On-X Valve Research Articles

Dynamic particle image velocimetry study of the aortic flow field of contemporary mechanical bileaflet prostheses

The characteristics of mechanical bileaflet valves, the leaflets of which open at the outside first, differ significantly from those of natural valves, whose leaflets open at the center first, and this fact affects the flow field down-stream of the valves. The direction of jet-type flows, which is influenced by this difference in valve features, and the existence of the sinus of Valsalva both affect the flow field inside the aorta in different ways, depending on the valve design. There may also be an influence on the coronary circulation, the entrance to which resides inside the sinus of Valsalva. A dynamic particle image velocimetry (PIV) study was conducted to analyze the influence of the design of prosthetic heart valves on the aortic flow field. Three contemporary bileaflet prostheses, the St. Jude Medical (SJM) valve, the On-X valve (with straight leaflets), and the MIRA valve (with curved leaflets), were tested inside a simulated aorta under pulsatile flow conditions. A dynamic PIV system was employed to analyze the aortic flow field resulting from the different valve designs. The two newer valves, the On-X and the MIRA valves, open more quickly than the SJM valve and provide a wider opening area when the valve is fully open. The SJM valve's outer orifices deflect the flow during the accelerating flow phase, whereas the newer designs deflect the flow less. The flow through the central orifice of the SJM valve has a lower velocity compared to the newer designs; the newer designs tend to have a strong flow through all orifices. The On-X valve generates a simple jet-type flow, whereas the MIRA valve (with circumferentially curved leaflets) generates a strong but three-dimensionally diffuse flow, resulting in a more complex flow field downstream of the aortic valve. The clinically more adapted 180 degrees orientation seems to provide a less diffuse flow than the 90 degrees orientation does. The small differences in leaflet design in the bileaflet valves generate noticeable differences in the aortic flow; the newer valves show strong flows through all orifices.

Correlation between ventricular flow field and valve closing sound of mechanical mitral prostheses

The Jyros (JR) valve and the newer On-X and MIRA valves, all installed antianatomically, were compared with the St. Jude Medical (SJM) valve in the mitral position to study the effects of valve design differences on the down-stream flow field and the associated valve closing sound. The dynamic particle image velocimetry method utilizing a high-speed video flow visualization technique was used to map the velocity field, and wavelet analysis of the sound was used to find the correlation between the ventricular flow field and the valve closing sound. Based on the experimental data, the following general conclusions can be made. In the velocity field directly below the mitral valve, where the distinct characteristic differences of the valve designs will be evident, twin symmetrical circulations were observed due to the divergent nature of the flow generated by the two inclined half-disks with the valve installed in the anti-anatomical orientation; the SJM, the On-X, and the MIRA valves generated a centrally downward circulation that opposed the valve leaflet closing movement, and resulted in relatively loud valve closing sounds.

Four-dimensional evaluation of implanted mechanical valve with 64-row multi-detector computed tomography

Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ejcts.2007.02.008. Fig. 1. The view of On-X valve from ascending aorta in systole and diastole. Surface of the mechanical valve leaflets could be seen clearly without contrast medium. They opened symmetrically and the opening angle of this artificial valve was appropriate. Fig. 2. The motion of the left ventricle and mechanical valve motion could be evaluated simultaneously.

Repair of Recoarctation and Aortic Valve Replacement with the On-X Valve in a Pediatric Patient: A Case Report

A 10-year-old boy had undergone conventional two-stage surgery that included repair of aortic coarctation with pulmonary artery banding as an initial operation followed by closure of a ventricular septal defect as a secondary procedure. Following these procedures, aortic coarctation recurred, and balloon angioplasty was performed three times. Aortic recoarctation, however, persisted, and aortic stenosis and regurgitation and pulmonary stenosis gradually developed. An operation was therefore performed to repair recoarctation, aortic stenosis and regurgitation, and pulmonary stenosis. Patch aortoplasty was performed for recoarctation. The aortic valve was replaced with a 19 mm On-X valve, with Konno root enlargement. Pulmonary arterial patch plasty was also performed. During aortic arch reconstruction, selective cerebral perfusion was performed via the innominate artery and left carotid artery, and the lower half of the body was perfused through a cannula in the left femoral artery. The postoperative course was uneventful, and aortography revealed a well-reconstructed aortic arch free of obstruction. There were no valve-related complications.

