprostheses have superior hemo-dynamics to intraannular porcine bioprostheses. Bioprostheses are especially recommended for aortic valve replacement in the elderly and women of childbearing age desirous of children. Mitral position and young age are risk factors for structural valve deterioration in bioprostheses.1 Several authors noted that structural valve deterioration of bioprostheses necessitating reoperation occurs nearly twice as frequently in the mitral position as in the aortic position.2,3 The main disadvantage of tissue valves is their limited long-term durability as the result of fibrocalcification and fatigue-related leaflet disruption. In this study, the 10-year results of 670 patients who underwent isolated mitral valve replacement with a Liotta porcine bioprosthesis are presented.
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MATERIALS AND METHODS
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Between May 1986 and December 1990, 670 patients underwent isolated mitral valve replacement with a Liotta porcine bioprosthesis. Patients who had concomitant valve replacement in the aortic or tricuspid position were excluded from this study. Of the 670 patients, 403 (60%) were female and 267 were male (40%). The mean age of the patients was 39.03 ± 4.57 years (range, 16 to 75 years). All of the patients were in New York Heart Association (NYHA) functional class III or IV preoperatively. Atrial fibrillation was present in 523 (78%) patients preoperatively. The predominant lesion was combined mitral stenosis and mitral insufficiency in 46% of the patients, 25% were suffering from mitral insufficiency, and 29% had mitral stenosis. Previous operations included: 117 closed mitral valvotomies, 5 open mitral valvotomies, and 5 mitral valve replacements with different types of mechanical valve prostheses. Coronary angiography was performed in all patients over the age of 50 years.
Standard techniques of cardiopulmonary bypass with a membrane oxygenator were used in all cases. Moderate hypothermia (28°C to 30°C), cold potassium cardioplegia, and topical hypothermia were used for myocardial protection. Since April 1987, cold crystalloid cardioplegic induction followed by cold intermittent blood cardioplegia and terminal warm blood cardioplegia was used. All valve replacements were performed with simple interrupted sutures. Pledget-supported U-sutures were not used except when the annulus was heavily calcified. Since 1986, the posterior mitral valve leaflet was preserved when feasible. The technique of the posterior valve preservation was as reported previously.4 When coronary artery bypass grafting was performed with saphenous vein or internal mammary artery, the distal anastomoses were performed first, followed by valve replacement, and finally the proximal anastomoses. Associated procedures comprised: 42 tricuspid valve reconstructions, 24 open aortic valvotomies, 10 atrial septal defect repairs, and 5 coronary artery bypass graft operations.
Oral anticoagulant therapy was employed within the first 3 postoperative months in the first 187 patients; these patients received 2.5 mg warfarin, 3 x 75 mg dipyridamole, and 250 mg aspirin daily, regardless of their prothrombin time. Warfarin was started on the 1st postoperative day, dipyridamole and aspirin were added to the regimen after removal of the chest tubes. After 3 months, all patients were maintained on antiplatelet drugs only. Subsequent patients were not given warfarin and received only antiplatelet medication starting immediately after the removal of chest tubes.
The Kaplan-Meier method was used for calculating actuarial probability of survival and morbidity events. In addition, a test for two proportions from independent groups was used to determine the statistically significant difference between two percentages. A p value less than 0.05 was considered statistically significant. All values reported are as mean ± standard deviation.
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RESULTS
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The operative mortality rate was 6% (40/670). The most frequent cause of mortality was low cardiac output (30 patients). The other causes of the early mortality were cerebrovascular accident (3 patients), respiratory failure (2 patients), mediastinitis (3 patients), renal failure (1 patient), and left ventricular posterior wall rupture (1 patient).
All surviving patients were followed up at 2, 6, and 12 months postoperatively and annually thereafter. Total follow-up was 3193.5 patient-years. The average follow-up period was 6.1 ± 2.5 years (range, 1 to 10 years). During the late period, 44 patients (1.4% per patient-year) died of various causes as shown on Table 1
. Postoperatively, 66.8% of the patients were in NYHA functional class I, 20.3% were in NYHA functional class II, 8.6% were in functional class III, and 4.3% were in functional class IV.
Long-term actuarial estimates of survival at 5 and 10 years for all patients were 94.6% ± 1.0% and 84.8% ± 2.7% respectively. The actuarial survival estimates according to gender at 10 years were 89.2% ± 3.9% for females and 88.2% ± 3.7% for males (Figure 1). The actuarial survival estimates subdivided according to age groups are shown in Figure 2. There was no statistically significant difference between the sex and age groups (p > 0.05).
The actuarial estimates of freedom from individual valve-related complications at 10 years according to sex and age groups and for all patients are summarized in Table 2. Structural valve deterioration developed in 198 patients (6.2% per patient-year). Actuarial estimates of freedom from structural valve deterioration at 5 and 10 years were 87.6% ± 1.5% and 28.5% ± 4.5%. There was no statistically significant difference between the sex and age groups (p > 0.05). Most (88%) of the patients who developed bioprosthesis dysfunction underwent repeat mitral valve replacement. Some patients (5%) would not agree to reoperation and 6.6% could not undergo reoperation because of a low ejection fraction. The period between implantation and the development of structural valve deterioration was 5.9 ± 1.8 years for female patients and 6.2 ± 1.8 years for males. This was not found to be statistically significant (p > 0.05).
