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Ann Thorac Surg 2004;77:527-531
© 2004 The Society of Thoracic Surgeons
a Department of Cardiac Surgery, Policlinico Hospital, University of Bari, Bari, Italy
Accepted for publication July 10, 2003.
* Address reprint requests to Dr Vitale, Istituto di Cardiochirurgia, Policlinico, Piazza Giulio Cesare 11, 70124 Bari, Italy.
e-mail: nicola_vitale{at}lycos.co.uk
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Abstract |
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METHODS: From November 1992 to December 2002, 328 patients underwent isolated aortic (AVR; 156) or mitral (MVR; 172) valve replacement with the Sorin Bicarbon mechanical valve. Concomitant surgery was performed in 83 patients (25.2%).
RESULTS: Total hospital mortality was 5.2%. Survival at 7 years was 79.5% for AVR and 82.4% for MVR. Kaplan-Meier freedoms from valve-related complications were as follows: thromboembolism 92.7% (AVR 94.8%, MVR 92.1%); bleeding 93% (AVR 91.9%, MVR 94.5%); nonstructural dysfunction 96.6% (AVR 94.7%; MVR 97.9%); endocarditis 97.7% (AVR 97.4%, MVR 98.1%); and reoperation 95.7% (AVR 96.6%, MVR 93.9%). Overall freedom from valve-related death was 93.2% (AVR 99.3%, MVR 91.2%). At the end of follow-up, 88.9% of survivors were in New York Heart Association class I or II.
CONCLUSIONS: The Sorin Bicarbon valve is a satisfactory mechanical valve prosthesis with low mortality and morbidity and good functional results.
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Introduction |
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First implanted in the late 1980s, the Sorin Bicarbon (SB; Sorin Biomedica, Saluggia, Italy) heart valve prosthesis was designed to improve bileaflet pyrolytic carbon valve performance. Its unique design features are the curved leaflets and the hinge mechanism based on the principle of rolling without sliding [1, 2]. The rolling without sliding movement is a kinematic coupling made between two spheric surfaces with different radii: a smaller one for the pivot and a larger one for the bottom of the housing recess. The movement of the leaflet involves continuous rolling movements with a single zero-velocity contact point that varies continuously; theoretically this would lead to zero friction and wear. This design allows a controlled amount of blood leakage through the hinges, even when the valve is closed.
Several reports have shown the reliability of the SB over the years [3–5]. Some years after the first implantations of Bicarbon valves Baxter-Edwards produced and made available on the market the Mira bileaflet valve prosthesis. The Mira valve is made up of the Bicarbon mechanical components mounted on the Baxter-Edwards sewing cuff [6]. With this in mind it is important to assess the clinical outcome with the SB valve because this might apply to the Mira valve as well.
This study comprises a consecutive series of patients undergoing valve replacement with SB valve at our center. We believe that each subgroup of patients undergoing valve replacement represents a specific entity as far as surgery and other valve-related complications are concerned, and that they are best analyzed as an entire population and separate groups. Therefore this report considers only those patients who have undergone isolated aortic or mitral valve replacement and does not take into consideration those patients undergone combined mitral and aortic valve replacements.
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Material and methods |
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Surgical technique and anticoagulation management
Patients were operated on under standard cardiopulmonary bypass in mild hypothermia (34°C). Patients undergoing concomitant replacement of the ascending aorta were operated on in deep hypothermia. Myocardial protection was achieved by infusing cold-blood cardioplegia in the aortic root in mitral patients, and directly in the coronary ostia in aortic patients.
Aortic valves were implanted with the leaflet axis perpendicular to the septum, whereas the mitral prostheses were implanted in reverse anatomic position.
Anticoagulation by heparin infusion was started 12 hours after surgery to keep a partial thromboplastin time ratio of 1.5 to 2.5. Sodium warfarin was given 48 hours after valve replacement to maintain an international normalized ratio (INR) level between 2.5 and 3.5. Heparin was stopped once the INR had reached the therapeutic level. After discharge patients' anticoagulation was controlled at the hospital anticoagulation clinic.
Follow-up
Surgery closing date for this study was May 2002. Data collection closing date was December 30, 2002. Patients were followed up routinely at our outpatient clinic. Patients not reviewed at the clinic were interviewed by telephone or mailed questionnaires. Of the 311 survivors at hospital discharge, 16 patients were lost to the follow-up, making the follow-up 94.8% complete. Of these 16 patients 12 were temporary immigrants and had left Italy at the time of interview; the remaining 4 patients had moved to unknown addresses. Cumulative follow-up is 1,060 years overall: 401 years for aortic patients and 659 years for mitral patients. The mean follow-up is 3.27 ± 2.83 years and the median 2.78 years.
Statistical analysis
Outcomes were reported according to the relevant guidelines for reporting valve-related mortality and morbidity [7]. Descriptive statistics were presented as mean ± standard deviation.
Estimated survival and freedom from event rates were calculated by the Kaplan-Meier methods with a confidence limit of 95%. The log-rank test was applied to compare Kaplan-Meier curves. The StatView statistical package (SAS Institute, Inc, Cary, NC) was used for the calculations.
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Results |
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Survival
A total of 27 patients died during the follow-up. Table 2
shows causes of late death. Estimated survival curves with hospital deaths divided by site of implant are presented in Figure 1.
