Interact CardioVasc Thorac Surg 2009;8:252-259. doi:10.1510/icvts.2008.183590
© 2009 European Association of Cardio-Thoracic Surgery
Follow-up papers - Valves |
Sorin BicarbonTM bileaflet valve: a 9.8-year experience. Clinical performance of the prosthesis after heart valve replacement in 587 patients
Kyriakos Spiliopoulos*,
Ayman Haschemi,
Paris Parasiris and
Bernhard M. Kemkes
Department of Cardiovascular Surgery, Städtisches Klinikum München GmbH, Heart Center Bogenhausen, Munich, Germany
Received 21 May 2008;
received in revised form 17 October 2008;
accepted 23 October 2008
 Presented in part at the 4th International Meeting on Cardiac Surgery. The Euro-Asian Bridge, May 26–27th, 2007, Doubai, UAE.
*Corresponding author. Abteilung für Herzchirurgie, Städtisches Klinikum München GmbH, Herzzentrum Bogenhausen, Englschalkingerstr. 77, 81925 München, Deutschland. Tel.: +89/9270 2631; fax: +89/9270 2605.
E-mail address: Kyriakosspili{at}aol.com (K. Spiliopoulos).
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Abstract
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Objective: To determine early and mid-term clinical performance of the Sorin BicarbonTM bileaflet prosthesis. Methods: Between January 1993 and October 2000, 1092 patients received at least one Sorin BicarbonTM prosthesis. Six hundred and fourteen of those fulfilled the inclusion criteria and were contacted by mail and/or telephone interview. Five hundred and eighty-seven (95.6%) patients aged 16.2–85.9 years (mean 61.5 years), 368 males and 219 females, were available for clinical evaluation. Four hundred and fifteen patients underwent aortic – (AVR) (70.7%), 122 mitral – (MVR) (20.8%), 50 double valve replacement (DVR) (8.5%). 86.4% of the patients were in NYHA functional class III or IV. Cumulative duration of follow-up is 2474 patient-years (py) with a maximum of 9.8 years. Results: Overall hospital mortality (30 days) rate was 4.2% (n=26). The early mortality rate was significantly higher in females and patients older than 70 years (P<0.05). Valve related early deaths were not documented. There were 49 late deaths (8.3%). Overall late mortality was 1.98%/patient-years. Cumulative survival rate at 9.8 years was for AVR, MVR and DVR, 80.1, 95.1 and 76.4, respectively. Multivariable logistic analysis identified high age at operation ( 70 years) as an independent mortality risk factor (P=0.03). Valve related complications were thromboembolism: 1.33%/patient-years (n=34), anticoagulant related hemorrhage: 1.21%/patient-years (n=30), bacterial endocarditis: 0.16%/patient-years (n=4), reoperation: 0.69%/patient-years (n=17), paravalvular leak: 0.69%/patient-years (n=17). No structural dysfunction of the prosthesis has been reported. Actuarial freedom from complications at 9.8 years was: thromboembolism 86.7%, major hemorrhage 92.3%, prosthetic valve endocarditis 99.1% and reoperation 95.8%. Conclusions: Sorin BicarbonTM prosthesis provides excellent clinical results and mid-term survival with very low complication rates comparable with those of other bileaflet prostheses currently in use.
Key Words: Mechanical valve replacement; Valve related complications
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1. Introduction
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The development of mechanical valves has been marked by design changes aimed at enhancing safety and efficiency, whilst minimizing deleterious features and complications. Consequently, the bileaflet model, first implanted clinically in 1977, has emerged as today's prosthesis of preference in many centers [1–5]. The BicarbonTM bileaflet valve (Sorin Biomedica, Saluggia, Italy) was introduced in 1990, having been designed to improve durability and hemodynamics and reduce thrombogenicity. The innovative design of the prosthesis minimizes blood stagnation and subsequent thrombosis. The aim of the present series is to evaluate the early and mid-term clinical performance of the Sorin BicarbonTM bileaflet valve.
