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Ann Thorac Surg 2005;79:1934-1938
© 2005 The Society of Thoracic Surgeons

Original article: Cardiovascular

10-Year Experience With the ATS Mechanical Valve in the Mitral Position

Constantin Stefanidis, MD*, Albert M. Nana, MD, Didier De Cannière, MD, PhD, Martine Antoine, MD, Jean-Luc Jansens, MD, Chi-Hoang Huynh, MD, Jean-Louis Le Clerc, MD

Department of Cardiac Surgery, Erasme Hospital, Free University of Brussels, Brussels, Belgium

Accepted for publication January 3, 2005.

* Address reprint requests to Dr Stefanidis, Erasme Hospital, Free University of Brussels, Route de Lennik 808, Brussels 1070, Belgium (E-mail: constantin.stefanidis{at}ulb.ac.be).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 References
 
BACKGROUND: The ATS Medical Open Pivot mechanical heart valve was introduced in 1992. Previous reports have focused on the low rate of thromboembolic complications in the aortic position. The purpose of this retrospective study is to analyze the rate of midterm thromboembolic events and other valve-related complications when the ATS Open Pivot valve is implanted in the mitral position.

METHODS: Between June 1992 and June 2002, 177 patients (63 male and 114 female; mean age 57.5 years) underwent mitral replacement with an ATS Open Pivot mechanical heart valve. Preoperatively, 17 patients (10%) were in New York Heart Association functional class II, 117 patients (66%) in class III, and 43 patients (24%) in class IV. Seventy-four patients (42%) were in chronic atrial fibrillation. Seventy-four mitral valve replacements (42%) were associated with other cardiac procedures. Etiologies included degenerative disease (56%), rheumatic disease (38%), and endocarditis (6%). On the second postoperative day, 100 mg acetylsalicylic acid and oral acenocoumarol (Sintrom) was introduced to obtain a target INR of 2.0 to 3.0. All patients were followed up by one cardiologist and underwent annual transthoracic echocardiographic examination.

RESULTS: Percent follow-up was 90.4%. Data represent 724 total patient-years. Mean follow-up was 48 ± 34 months (range, 1 to 119). Operative morbidity was 15%. Overall hospital mortality was 2.8% (5 patients). At hospital discharge, the mean INR for all the patients was 2.38 ± 0.68 (range, 1.32 to 6.44). Five early neurologic complications occurred: 3 transient cerebrovascular accidents and 2 strokes. Three late transient cerebrovascular ischemic accidents occurred at 3, 4, and 6 years, respectively. No other complications such as paravalvular leak, valve dysfunction, thrombosis, or valve explant occurred. Postoperative echocardiographic data revealed low mean pressure gradient as related to the valvular size.

CONCLUSIONS: The ATS Medical Open Pivot mitral valve demonstrates low rates of bleeding, thromboembolic, and other valve-related complications.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 References
 
The ATS Medical Open Pivot heart valve (ATS Medical, Minneapolis, Minnesota) was introduced in May 1992. A description of the valve is published elsewhere [1]. The ATS Open Pivot valve has three characteristics that we consider improvements to the traditional bileaflet design: a convex spherical hinge mechanism, the absence of projecting pivot guards, and the ability to rotate the prosthesis within its housing. The hinge mechanism is constructed so that blood flowing through the valve housing will have a washing effect in contrast to a concave mechanism that may induce turbulence. The open pivot hinge also promotes particularly rapid leaflet closure with a very low element of regurgitation and surprisingly quiet valve closure sounds. These features make this valve completely different from other bileaflet models in that there are no cavities in the valve ring in which stasis or eddy currents may develop; that may lead to better washout of the blood and result in fewer thromboembolic events. Since its introduction, early clinical studies reported a low rate of valve-related complications, and low anticoagulation regimens have also been proposed [1–3]. The purpose of this study is to report midterm results for patients implanted with the ATS Open Pivot heart valve in the mitral position.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 References
 
