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Ann Thorac Surg 2003;75:444-452
© 2003 The Society of Thoracic Surgeons

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Original article: cardiovascular

The initial experience with the ATS Medical mechanical cardiac valve prosthesis

^a Cardiac Surgical Associates, Minneapolis, Minnesota, USA
^b University Hospital, Gent, Belgium
^c The Prince Charles Hospital, Brisbane, Queensland, Australia

Accepted for publication July 26, 2002.

* Address reprint requests to Dr Emery, 920 East 28th St, Suite 420, Minneapolis, MN 55407, USA
e-mail: remery{at}csa-heart.com

	Abstract

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
BACKGROUND: From May 1994 through October 2000, a total of 1,146 patients underwent valve replacement with the ATS Medical mechanical cardiac valve prosthesis under a study protocol approved by international ethics committees (non–United States participants) or under a United States Food and Drug Administration–approved Investigational Device Exemption study. The study took place at 19 domestic and three international centers.

RESULTS: Aortic valve replacement (AVR) was conducted in 801 patients (309 with coronary bypass) and mitral valve replacement (MVR) in 345 patients (78 with coronary bypass). Overall operative ( 30 days post implant) mortality was 2.1% (17 AVR = 2.1%, 7 MVR = 2.0%), 7 of which (AVR = 4, MVR = 3) were valve related. In 2,086 patient-years (1,459 AVR patient-years, 627 MVR patient-years) of follow-up, there were an additional 50 patient deaths of these, 18 were valve related, 9 due to anticoagulant related bleeding, 5 sudden/unexplained, and 1 each after stroke, thrombosis, prosthetic valve endocarditis, and thromboembolism. Late (>30 days post implant) valve-related complications included: transient and chronic thromboembolism (27 AVR (linearized rate 1.85%/patient-year) and 20 MVR (3.19%/patient-year), of which 11/47 (0.53%/patient-year) had chronic deficits, thrombosis (1 AVR = 0.07%/patient-year and 4 MVR = 0.64%/patient-year), paravalvular leak (10 AVR = 0.69%/patient-year and 8 MVR = 1.28%/patient-year), anticoagulant related hemorrhage (34 AVR = 2.33%/patient-year and 8 MVR = 1.28%/patient-year), prosthetic valve endocarditis (3 AVR = 0.21%/patient-year and 2 MVR = 0.32%/patient-year), and structural valve failure or dysfunction (0%). Echocardiographic gradients were proportional to valve size and did not significantly change over the follow-up period.

CONCLUSIONS: This study documented the ATS Medical mechanical cardiac valve prosthesis to be a valuable addition to the surgeon’s armamentarium in the treatment of cardiac valvular disease.

	Introduction

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
The all–pyrolytic carbon bileaflet design of prosthetic mechanical heart valves was introduced clinically in 1977 and is the dominant model being implanted [1]. The bileaflet design represented a radical departure from other valve models and markedly improved hemodynamics. Despite global acceptance and improvement in short- and long-term outcomes, valve-related problems remain and suggest the need for refinement of design and construction [2]. Advances in pyrolytic carbon–coating technology have allowed a new bileaflet valve design, the ATS Open Pivot Bileaflet Mechanical Heart Valve Prosthesis (ATS Medical, Inc, Minneapolis, MN) to be introduced to address these issues (Fig 1). These developments in pyrolytic carbon–coating technology, coating over a mandrel, allowed design features not available in other bileaflet valves. The ATS prosthesis thus differs from other bileaflet models in that there are no cavities in the valve ring in which stasis or eddy currents may develop; rather, the valve leaflets hinge on convex pivot guides on the pyrolytic carbon orifice ring. This allows a low profile with no cavities in the region of the pivot area. The pivot guides are fully exposed to blood so there is transcyclical washing of the leaflets. The sewing cuff is mounted on a titanium ring allowing rotation during implantation and radiopacity for easy visualization by roentgenography. The leaflets also contain 20% tungsten for radiopacity. Valve noise is a bothersome problem for some patients [3]. Phonocardiographic studies have indicated less valve noise when compared to other bileaflet mechanical valve prostheses, thus improving patients’ quality of life. In early studies, theoretical flow models demonstrated that there was a potential for lower valve-related complications [4–6]. Low complication rates have been documented in a randomized trial confirming these results [7]. The ATS valve was first investigated in this study outside the United States in May 1994. After a significant accumulation of worldwide experience, the US studies began with the first implant in January 1997 under an investigational device exemption from the US Food and Drug Administration (FDA). This study was scrutinized by the investigators, the Data Safety Monitoring Board (DSMB), and FDA investigators with comprehensive data submissions to the FDA. Investigators and investigating centers for this study were selected for their ability to meet the study criteria and to perform the extended follow-up as required by the study. A complete list of principal investigators and investigating centers is found in Table 1.