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2. Materials and methods
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2.1. Methods
All preoperative and part of the postoperative data were prospectively collected for 614 consecutive patients undergoing heart valve replacement (VR) at the Krankenhaus München Bogenhausen, Munich, Germany between January 1993 and October 2000. These data are part of a data registry of all cardiac surgical patients at our department. Early postoperative transthoracic echocardiographic studies were performed early after surgery (3rd postoperative day [POD]) and prior hospital discharge (10th–14th POD). Follow-up data were gathered in the time period of January 2002–April 2003, predominantly by mail and telephone contact with the patients and/or their referring physicians according to a detailed questionnaire. This included among others the current anticoagulation level, laboratory as well echocardiographic data. In 165 patients status post AVR the follow-up examinations including clinical examination, lab control and transthoracic echocardiography were performed at our institution. The mean follow-up period was 5.8 years with a maximum of 9.8 years.
2.2. Patient group
Our study group included 614 patients after VR with a mechanical prosthesis. Twenty-seven patients have been lost to follow-up, which was accordingly complete in 95.6% (587/614). Four hundred and seventy-eight out of 1092 patients did either not fulfill the inclusion or they met at least one of the exclusion criteria (Table 1) and were excluded from the study. Three hundred and sixty-eight males and 219 females, aged 16.2–85.9 years (mean 61.5 years), were available for clinical evaluation. Four hundred and fifteen patients underwent aortic – (AVR) (70.7%), 122 mitral – (MVR) (20.8%), 50 double valve replacement (DVR) (8.5%). Total cumulative follow-up was 2474 patient-years (AVR: 1751 patient-years, MVR: 505 patient-years, DVR: 218 patient-years). Demographic and clinical characteristics of the patients are summarized in Table 2.
2.3. Operative technique
All patients were operated with cardiopulmonary bypass (CPB) under moderate hypothermia (32–34 °C). A cold hyperkalemic crystalloid solution (Brettschneider) was used for myocardial protection. Postoperatively all patients were admitted to the intensive care unit. Anticoagulation therapy was initiated on the 1st POD with intravenous substitution of heparin in order to achieve a partial thromboplastin time (PTT) between 60 and 80 s. Oral intake of cumarin was started concurrently with heparin on the 1st POD if possible. Our practice was to establish an international normalized ratio (INR) of 3.0 (acceptable range 2.5–3.5).
Clinical status was rated using the classification of the New York Heart Association (NYHA).
Perioperative mortality was defined as death occurring within 30 days of cardiac surgery, or death prior to hospital discharge regardless of cause. Late mortality was defined as mortality after 30 days of cardiac surgery and hospital discharge. The cause of death was classified as being non-cardiac, cardiac but of a valve related cause (due to valve related complications) or cardiac of a non-valve related cause (heart failure, myocardial infarction, arrhythmia, sudden death). The valve related complications were defined according to the recently suggested guidelines for reporting mortality and morbidity after cardiac valve interventions as hemorrhage, thromboembolism, prosthetic valve endocarditis, device thrombosis, structural valve deterioration and non-structural dysfunction including paralvular leak [6].
2.4. Statistical methods
Continuous variables are presented as mean±standard deviation (S.D.) unless otherwise stated. For univariate analysis of the early mortality, a Pearson  2-test or the Fisher exact test was used to test for differences between groups, and multivariable early mortality analysis was performed by Loglinear estimation of a statistical model including the variables of interest.
Long-term survival estimates and the valve related complications were calculated using the method of Kaplan–Meier, whereas univariate comparisons of survival data were tested using the Log-rank and the 2-test. Linearized rates, expressed as percentage per patient-year (%/patient-years), were calculated by dividing the number of events by the total follow-up time in years and multiplied by 100. Survival and complication-events were analyzed with regard to gender, age at operation, preoperative clinical status, type of operation and site of implant.
For the multivariate analysis of late mortality the proportional hazard model of Cox was assembled and predictions were derived.
A P-value was considered statistically significant when <0.05.
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3. Results
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3.1. Mortality
Twenty-six patients died within the 30 days after operation, or prior hospital discharge, which resulted in an early mortality rate of 4.2%. For patients after AVR, MVR and DVR the early mortality rate was 3.5%, 5.2% and 8.4%, respectively. Loglinear analysis revealed a significant higher early mortality rate in patients with preoperative NYHA class IV (P=0.003). Causes of early death with regard to the type of operation are listed in Table 3. Four patients shown in this table died due to embolic events with stroke which occurred intraoperatively. After complete reversal of anesthesia the patients showed clinical signs of cerebral embolism documented by CCT-scan, thus valve related early deaths could not be detected.
