Ann Thorac Surg 1996;61:1182-1187
© 1996 The Society of Thoracic Surgeons
Original Article: Cardiovascular
Ten Years' Experience of Aortic Valve Replacement With the Omnicarbon Valve Prosthesis
Tomio Abe, MD,
Koji Kamata, MD,
Kenji Kuwaki, MD,
Kanshi Komatsu, MD,
Sakuzo Komatsu, MD
Department of Thoracic and Cardiovascular Surgery, Sapporo Medical University School of Medicine, Sapporo, Japan
Accepted for publication December 9, 1995.
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Abstract
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Background. There are few clinical studies on late follow-up of the Omnicarbon monoleaflet valve. We report our 10-year experience with this valve in the aortic position and also compare late hemodynamic performance of this valve with that of the CarboMedics valve in the aortic position.
Methods. From January 1985 to June 1995, 117 consecutive patients underwent aortic valve replacement (AVR) with the Omnicarbon valve. There were 66 men and 51 women aged 13 to 69 years (mean age, 50 ± 12 years). They were divided into three groups: group 1 (43 patients) had isolated AVR, group 2 (36) had AVR and concomitant operations, and group 3 (38) had combined AVR and mitral valve replacement. Follow-up was 96.6% complete and consisted of 882.7 patient-years (range, 2.5 to 10.6 years; mean follow-up, 7.5 ± 2.7 years).
Results. There were three early deaths (2.6%) and 18 late deaths (2.0%/patient-year) ten of which were due to valve-related causes and eight, nonvalve-related causes. Survival rates at 10 years in groups 1, 2, and 3 were 77.6%, 82.4%, and 78.6%, respectively. The overall rates of freedom from valve-related complications in groups 1, 2, and 3 at 10 years were 77.4%, 100%, and 80.9%, respectively. The rates of freedom from the following complications in groups 1, 2, and 3 at 10 years were as follows: thromboembolism-94.8%, 100%, and 89.4%, respectively; valvar thrombosis-95.0%, 100%, and 100%; anticoagulant-related hemorrhage-93.6%, 100%, and 93.4%; prosthetic valve endocarditis-93.0%, 100%, and 97.2%; and reoperation-90.6%, 100%, and 97.2%. There were no significant differences between groups. All survivors showed marked improvement in New York Heart Association functional class, from 86% in classes III and IV preoperatively to 96% in classes I and II postoperatively. The Omnicarbon valve exhibited no significant difference in hemodynamic performance after isolated AVR compared with the CarboMedics bileaflet valve at the same follow-up periods.
Conclusions. This 10-year study confirms that the Omnicarbon valve is a durable prosthesis and provides excellent functional improvement with low rates of thromboembolism and valvar thrombosis in the aortic position.
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Introduction
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Several types of monoleaflet valves are used clinically in both the aortic and mitral positions [1–3]. There is a general perception that monoleaflet valves exhibit higher rates of thromboembolism and anticoagulant-related mortality and morbidity than bileaflet valves [4–6]. The Omnicarbon (OC), an all-carbon monoleaflet valve, was evolved from the Omniscience (OS) design by changing the housing material from titanium metal to pyrolytic carbon. There are few clinical reports on this prosthesis at late follow-up [7–10]. The aim of this study was to report our 10-year clinical experience with the OC valve in the aortic position, with particular attention paid to postoperative thromboembolism, valvar thrombosis, anticoagulant-related complications, and prosthetic valve endocarditis (PVE). We also compared the OC with the bileaflet CarboMedics (CM) valve in regard to hemodynamic performance in the aortic position in the late postoperative period.
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Material and Methods
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From January 1985 to June 1990, 117 patients underwent aortic valve replacement (AVR) with the OC prosthesis. There were 66 men and 51 women aged between 13 and 69 years with a mean age of 49.9 ± 12.0 years. The type of aortic valve lesion was aortic regurgitation in 70 patients (annuloaortic ectasia in 21) and combined aortic stenosis and mild aortic regurgitation in 45. Two patients had malfunctioning previously implanted prostheses (Table 1
). Preoperative angiographic and hemodynamic evaluations were performed in all patients except those with active infective endocarditis or severe congestive heart failure. Two-dimensional echocardiography and pulsed Doppler echocardiography were also carried out in all patients before and after operation. Preoperatively, 14% of the patients were in New York Heart Association functional class II, 61% were in class III, and 26% were in class IV.
