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The Edwards MIRA bileaflet mechanical prosthesis, a heart valve not yet available in the United States, is designed with a unique hinge mechanism, curved leaflets, and thin titanium housing. We performed this study to investigate its clinical performance and postoperative hemodynamic results.
We implanted 58 Edwards MIRA prostheses in 51 patients in the aortic (n=18), mitral (n=26), and aortic and mitral (n=7) positions. Patients' ages ranged from 25 to 84 years (mean age, 53.7 ± 13.6).
Operative mortality was 2% (n=1), and late mortality was 4% (n=2). Thromboembolic events were observed in 2 patients (valve thrombosis in 1 and a cerebrovascular event in 1). There were no complications related to anticoagulation. No signs of valvular dysfunction or paravalvular leakage were observed. Peak transvalvular gradients of the aortic prostheses ranged from 24.25 ± 5.32 mmHg for the 21-mm valve to 11 ± 1.41 mmHg for the 25-mm valve. The effective orifice area ranged from 1.99 ± 0.12 cm2 for the 21-mm valve to 2.44 ± 0.17 cm2 for the 25-mm valve. The mean transvalvular gradients of the mitral prostheses ranged from 5.85 ± 2.91 mmHg for the 27-mm valve to 4.5 ± 0 mmHg for the 31-mm valve. The effective orifice area ranged from 2.31 ± 0.03 cm2 for the 27-mm valve to 2.64 ± 0.05 cm2 for the 33-mm valve.
These preliminary data suggest good hemodynamic function and a low rate of valve-related complications in the use of the Edwards MIRA mechanical prosthesis.
Since the 1st mechanical heart valve was implanted, bileaflet prostheses have been the most frequently implanted artificial heart valves. Although mechanical heart valves have improved substantially over the years, they still have some disadvantages.
The Edwards MIRA mechanical bileaflet valve (Edwards Lifesciences; Irvine, Calif) is constructed with pyrolytic carbon leaflets, a titanium-alloy Carbofilm™-coated housing (Sorin Biomedica Cardio S.p.A; Saluggia (VC), Italy), and a keyhole-shaped hinge area. This valve is not currently available for use in the United States.
We performed this prospective study to investigate the clinical performance and postoperative hemodynamic results of the Edwards MIRA mechanical heart valves. In doing so, we hoped to minimize our patients' mechanical heart valve complications and to achieve hemodynamic performance close to normal.
From August 2002 through April 2003, 51 patients underwent Edwards MIRA heart valve implantation at our hospital. There were 21 (41%) men and 30 (59%) women. Their ages ranged from 25 to 84 years (mean, 53.7 ± 13.6 years). The causes of the valvular disease were acute rheumatic fever in 44 patients (86%), coronary artery disease in 4 patients (8%), degeneration in 1 patient (2%), senile calcification in 1 patient (2%), and congenital disease (bicuspid aorta) in 1 patient (2%). The characteristics of the diseased valves are shown in Table I. The preoperative New York Heart Association (NYHA) functional classification was class I in 4 patients (8%), class II in 11 patients (22%), class III in 22 patients (43%), and class IV in 14 patients (28%). A majority of the patients (n=33, 65%) were in atrial fibrillation preoperatively. Clinical data are shown in Table II. Patients with mixed types of prostheses or acute endocarditis were excluded.
Surgical Data. Operations were performed with standard cardiopulmonary bypass using cold blood cardioplegia, topical cooling, and terminal warm blood cardioplegia for myocardial protection. Cardioplegic solution was infused directly into the coronary ostia, aortic root, or coronary sinus at 20-minute intervals. Valves were implanted in either the supra-annular or the intra-annular position. In total, 33 mitral and 25 aortic valves were replaced. Intraoperatively, mitral valves were found to be stenotic in 13 patients (39%), regurgitant in 8 patients (24%), and mixed in 12 patients (36%). The most common size of implanted mitral valve was 29 mm (15 patients). The 25 aortic valves were found be stenotic in 8 patients (32%), regurgitant in 4 patients (16%), and mixed in 13 patients (52%). The most common size of implanted aortic valve was 23 mm (15 patients). Aortic valve sizes varied from 21 to 25 mm, and mitral valve sizes varied from 27 to 33 mm (Table II). The Edwards MIRA mechanical heart valves were model 3600 (aortic position) or 9600 (mitral position).
