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Ann Thorac Surg 1999;68:881-886
© 1999 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Long-term clinical experience with the omnicarbon prosthetic valve

^a Servicio de Cirugía Cardiovascular, Hospital Universitario "La Fé", Valencia, Spain

Address reprint requests to Dr José M. Caffarena, Servício de Cirugía Cardiovascular, Hospital Universitario "La Fé," Avda de Campanar 21, 46009 Valencia, Spain

	Abstract

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Background. From February 1985 to December 1994, 781 Omnicarbon valve prostheses were implanted in 647 patients. These were 357 male and 290 female patients with a mean age of 53.5 ± 10.5 years (range, 4 to 78 years). Before operation, 81% of the patients were in New York Heart Association class III or IV, 16% were in class II, and only 3% were in class I.

Methods. There were 227 aortic valve replacements (AVR) (35%), 286 mitral valve replacements (MVR) (44%), and 134 double-valve replacements (DVR) (21%) (AVR + MVR). Follow-up was 96.3% complete and consisted of 2,746 patient-years (mean follow-up, 4.6 years, and maximum follow-up, 10.7 years).

Results. Hospital mortality rates were 7.0% for AVR, 8.0% for MVR, and 8.2% for DVR. The annualized rate of anticoagulant-related hemorrhage was 0.8% per patient-year, and thromboembolism occurred at a rate of 0.7% per patient-year. No structural failure was observed during 10-year follow-up. Twenty-one instances of nonstructural dysfunction (two, pannus growth, and 19, dehiscence) of the Omnicarbon valve occurred in 20 patients, an incidence of 0.8% per patient-year. Hemolytic anemia was observed only in the presence of valvular dehiscence (6 of 19). Eight patients (0.3% per patient-year) had development of prosthetic valve endocarditis (4, AVR; 2, MVR; and 2 DVR). At the end of 10 years of follow-up, 91% of the survivors were in New York Heart Association class I or II. The overall survival rate at 10 years was 82.5% ± 2.6% (85.0% ± 3.9%, AVR; 81.0% ± 4.1%, MVR; and 82.5% ± 2.6%, DVR). Considering only valve-related deaths, the survival rate at 10 years was 91.9% ± 2.4% (90.0% ± 2.7%, AVR; 93.1% ± 3.8%, MVR; and 90.0% ± 1.8%, DVR).

Conclusions. Clinical results over a 10-year follow-up are excellent with the Omnicarbon prosthesis.

	Introduction

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The first valve substitutions with mechanical prostheses date from the 1960s and continual modifications have improved the clinical results. Nevertheless, the classic complications described by the Ad Hoc Liaison Committee for Standardizing Definitions of Prosthetic Heart Valve Morbidity [1]—thromboembolism, endocarditis, valvular thrombosis, structural failure, and events caused by anticoagulation therapy—continue to occur.

The Cruz-Kaster valve, designed at the University of Minnesota in the 1960s, can be considered the ancestor of the Omnicarbon prosthesis. Using that design, Dr C. W. Lillehei made changes in the structure of the valve and in the materials, thus producing the Lillehei-Kaster valve. This model offered hemodynamic advantages with respect to its predecessors, and implantations began in 1970. Improvements in valve geometry culminated in the development of new generations of monoleaflet valves. The first modifications consisted of reducing the thickness of the disc and increasing both the effective area and the size of the smaller orifice. These were the Omniscience valve models: the investigational design, which is obsolete, and then the modified design, which is currently available. A further improvement was to replace the titanium ring by pyrolytic carbon, thereby producing the all-carbon Omnicarbon valve.

The Omnicarbon valve has been implanted in our hospital since 1985. In this study, we present long-term results with 647 patients.

	Material and methods

Top Abstract Introduction Material and methods Results Comment References

 
Prosthesis
The Omnicarbon valve (Medical Incorporated, Minneapolis, MN) consists of a rotatable housing ring covered with a flexible suture ring, which adapts well to the native annulus, and a curved, freely rotating disc, which is retained by two shields extending from the ring. The disc pivot axis forms two orifices, one larger than the other, and has a maximum opening angle of 80 degrees.

Patient population
Between February 1985 and December 1994, a total of 781 Omnicarbon valve prostheses were implanted in 647 patients in "La Fé" Hospital, Valencia. There were 357 male (55%) and 290 female (45%) patients between 4 and 78 years old (mean age, 53.5 ± 10.5 years). Distribution of the patients by age is shown in Figure 1.

View larger version (22K): [in this window] [in a new window]   Fig 1. Distribution of patients by age.