Operative Procedure
All patients had a median sternotomy, and the operation was performed with standard cardiopulmonary bypass using a membrane oxygenator and moderate hypothermia of 28° to 30°C. Cold blood cardioplegic solution (20 mEq/L of K+) was administered by antegrade coronary perfusion at 30-minute intervals during aortic cross-clamping. After meticulous debridement of the valve annulus, the aortic valve was always inserted in the infraannular position with the major opening to the outer side of the ascending aorta. Mitral valves also were inserted in the antianatomic position using interrupted mattress sutures.
Anticoagulation Regimen and Follow-up Studies
Anticoagulation with warfarin sodium and bucolome (Takeda Pharmaceutical Industries) was routinely commenced on postoperative day 3 and usually resulted in therapeutic levels by postoperative day 5 or 6 using the thrombo-test of 15% to 25%, corresponding to an international normalized prothrombin time ratio of 2 and 3.5. The patients were contacted by phone and examined in our hospital or in other clinics for follow-up.
Follow-up was complete for 96.6% of patients (4 were lost to follow-up) and ranged between 2.5 and 10.6 years, (mean follow-up, 7.5 ± 2.7 years). The cumulative follow-up was 882.7 patient-years (AVR, 273.7 patient-years; AVR + other procedures, 261.7 patient-years; AVR + mitral valve replacement [MVR], 347.3 patient-years). Definition of morbidity followed the guideline's of Edmunds and colleagues [11]. The linear incidence of events was calculated as the total number of events divided by the total number of patient-years.
Statistical Analysis
Data are expressed as the mean ± the standard deviation and the range. All survival curves and event-free curves were described by using Kaplan-Meier analysis and subjected to a log-rank test. The results of hemodynamic evaluations were subjected to Student's nonpaired t test. Differences were considered significant if the p value was less than 0.05.
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Results
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Patient Demographics
The causes of valvar disease were as follows: rheumatic in 41 patients (35%); degenerative in 34 (29%); infective endocarditis in 12 (10%); aortic bicuspid in 10 (9%); Marfan's syndrome in 8 (7%); aortitis in 6 (5%); and other in 6 (5%). The surgical procedures for the 117 patients are listed in Table 2. Isolated AVR was performed in 43 patients (37%) (group 1). Concomitant operations were performed in 74 patients (63%); 36 had AVR + other surgical procedures including the Bentall procedure (group 2), and 38 had combined AVR and MVR (group 3). Nineteen patients (16%) had undergone a previous operation, including ten open mitral commissurotomies, five prosthetic valve replacements, two congenital cardiac repairs, and two mitral valve repairs.
The size of the prostheses used ranged from 23 to 27 mm in the aortic position. The prosthetic valves used for MVR were the Duromedics valve in 29 patients and the St. Jude Medical (SJM) valve in 10 patients; tricuspid valve replacement was performed with the SJM valve in 1 patient.
Early Deaths
Death within 30 days of operation occurred in 3 (2.6%) of the 117 patients. The causes were low cardiac output, multiple-organ failure, and renal failure in 1 patient each. There were no deaths (0/43) after isolated AVR (group 1), one death (1/36, 2.8%) after AVR + concomitant procedures (group 2), and two deaths (2/38, 5.3%) after AVR + MVR (group 3).
Valve-Related Complications
Meticulous monitoring and follow-up studies were carried out in every patient for thromboembolism, valvar thrombosis, anticoagulant-related hemorrhage, PVE, hemolysis, structural failure of the valve, and reoperation. The overall rates of freedom from valve-related complications in groups 1, 2, and 3 at 10 years were 77.4%, 100%, and 80.9%, respectively (Fig 1). There were no significant differences in these complications between groups.
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Fig 1. . Overall rates of freedom from valve-related complications after aortic valve replacement with Omnicarbon valve. There were no significant differences between groups.
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Thromboembolic events were observed in 5 patients (0.57%/patient-year). Permanent hemiplegia was noted in 2 patients; it developed in 1 6 years after AVR + MVR (group 3) and in the other, 8 years after AVR + other procedures (group 2). One fatal thromboembolus occurred in the AVR + MVR group (0.29%/patient-year). The cause of all thromboembolic events was cerebral embolism. Figure 2 shows that the thromboembolism-free curves for groups 1, 2, and 3 10 years after operation were 94.8%, 100%, and 89.4%, respectively. There was no significant difference between groups.