The mean aortic cross-clamp time was 64.1 ± 23.5 min, and the cardiopulmonary bypass time was 93.0 ± 29.9 min. Concomitant cardiac procedures were performed in 18 of the 51 patients (35%) (Table III).
Anticoagulation. On the 1st day after the operation, all patients received oral warfarin. The target international normalized ratio (INR) range was 2.5 to 3.5.
Follow-Up. Physical examination, electrocardiography, blood tests, and echocardiography were performed postoperatively in all patients at 1 month, 3 months, 6 months, and 1 year. Standard apical and parasternal (long- and short-axis) views were obtained transthoracically by using the Hewlett-Packard Sonos 2500 System (Philips Medical Systems; Andover, Mass).
Statistical Analysis. All statistical analyses were performed using SPSS version 10.0 for Windows 98 (SPSS Inc.; Chicago, Ill). All data are presented as mean ± standard deviation. Actuarial estimates of morbid events were calculated by the Kaplan-Meier survival analysis method.
Twenty-six mitral, 18 aortic, and 7 double valve replacements were performed in 51 patients. All patients successfully underwent follow-up. The total follow-up time was 740 months (mean, 14.5 months).
Mortality Rates. The early mortality rate (within the first 30 postoperative days) was 2%—a patient who had undergone surgery while in cardiogenic shock could not be weaned from cardiopulmonary bypass. The late mortality rate was 4% (2 patients). One patient died of a noncardiac cause (colon carcinoma), and the other experienced probable sudden cardiac death, both after 14 postoperative months.
Morbidity. Four patients (8%) underwent reoperation during the postoperative period because of pericardial tamponade, bleeding, or both. Adynamic ileus, observed in 1 patient, was resolved by medical treatment, and acute cholecystitis, in another patient, required operation. Generalized convulsion, in 1 patient, was controlled by the anticonvulsant drug phenytoin sodium. In this patient, no organic disorder could be detected by computed brain tomography, so convulsion was thought to have been caused by high serum theophylline levels. Temporary atrial fibrillation, resolved by medical treatment (amiodarone), was observed in 6 patients.
The mean intensive care unit stay was 1.78 ± 0.69 days, and the overall hospital stay was 7.36 ± 3.54 days.
Functional Results. Postoperative follow-up showed substantial functional improvement in the majority of patients. Postoperatively, 39 patients (77%) were in NYHA class I and 12 patients (24%) were in NYHA class II, whereas most patients had been in NYHA class III or IV before the operation (Fig. 1).
Valve-Related Complications. On the 45th postoperative day, 1 patient (2%) underwent reoperation because of thrombus formation on the valve. She had not taken her warfarin during the previous week, and her INR value was found to be 1.1. The thrombus was extracted urgently. She is still under follow-up, is doing well, and takes the appropriate medication regularly. In another patient, whose aortic valve had been replaced 26 months before, a cerebrovascular event resulted in dysarthria. No intracardiac thrombus could be detected by echocardiography, and the dysarthria resolved spontaneously. There were no instances of anticoagulant-related bleeding, structural valve deterioration, or paravalvular leakage in the study group.
Hemodynamic Evaluation. The results for prosthetic valves in aortic and mitral position are shown in Table IV. With all measured values taken into consideration, the peak aortic and mean mitral transvalvular gradients and mean effective orifice areas (EOAs) were calculated. The peak transvalvular gradients of the aortic prostheses ranged from 24.25 ± 5.32 mmHg for the 21-mm valve to 11 ± 1.41 mmHg for the 25-mm valve. The EOA ranged from 1.99 ± 0.12 cm2 for the 21-mm valve to 2.44 ± 0.17 cm2 for the 25-mm valve. The mean transvalvular gradients of the mitral prostheses ranged from 5.85 ± 2.91 mmHg for the 27-mm valve to 4.5 ± 0 mmHg for the 31-mm valve. The EOA ranged from 2.31 ± 0.03 cm2 for the 27-mm valve to 2.64 ± 0.05 cm2 for the 33-mm valve.