Multicentered European Study on Safety and Effectiveness of the On-X Prosthetic Heart Valve: Intermediate Follow-Up

This study was performed to determine the safety and effectiveness of the On-X valve, a novel mechanical valve substitute. Eleven centers participated in a European, multicentered, longitudinal, nonrandomized study of the On-X valve performance. Isolated aortic or mitral valve replacement with an On-X valve was studied in 301 patients. Aortic valve replacement was performed in 184 patients (average follow-up, 5.0 years), whereas mitral valve replacement was performed in 117 patients (average follow-up, 4.4 years). In patients with aortic valve replacement, mean transvalvular pressure gradients ranged from 8.3 to 4.7 mm Hg and effective orifice areas from 1.5 to 2.7 cm2, for 19-mm through 25-mm valves, respectively. After mitral valve replacement, mean gradient was 4.2 mm Hg and effective orifice area by pressure half-time was 2.6 cm2 regardless of valve size. Hemolysis was low, with postoperative serum lactate dehydrogenase at 225 +/- 41 IU (mean +/- standard deviation) or 253 +/- 65 IU, after aortic valve replacement or mitral valve replacement, respectively (upper normal value, 250 IU). At 1 year or greater postoperatively, 91.6% of patients after aortic valve replacement and 84.6% after mitral valve replacement were in New York Heart Association functional class I or II. Adverse event rates in percent per patient-year after aortic valve replacement or mitral valve replacement were thromboembolism, 0.88 or 1.76; thrombosis, 0.11 or 0.20; bleeding, 0.77 or 1.96, respectively. Late mortality was 1.97% or 2.55%, respectively. At the intermediate follow-up, the On-X valve exhibited improved hemodynamics, low hemolysis with in-range lactate dehydrogenase, and low adverse event rates, particularly in the aortic position.

Dynamic particle image velocimetry flow analysis of the flow field immediately downstream of bileaflet mechanical mitral prostheses

New dynamic particle image velocimetry (PIV) technology was applied to the study of the flow field associated with prosthetic heart valves. Four bileaflet prostheses, the St. Jude Medical (SJM) valve, the On-X valve with straight leaflets, the Jyros (JR) valve, and the Edwards MIRA (MIRA) valve with curved leaflets, were tested in the mitral position under pulsatile flow conditions to find the effect of the leaflet shape and overall valve design on the flow field, particularly in terms of the turbulent stress distribution, which may influence hemolysis, platelet activation, and thrombus formation. Comparison of the time-resolved flow fields associated with the opening, accelerating, peak, and closing phases of the diastolic flow revealed the effects of the leaflet shape and overall valve design on the flow field. Anatomically and antianatomically oriented bileaflet valves were also compared in the mitral position to study the effects of the orientation on the downstream flow field. The experimental program used a dynamic PIV system utilizing a high-speed, high-resolution video camera to map the true time-resolved velocity field inside the simulated ventricle. Based on the experimental data, the following general conclusions can be made. High-resolution dynamic PIV can capture true chronological changes in the velocity and turbulence fields. In the vertical measuring plane that passes the centers of both the aortic and mitral valves (A-A section), bileaflet valves show clear and simple circulatory flow patterns when the valve is installed in the antianatomical orientation. The SJM, the On-X, and the MIRA valves maintain a relatively high velocity through the central orifice. The curved leaflets of the JR valve generate higher velocities with a divergent flow during the accelerating and peak flow phases when the valve is installed in the anatomical orientation. In the velocity field directly below the mitral valve and normal to the previous measuring plane (B-B section), where characteristic differences in valve design on the three-dimensional flow should be visible, the symmetrical divergent nature of the flow generated by the two inclined half-disks installed in the antianatomical orientation was evident. The SJM valve, with a central downward flow near the valve, is contrasted with the JR valve, which has a peripherally strong downward circulation with higher turbulent stresses. The On-X valve has a strong central downward flow attributable to its large opening angle and flared inlet shape. The MIRA valve also has a relatively strong downward central flow. The MIRA valve, however, diverts the flow three-dimensionally due to its peripherally curved leaflets.

The disk of bileaflet mechanical mitral valve prosthesis jammed by ruptured papillary muscle

The disk of bileaflet mechanical mitral valve prosthesis jammed by ruptured papillary muscle