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Bleeding
In detail, 14 bleeding events were recorded, 6 events occurred in aortic patients and 8 events in mitral patients. In the 6 aortic patients, 3 had a major hemorrhage, 2 cerebral, and 1 gastrointestinal. This latter patient died as a direct consequence of bleeding. The remaining 3 patients had a minor bleeding, 2 nasal and 1 urinary tract bleeding. Of the 8 mitral patients, 5 experienced a major bleeding, 2 cerebral and 3 gastrointestinal. One patient died after cerebral hemorrhage. The remaining 3 patients had a minor nasal bleeding. In 9 patients of 14 the mean INR level was 4.2 ± 0.5; the remaining 5 patients had a mean INR level of 3.3 ± 0.4 at the time of hemorrhage. Kaplan-Meier freedoms from bleeding are presented in Figure 4.
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Comment |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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With regard to the operative mortality recorded in our series, it was within the expected range for heart valve replacement although 25.2% of patients had concomitant cardiac surgery [3–5, 8, 9]. The death rate was similar in the two groups despite 12 patients undergoing AVR who were operated on in emergency because of acute type A aortic dissection. Nonetheless, operative mortality is not a measure of valve performance because the former is influenced more by the patient's preoperative characteristics than the valve prosthesis itself.
As far as survival of our patients is concerned, freedoms from late deaths at 7 years are 79.5% ± 5.4% and 82.4% ± 6.1% for aortic and mitral patients, respectively. These outcomes are similar to those observed in the study on Bicarbon valves by Borman and colleagues [3] and Goldsmith and coworkers [4] and also similar to those reported by other authors in patients with St. Jude Medical or CarboMedics valves after 7 years of follow-up [8–10].
Thromboembolism is by far the most applied measure for the assessment of long-term mechanical valve performance. The freedom from thromboembolic complications in our series was 92.1% in mitral patients, 94.8% in aortic patients, and 92.7% overall. As expected most of the thromboembolic events occurred in patients with mitral prosthesis and in atrial fibrillation. Unfortunately, it was difficult to establish whether thrombi originated from the valve prosthesis or the atrial walls because echocardiograms carried out at the time of hospital admission failed to show clots on valves or in cardiac chambers. In addition the INR levels at the time of the events were within therapeutic ranges in all patients, and one may speculate that the triggering mechanism might have occurred over the previous days when the INR level might have been below the desired range. The outcomes in our series are in line with thromboembolic rates reported by Borman and colleagues in patients with SB valves [3]. On the other hand, Goldsmith and associates [4] observed unexpected higher thromboembolic episodes in SB aortic patients than in the group of mitral patients. The authors explained this finding by the presence of arterial disease in the aorta or carotid arteries as well as microembolism [4].
The thromboembolic freedoms observed in our series are higher than those seen with St. Jude Medical or CarboMedics valves at 7 and 5 years, respectively [8–10]. Emery and associates [9] report an excellent freedom from thromboembolism with the St. Jude Medical aortic valve at 20 years.
Hemorrhagic complications were seen in a total of 14 patients, 6 aortic and 8 mitral patients. Estimates of freedom from bleeding were 93% for the entire population and 92% and 94% for aortic and mitral patients, respectively. All bleeding events did not occur in patients older than 75 years of age as one might have expected according to some authors who observed a higher rate of bleeding in patients older than 70 years of age [11]. Our estimates are slightly lower than those reported by Borman and associates [3], being 94.6% for the entire population and 93.5% for aortic and 96.9% for mitral patients. Goldsmith and associates [4] observed an 88.6% and 90.8% freedom at 4 years for aortic and mitral patients, respectively. Our estimates are higher than those reported by Zellner and associates [8] in their 16-year experience with the St. Jude Medical valve. These authors report a 7-year freedom from bleeding of approximately 90% in mitral patients and 82% in aortic patients. Other large series have also observed a higher incidence of anticoagulant-related bleeding after aortic valve replacement compared with patients who underwent mitral valve replacement [9, 10]. Emery and associates [9] reported a freedom from bleeding of 80% at 20 years in patients 60 to 70 years of age with St. Jude Medical aortic valves. As a consequence of our retrospective study, we weighted the risk of bleeding against the favorable low thromboembolic rate of the SB valve prosthesis, because this latter finding was consistent with previous reports [3–5]. Therefore, recently we aimed at reducing the rate of bleeding by lowering our INR target in aortic patients from between 2.5 and 3.5 to between 2.0 and 2.5.
Few cases of nonstructural dysfunction were recorded in our series, all paravalvular leaks but one. The cause of nonendocarditic paravalvular leak was a heavily calcified native valve annulus. The 2 patients with compensated hemolytic anemia had no echocardiographic evidence of periprosthetic leakage.
As far as endocarditis is concerned the number of cases observed during the follow-up was low, keeping the estimates of freedom from this complication in the high ranges. Nonetheless we believe that endocarditis may not be a valid measure for long-term evaluation of a valve prosthesis because most of the time, the extent of the complication is determined by several patient-related factors other than the technical features of the valve prosthesis. Therefore comparing rates of endocarditis among series of patients with different mechanical valve prostheses may be a bit hazardous.
The New York Heart Association functional status of surviving patients significantly improved when compared with the New York Heart Association status before surgery. Whereas 66.9% of patients were in New York Heart Association class III or IV preoperatively, 88.9% achieved class I or II postoperatively.
The main bias of our report is that it was carried out in a retrospective manner; therefore, it possesses all the pitfalls of such design. Moreover no echocardiographic hemodynamic data on prosthetic valve performances were available to support the encouraging clinical findings.
In conclusion, the result of our 7-year evaluation of the SB prosthesis confirms the positive outcomes seen in a previous midterm report. Implantation of an SB mechanical valve in the aortic or mitral position yielded results similar to those observed during the same length of follow-up in a series of patients with different mechanical valve prostheses. Therefore the SB valve is a valid substitute when valve replacement with a mechanical device is contemplated.
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