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Fig 2. . Actuarial freedom from thromboembolism after aortic valve replacement with Omnicarbon valve. There were no significant differences between groups.
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Valvar thrombosis was observed in 1 patient in group 1 7.3 years postoperatively, and the rate of freedom from valvar thrombosis at 10 years was 95.0% (Fig 3). Anticoagulant-related hemorrhage was observed in 4 patients, 3 of whom died. The rates of freedom from anticoagulant-related hemorrhage 10 years after operation were 93.6% for group 1, 100% for group 2, and 93.4% for group 3 (Fig 4). Prosthetic valve endocarditis was also observed in 4 patients (0.45%/patient-year), 3 of whom died after AVR (group 1) (1.1%/patient-year). One had reoperation 3 months after AVR. The PVE–free rates 10 years after operation were 93.0% for group 1, 100% for group 2, and 97.2% for group 3 (Fig 5).
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Fig 3. . Actuarial freedom from valvar thrombosis after aortic valve replacement with Omnicarbon valve. There were no significant differences between groups.
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Fig 4. . Actuarial freedom from anticoagulant-related hemorrhage after aortic valve replacement with Omnicarbon valve. There were no significant differences between groups.
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Fig 5. . Actuarial freedom from prosthetic valve endocarditis (PVE) after aortic valve replacement with Omnicarbon valve. There were no significant differences between groups.
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Reoperations in connection with valve-related complications were performed in 4 patients. The reasons were PVE in 2 within 12 months after isolated AVR and in 1 3 months after AVR + MVR and valvar thrombosis in 1 patient 7.3 years after isolated AVR. The 10-year reoperation-free rates were 90.6% in group 1, 100% in group 2, and 97.2% in group 3. There were no significant differences between groups (Fig 6).
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Fig 6. . Actuarial freedom from reoperation after aortic valve replacement with Omnicarbon valve. There were no significant differences between groups.
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Hemodynamic Evaluation
Cardiac function before and 10 to 127 months after operation, measured at a mean interval of 44.5 months, was studied in the aortic position by pulsed Doppler echocardiography. Nineteen patients who underwent isolated AVR with the OC valve were evaluated and compared at identical follow-up periods (11 to 107 months; mean interval, 44.1 months) with 18 patients who underwent isolated AVR with the CM valve (CarboMedics, Austin, TX) (Fig 7). The mean aortic pressure gradients across the OC aortic valve were 16.3 ± 6.4 mm Hg in the 23-mm size (23A), 15.8 ± 6.9 mm Hg in the 25-mm size (25A), and 11.5 ± 5.2 mm Hg in the 27-mm size (27A). The respective values with the CM valve were 13.4 ± 7.2 mm Hg, 12.7 ± 4.1 mm Hg, and 9.4 ± 1.1 mm Hg. The mean effective orifice areas of the OC valve were 1.31 ± 0.62 cm2 (23A), 1.41 ± 0.58 cm2 (25A), and 1.48 ± 0.74 cm2 (27A), whereas those of the CM valve were 1.24 ± 0.44 cm2 (23A), 1.38 ± 0.31 cm2 (25A), and 1.71 ± 0.81 cm2 (27A). There were no significant differences in mean aortic pressure gradients and mean effective orifice areas between the two prostheses in any valve size; generally, the bileaflet CM prosthesis had slightly decreased estimated mean aortic pressure gradients, and the monoleaflet OC prosthesis had slightly increased mean effective orifice areas.
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Fig 7. . Comparison of mean aortic pressure gradients (AMG) and mean effective orifice areas (EOA) between 19 patients who had isolated aortic valve replacement (AVR) with the Omnicarbon valve (OC) and 18 patients who had AVR with the CarboMedics valve (CM) was made at the same follow-up interval. There were no significant differences between the two prostheses in any valve size.
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Late Deaths
Eighteen patients (2.0%/patient-year) died late during follow-up. The causes of death are listed in Table 3. Late mortality occurred in 7 patients (2.6%/patient-year) in group 1, 5 (1.9%/patient-year) in group 2, and 6 (1.7%/patient-year) in group 3. Ten deaths were valve related and 8, nonvalve related. There was no significant difference in late deaths between the three groups.
