Asian Cardiovasc Thorac Ann 1998;6:23-27
© 1998 Asia Publishing EXchange Pte Ltd
Mitral Valve Replacement with Bioprosthesis in Age Group Fifty to Sixty-Five Years
Salih Fehmi Katircio
lu, MD,
Birol Yamak, MD,
Tulga Ulus, MD,
Levent Birinciolu, MD,
Ahmet Sarita
, MD,
Ouz Tademir, MD,
Kemal Bayazit, MD
Department of Cardiovascular Surgery Türkiye Yüksek  htisas Hospital Ankara, Turkey
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Salih Fehmi Katirciolu, MD Department of Cardiovascular Surgery Türkiye Yüksek htisas Hospital 06100 Sihhiye Ankara, Turkey Tel:90 312 310 3080 Fax:90 312 466 3202 Email:Ulus{at}escortnet.com
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ABSTRACT
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Between 1982 and 1990, 151 patients aged 50 to 65 years of age underwent isolated mitral valve replacement with a bioprosthesis. Overall hospital mortality was 10.6% (16/151). The total cumulative follow-up period was 527.6 patient-years with a mean of 4.34 ± 2.53 years and a range of 2 months to 10.9 years. During the follow-up period, 27 patients (5.11% per patient-year) developed bioprosthesis dysfunction of whom 26 were reoperated and one was treated medically, 4 patients had thromboembolic complications (0.75% per patient-year), one patient (0.18% per patient-year) had anticoagulant-related bleeding, and two patients (0.37% per patient-year) had a paravalvular leak (one was reoperated). Total valve-related complications were 6.44% per patient-year. Late mortality was 2.65% per patient-year (14/151). Ten-year actuarial survival was 78.5%. Freedom from bioprosthesis dysfunction was 56.6%, from thromboembolic complications 95.8%, and from all complications 49.6%. Our findings of a high rate of bioprosthesis dysfunction as well as a low rate of thromboembolic complications after mitral valve replacement with a bioprosthesis in older patients suggests that the use of bioprostheses should be limited.
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INTRODUCTION
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Biological cardiac valve substitutes have been used worldwide since Carpentier and colleagues1,2 reported the gluteraldehyde fixation techniques for biological tissues. There is a growing awareness that the proportion of elderly in the population is increasing rapidly and the older age groups are pursuing more active and productive lives. As this segment of the population continues to grow, more patients will require cardiac operations.2 Bioprostheses are considered to ensure a good quality of life with low rates of thromboembolism, structural valve deterioration, anticoagulant-related bleeding, or thrombosis of the valve. In populations with a low compliance with anticoagulant regimens, the use of mechanical valves is associated with high rates of thromboembolism, valve thrombosis, or fatal anticoagulant-related hemorrhage.3,4
Recognizing that the need for valve operations in the elderly is increasing has focused attention on the choice of prostheses.2 In some instances the use of biological valves in elderly patients may be justified because of contraindications to mechanical prostheses.1 In this study we report our clinical experience with a biological mitral valve prosthesis.
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MATERIALS AND METHODS
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Between 1986 and 1990, 151 patients who were 50 years of age or older underwent isolated mitral valve replacement with a St. Jude Bioimplant (St. Jude Medical, St. Paul, MN, USA) in the cardiovascular surgery clinic of Türkiye Yüksek I.htisas Hospital. Patient characteristics are listed in Table 1
. Eighty-five patients (56.3%) were female and 66 (43.7%) were male. The mean age at operation was 53.7 ± 3.2 years (range 50 to 65 years) for females and 54.6 ± 3.7 years (range 50 to 65 years) for males. Preoperatively, 41% of the patients had pure mitral stenosis, 29% had pure mitral insufficiency, and 30% had mixed lesions. Most of the patients had rheumatic mitral valve disease. Before surgery, 66% were in New York Heart Association functional classes III or IV and 34% were in class II. Echocardiography and cardiac catheterization were employed for preoperative diagnosis. Coronary angiography was routinely performed and 5 patients underwent concomitant coronary artery bypass grafting. Three patients had undergone a closed mitral commissurotomy and another 3 had a previous mitral valve replacement.
OPERATIVE TECHNIQUE
All operations were performed with standard techniques of cardiopulmonary bypass using a membrane oxygenator (Terumo Corp., Tokyo, Japan). Moderate total body hypothermia (28° to 30°C), cold potassium cardioplegia, and topical cooling were used for myocardial protection. All valve replacements were performed with simple interrupted sutures; pledget-supported U-sutures were used if the annulus was heavily calcified. Hemodynamically stable patients were extubated as soon as they recovered from the anesthesia. They received dypridamole (225 mg per day) and aspirin (250 mg per day) following removal of the mediastinal tubes. They continued on this regimen after discharge from the hospital.