View larger version (67K): [in this window] [in a new window]   Fig 1. (A) Line drawing and (B) photographs of the ATS Medical mechanical cardiac valve prosthesis with the leaflet in the open position. Note the convex pivot area, which is different from other bileaflet valves; this configuration is related to advances in pyrolytic carbon coating.

	Material and methods

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

Surgical techniques
Operative procedures were typically conducted on cardiopulmonary bypass (CPB) via midline sternotomy using a centrifugal pump and membrane oxygenation. Cardioplegic solution of blood or crystalloid was surgeon specific and used in all cases. In coronary artery bypass graft (CABG) patients, vein grafts were most commonly performed first, followed by valve replacement. Internal mammary artery grafting was conducted last. For valve replacement, the interrupted mattress suture technique with braided suture was most commonly used. Of the 801 aortic valve implantations, 204 (25%) used the newer Advanced Performance (AP) series. In this modification, materials used and the primary design and manufacture of the standard valve were unchanged. Redesigned, the AP model reduces the external sewing cuff bulk and reduces the titanium outer ring from within the tissue annulus. Using the AP modification, a larger valve size or geometric flow orifice area may be implanted into any given annulus diameter. This translates into an increase in geometric flow orifice area for any given tissue annulus diameter and, theoretically, lower pressure gradients across the valve size implanted. The patient benefits from the internal orifice area of a 3-mm larger valve size. For example, a 20-mm tissue annulus diameter AP valve has the same size geometric flow orifice as a 23-mm standard tissue annulus diameter. In the majority of patients, subcutaneous heparin (5,000 units every 8 hours) was administered starting on postoperative day 1 until the INR on oral anticoagulation reached therapeutic levels. Oral anticoagulation therapy with warfarin sodium with or without aspirin was used to maintain appropriate INR levels and was recommended in all patients.

Statistical analysis
Continuous variables are reported as the mean ± standard deviations. Survival rates were calculated using nonparametric actuarial Kaplan-Meier calculations. Linearized rates are expressed in percent per patient year. The SPSS statistical software package (SPSS, Chicago, IL) was used for data analysis.

	Results

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Over the 77 months of the study, 1,146 patients (695 male and 451 female) were enrolled, with a total follow-up of 2086 patient years (1459 AVR and 627 MVR). Mean patient age at the time of implant was 61 ± 14 years. Mean follow-up time was 22 ± 16 months and follow-up was 95% complete. Aortic valve replacement was performed in 801 or 70% of the total group and MVR in 345 (30%) patients. Patient demographics are shown in Table 3. Combined procedures were completed including CABG (n = 387, 34%) and others (n = 209, 18%). Pre- and postoperative (1 year) NYHA classifications are shown in Table 4.

View larger version (15K): [in this window] [in a new window]   Fig 2. Freedom from valve-related deaths in patients undergoing aortic valve replacement (AVR) or mitral valve replacement (MVR), with the ATS Medical mechanical cardiac valve prosthesis of up to 5 years follow-up.

View larger version (16K): [in this window] [in a new window]   Fig 3. Anticoagulant-related hemorrhage in patients undergoing aortic valve replacement (AVR) or mitral valve replacement (MVR) with the ATS Medical mechanical cardiac valve prosthesis of up to 5 years follow-up.

View larger version (16K): [in this window] [in a new window]   Fig 4. Thromboembolism in patients undergoing aortic valve replacement (AVR) or mitral valve replacement (MVR) with the ATS Medical mechanical cardiac valve prosthesis of up to 5 years follow-up.