View larger version (20K): [in this window] [in a new window]   Fig 2. Distribution of valve sizes.

View larger version (24K): [in this window] [in a new window]   Fig 3. Distribution of type of valve replacement by sex. (AVR = aortic valve replacement; DVR = double-valve replacement [AVR + MVR]; MVR = mitral valve replacement.)

One hundred nineteen patients (18.4%) had had a previous cardiac operation. Commissurotomy was the most frequent procedure (73 instances, 50 open and 23 closed). The next most common prior procedure was valve replacement (56 instances). Twenty-six of these 119 patients had had more than one prior heart operation.

Surgical procedure
All patients had a median sternotomy, and the operation was performed with standard cardiopulmonary bypass. Myocardial protection consisted of intermittent cold crystalloid cardioplegia administered in an antegrade manner and irrigation of the pericardium with cold saline solution. The prostheses were implanted using interrupted suture technique reinforced with Teflon felt pledgets. In general, the mitral prosthesis was oriented with the larger orifice toward the outflow tract of the left ventricle because we preserve the posterior leaflet and wish to avoid interference with the retained tissues. Aortic valves were oriented with the larger orifice toward the right coronary sinus. Prostheses were rotated after implantation when necessary.

One hundred eighteen concomitant operations were performed in 112 patients (17.3%). The associated procedures were as follows: tricuspid annuloplasty, 38 patients; coronary artery bypass grafting, 21; mitral commissurotomy, 13; left atrial thrombectomy, 11; correction of congenital cardiopathy, 5; correction of aortic disease, 4; myectomy, 4; partial longitudinal resection of dilated ascending aorta, 3; ascending aortic supracoronary graft replacement, 3; permanent pacemaker implantation, 2; pericardiectomy, 1 patient; and other, 13 patients.

Heparin sodium was combined with acenocoumarol when Quick test resulted higher than 40%. Administration started 24 hours after the intervention. When this program began, prothrombin levels were measured in terms of the percent activity, and we targeted the range of 20% to 35%. For the past several years, we have employed the international normalized ratio system to monitor prothrombin time. Anticoagulant therapy is adjusted for each patient to maintain in international normalized ratio between 2.5 and 3.5 in MVR or DVR patients and between 2.0 and 3.0 in AVR patients. We did not prescribe aspirin or dipyridamole in association with anticoagulation therapy for any of these patients because we have had good results with this approach.

Follow-up
Follow-up has been accomplished by personal telephone contact (32%) or by medical examination (68%). Follow-up was complete for 96.3% of patients (24 were lost to follow-up). The mean follow-up was 4.6 ± 0.1 years, the maximum follow-up was 10.7 years, and the cumulative follow-up for the 597 patients at risk was 2,746 patient-years (AVR, 970 patient-years; MVR, 1,210 patient-years; and DVR, 566 patient-years). The follow-up investigation was performed in the 8 months between March and November 1996.

Statistical analysis
Classification of the causes of morbidity and mortality was accomplished following the guidelines published by The Society of Thoracic Surgeons and The American Association for Thoracic Surgery [1]. Data are expressed when appropriate as the mean ± the standard deviation, a simple percentage, or a linearized rate of events (% per patient-year) with 95% confidence interval. All the survival curves and event-free curves were calculated using the actuarial method and are expressed with the standard error.

	Results

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30-day mortality
Fifty patients (7.7%) died during the early postoperative period (< 30 days or before hospital discharge). The hospital mortality rate for AVR was 7.0% (16 of 227); for MVR, it was 8.0% (23 of 286); and for DVR, it was 8.2% (11 of 134). The causes of death were as follows: cardiac insufficiency, 19 patients; noncardiac organ failure, 19; thromboembolism, 2; dehiscence, 2; hemorrhage, 2; neurologic event, 2; sudden or unexplained, 2; and arrhythmia, 2.

Late postoperative mortality
A total of 51 patients (16 AVR, 25 MVR, and 10 DVR) died late postoperatively. This yields a linearized rate of 1.9% per patient-year (95% confidence interval, 1.4% to 2.4% per patient-year): 1.6% per patient-year (1.2 to 2.0), 2.1% per patient-year (1.7 to 2.5), and 1.8% per patient-year (1.2 to 2.3) for AVR, MVR, and DVR, respectively. The causes of late death were noncardiac in 12 patients, valve-related in 23 patients (sudden, 3; hemorrhage, 1; endocarditis, 4; dehiscence, 5; thromboembolism, 1; valvular thrombosis, 1; and unknown, 8), and other cardiac related in 16 patients (myocardial infarction, 3; arrhythmia, 1; and cardiac insufficiency, 12).