Between June 1992 and June 2002, 177 patients underwent mitral valve replacement at Erasme University Hospital and received an ATS Open Pivot valve. The study includes 114 women (65%) and 63 men (35%). The mean age was 57.5 years (range, 28 to 78). According to New York Heart Association classification, 17 patients (10%) were in NYHA class II, 117 patients (66%) in class III, and 43 patients (24%) in class IV. Seventy-four patients (42%) had atrial fibrillation before surgery. For 42 patients (24%), the mitral valve replacement was their second cardiac operation. In addition, 74 mitral valve replacements (42%) were associated with concomitant cardiac operations. Etiologies included degenerative disease (56%), rheumatism (38%), and endocarditis (6%). The high percentage of rheumatic etiology is due to the majority of these patients being referred from North Africa. Patient demographic data are depicted in Table 1.


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  		Table 1. Patient Demographics
 
Surgical Procedure
Patients were operated on through a median sternotomy with mild hypothermia and cardiopulmonary bypass (CBP). Myocardial preservation was made by anterograde cold crystalloid cardioplegia and topical surface cooling. In the majority of cases, the native posterior leaflet of the mitral valve was not excised. The valve annulus was measured with an ATS sizer and the ATS Open Pivot mitral valve was implanted with the free edges of the leaflets oriented perpendicularly to the interatrial septum and sutured with interrupted simple sutures. All patients received an intraoperative echocardiography examination.

Postoperative Care
Postoperative recovery was conducted in the intensive care unit (ICU) until the patients were weaned from ventilation and inotropic support. Patients were transferred to the hospitalization ward after 45.1 ± 71.4 hours. On the second postoperative day, the drainage tube was removed and oral acenocoumarol (Sintrom, Novartis Pharma, Vilvoorde, Belgium) was initiated with a target international normalized ratio (INR) of 2.0 to 3.0. In addition, 100 mg acetylsalicylic acid was added as daily antiplatelet therapy. Echocardiographic monitoring was performed between the fifth and eighth postoperative day with a transthoracic bidimensional Hewlett-Packard Sonos 5500 ultrasound imaging system using a 2.5 MHz transducer (Hewlett-Packard, Andover, Massachusetts). The valve gradient was calculated by means of the modified Bernoulli equation. Operative results are reported in Table 2. Valve size distribution and associated postoperative gradients are reported in Table 3.


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  		Table 2. Operative Results
 

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  		Table 3. Valve Size Distribution and Postoperative Mean Gradient
 
Patient Follow- Up
After hospital discharge, long-term anticoagulation management was under the direction of the general practitioner to maintain INR between 2.0 and 3.0. Echocardiographic follow-up was performed postoperatively at 3 months, 6 months, and annually thereafter by one cardiologist. All patients were followed up annually in the outpatient clinic by the operative cardiac surgeon. Current patient health status was collected by phone by the author between the dates of August 2002 and November 2004. The data collection protocol required contacting both the patient and the patient’s following physician. Patients were asked to report adverse events, and then the most recent INR measurement and self-reported adverse events were verified with the appropriate following physician.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 References
 
Follow-up for this patient group was 90.4%, and 724 total patient-years are represented. Mean follow-up is 48 ± 34 months (range, 1 to 119). Demographic data are depicted in Table 1.

Operative Morbidity and Mortality
Mean ICU stay was 45.1 ± 71.4 hours, and mean postoperative stay was 12.4 ± 7.7 days. Operative morbidity was 15%. We recorded 16 revision cases during the hospitalization: 4 for bleeding and 12 for pericardial effusion requiring pericardial drainage. Five early neurologic complications occurred: 3 transient cerebrovascular embolisms and 2 strokes. The first stroke occurred in a patient under cardiac arrest who underwent drastic resuscitation. The second case was a patient undergoing a reoperation and was in chronic atrial fibrillation. Overall hospital operative mortality was 2.8% (5 patients). These included two compassion cases in end-stage valvulopathy who died in the operating room and 3 patients who died in the ICU of cardiogenic, septic, and multiorgan failure respectively. During the fifth and eighth postoperative days, echocardiographic assessment revealed a very low mean gradient pressure by valve size (Table 3). At hospital discharge, the mean INR for all patients was 2.38 ± 0.68 (range, 1.32 to 6.44).