Prosthetic valve endocarditis
Seven patients were diagnosed with endocarditis. Two patients experienced early events, one completely resolved with antibiotic treatment. The other patient died on postoperative day 20 of cardiac arrest; this was also the day of discovery of the endocarditis, and therefore no treatment had been provided. Of the 5 late events, 3 resolved completely on antibiotic therapy and 2 required explantation. Freedom from prosthetic valve endocarditis at 5 years is 99% AVR and 99% MVR (Table 6).

Valve thrombosis
One patient developed a valve thrombosis in the aortic position. Three patients developed 4 cases of valve thrombosis in the mitral position. One mitral valve patient died as the result of a cardiac arrest, which related to the valve thrombosis. Event rates for valve thrombosis are AVR 0.07%/patient-year and MVR 0.64%/patient-year. Freedom from thrombosis is 0.9985 ± 0.00 and 0.9885 ± 0.02 (5-year Kaplan-Meier) for AVR and MVR, respectively (Table 7).

Valve failure or dysfunction
There was no structural valve failure or dysfunction. Freedom from structural failure or dysfunction was 100% for AVR and MVR at 5 years (Table 6).

Explantation
Six patients (1 early, 5 late; AVR linearized rate = 0.21%/patient-year, MVR = 0.56%/patient-year) underwent explantation of the ATS valve during the course of the study. Three aortic patients experienced late events, 1 due to perivalvular leak and 2 due to endocarditis. One patient receiving a mitral valve had the ATS valve explanted 12 days postoperatively. The valve was replaced with a tissue valve to eliminate the need for anticoagulation in preparation for a heart transplant. Two mitral patients experienced valve thrombosis late; these also led to explantation. Freedom from explant is 99% AVR at 5 years and 99% MVR (Table 7).

NYHA functional classification
Aortic patients with a NYHA classification of I or II increased from 40% preoperatively to 98% at 1-year postimplantation. Mitral valve patients improved from 27% preoperatively compared to 96% at 1 year postimplantation, respectively. Postoperative change from preoperative NYHA classification is summarized in Table 4.

Echocardiographic follow-up
Echocardiographic follow-up results are shown by size in Table 8 for aortic standard and aortic AP valves and for mitral valves. At 1-year follow-up examination, the mean aortic gradient was 12 ± 7 mm Hg (range 1.04 to 65.8 mm Hg). There was a trend toward decreased mean gradients at 1 year. Mean gradients of both AVR and MVR were inversely related to valve size. Calculated valve effective orifice area is also included in the tables.

	Comment

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

This design also offers quieter closure sounds documented phonocardiographically. Historically, the St. Jude Medical Prosthesis has scored the lowest decibel readings. However, it has been demonstrated that the ATS valve has an even lower closing sound [3, 12]. The medical literature has documented the untoward effects of valve noise on patient quality of life [12]. Patients often report that they find the sound produced by their heart valve to be disturbing both to themselves and to those around them. The ATS leaflets pivot on semispheres projecting into the valve orifice rather than leaflets that pivot on "ears" inserted into cavities in the valve orifice, as with other bileaflet valve designs. These design differences contribute to different noise levels. Sezai and colleagues [3] reported 46% of patients with the St. Jude Medical Heart Valve (St. Jude Medical, Little Canada, MN) reported disturbances associated with the valve sound 1 month postoperatively, compared to 0% of patients with the ATS valve. In this study, less than 5% of the patients reported disturbances related to the sound of their valve (disturbing from time to time or frequently disturbing).

Mechanical valve prostheses offer the advantage of longevity after native valve replacement, yet there is a life-long need for anticoagulation. The incidence of prostheses-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 [13–16]. The current study was conducted with a closely followed population, with follow-up totaling 2,086 patient-years. Investigating centers were specifically chosen for their ability to conduct intensive follow-up screening. Even minor events in patient follow-up, including such events as dizziness (due to TE) and bruising (due to ARH), were considered valve-related events. Importantly, most TE events were minimal: 48/64 (75%) were transient. Mortality and disability were very low. Data are also accumulating that patient-related factors rather than valve-related factors may be more important in TE risk [17, 18]. Thus, the target INR should be individualized rather than grouped for valve replacement situs per se. The incidence of ARH was higher than the incidence of TE. There were 32 minor and 55 major events, indicating room for continued improvement in reducing INR levels, particularly in patients without risk factors for TE such as regional wall motion abnormalities, depressed ejection fraction, or atrial fibrillation. Regarding the ARH events, surprisingly, there was a higher incidence in AVR patients, and events could not be correlated with the level of INR.