Postoperative Clinical Data
The actuarial survival rate at 10 years was 77.4%. Thus, of all 117 patients, 92 were still alive: 77.6% of those having isolated AVR (group 1), 82.4% of those having AVR + concomitant procedures (group 2), and 78.6% of those having AVR + MVR (group 3) (Fig 8). The overall valve-related survival rate at 10 years was 85.2% (87.6% in group 1, 90.3% in group 2, and 80.9% in group 3) (Fig 9). All patients showed substantial improvement in regard to New York Heart Association functional class after operation. Preoperatively, 60% (71/117) were in New York Heart Association class III and 26% (30/117) in class IV, whereas at the time of this report, 82% (75/92) were in class I, 14% (13/92) were in class II, and only 4% were in class III.
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Fig 8. . Actuarial survival rate 10 years after aortic valve replacement with Omnicarbon valve. There were no significant differences between groups.
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Fig 9. . Actuarial valve-related survival rate 10 years after aortic valve replacement with Omnicarbon valve. There were no significant differences between groups.
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Comment
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The all-carbon monoleaflet OC heart valve was evolved from the OS valve design by changing the housing material from titanium to pyrolytic carbon. When the housing and leaflet materials were switched from titanium to all pyrolytic carbon and the pivot was shortened to form a low profile, the incidences of thromboembolism, valvar thrombosis, and reoperation were significantly decreased compared with those of the OS valve prosthesis in our previous report [8]. Other authors [12, 13] have found this prosthesis superior to other mechanical valves on the basis of in vitro performance studies, but reports using clinical results [7–9] have been limited, and the long-term clinical results and its late hemodynamic performance in the aortic position remain uncertain.
The early (30-day) mortality rate in our series was 2.6%, which is lower than figures from other centers [1–3, 6, 7]. The major causes of early death were related to the preoperative clinical status of the patients. The mortality rate was 0% for isolated AVR (group 1), 2.8% (1/36) for AVR + concomitant procedures (group II), and 5.3% (2/38) for AVR + MVR (group III). Keenan and associates [14] reported a higher mortality rate (10.3%) with the monoleaflet Medtronic-Hall valve (Medtronic, Minneapolis, MN) than the SJM valve; however, it is notable that most (53%) of those recipients were in New York Heart Association class IV before operation, whereas only 26% of the patients in this series were in class IV. The higher incidence of early mortality in group 3 seems to be attributable to the underlying complicated lesions and the preoperative status of the patients.
Nonetheless, patient survival based on actuarial 10-year freedom was high (77.4%) (77.6% in group 1, 82.4% in group 2, and 78.6% in group 3) and was comparable to that of the SJM valve (47% to 82%) [15–17]. Late mortality increased, and the survival rate decreased from 78.6% at 5 years to 77.4% at 10 years. When the causes of late death were analyzed, it was found that ten (55.6%) of the 18 late deaths were due to valve-related complications; among nonvalve-related deaths, the chief cause was congestive heart failure.
Thromboembolism, anticoagulant-related hemorrhage, and PVE have been major risk factors in patients with mechanical prosthetic valves, but the development of new prostheses with improved hemodynamic performance and materials that lessen thrombogenicity has sharply reduced the rate of thromboembolic events [8]. In this series, 5 patients sustained this complication; the linearized incidence of thromboembolism in the entire group was 0.57%/patient-year, which is much lower than the results of 2.4%/patient-year for the Medtronic-Hall valve as reported by Keenan and co-workers, [14] the 1.49%/patient-year for the SJM valve as found by Arom and colleagues [16], and the 1.2%/patient-year for the OS valve as reported by Damle et al [1].
On the basis of in vitro performance studies, Yoganathan [12], Knott [13], and their associates ascribed the lower incidence of thromboembolism of this prosthesis over other mechanical valves to its hingeless design. In fact, in regard to our previous report [8] comparing the OC and OS prostheses at 4 years, the linearized thromboembolism-free rates in the OC group (0.7%/patient-year) were significantly lower than those in the OS group (6.2%/patient-year), and in the present series, we have one case of valvar thrombosis (0.11%/patient-year) with the OC valve at 10 years' follow-up.