Early clinical experience with the On-X prosthetic heart valve

The study aimed to assess the performance of the On-X valve (Medical Carbon Research Institute, Austin, TX). Between December 2000 and January 2003 On-X valves were implanted in 400 patients aged 19-85 years (mean: 55.6+/-16), 290 males and 210 females. There were 120 cases of aortic valve replacement (AVR), 258 mitral valve replacement (MVR) and 22 combined aortic and mitral valve replacement (DVR). Additional procedures were performed in 144 patients. Patients were followed up prospectively at 3- to 6-month intervals. Mean follow-up was 38.4+/-11.8 months (maximum 55.6 months). Overall hospital mortality was 3.5%. Freedom from adverse events at 4 years in the study were as follows: thromboembolism, 99.1% for AVR, 98.3% for MVR and 94.7% for DVR patients; thrombosis, 100% for AVR, 99.2% for MVR and 94.7% for DVR; bleeding events, 99.1% for AVR, 99.2% for MVR and 88.8% for DVR; prosthetic endocarditis, 98.2% for AVR, 99.2% for MVR and 94.7% for DVR. Overall survival at 4 years was 92+/-1%. At echocardiographical examination within 1 year of the AVR, the mean aortic valve gradient was 12.8+/-6, 10.3+/-3, 9.0+/-4, 8.3+/-3, and 6.2+/-3 mmHg for 19, 21, 23, 25, 27/29 mm valve sizes, respectively. MVR mean gradient was 4.9+/-2, 4.5+/-1.2 and 4.0+/-0.8 mmHg for 25, 27/29, 31/33 mm valve sizes, respectively. On-X valve is a highly effective mechanical valve substitute with low morbidity and mortality and good functional results.

A randomized comparison of the MCRI On-X and CarboMedics Top Hat bileaflet mechanical replacement aortic valves: Early postoperative hemodynamic function and clinical events

This study compared hemodynamic function and clinical events in consecutive patients randomly assigned to receive a wholly supra-annular replacement valve or a valve with an intra-annular component. Fifty-two patients with an average age of 62 years (range 40-74 years) were sized for both a CarboMedics Top Hat valve (CarboMedics Inc, Austin, Tex) and an MCRI On-X valve (Medical Carbon Research Institute, LLC, Austin, Tex) before random assignment to receive either valve type. Echocardiographic and clinical assessments were performed in the immediate postoperative period and at 1 year. The mean effective orifice areas were 1.41 +/- 0.42 cm2 for the Top Hat and 2.17 +/- 0.78 cm2 for the On-X (P < .0001). The mean pressure differences were 12.2 +/- 4.4 mm Hg and 6.9 +/- 3.6 mm Hg, respectively (P < .0001). New York Heart Association functional class was better with the On-X than the Top Hat valves, but there were no differences in clinical events, regression of left ventricular mass, or measures of hemolysis. The partially intra-annular MCRI On-X valve was hemodynamically superior to the wholly supra-annular CarboMedics Top Hat valve. However, there were no differences in early clinical outcomes between the two valve types.

A207 Dynamic PIVによる機械的人工心臓僧帽二葉弁まわりの流れ解析

Three bi-leaflet prostheses (St. Jude Medical, Jyros and On-X valve), were tested in the mitral position under the pulsatile-flow condition. The Dynamic PIV system was employed to analyze the flow field affected by the leaflet shapes and valve designs. The Dynamic PIV system allows to acquire 1000 time-varying velocity fields at 1kHz by using Nd:YLF laser, which is synchronized with a high resolution camera (1024×1024 pixel). Detailed chronological comparison of the flow fields associated with the opening, accelerating, peak and closing phase of the flow revealed the significance of the leaflet and overall valve designs on the flow field. The small difference in leaflet configuration in the bi-leaflet prostheses generates noticeable differences on the flow.

892 Diagnostic assessment of leaflet motion in prosthetic mitral and aortic valve by transthoracic and transesophageal echocardiography

Results: In more than 75% of pts. the marked postoperative improvement of NYHA class was observed. The LV mass decreased significantly in 3 year's observation in On-X valves group from 341 to 241g (p 1,7m2 (p<0.05). Analyzed group of small size On-X valves present significant lower peak and mean stress gradient, independent on valve size and BSA. The mean value of peak stress gradient on small-size aortic prostheses increased in 2nd and 3rd year after implantation (p<0.05). Conclusion: Good clinical outcome and LV mass reduction after small-size aor- tic valve replacement were not correlated with high stress gradient of analyzed valves. Small size On-X valves prostheses contoured with a similar ratio of length- to-diameter for reducing turbulence and lowering pressure gradients shown an ex- cellent performance in aortic position with very good LV mass regression in long term observation. (0.54 - 1.69) At rest on treadmill we assessed MaxG, MeanG, Stroke Volume (SV), VR and IDV. The same items were evaluated at peak exercise (just before stoping treadmill), performed using modified Bruce protocol. All exams were recorded in VHS tape and in optical disk. Results: Four patients were excluded from analysis, due to insatisfatory quality of images (1 patien) or evidence of significant intraventricular gradients with telesys- tolic peak (3 patients). Max G at rest: 44.8 ± 21.5 mmHg and at peak: 73.2 ± 40.5 mmHg, p< 0.01; MeanG at rest: 26.9 ± 16.9 mmHg and at peak: 48 ± 24.6 mmHg, p<0.01: VR at rest 172 ± 118 dynes.s.cm5 and at peak: 231.7 ± 129 dynes.s.cm5, p<0.05; IDV at rest: 0.46 ± 0.32, and at peak 0.48 ± o.32, p= ns. Conclusions: 1) Frequently, pts with AS develop significant intraventricular gradi- ents with exercise. 2) Isotonic exercise in orthostatic position, with its consequent increase in flow, influences all the Doppler parameters of AS severity, except IDV (indirect marker of effective valve area). 3) These results suggest that echocardio- graphic evaluation of aortic stenosis can be complemented with dynamic parametes acquired during isotonic exercise on treadmill and it might allow a better understand of pathophysiology and symptoms of aortic valve disease.