Importantly, improvements in the management of anticoagulation are ongoing. Patient self-monitoring devices have been recently approved by the FDA and funded by United States Medicare. Horstkotte and colleagues [19, 20] reported patients in the therapeutic range for INR a higher percentage of the time when self-testing was used, especially important as they also noted that the VRE occurred during swings in INR levels as opposed to stable INR levels. In a prospective randomized trial, Sidhu and O’Kane [21] reported improved results in patients that self tested. The addition of low-dose aspirin may also allow for lower target INR levels [10]. There are growing data that there is no difference in anticoagulant related complications in elderly as compared to younger heart valve patients; therefore, the requirements for anticoagulants in conditions such as atrial fibrillation may serve as an indication for the use of an easily implantable durable valve such as the ATS prosthesis in selected older patients [22–24]. Khan and colleagues [25] have also demonstrated that the risk of TE is similar between mechanical and bioprostheses over 20 years.

Prior studies completed out of the US revealed similar excellent performance in terms of valve-related complications [4, 5, 26]. Valve-related complications may also be more common during the first year of patient follow-up [6], and the maximal time of follow-up in this initial experience is relatively short (mean 22 ± 16 months, range 0 to 67 months). The mean mitral gradient seen in our patient group with valves of 27–33 mm is similar to that reported previously with earlier series evaluating the ATS, St. Jude Medical, and Medtronic-Hall mechanical valve prostheses [4, 5]. Similarly, aortic gradients are consistent with those reported previously for the St. Jude Medical prosthesis [4, 27].

Echocardiographic gradients were proportional to valve size as expected (Table 8). Occasionally, in smaller prostheses, higher gradients were noted. Echocardiography measures velocity, not gradients, and velocity wave depending on the flow orifice intergraded. Velocity measured is the central orifice of a bileaflet valve consistently higher than that of the lateral orifices and higher than simultaneously obtained catheter gradients [28]. This may explain why in smaller prostheses, effective orifice area calculated by the continuity equation is lower clinically, whereas that measured in vitro due to the greater difficulty in orifice integration.

Long-term data on the ATS valve are not available, but others have reported excellent long-term results with bileaflet mechanical valves [25, 29]. At 10 years, survival is similar between patients having aortic or mitral mechanical or bioprostheses; yet, even this follow-up may be too short, as the incidence of bioprosthetic valve failure steepens at 12 to 18 years and is incremental. Khan and colleagues [25] and others [30, 31] have shown that over 20 years, the VRE rate favors mechanical prostheses.

Although follow-up has been short, there has been no postoperative structural failure of the ATS valve. In fact, in more than 50,000 implants worldwide to date, there have been no reported postoperative structural failures (personal communication, Manny Villafana, 2001, ATS Medical). The ATS valve is a new addition to the armamentarium for the cardiac surgeon. Although early overall valve-related complications are similar to other bileaflet prostheses, most events were of minor significance. This valve design offers the opportunity to individualize anticoagulant therapy for patients with no risk factors for TE to be managed at lower INR levels and add low-dose aspirin for patients with low risk factors for TE. Decreased valve sound will provide improvement for patient quality of life. Studies to modify anticoagulation toward lower intensity are warranted.

	Acknowledgments

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
The authors acknowledge the invaluable assistance of Ronda Isakson, whose meticulous data gathering and correlation made the construction of this manuscript possible. We also thank Drs Thomas Knickelbine, Terrence Longe, Kevin Harris, and Peter Stokeman for their assistance in assessment and correlation of echocardiographic data; Carla Erickson, RN, MS, Director of the Cardiac Surgical Associates Research Foundation; and Jean Sherman, RDS, cardiac sonographer, for her valuable contributions.

	Footnotes

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
^* A complete list of Investigators for the ATS Clinical Open Pivot Heart Valve Food and Drug Administration Study is provided in Table 1.

	References

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Robert W. Emery Guido J. Van Nooten Peter J. Tesar Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Emery, R. W. Articles by Tesar, P. J. Search for Related Content PubMed PubMed Citation Articles by Emery, R. W. Articles by Tesar, P. J. Related Collections Valve disease