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Table 2. The Actuarial Estimates of Freedom from Individual Valve-Related Complications at 10 Years According to Sex, Age Group, and for all Patients
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Reoperation was performed on 183 patients (5.7% per patient-year) for either native aortic valve disease or valve-related complications. The reoperation mortality was 9.3%. Structural valve deterioration was the reason for reoperation in 175 patients, 6 patients underwent reoperation for native aortic valve disease (bioprostheses normal), 1 patient for paravalvular leak, and 1 patient for tricuspid stenosis. Twenty-two of the 175 patients required combined aortic valve replacement for native aortic valve disease in spite of the indication for reoperation being structural deterioration of the bioprosthesis. Estimates of freedom from reoperation at 5 and 10 years for all patients were 88% ± 1.5% and 28.6% ± 6.9% respectively.
Thrombolic events were recorded in 21 patients (0.6% per patient-year) during the follow-up period. Three of these events were fatal. Estimates of the freedom from thromboembolism at 5 and 10 years were 98.6% ± 0.5% and 90.8% ± 2.2% respectively.
Oral anticoagulant-related hemorrhage developed in 14 patients (0.4% per patient-year) with 3 fatal outcomes. Actuarial estimates of freedom from oral anticoagulant- related hemorrhage at 5 and 10 years were 98.4% ± 0.6% and 94.1% ± 1.9% respectively.
Two patients developed paravalvular leak. One of these patients underwent reoperation and the other received medical therapy. Estimates of the freedom from paravalvular leak at 10 years was 99.6% ± 0.3%.
Two hundred and twenty-eight patients (7.1% per patient-year) developed valve-related morbidity and mortality. Estimates of freedom from all valve-related complications at 5 and 10 years were 84.7% ± 1.6% and 23.9% ± 14.2% respectively.
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DISCUSSION
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The Liotta low-profile porcine bioprosthesis was designed to minimize complications due to excessive protrusion of the stent prongs in the left ventricle and to avoid potential left ventricle-prosthesis mismatch occasionally observed with the standard high-profile bioprosthesis.5,6 Frequently, the left ventricular cavity is not enlarged in patients with mitral stenosis. The characteristic low profile of this valve avoids left outflow obstruction as well as trauma of the left ventricular wall.7
Reoperation was performed after a mean period of 5.9 ± 1.8 years for female patients and 6.2 ± 1.8 years for male patients in this study, compared with 7.9 ± 2.1 years reported recently by Ius and colleagues5 and 6.3 ± 1.5 years in an earlier study.6 The majority of our patients were females in the 31 to 40 year age group. Previous studies identified young age as a significant risk factor for structural deterioration of bioprostheses.8,9 Based on age at the time of operation, need for reoperation was most frequent in the younger age group in our study. Degenerative complications do not lead to a catastrophic outcome and the overall reoperation mortality was 9.3%. Young age, increased experience, and the use of standardized surgical techniques have improved the results of reoperation for bioprosthetic failure in recent years. A further reduction in operative risk can be expected with better patient selection based on careful noninvasive assessment of valve performance to detect the initial signs of bioprosthetic failure.
The leading cause of bioprosthetic valve dysfunction is structural deterioration, the incidence of which begins to increase 5 to 6 years after implantation.5,6,17 Event-free estimates are reported to be 14.3% to 45% in different series.3,9,18,19 Although no statistically significant difference was found between the sex or age groups, structural valve deterioration was more common for the patients less than 30 years of age compared to those over 40 years of age.
Valve regurgitation is the usual mode of bioprosthetic failure in the mitral position. These pathologic findings seem to confirm that a low-profile design, that implies bulging of the right coronary cusp, entails the risk of increased stress at the commissures, accelerated calcification, and tearing.5,6 Common findings in all explanted valves were cusp prolapse, cusp tears, and commissural rupture related to various degrees of tissue calcification, constantly leading to severe prosthetic incompetence. Our experience showed that the Liotta bioprosthesis used for mitral valve replacement had limited long-term durability that was affected by the unique prosthetic design.
There is still controversy regarding the use of anticoagulant therapy after valve replacement with a bioprosthesis.10 In the beginning of our experience, we used our clinic's anticoagulation protocol in the first 187 patients.11,12 Thereafter, all patients were maintained on antiplatelet drugs only. The majority of our patients come from rural areas and showed low compliance with oral anticoagulation. Thromboembolism and oral anticoagulant-related bleeding were infrequent complications, consistent with the main advantage of implanting bioprosthetic valves. However, when thromboembolism and oral anticoagulant- related bleeding occurred, they were both associated relatively high fatality rates. These results are comparable to those of previously reported series.9,13,16 Our study confirmed that porcine bioprostheses have a low rate of thromboembolic episodes even without anticoagulation.
We concluded that the Liotta porcine bioprosthesis developed an early and very high complication rate in this young patient population. The majority of our patients were females of childbearing age and we regard the possibility of pregnancy as the strongest indication for bioprosthetic valve usage in the mitral position. Our experience indicates that bioprostheses should be considered only for patients in whom anticoagulation may be hazardous or difficult.
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Acknowledgments
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Statistical analysis was made by Kenan Kose from the University of Ankara, Department of Biostatistics.
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REFERENCES
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ABSTRACT
INTRODUCTION
