Ann Thorac Surg 2006;82:853-857
© 2006 The Society of Thoracic Surgeons
Original article: Cardiovascular
Leaflet Movement of the ATS Valve in the Aortic Position: Unique Behavior Observed in 19-mm Valves
Shigeaki Aoyagi, MD*,
Koichi Arinaga, MD,
Shuji Fukunaga, MD,
Eiki Tayama, MD,
Tomokazu Kosuga, MD,
Hidetoshi Akashi, MD
Department of Surgery, Kurume University School of Medicine, Kurume, Japan
Accepted for publication April 25, 2006.
* Address correspondence to Dr Aoyagi, Department of Surgery (2), Kurume University School of Medicine, 67 Asahi-machi, Kurume 830-0011, Japan (Email: aoyagi{at}med.kurume-u.ac.jp).
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Abstract
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BACKGROUND: Leaflet opening angles of ATS valves in vivo tend to be less than those reported by the manufacturer, and there is a wide variation in opening angles even among valves of the same size.
METHODS: Leaflet movement of aortic ATS valves was evaluated by cineradiography in 77 patients. The mean period from valve replacement to cineradiography was 40.2 months, and during that period, the ATS valve was replaced due to prosthetic valve obstruction in 1 of the 77 patients.
RESULTS: In 76 patients with a normally functioning ATS valve, the mean opening angle of 19-mm valves (66.3° ± 2.3°) was significantly less (p < 0.0001) than that of ATS valves 21 mm or larger (72.2° ± 3.8° in 21-mm, 72.4° ± 2.8° in 23-mm, and 72.8° ± 2.9° in 25-mm valves). No significant differences were found in the opening angles of ATS valves 21 mm or larger, and the opening angles exceeded 65° in all 69 patients with valves in this category. In one case of obstruction in a 21-mm valve, the opening angle was 57.5°. The closing angle was 24.9° ± 1.3°, which corresponded well with the manufacturer's in vitro data.
CONCLUSIONS: The opening angle in the 19-mm ATS aortic valve is significantly less than that in valves 21 mm or larger, and an opening angle of less than 65° probably indicates prosthetic valve obstruction in aortic ATS valves sized 21 mm or larger.
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Introduction
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In an Advancing The Standard (ATS) (ATS Medical Inc, Minneapolis, MN) valve, leaflet movement is controlled by spherical convex pivot guides located on the inner circumference of the orifice ring, in contrast to the concave pivot guides in traditional bileaflet valves. ATS leaflet movement can easily be observed in vivo by cineradiography because of the 20% tungsten content of the pyrolytic carbon material. According to the manufacturer's data, the fully opened leaflets have an opening angle (defined as the angle between the leaflet and the orifice ring) of 85°.
Hemodynamic performance of the ATS valve is excellent; however, our cineradiographic study [1] has demonstrated that the leaflet opening of normally functioning ATS valves in vivo is less than that observed in vitro and reported by the manufacturer. Furthermore, a wide variation among the measured opening angles in valves of the same size is observed because of leaflet fluttering at the maximal opening position [2]. The most important clinical problem with this type of leaflet movement is differentiating normally functioning valves from malfunctioning valves. We recently used cineradiography and echocardiography to diagnose a case of obstruction of the aortic ATS valve that was later confirmed during a redo operation.
In this study, we clinically evaluate leaflet movement of ATS valves in the aortic position by cineradiography and discuss the diagnostic implications of cineradiography as a means of detecting obstruction of the aortic ATS valve.
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Patients and Methods
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This study was approved by the Ethics Committee of Kurume University School of Medicine in April 17, 2006, and the need for patient consent was waived. Between July 1996 and May 2005, 167 patients underwent aortic valve replacement (AVR) with the ATS valve at our hospital. Of these 167 patients, 77 patients annually or biannually visited our outpatient department and received simultaneous cineradiographic and echocardiographic evaluations of the ATS valve in the aortic position. These 77 patients form the basis of this study, and their clinical characteristics are summarized in Table 1. There were 47 men and 30 women with a mean age of 58.7 ± 10.4 years (range, 18 to 72 years). Valve lesions requiring AVR were regurgitation in 45 patients, stenosis in 17, mixed lesion in 10, and prosthetic valve failure in 5. The prosthetic valve size used was 19 mm in 7 patients, 21 mm in 19, 23 mm in 32, and 25 mm in 19. Concomitant operative procedures such as mitral valve replacement or repair, aortic root replacement, maze procedure, and coronary artery bypass grafting were performed in 39 patients at the time of AVR.