The overall survival rate at 10 years, including all 101 causes of death, is 82.5% ± 2.6% (85.0% ± 3.9% for AVR, 81.0% ± 4.1% for MVR, and 82.5% ± 2.6% for DVR). The survival curves according to type of valve replacement are shown in Figure 4. Overall survival at 10 years considering only valve-related deaths is 91.9% ± 2.4% (90.0% ± 2.7% for AVR, 93.1% ± 3.8% for MVR, and 90.0% ± 1.8% for DVR). The actuarial freedom from valve-related death is shown in Figure 5. If only late mortality is considered, the overall 10-year survival rate is 92.6% ± 1.6% (93.8% ± 2.4% for AVR, 89.7% ± 2.9% for MVR, and 96.6% ± 1.9% for DVR).

View larger version (31K): [in this window] [in a new window]   Fig 4. Overall actuarial survival curve (at 10 years). The numbers below the time axis indicate patients at risk (at 2-year intervals). (AVR = aortic valve replacement; DVR = double-valve replacement [AVR + MVR]; MVR = mitral valve replacement.)

View larger version (32K): [in this window] [in a new window]   Fig 5. Actuarial curves of freedom from valve-related death. The numbers below the time axis indicate patients at risk (at 2-year intervals). (AVR = aortic valve replacement; DVR = double-valve replacement [AVR + MVR]; MVR = mitral valve replacement.)

There were three cases of valvular thrombosis (all in the MVR group). The linearized rate is 0.1% per patient-year (0 to 0.2) (0.2% per patient-year for [0 to 0.5] for MVR). One of the patients had renal failure 90 months after the intervention and died of valvular thrombosis and cardiogenic shock 3 months after the renal thromboembolic event; the anticoagulation range measured a few weeks prior to death was correct. Another patient died 3 months after intervention to remedy valvular thrombosis; this patient was seen with an incorrect anticoagulation (60% Quick test). The third patient discontinued anticoagulant treatment and is well after reoperation and explantation of the valve. The actuarial freedom from valvular thrombosis is 98.9% ± 0.7% at 10 years (97.5% ± 1.7% for MVR).

Anticoagulant-related hemorrhage
Twenty-three instances of hemorrhage occurred in 22 patients (10 AVR, 9 MVR, and 3 DVR), corresponding to a linearized rate of 0.8% per patient-year (0.5 to 1.2): 1.0% per patient-year (0.4 to 1.7) for AVR, 0.8% per patient-year (0.3 to 1.3) for MVR, and 0.5% per patient-year (0 to 1.1) for DVR]. In 1 patient, a left brain hemorrhage caused death. The actuarial 10-year freedom from hemorrhagic events is 89.1% ± 3.4% (90.5% ± 4.7% for AVR, 85.4% ± 6.6% for MVR, and 93.4% ± 3.8% for DVR).

Structural failure
No case of structural failure occurred with the Omnicarbon valve.

Endocarditis
Eight patients were seen with endocarditis on the valve prosthesis (4 AVR, 2 MVR, and 2 DVR). In 6, the causal agent was identified as Staphylococcus aureus (2 patients), Streptococcus viridans (2), and coagulase-positive S aureus (2). This corresponds to a linearized rate of 0.3% per patient-year (0.1 to 0.5): 0.4% per patient-year (0 to 0.8) for AVR, 0.2% per patient-year (0 to 0.4) for MVR, and 0.4% per patient-year (0 to 0.9) for DVR]. Three patients died of endocarditis, 4 underwent successful reoperation to replace the prosthesis, and 1 died during reoperation. The actuarial 10-year freedom from endocarditis is 98.1% ± 0.7% (97.6% ± 1.2% for AVR, 99.1% ± 0.6% for MVR, and 96.8% ± 2.2% for DVR).

Nonstructural dysfunction of prosthesis
Twenty-one cases of nonstructural dysfunction of the Omnicarbon valve were observed in 20 patients (5 AVR, 10 MVR, and 5 DVR), a linearized rate of 0.8% per patient-year (0.4 to 1.1): 0.5% per patient-year (0.1 to 1.0) for AVR, 0.8% per patient-year (0.3 to 1.3) for MVR, and 1.1% per patient-year (0.2 to 1.9) for DVR. The causes of nonstructural failure included pannus obstruction and paravalvular dehiscence. Actuarial freedom from nonstructural dysfunction is 91.2% ± 2.5% at 10 years (94.8% ± 2.4% for AVR, 88.8% ± 5.0% for MVR, and 90.1% ± 5.0% for DVR).