Regarding the late mortality, 49 patients (8.3%) died during the follow-up. Ten patients died because of malignant diseases, seven due to central neurological events, three due to bleeding events, and six because of pneumonia. One patient status post AVR developed prosthesis endocarditis and died due to cardiac failure. Eleven patients died because of a non-valve related cardiac death and in 11 cases of late mortality, the cause of death could not be detected and have been classified as death of an unknown cause. In summary, the valve related – (including deaths of an unknown cause), the cardiac but non-valve related – and the non-valve related – late mortality rate was 3.92%, 1.96% and 2.85%, respectively. Overall late mortality rate at 9.8 years was 1.98% per patient-year and regarding the implant site it was for AVR, MVR and DVR 2.3%/patient-years, 0.6%/patient-years and 2.4%/patient-years, respectively (Fig. 1). The actuarial cumulative survival rate at 9.8 years with regard to the type of the operation is presented in Table 4. Multivariable logistic analysis identified high age at operation (70 years) as an independent mortality risk factor (P=0.03). The late mortality analysis concerning gender and preoperative clinical status (NYHA class) did not reveal any significant differences.
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Table 4 Valve related complications after replacement with the Sorin BicarbonTM prosthesis with regard to the type of operation
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3.2. Morbidity
3.2.1. Clinical status
At follow-up, 79% of survivors were in functional class I or II. Those patients reported of a significant improvement postoperatively of their clinical condition.
3.3. Valve related complications
3.3.1. Bleeding
Thirty patients reported bleeding events. Fourteen events were gastrointestinal-, six ENT- and three subdermal- bleeding. One patient had blunt abdominal trauma with splenic injury and hemorrhage. Six patients developed intracerebral bleeding. All abdominal bleedings required hospital admission and the patient with the splenic injury underwent splenectomy. Three out of six patients with intracerebral bleeding died. In 14 out of 30 cases the INR was out of range (>3.5) at the time of the event. The overall actuarial freedom from bleeding was 92.3% at 9.8 years. The overall hemorrhage rate was 1.21%/patient-years.
3.3.2. Thromboembolism
Thromboembolic events occurred in 34 cases, despite the patients being on anticoagulant therapy. Thirteen (38.3%) patients reported major thromboembolic events with severe neurological symptoms and 21 (61.7%) were minor thromboembolic episodes (10 transient ischemic attacks, four visual defects with amaurosis fugax, seven events with recurrent paresthesia). Fourteen patients presented at time of the event arrhythmia with atrial fibrillation and 20 patients were in stable sinus rhythm. Regarding the anticoagulation level, 16 patients had an INR out of range (<2.5) and 18 patients were adequately anticoagulated. The overall actuarial freedom from thromboembolic events was 86.7% at 9.8 years. The occurrence rate for thromboembolic events was 1.33%/patient-years.
3.3.3. Valve thrombosis
Valve thrombosis occurred in one male patient status post AVR, who has been on admission underanticoagulated with INR<2.5 and presented history of atrial fibrillation and two episodes of TIA. The patient was reoperated and received a biological prosthesis.
3.3.4. Prosthetic valve endocarditis
Four patients developed prosthetic valve endocarditis, of whom two were successfully reoperated, one was treated with antibiotics and one died prior to scheduled reoperation because of congestive heart failure. The overall freedom from prosthetic valve endocarditis was 99.1% at 9.8 years, whereas the valve endocarditis rate was 0.16%/patient-years.
3.3.5. Non-structural prosthesis dysfunction
In the follow-ups a paravalvular leak was detected in 17 cases. Fourteen patients showed higher grade regurgitation and were therefore been reoperated. All of them survived the reoperation and recovered well. The remaining three patients showed, in the echocardiographic tests, paravalvular leaks without hemodynamic relevance. The paravalvular leak caused mild hemolysis in two cases, which were conservatively managed by supplementation with iron and folic acid. The incidence of valve dehiscence with paravalvular leak was for AVR, MVR and DVR 0.57%/patient-years, 0.12%/patient-years, and 0.44%/patient-years, respectively.