Late Morbidity and Mortality
Three late transient cerebrovascular ischemic accidents occurred at 3, 4, and 6 years, respectively. The first late transient cerebrovascular ischemic case occurred 3 years postoperatively from an endocarditis septic embolism in a patient in atrial fibrillation with his INR within the target range (2.0 to 3.0). The patient had been successfully treated by antibiotics. Two cases occurred in patients with their INR below the target range. The linearized rate for thromboembolic events is 0.45% per patient-year. No other complications such as paravalvular leak, valve thrombosis, explantation, or valve dysfunction occurred. Valve-related complications are listed in Table 4.


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  		Table 4. Linearized Rates for Valve-Related Complications Occurring More Than 30 Days After Surgery
 
The percent survival is depicted in the Kaplan-Meier curve portrayed in Figure 1.



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  		Fig 1. Patient survival. There were 125 cases remaining after 1 year, 104 after 3 years, 84 after 5 years, and 31 after 10 years. Solid line represents parametric estimates enclosed within 95% CI (dotted lines). (CI = confidence interval.)

 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
References
 
The ideal mechanical valve prosthesis should provide life-long durability and a degree of thrombogenicity comparable with tissues valves with a low anticoagulation regimen and a very low pressure gradient. Mechanical valve prostheses, in comparison with biological valve prostheses, offer the advantage of longevity and durability.

In 1977, St. Jude Medical (St. Paul, Minnesota) introduced the first mechanical valve with a bileaflet valve design. At that time, this was a radical change for prosthetic heart valve design. Continuous refinement of this first bileaflet valve led manufacturers to launch numerous mechanical valve prostheses, with the goal to improve hemodynamics and patient health outcomes. However, despite advances in technology and improvement in long-term outcomes, the ideal valve does not yet exist. The incidence of prosthesis-related complications are similar for modern bileaflet valves but vary with the patient population, intensity of follow-up, patient-related risk factors, and recommended level of anticoagulation [4, 5].

In 1992, ATS Medical introduced a new bileaflet mechanical heart valve prosthesis with an open pivot design, which results in minimal regurgitation. Blood flows through the valve orifice and washes over the spheres and hinge mechanism rather than being subject to cavitation. The valve housing allows rotation of the valve once sewn in place. There are no projecting pivot guards.

In addition, data indicate that the valve has a low noise level. One study indicated that 84% of patients implanted with the valve could not hear the valve or were never bothered by it, while 15% indicated they were occasionally bothered by the valve noise [21].

Previous clinical results with this new bileaflet valve demonstrated an equivalence with those of the mechanical bileaflet valves (St Jude Medical and Carbomedics) even in severely disabled patients with many reoperations [1]. These studies also reported a very low rate of thromboembolism events despite a reduced level of anticoagulation [1]. Authors reported a rate of thromboembolism at 0.75% per patient-year in the first year after implantation (compared with 1.35% and 2.5% in the authors’ experience with St Jude Medical and Carbomedics bileaflet valves, respectively). In the same study, the linearized rates of 1.49% per patient year and 2% per patient year were similar to previous reports.

The ATS Open Pivot valve has demonstrated very low rates of thromboembolic events. This observation has resulted in some researchers, such as Van Nooten and associates [1–3], to lower their anticoagulation regimen for the valve when implanted in the aortic position. The addition of antiplatelet drugs may be useful in preventing thromboembolic events, possibly allowing a further reduction in the anticoagulant dose [6, 7].

Importantly, patient-related risk factors such as wall motion instability, depressed ejection fraction, or atrial fibrillation rather than valve-related factors may be more important in thromboembolic risks [8, 9]. The European Society of Cardiology has developed recommendations for anticoagulation for mechanical heart valves in the mitral position for the current "second generation" valves. European guidelines recommend a target INR of 3.0 to 3.5 in the mitral position and 2.5 to 3.0 in the aortic position. That may need to be adjusted if other underlying risk factors for thromboembolism and stroke are present [10]. Other authors and associations such as the American College of Chest Physicians Guidelines, the American College of Cardiology, and the American Heart Association recommend an INR of 2.5 to 3.5 for patients with a mechanical heart valve in the mitral position [11, 12].