The mean period from AVR to the most recent cineradiographic examination was 40.2 ± 20.3 months (range, 4.6 to 76.6 months). The cardiac rhythm at the time of cineradiographic examinations was normal sinus rhythm in 68 patients, atrial fibrillation in 5, and pacing rhythm by an implanted pace maker in 4. One patient underwent replacement of the ATS valve for prosthetic valve obstruction 3 years after AVR [3].
The standard technique of cardiopulmonary bypass with moderate hypothermia was used, and antegrade and retrograde cold blood cardioplegia was routine. At AVR, the ATS valve was fixed in the supraannular position with pledgeted non-everting mattress sutures, and the pivot of the ATS valve was placed perpendicular to the septum.
Postoperative anticoagulant therapy, consisting of warfarin and a platelet inhibitor (acetylsalicylic acid, 100 mg/day), was usually instituted within 48 hours after the operation, and the international normalized ratio was kept at about 1.6 to 2.5.
Cineradiography and Echocardiography
Cineradiography was performed by the method we described previously [4] to obtain a tangential view of the implanted ATS valve. The opening and closing angles (in degrees) were calculated as the angle between the leaflet and the orifice ring in the fully open and closed positions, respectively, and in the cases showing asymmetric movement of two leaflets, two opening angles were averaged, as shown in Figure 1. According to the manufacturer's data, the opening and closing angles of the ATS valve are 85° and 25°, respectively. By design, both angles are the same for all sizes of ATS valves and for the aortic and mitral models.
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Fig 1. Cineradiograms show the ATS valve in the aortic position and measurements of opening (O) and closing angles (C).
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Two-dimensional echocardiography and Doppler echocardiography were performed using the method previously reported [1, 5]. The aortic dimension was measured in parasternal long-axis imaging planes in M-mode and two-dimensional echocardiograms. The velocity profiles across the ATS valve were obtained by placing the transducer in the apical position. For continuous-wave Doppler measurements, the transmitted beam was placed as close to perpendicular to the plane of the valve ring as possible.
Statistical Analysis
Data are expressed as mean values ± SD. Continuous variables were analyzed by the Student t test. We used correlation and simple regression tests to evaluate the correlation between the Doppler data and the opening angle. Values of p < 0.05 were considered to be statistically significant. Statistical analysis was performed with StatView 4.5 software (Abacus Concepts, Inc, Berkeley, CA).
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Results
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Cineradiographic Data
In the 76 patients with normally functioning ATS valves, the mean opening angles measured by cineradiography were 71.9° ± 3.5° (range, 63° to 80°) and closing angles were 24.9° ± 1.3° (range, 23° to 29°). The closing angle of the leaflets corresponded closely with the manufacturer's in vitro data; however, the opening angle in vivo was less than that reported by the manufacturer, as demonstrated in our previous study [1]. By valve size, the mean (range) opening angle was 66.3° ± 2.3° (63.0° to 69.0°) in 19-mm valves, 72.2° ± 3.8° (66.5° to 80.0°) in 21-mm valves, 72.4° ± 2.8° (68.0° to 77.5°) in 23-mm valves, and 72.8° ± 2.9° (68.5° to 80.0°) in 25-mm valves, as shown in Figure 2. The mean opening angle in 19-mm valves was significantly less (p < 0.0001) than that in 21-mm, 23-mm, and 25-mm valves, but no significant differences were found in the mean opening angles between 21-mm valves and 23-mm or 25-mm valves, or between 23-mm and 25-mm valves. In the 21-mm, 23-mm, and 25-mm ATS valves, the opening angles exceeded 65° in all 69 patients studied and exceeded 62.5° in the 19-mm valves.