In total 17 patients had to be reoperated. The overall freedom from reoperation irrespective of cause was 95.8% at 9.8 years. The linearized rate for reoperation was 0.69%/patient-years.
3.3.6. Structural valve dysfunction
There were no events of structural valve dysfunction. Hence, freedom from structural valvular deterioration at 9.8 years was 100%.
The valve related complications as well as the freedom rates with regard to the type of operation are summarized in Table 4.
3.4. Echocardiographic data
Echochardiographic data regarding the hemodynamic performance of the prosthesis were gathered in approximately 81% (n=336 patients) of the cases status post AVR and in 55% (n=67) of the patients after MVR. One hundred and sixty-five of the prostheses in aortic position were followed up at our institution. Transthoracic echocardiography showed that, in the mean 5.6 years after implantation, aortic valves had a mean effective orifice area (EOA) of 2.18±1.21 cm2, with peak and mean pressure gradients of 22.54±7.88 and 10.95±4.04 mmHg, respectively. The mean EOA of mitral valve prostheses was 2.62±0.61 cm2, with peak and mean pressure gradients of 11.8±4.3 and 5.1±1.1 mmHg, respectively. The pressure gradients with regard to the size of the prosthesis in the aortic position are given in Table 5.
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4. Discussion
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Approximately 210,000 patients, worldwide, undergo valve replacement surgery annually [7]. Roughly, two-thirds of this total have mechanical valves implanted. Accordingly, there is much ongoing investigation related to improving prosthetic valve construction. Bileaflet cardiac prostheses have shown a low incidence of complications and good hemodynamic performance. The Bicarbon valve, a third generation bileaflet mechanical prosthesis, has many unique design features offering a potentially durable model with minimal thrombogenicity and hemolysis and improved hemodynamic performance.
The present series consists mainly of the mortality and morbidity analysis as well the impact on the clinical outcome of 629 Sorin BicarbonTM prostheses implanted in 587 patients and represents the largest reported single-center experience with this bileaflet prosthesis. The results regarding clinical complication rates were compared with those for other currently used bileaflet mechanical valves.
The early (30 days) (4.2%) and late mortality (8.3%) rates of our series were comparable with those reported by other series of mechanical prostheses [8–13]. The mortality rate in our study was predominantly influenced by age, gender and type of operation. Regarding the hospital (30 days) mortality; it was nearly up to 2.2-fold higher in females, older than 70 years and in preoperative NYHA class III or IV patients. The interaction between age at operation and gender in relation to early (30 days) mortality as well as to late survival is represented in Fig. 2. Early mortality was higher in female patients regardless of age at operation and was statistically significant in the age group of 40–70 years, which included the majority of the study population (>70%). Concerning late survival, female patients showed lower survival rates at 9.8 years in both age groups (<70 years and 70 years). Nevertheless, the differences between males and females were not significant. Age at operation 70 years was in the univariate analysis significantly influential regarding the late outcomes and could be identified by multivariable logistic analysis as an independent late mortality risk factor. A demographic analysis was performed in order to clarify the gender-influence in the mortality rates. Females were in the mean 3.13 years older than males at the time of operation, underwent more often mitral valve replacement (35.6%) and showed, therefore, a significantly higher incidence of preoperative atrial fibrillation (34.7%), whereas preoperative NYHA status, LVEF and BMI were comparable between both groups. The influence of female gender in the outcomes after cardiovascular operations still remains unclear. Our findings regarding, particularly, the early mortality in correlation with the demographic differences described above, are leading us and also other investigators to the proposed hypothesis, that hormonal pathways, including abnormalities of the estrogen receptor, ovarian dysfunction, premature menopause, and proinflammatory properties of hormone replacement therapy, may be a potentially important cause for increased mortality rates in female patients after cardiac operations [14, 15].
As with other bileaflets, patients require lifelong, well-controlled anticoagulation. Concerning the localization of bleeding; the most common sites of minor bleeding are the nose and mouth, accounting for over one-third of episodes and the gastrointestinal tract is the most frequent source of major bleeding [16]. In our study, six minor bleeds (66.6%) occurred in the ENT-tract and 14 out of 20 major bleeds were in the GI-tract. All major bleeds in the present series were anticoagulant related. Three late deaths from this complication succumbed from extensive intracerebral hemorrhage (ICH). In the general population, more than 90% of all ICH occurs in patients who are not on anticoagulants, whereby the risk of ICH in patients on anticoagulants is reported to be between 8 and 11 times greater than the non-anticoagulated population [17]. In our series, 14 out of 30 patients with bleeding events were at the time of the event overanticoagulated with an INR, which was out of range (>3.5).