The principal complication of oral anticoagulants such as warfarin is bleeding. Age, history of stroke, gastrointestinal bleeding, renal insufficiency, and anemia are additional risk factors for major bleeding. It was demonstrated that lowering the INR range from 3.0 to 4.5, to 2.0 to 3.0, reduced bleeding to clinically significant levels [22]. A study of patients with mechanical prosthetic heart valves who followed a high-intensity regimen (INR range, 7.4 to 10.8) versus patients following a lower intensity regimen (INR range, 1.9 to 3.6) found no difference in thromboembolic events, but did report a higher incidence of bleeding in the higher intensity group [13]. A more recent trial showed that the addition of acetylsalicylic acid (100 mg daily) to warfarin (INR 3.0 to 4.5) reduced mortality, cardiovascular mortality, and stroke considerably compared with warfarin alone [14].

In our 10-year experience with the ATS Medical Open Pivot mitral valve, we have observed a low rate of valve-related complications. Patients undergoing mitral valve replacement are usually at an advanced stage of their disease. Wall motion instability, depressed ejection fraction, and atrial fibrillation are not uncommon. Thus, we consider that the design of the valve is an important risk factor for thromboembolism. Patient-related risk factors are certainly important, but that does not appear clearly in this study.

The valve orientation is another risk already mentioned. In the mitral position, Westaby and colleagues [3] mentioned that it is not essential to give a particular orientation in the majority of patients. The principal aim is to preserve the mitral subvalvular apparatus and provide free motion of the leaflets [3, 15, 16]. The low profile of the ATS Open Pivot valve housing ensures minimal leaflet exposure and substantial posterior wall clearance when preserving the mitral subvalvular apparatus. In all cases, the mechanical valve was inserted perpendicularly with the native posterior leaflet kept in place, when possible, and we have not experienced restriction of leaflet mobility and rotation.

Preservation of the chordae and papillary muscles is more important for patients with degenerative mitral regurgitation than for patients with rheumatic disease, in which the annulus is fixed by the fibrotic process and left ventricular function is well preserved [17, 18]. In the presence of mild aortic regurgitation, Westaby and coworkers [3] recommend orientating the mitral prosthesis in the antianatomic configuration so that the regurgitant jets cannot limit the opening of the anterior leaflet.

The design of the ATS Open Pivot hinge also promotes particularly rapid leaflet closure with very low regurgitation and quiet valve closure sounds. In practice, the valve is inaudible, and past studies indicate that patients appreciate the quietness of this valve, which contributed considerably to their comfort [19, 20].

Van Nooten and colleagues [2] described well the first clinical experience with the ATS Open Pivot valve design in aortic and mitral positions. Our institution implanted its first ATS Medical valve in the mitral position in June 1992. Since then, we continue to implant this valve in the aortic and mitral positions and have been satisfied with its performance.

In conclusion, we believe the ATS Open Pivot mechanical heart valve in the mitral valve position provides good results in terms of hemodynamic performance and valve-related complications when patients target an INR range of 2 to 3 and supplement their regimen with 100 mg acetylsalicylic acid.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 References
 