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Fig 2. Opening angles measured by cineradiography in the 77 patients with an ATS valve. The dashed line represents an opening angle of 65°.
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Echocardiographic Data
Echocardiographic data obtained in the 76 patients are summarized in Table 2. As a whole, prosthetic valve orifice area indexed to body surface area (EOAI) was 1.10 ± 0.27 cm2/m2 (range, 0.61 to 1.76 cm2/m2). The mean ratio of the aortic dimension to the orifice ring diameter of the ATS valve designed by the manufacture was 1.94 ± 0.20 in 19-mm valves, 1.85 ± 0.24 in 21-mm valves, 1.83 ± 0.25 in 23-mm valves, and 1.74 ± 0.27 in 25-mm valves. This ratio was larger in the smaller-sized ATS valves, but no statistically significant differences were seen between any of the four ATS valve sizes. No significant correlation was found between the opening angle and any of the echocardiographic data.
Data in Prosthetic Valve Obstruction
Obstruction of the aortic ATS valve occurred in a patient with a 21-mm valve [3]. In the period immediately after AVR, Doppler echocardiography revealed a peak velocity of 2.32 m/s, a mean pressure gradient of 12.3 mm Hg, and EOAI of 1.42 cm2/m2. Three years later, in addition to the appearance of a loud systolic murmur, Doppler data showed a peak velocity of 3.63 m/s, a mean pressure gradient of 33.4 mm Hg, and EOAI of 0.95 cm2/m2. At that time, the opening angle of the ATS valve was 57.5°, and the closing angle was 24.5° on cineradiograms (Fig 3A,
3B). In this patient, overgrown pannus without thrombus on the left ventricular aspect of the valve was the cause of valve obstruction, as determined at the redo operation (Fig 3C, 3D).
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Fig 3. Leaflet movement in the case of obstruction of the ATS valve and the resected overgrown pannus. (A) Opening angle is 57.5°, (B) closing angle is 131°. (C) An operative photograph (surgeon's view) shows overgrown pannus (arrows) on the ventricular aspect of the ATS valve. (D) The resected overgrown pannus.
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Comment
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This study has clinically demonstrated that leaflet movement in the 19-mm valve is significantly different from that in valves 21 mm or larger, and that an opening angle of less than 65° on cineradiograms probably indicates prosthetic obstruction in aortic ATS valves, except in the 19-mm valve.
The distinctive characteristic of the ATS valve is its open pivot design, in which the leaflet pivot point and stops are all convex and located on the inner circumference of the orifice. According to the manufacturer's data, the fully opened leaflets of the ATS valve have an opening angle of 85°. However, the opening of the normally functioning ATS valves in vivo is less than that observed in vitro and reported by the manufacturer [1]. As for the mechanisms of in vivo leaflet movement of the ATS valve, we have demonstrated that leaflet movement behavior is affected significantly by the configuration at the outlet of the ATS valve, especially when there is an abrupt enlargement, because leaflet movement responds to the divergent streamline from the axis of the conduit [6].
Feng and colleagues [2, 7] have experimentally shown that in addition to the divergent downstream flow, a local flow field induced by the unique open pivot, referred to as the pivot effect, also influences leaflet opening in the ATS valve. The leaflets open because of a pressure differential between the two sides of the leaflet; however, in the open position, the pivot effect generates a force that acts in the opposite direction. The resulting pressure field across the valve produces a moment that prevents the valve from opening fully. Furthermore, in the abrupt enlargement outflow configuration, the opening moment decreases rapidly as the ratio of enlargement increases, which is defined as the ratio between the enlargement diameter at the outlet to the orifice ring diameter of the ATS valve [7].
The aortic dimension measured by echocardiography does not directly correspond to the dimensions of the sinus of Valsalva; however, the diameter of the ascending aorta is very close to that of the sinus of Valsalva (0.81 to 0.87:1) [8]. In this study, the ratio of the aortic dimension to the orifice ring diameter of the ATS valves used was larger in the smaller-sized ATS valves, but no statistically significant differences were seen between any of the four different valve sizes. Nevertheless, the opening angles in 19-mm valves were significantly less than those in the valves 21 mm or larger. These results suggest that the reverse moment induced by the pivot effect is stronger in the 19-mm valve compared with that in the valves 21 mm or larger. Indeed, Feng and colleagues [9] have experimentally demonstrated that the small-sized ATS valve has a stronger pivot effect because although the orifice diameter is smaller, the size of the open pivot remains unchanged.