STATISTICAL METHODS
Standard actuarial (life-table method) and linearized statistical techniques as described by Grunkemeier and Starr6 and Bodnar and colleagues7 were used to calculate the actuarial survival rate with 95% confidence limits, as well as the incidence of valve-related events and their consequences. In addition, we calculated the actuarial survival rate and 10-year valvular dysfunction-free survival. Definitions of valve-related events were according to the standard guidelines.8 Valve-related events were classified as bioprosthesis dysfunction or thromboembolism. Patients who died during the operation or before discharge from the hospital were included in the hospital mortality. Patients who died from unknown causes were not included in the number of valve-related deaths but were included in the actuarial survival rate calculations. Patients with inoperable valvular dysfunction diagnosed at their last examination and patients who were lost to follow-up were added to the withdrawal group and valve-related complication calculations. In calculating event-free survival rates, thromboembolism, valvular dysfunction, and anticoagulant-related hemorrhage were included regardless of whether the event ended in death.
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RESULTS
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Of the 151 patients, 16 patients (9 female and 7 male) died early after surgery or before discharge. Most of the deaths were attributed to low cardiac output. The overall hospital mortality rate was 10.6%. Fourteen patients (9 female and 5 male) died during the follow-up period. In 6 cases, death occurred after reoperation and was considered valverelated. All causes of late death are listed in Table 2. The linearized rate of late mortality was 2.65% per patient-year and the overall actuarial survival rate at 10 years was 78.5% (Figure 1). Follow-up information was obtained mainly from the outpatient clinic at our institute and patient questionnaires. The follow-up was complete for 93% of the study group. The cumulative follow-up period was 527.6 patient-years with a mean of 4.34 ± 2.53 patient-years (range 8 months to 9.9 years).
VALVE-RELATED EVENTS
During the 10-year follow-up period, 27 patients experienced structural deterioration of the implanted mitral valve (Table 3). The freedom from structural deterioration was 89.9% ± 4.1% at 5 years and 51.7 ± 20.4% at 10 years (Figure 2). Retrospective analysis of patients with structural deterioration revealed that 20% (17) of females and 14% (9) of male patients experienced structural deterioration. The mean time at which structural deterioration occurred was 5.5 ± 1.4 years. Of the patients who experienced structural valve deterioration, 18 had torn valves and 8 had calcified valves.
There were 4 cases of thromboembolism of the prosthesis (0.75% per patient-year) during the follow-up period (Table 3
). In addition, there was one central nervous system embolism, one transient ischemic attack, and 2 cases of peripheral arterial thromboembolism. The actuarial estimate showed the freedom from thromboembolism to be 95.8% ± 3.3% at 10 years (Figure 3).
Paravalvular leak was identified in two patients (0.37% per patient-year). One of these patients was reoperated and survived; the other was in an inoperable state and died. The freedom from paravalvular leak was 98.6% ± 1.5% at 10 years (Figure 4). All valve-related complications, which comprised valve-related death, reoperation, thromboembolism, and paravalvular leak, were taken into account in the linearized rate of 6.25% per patient year (Table 3, Figure 5) and the freedom from all valve-related complications was 49.6% ± 20.0% at 10 years (Figure 6).
In the 10-year follow-up period, 27 patients underwent reoperation (527.6% per patient-year). In all but one of these patients, reoperation was because of bioprostheses dysfunction. The mean age at reoperation was 58.9 ± 2.9 years and 18 (66.7%) of these 27 patients were female. Our analysis showed the 10-year freedom from reoperation to be 56.6% ± 15.2% (Figure 7).
There were 10 valve-related late deaths. Six of these occurred among the 27 patients who underwent reoperation for bioprosthesis dysfunction, two were due to cardiomyopathy, one was caused by thromboembolism, and the other was a case of structural valve deterioration that was inoperable.