The main goal of heart valve surgery is to repair and preserve the native valve. However, when that is not possible, surgeons have to choose appropriate prostheses for valve replacement. The Edwards MIRA bileaflet mechanical valve, which has curved leaflet structure unlike other mechanical heart prostheses, has been commercially available in Europe since 1998.
Edwards maintains that the curved leaflets and thin housing of the Edwards MIRA valve improve its hemodynamic performance. The hinge cavity provides a constantly varying single point of contact between the pivot and housing. An open channel in the hinge cavity enables continuous washing during the entire cardiac cycle, to reduce the risk of blood stasis. The housing consists of titanium alloy coated with Carbofilm, a very thin turbostratic carbon film that has a high-density crystalline structure. Curved leaflets are said to optimize hemodynamics by promoting natural flow patterns, thereby minimizing both turbulence and blood stasis. The leaflets are constructed of pyrolytic carbon.1,2
In this study, we investigated the clinical performance and postoperative hemodynamic results of Edwards MIRA mechanical heart valves, which have been used in our hospital for valve replacements since August 2002. No technical problems were encountered in either intra-annular or supra-annular placement, in either the aortic or the mitral position.
The most common complications due to mechanical heart valves are thromboembolism and valve thrombosis. Various factors are responsible for valve thrombosis and thromboembolic events. The most important of them is the inappropriate use of anticoagulant drugs. In our series, 1 patient (2%), on the 45th postoperative day, underwent reoperation because of mitral valve thrombosis. This patient had failed to take her prescribed warfarin for the previous week, and her INR value was 1.1. For that reason, it would not be accurate to attribute this complication to a specific mechanical heart valve. In another instance of a thrombotic event, dysarthria developed 26 months after the operation in a patient who had an aortic valve prosthesis. Irregular warfarin usage was the probable reason, because the patient's INR value was found to be 1.6. Even with these 2 cases taken into consideration, freedom from thrombotic events was found to be 96% for 2 years (Fig. 2). Thromboembolism and valve thrombosis rates were not higher than for other mechanical heart valves. Debétaz and colleagues3 reported a systemic embolism rate of 2.3% per pt-yr and a valve thrombosis rate of 0.1% per pt-yr for St. Jude mechanical heart valves. Rödler and co-authors2 reported thromboembolic events as 1.6% per pt-yr for CarboMedics mechanical valves. In comparing St. Jude with CarboMedics mechanical prostheses, Jamieson's group4 reported a total thromboembolic event rate of 5.4% per pt-yr in multiple valve replacements. In yet another study,5 thromboembolic event rates were reported as 5.4% per pt-yr for St. Jude and 4.4% per pt-yr for CarboMedics mechanical prostheses. Similar rates have been reported for Edwards MIRA prostheses.1,6,7
The incidence of bleeding in association with oral anticoagulation has been reported to be 2.3% to 3.3% per pt-yr.2,3 This complication was not observed in our series. Other valve-related complications, such as paravalvular leakage and prosthetic valve endocarditis, were also not observed. Lactate dehydrogenase was slightly increased, to mean values of 231.4 ± 84.3 U/L (normal value, 80–240 U/L).
During the early and mid-term postoperative periods, there were 3 deaths. One of them was not cardiac related. The overall mortality rate was 5.88%, and the actuarial 2-year survival rate after valve replacement with Edwards MIRA mechanical heart valves was calculated as 94.32% (Fig. 3). These results closely match those in the literature. In replacements with St. Jude mechanical valves, Debétaz and associates3 reported a hospital mortality rate of 3.1% and a late mortality rate of 4.2%. Borman and De Riberolles8 observed an early mortality rate of 5% in their series comprising patients whose valves were replaced with Sorin Bicarbon mechanical heart valves (Sorin Biomedica). In other studies of Edwards MIRA heart valves, early and late mortality rates have been reported as 1.18%,1 3.8%,2 and 1.9%.3
Although the size of our population is small, our initial experience has been that Edwards MIRA mechanical heart valves display good hemodynamic function and a low rate of valve-related complications. These favorable early and mid-term results must await long-term results for a final appraisal of the Edwards MIRA valve.
Address for reprints: Arzum Kale, MD, Department of Cardiovascular Surgery, Bayindir Hospital, 06520 Sogutozu, Ankara, Turkey. E-mail: moc.liamtoh@elakmuzra