The next most frequent valve-related complication was anticoagulant-related hemorrhage, which occurred at a rate of 0.45%/patient-year in this series. Three of the four events were fatal (0.36%/patient-year); thus, this complication has been the major contributor to valve-related mortality. Czer and co-workers [15] reported a higher incidence (2.8%/patient-year) of this complication in 29 patients with the SJM valve in the aortic position, and of 27 events, seven (26%) resulted in death. There were no significant differences in actuarial rates of freedom from hemorrhage by valve position, with 86% ± 2% of patients free from hemorrhage at 9 years. They lowered the upper limit of target prothrombin time ratio from 2.5 to 2.0 to reduce anticoagulant-related hemorrhage, and the linearized rate of hemorrhage decreased by 44% (from 2.8%/patient-year to 1.5%/patient-year). In a previous study [18] and the present series, anticoagulation with warfarin and bucolome was used and maintained our target thrombo-test of 15% to 25%, corresponding to an international normalized prothrombin time ratio of 2.0 and 3.5. The linearized rate of hemorrhage was 0.45%/patient-year in the aortic position, with 96.6% of patients free from hemorrhage. Kopf and colleagues [19] reported that target prothrombin time ratios of 1.3 to 1.5 for the SJM valve resulted in comparable linearized rates of hemorrhage (1.3%/patient-year) without an increase in thromboembolic complications. Therefore, it is possible that less intense warfarin regimens may reduce hemorrhagic risk while maintaining thromboembolic protection in the all-carbon valve prosthesis.
The incidence of PVE in the aortic position with the OC valve, 0.45%/patient-year, was higher than that of the CM valve, 0%, [18] and comparable to that of the SJM valve, 0.5%/patient-year [16]. This incidence with the monoleaflet valves (0.7%/patient-year to 1.9%/patient-year) [1, 6–10, 14] was higher than that with the bileaflet valves (0%/patient-year to 0.6%/patient-year) [15–19]. Peter and coauthors [9] reported the incidence of PVE with the OC valve in the aortic position was 1.9%/patient-year. In the present study, we cannot explain why there was a high incidence of PVE with the monoleaflet valves compared with that of the bileaflet valves as reported in the literature [1, 6–10, 14–19]. It was definitely not attributable to the design of the OC valve, which has a limited flow-velocity profile with a limited opening leaflet angle; increases in the stagnant areas and the amount of turbulence might contribute to PVE. In this study, valvar thrombosis developed in 1 patient. In a previous study [8], however, in 46 patients who had cinefluorography at this follow-up period, the opening angles of the prosthesis at rest in the aortic position were not always fully open to the 80-degree angle (range, 41 to 67 degrees; mean angle, 52 ± 7 degrees) at the end-systolic phase.
During follow-up, the hemodynamic performance of this prosthesis was compared with that of the bileaflet CM prosthesis in the aortic position by noninvasive studies. There were no significant differences in pressure gradients or effective valve orifice areas with each valve size; however, the monoleaflet OC prosthesis showed a slightly increased estimated mean aortic pressure gradient, and the bileaflet CM had a slightly increased mean effective orifice area.
The functional status of the surviving patients with this valve was favorable compared with their status before operation. Whereas 86% were in New York Heart Association class III or IV preoperatively, 96% achieved class I or II by the mean follow-up of 7.5 ± 2.7 years. There was zero incidence of major hemolysis and no structural failure of the valves during follow-up. Hemolysis caused by this prosthesis has been reported to be too low to cause concern [7, 9].
In conclusion, the clinical data obtained in the present study suggest that the improvement of the housing material and the valve mechanism of the OC valve has contributed much to its antithrombotic characteristics. The mechanism of the variable opening angles obtained in the in vivo study should be evaluated in each patient, with specific attention to the opening angle and the pressure gradient. In regard to the durability of this prosthesis, the results of this 10-year follow-up study indicate that it is completely satisfactory. In addition, the prosthesis provides functional improvement.
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Footnotes
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Address reprint requests to Dr Abe, Department of Thoracic and Cardiovascular Surgery, Sapporo Medical University, South 1, West 17, Chuo-ku, Sapporo, Hokkaido, 060 Japan.
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References
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Abstract
Introduction