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DISCUSSION
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Although the replacement of heart valves is a standard procedure, ideal valve design is still evolving. All prostheses are associated with a varying degree of valve-related complications that limit their clinical use. For this reason clinical success after valve replacement is evaluated by patient survival, freedom from valve-related complications such as reoperation, thromboembolism, and hemorrhage due to anticoagulant intake.1,3,9–14 The choice of prosthesis for a particular patient depends largely on the surgeon's preference. The most critical decision is whether to select a mechanical valve or a bioprosthesis.15 Although mechanical prostheses have long-term durability, this advantage is offset by their thrombogenicity and the need for anticoagulants.5
In this retrospective study we evaluated the long-term results of bioprostheses in the mitral position in older patients. The hospital mortality rate in this study was higher than the mortality rate reported by Jamieson and colleagues12,15 in all age groups (9.5%). However, mortality rates in older age groups of 13.4% to 14.3% have been reported for mitral valve replacement.2,3,9,11,14,16–20 We previously reported5 an early hospital mortality rate of 8% with mechanical valves in patients over 50 years of age compared with a rate of 14.3% in the study by Pupello and colleagues2 in patients over 70 years of age.
The actuarial survival rates in this study on mitral valve replacement with a bioprosthesis were 87.9% at 5 years and 78.5% at 10 years, which are higher than those reported by other authors such as Akins and colleagues21 where it was 51% at 10 years or Jamieson's group12,15,22 who had survival rates of 77% at 5 years and 54% at 10 years. Our higher survival rate can be attributed to the relatively younger age of our patients and also to the fact that there were fewer associated procedures in our group. In our country the average life span is 65 years, therefore, 50 years of age is considered elderly.
Biological prostheses have been recommended for valve replacement surgery in the elderly because of the reduced incidence of structural failure in this age group and the opportunity to avoid anticoagulation therapy.3,9,11–14 However, structural valve deterioration has become recognized as the predominant valve-related complication. According to Jamieson and colleagues12,15,22 even though structural deterioration occurred at all ages, the freedom from structural deterioration was greater with advancing decades of age. In this study, bioprostheses deterioration was 5.11% per patient-year, freedom from structural deterioration for 5 years was 89.9% ± 4.1%, and for ten years it was 51.7% ± 20.4%. The comparable results from the series of Akins and Jamieson for ten years were 75% and 71%, respectively.12,15,21,22 Most of our patients had valvular diseases of rheumatic origin and a younger mean age than patients in western countries where age groups of 65 years and older were studied.2–4 Due to the younger age and sometimes the continuing nature of the rheumatic disease process, bioprosthesis usage was limited in our patients on the basis of low durability. Many other surgeons also favor mechanical prostheses in this subset of patients because of the better structural durability and presumably low rate of reoperation in spite of the higher risk of anticoagulantrelated complications.5
The statistically significant difference between the actuarial rates in respect of gender is quite important and we believe this is due to higher structural valve deterioration and reoperation rates in women. In agreement with the groups of Jamieson12,15 and Magilligan19 we noted a higher incidence of structural valve deterioration in females.1 In our study 20% of the women had structural deterioration and of the 26 patients with structural deterioration 65% (n = 17) were female. In addition, 18 of the 27 patients (66.7%) who required reoperation were female. Females accounted for 83.3% of the reoperation mortality.
There is still controversy regarding the use of anticoagulant therapy after valve replacement with a bioprosthesis. None of our patients received anticoagulant therapy but they were treated with 225 mg dypridamole and 250 mg aspirin daily after the chest tubes were removed. Due to the increased risk of bleeding with anticoagulant therapy and the difficulty of adequate long-term monitoring, we decided to use only antiaggregant therapy. However, we observed reasonably low rates of thromboembolic complications. Our results showed a greater freedom from thromboembolism (95.8% at 5 years and 95.8% at 10 years) than Akins and colleagues21 (freedom from thromboembolism 87% at 10 years) and Jamieson's group12,15,22 (freedom from thromboembolism 76%).1,11,14,16 Thromboembolic complications are major problems limiting the long-term durability of all mechanical valves. Late thromboembolic events (including mechanical valve thrombosis) occurred at a rate of 1.5% per patient-year in Ibrahim and colleagues15 series. When compared with catastrophic failures of mechanical valves, most patients with bioprosthesis experienced structural valve deterioration with slow progression and high levels of functional capacity. In our study, almost all patients having structural deterioration of the valve were reoperated electively, with a perioperative mortality rate comparable to primary operations. This supports the use of bioprostheses in appropriate patients.
We therefore recommend the use of bioprostheses for valve replacement surgery in selected elderly patients but further studies are necessary to compare the long-term results of patients given mechanical valves and treated with low-dose oral anticoagulation with those of patients given bioprostheses and treated with antiaggregant therapy.
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ABSTRACT
INTRODUCTION