  1. Emery RW, Van Nooten GJ, Tesar PJ. The initial experience with the ATS medical mechanical cardiac valve prosthesis Ann Thorac Surg 2003;75:444-452.[Abstract/Free Full Text]
  2. Van Nooten GJ, Caes F, François K. Clinical experience with the first 100 ATS heart valve implants Cardiovasc Surg 1996;4:288-292.[Medline]
  3. Westaby S, Van Nooten G, Sharif H. Valve replacement with the ATS open pivot bileaflet prosthesis Eur J Cardiothorac Surg 1996;10:660-665.[Abstract]
  4. Bernal JM, Rabasa JM, Gutierrez-Garcia F, Morales C, Nistal JF, Revuelta JM. The CarboMedics valveexperience with 1,049 implants. Ann Thorac Surg 1998;65:137-143.[Abstract/Free Full Text]
  5. Mehta RH, Bruckman D, Das S, et al. Implications of increased left ventricular mass index on in-hospital outcomes in patients undergoing aortic valve surgery J Thorac Cardiovasc Surg 2001;122:919-928.[Abstract/Free Full Text]
  6. Ageno W, Turpie AGG, Steidl L, et al. Comparison of a daily fixed 2.5-mg warfarin dose with a 5-mg, international normalized ratio adjusted, warfarin dose initially following heart valve replacement Am J Cardiol 2001;88:40-44.[Medline]
  7. Stein PD, Alpert JS, Bussey HI, Dalen JE, Turpie AGG. Antithrombotic therapy in patients with mechanical and biological prosthetic heart valves Chest 2001;119(1 Suppl):220S-227S.[Free Full Text]
  8. Horstkotte D, Scharf RE, Schultheiss HP. Intracardiac thrombosispatient-related and device-related factors. J Heart Valve Dis 1995;4:114-120.[Medline]
  9. Grunkemeier GL, Wu YX, Jin R. Statistical analysis of heart valve outcomes J Heart Valve Dis 2002;11(Suppl):S2-S7.
  10. Gohlke-Barwolf, Acar J, Oakley C, et al. Guidelines for prevention of thromboembolic events in valvular heart disease. Study Group of the Working Group on Valvular Heart Disease of the European Society of Cardiology?? Eur Heart J 1995;16:1320-1330.[Free Full Text]
  11. Stein PD, Alpert JS, Dalen JE, et al. Antithrombotic therapy in patients with mechanical and biological prosthetic heart valves Chest 1998;114(5 Suppl):602S-610S.[Abstract/Free Full Text]
  12. American College of Cardiology/American Heart Association ACC/AHA guidelines for the management of patients with valvular heart diseasea report of American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Patients with Valvular Heart Disease). J Am Coll Cardiol 1998;32:1486-1588.[Free Full Text]
  13. Turpie AGG, Gunstensen J, Hirsh J, et al. Randomized comparison of two intensities of oral anticoagulation therapy after tissue heart valve replacement Lancet 1988;1:1242-1245.[Medline]
  14. Turpie AGG, Gent M, Laupacis A, et al. A comparison of aspirin with placebo in patients treated with warfarin after heart-valve replacement N Engl J Med 1993;329:524-529.[Abstract/Free Full Text]
  15. David TE. Mitral valve replacement with preservation of chordae tendineaerationale and technical considerations. Ann Thorac Surg 1996;41:680-682.
  16. Miki S, Kushuhara K, Ueda Y, Koreda M, Ohkita Y, Tahta T. Mitral valve replacement with preservation of chordae tendineae and papillary muscles Ann Thorac Surg 1988;45:28-34.[Abstract]
  17. David TE, Burns RJ, Bacchus CM, Druck MN. Mitral valve replacement for mitral regurgitation with and without preservation of chordae tendineae J Thorac Cardiovasc Surg 1984;88:718-725.[Abstract]
  18. Kurzrok S, Sing AK, Most AS, Williams DO. Thrombolytic therapy for prosthetic cardiac valve thrombosis J Am Coll Cardiol 1987;9:592-598.[Abstract]
  19. Sezai A, Shiono M, Orime Y. Evaluation of valve sound and its effects on ATS prosthetic valves in patients’ quality of life Ann Thorac Surg 2000;69:507-512.[Abstract/Free Full Text]
  20. Shiono M, Sezai Y, Sezai A, et al. Multi-institutional experience of the ATS open pivot bileaflet valve in Japan Ann Thorac Cardiovasc Surg 1996;2:51-58.
  21. Emery RW, Van Nooten GJ, Tesar PJ. The initial experience with the ATS medical mechanical cardiac valve prosthesis Ann Thorac Surg 2003;75:444-452.
  22. Saour JN, Sieck JO, Mano LAR, et al. Trial of different intensities of anticoagulation in patients with prosthetic hearts valves N Engl J Med 1990;322:428-432.[Abstract]



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