The incidence of thromboembolic events occurring in patients with Bicarbon valves corresponds with those reported for other currently used bileaflet valves [1, 3, 5, 18, 19]. Linearized rates for the above-mentioned complications are very similar to ours (Table 5). Of the 33 embolic events reported, twelve were major cerebral emboli with significant neurological deficit, of which seven were fatal. Patients after DVR showed at 9.8 years the lowest freedom rate of thromboemolism with 81%. Most series of valve replacement report lower embolic rates after AVR [20], in whom ischemic cerebrovascular events are closely associated with stroke risk factors such as hypertension, nicotine abuse and arterial disease [21]. Not all cerebral events are ischemic nor that all ischemic events are embolic. Patients who suffer such an event should be investigated for underlying risk and trigger factors, so that measures can be taken to minimize the risk of further events. This is important in patients who suffered recurrent embolism. In the present study, 13 out of 33 patients with episodes of thromboembolism presented history of atrial fibrillation. Twenty-one patients reported minor thromboembolic events. These patients are not usually referred to hospital with the result that it is missed to assess coagulability at the time of the event. A major cause of recurrent embolism is non-compliance with the anticoagulation treatment. The problem can be solved by education and by involving the patient more in his/her own anticoagulation control [22]. In the present series we observed 64 cases with anticoagulant related complications. Twenty-three patients (39.7%) used the self-controlling method for specification of the anticoagulation level, 38 of them had their levels controlled in time intervals of 3–4 weeks by their general practitioners and three patients performed self-controlling on the one hand and were concurrently followed as well by their practitioners on the other. The courses for self-anticoagulation control are offered at our institution since 2000; thus there are a lot of patients in our series, who have been operated on before and, therefore, they were at the beginning controlled by their practitioners until they switched over to the self-management of the anticoagulation level. In general there is a trend, that the younger, still in normal life ‘active’ patients prefer the self-management method, whereas the older patients trust their general practitioners for the anticoagulation management.
Prosthesis dehiscence can lead to paravalvular leaks resulting in regurgitation and hemolysis. The occurrence of paravalvular leaks result either due to acute infective endocarditis with changes within the annulus or para-annular area, or due to calcification of the annulus combined sometimes with deficiencies in the suturing technique. In some series the incidence of valve dehiscence was 1.7% in aortic and 2% in mitral prostheses [23]. In the present study, 14 patients were reoperated due to paravalvular leak. The review of the operation-reports showed that the occurrence of paravalvular leak was in two cases due to acute ascending aortic dissection and in eleven cases due to calcification and/or incomplete decalcification of the annulus. Four patients developed postoperatively valve endocarditis with positive blood cultures and clinical signs. One of them was treated successfully with antibiotics and two were reoperated. One patient addicted to heroin developed valve endocarditis after AVR, was scheduled for reoperation, but he died prior to surgery due to left ventricular heart failure. In our cumulative experience we observed one case of valve thrombosis with obstruction and narrowing of the effective orifice. The patient (status post AVR, with history of atrial fibrillation, recurrent episodes of TIA and non-compliance with anticoagulation) was reoperated and survived. Our findings regarding the reoperation rate (Table 4) irrespective of cause are similar to those of other series [13, 24, 25].
No structural dysfunction of the prosthesis has been reported in our series. This finding confirms the strength and durability of the materials used for both the housing and the leaflets and the efficacy of the hinge mechanism.
In summary, the overall freedom at 9.5 years of valve related complications including: valve related late mortality, bleeding, thromboembolism, prosthesis endocarditis, paravalvular leak and reoperation irrespective of cause was approximately 71.5% (Fig. 3) resulting in a complication rate of 3.8%/patient-years.
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5. Conclusions
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The Sorin BicarbonTM prosthesis showed in the present series excellent clinical results and mid-term survival with very low complication rates comparable with those of other bileaflet prostheses currently in use. No structural dysfunction was detected to date.
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Abstract
1. Introduction