In the present study, the pivot size, defined as pivot proportion [9], was calculated to be 11.5% in the 19-mm valves (Fig 4). The pivot proportion in the 19-mm valve was relatively large compared with the 7.7% to 9.5% in the 21-mm to 25-mm valves. According to these data, a strong pivot effect due to the relatively large size of the open pivot is probably the mechanism that restricts the maximal opening angle in the 19-mm valves compared with that in the valves 21 mm or larger.
Cineradiography and echocardiography are reliable techniques to detect malfunction, particularly obstruction, of prosthetic valves [1, 4, 10], because cineradiography provides information about leaflet movement and echocardiography gives information on the hydrodynamic performance. In contrast to traditional bileaflet valves with concave pivot guides, in which the leaflets open in any outflow configuration [2], the leaflets did not fully open in vivo even in the normally functioning ATS valves, and a wide variation was observed in the measured opening angles of valves of the same size. These facts suggest that detection of prosthetic valve obstruction by cineradiography alone would be very difficult in patients with the ATS valve. The results of this study indicate that a combination of echocardiography and cineradiography is essential for early detection and correct diagnosis of prosthetic valve obstruction in the ATS valve.
In conclusion, we evaluated the opening angles of the leaflets in normally functioning ATS valves in the aortic position by cineradiography, and we also examined the cineradiographic and echocardiographic findings in a case of obstruction of the aortic ATS valve. Leaflet opening in the 19-mm valve is significantly less than that in valves 21 mm or larger, and an opening angle of less than 65° on cineradiograms probably indicates prosthetic valve malfunction in aortic ATS valves 21 mm or larger.
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References
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- Aoyagi S, Kawara T, Fukunaga S, et al. Cineradiographic evaluation of ATS open pivot bileaflet valves J Heart Valve Dis 1997;6:258-263.[Medline]
- Feng Z, Nakamura T, Fujimoto T, Umezu M. In vitro investigation of opening behavior and hydrodynamics of bileaflet valves in the mitral position Artif Organs 2002;26:32-39.[Medline]
- Teshima H, Aoyagi S, Hayashida N, et al. Dysfunction of an ATS valve in the aortic positionthe first reported case caused by pannus formation. J Artif Organs 2005;8:270-273.[Medline]
- Aoyagi S, Higa Y, Matsuzoe S, et al. Obstruction of the St. Jude Medical valve—diagnostic and therapeutic values of cineradiography Thorac Cardiovasc Surg 1993;41:357-363.[Medline]
- Aoyagi S, Yasunaga H, Sato H, et al. Doppler echocardiographic evaluation of the St. Jude Medical valve Artif Organs Today 1995;5:49-57.
- Tayama E, Feng Z, Oda T, et al. ATS prosthetic valve motionan in vitro analysis. J Heart Valve Dis 2000;9:408-414.[Medline]
- Feng Z, Umezu M, Fujimoto T, et al. Analysis of ATS leaflet behavior by in vitro experiment J Artif Organs 1999;2:46-52.
- Kunzelman KS, Grande KJ, David TE, Cochran RP, Verrier ED. Aortic root and valve relationships. Impact on surgical repair J Thorac Cardiovasc Surg 1994;107:162-170.[Abstract/Free Full Text]
- Feng Z, Nakamura T, Fujimoto T, Umezu M. Influence of valve size on the hydrodynamic performance of the ATS valve J Artif Organs 2001;4:303-307.
- Aoyagi S, Nishimi M, Kawano H, et al. Obstruction of St. Jude Medical valves in the aortic positionSignificance of a combination of cineradiography and echocardiography. J Thorac Cardiovasc Surg 2000;120:142-147.[Abstract/Free Full Text]
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Abstract
Introduction