Two patients (1 MVR and 1 DVR) had development of pannus growth, and both underwent successful reoperation with valve explantation. In the patient with DVR, pannus growth developed on the aortic valve, and paravalvular dehiscence affected the mitral valve, which was resutured at reoperation 42 months postoperatively. Reoperation on the patient in the MVR group took place 52 months postoperatively. The linearized rate of pannus obstruction is 0.07% per patient-year (0 to 0.2) for all patients and 0.1% per patient-year (0 to 0.2) for MVR and 0.2% per patient-year (0 to 0.5) for DVR. Actuarial freedom from pannus growth is 99.5% ± 0.4% at 10 years (99.5% ± 0.5% for MVR and 98.5% ± 1.5% for DVR).

There were 19 patients with dehiscence (5 AVR, 9 MVR, and 5 DVR), a linearized rate of 0.7% per patient-year (0.4 to 1.0): 0.5% per patient-year (0.1 to 1.0) 0.7% per patient-year (0.2 to 1.2) and 0.9% per patient-year (0.1 to 1.7) for AVR, MVR, and DVR respectively. Actuarial freedom from dehiscence is 91.6% ± 2.4% at 10 years (94.8% ± 2.4% for AVR, 89.2% ± 5.0% for MVR, and 90.2% ± 4.9% for DVR). Eighteen of these patients underwent reoperation; 3 died during this procedure or in the early postoperative period, and 2 died after hospital discharge. The remaining 13 underwent satisfactory reoperation; in 6, the valve was explanted. One patient died prior to reoperation of severe respiratory insufficiency. Six of the 19 patients had hemolytic anemia as a result of the paravalvular leak. Clinically significant hemolysis was observed only in the presence of valvular dehiscence.

Reoperation
Twenty-seven patients (10 AVR, 10 MVR, and 7 DVR) had reoperation. The linearized reoperation rate is 1.0% per patient-year (0.6 to 1.4): 1.0% per patient-year (0.4 to 1.7) for AVR, 0.8% per patient-year (0.3 to 1.3) for MVR, and 1.2% per patient-year (0.3 to 2.2) for DVR. The causes of reoperation were dehiscence in 18 patients, endocarditis in 5, pannus growth in 2, and thrombosis in 2. The actuarial freedom from reoperation at 10 years is 90.0% ± 2.5% (91.2% ± 2.7% for AVR, 90.2% ± 4.0% for MVR, and 87.8% ± 5.2% for DVR).

Clinical outcome
At the last follow-up examination, 91.0% of the patients were in New York Heart Association class I or II.

	Comment

Top Abstract Introduction Material and methods Results Comment References

 
The all-carbon monoleaflet Omnicarbon heart valve evolved from the Omniscience valve design with the change in the housing material from titanium to pyrolytic carbon. As a result of this change, the incidences of thromboembolism, valvular thrombosis, and reoperation were significantly decreased compared with those of the Omniscience valve prosthesis [2].

Thromboembolism and anticoagulant-related hemorrhage are the most important complications associated with mechanical prostheses. Our 10-year follow-up study of the Omnicarbon valve shows a combined linearized incidence of thromboembolism and hemorrhage ranging from 1.1% per patient-year to 1.7% per patient-year depending on valve position. These findings agree with those of others [2–6] for the same valve and are somewhat lower than rates averaged for other mechanical valves in review articles [7, 8] and in dedicated studies [9–14]. The linearized incidences of endocarditis and of paravalvular dehiscence agree with results of others (Tables 1 and 2).

The 30-day mortality rate in our patient population was 7.7%, which is comparable to the rates of others [13, 19–23]. As a rule, 30-day mortality is not considered to be related to the implanted prosthesis but rather to reflect the preoperative state of the patient. Several risk factors in our patient population contributed to 30-day mortality: 81% of the patients were in New York Heart Association class III and IV, patients requiring valve replacement because of aortic dissection or endocarditis were not excluded from this study, and 18.4% of the procedures were cardiac reoperations.

In conclusion, our 10-year clinical results with the Omnicarbon mechanical prosthesis are excellent with a low incidence of thromboembolism, no major hemolysis, no structural failure, good cardiac improvement, and a relatively high survival rate (82.5% ± 2.6%). These findings lead us to conclude that the Omnicarbon valve design characteristics are satisfactory and that the low incidence of thromboembolic complications may reflect certain design features unique to the Omnicarbon valve.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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