893 Long-term analysis of hemodynamic function and left ventricular mass regression after implantation of small-size mechanical valve prostheses in aortic position. Comparative evaluation of On-X valves

893 Long-term analysis of hemodynamic function and left ventricular mass regression after implantation of small-size mechanical valve prostheses in aortic position. Comparative evaluation of On-X valves

The On-X prosthetic heart valve at five years

Background Multicenter clinical trials were conducted in Europe and North America to evaluate the performance of the On-X bileaflet heart valve prosthesis (Medical Carbon Research Institute, Austin, TX). Methods A total of 532 patients underwent implantation, 303 for aortic valve replacement (AVR) and 229 for mitral valve replacement (MVR), at 20 centers from September 1996 to July 2001. The study followed the guidelines of the AATS/STS. Mean follow-up was 23 months (total 1024 patient-years; maximum 5 years). Poolability analysis was performed to show the equivalence of the populations. Results Patients and results were found to be similar and poolable. Freedom from adverse events at 2 years in the study were as follows: thromboembolism, 96.0% for AVR patients and 96.3% for MVR; thrombosis, 100% for AVR and 100% for MVR; bleeding events, 96.6% for AVR and 95.7% for MVR; and overall mortality, 95.2% for AVR and 92.4% for MVR. Median lactate dehydrogenate levels were in the normal range for AVR and MVR patients at all intervals. At 1 year, AVR echocardiographic results for the 19 to 25 valves, respectively, ranged from 1.5 to 2.8 cm 2 for effective orifice area and 9.2 to 4.7 mm Hg for mean gradient, and MVR effective orifice area by pressure half-time was 2.8 cm 2 and mean gradient was 4.2 mm Hg. Conclusions The two trials have given similarly excellent results for the On-X valve.

Mock loop testing of On-x prosthetic mitral valve with Doppler echocardiography.

Previous in vitro testing (mainly in aortic position) and clinical experience (often based on Doppler echocardiographic observations) demonstrated an excellent hemodynamic behavior of the On-X valve. However, integrative studies including simultaneous hemodynamic pressure and flow measurements and Doppler echocardiography are lacking. Using our computer-controlled mock loop system, two samples of the Mitral 27/29 and one sample of the Conform-X Mitral 25/33 are tested in mitral position. Data include transvalvular pressure gradient and flow as well as transthoracic Doppler echocardiography. The valves are tested under three pressure conditions (ventricular systolic pressure of 100, 130, and 160 mm Hg) at three different heart rates (60, 100, and 140 beats/min). In addition, ventricular pressure conditions simulating fibrillation are imposed. Both valve types show similar hydrodynamic characteristics and have an effective orifice area of 2.1 cm2 and a performance index of 0.56 for a cardiac output of 3.5 L/min. Regurgitant volumes remain below 6 ml.

In vitro investigation of opening behavior and hydrodynamics of bileaflet valves in the mitral position.

The performance of four 25 mm bileaflet valves of different designs was evaluated in the mitral position of our own pulse simulator. With the aid of a high-speed video camera, it was demonstrated that both the St. Jude Medical (SJM) valve (Hemodynamic Plus [HP] Series, St. Jude Medical, Inc., St. Paul, MN, U.S.A.) and the CM valve (CarboMedics, Inc., Austin, TX, U.S.A.) were able to open fully and that the CM valve fluttered much more vigorously at the fully open position than did the SJM HP valve. Conversely, neither the ATS valve (ATS Medical, Inc., Minneapolis, MN, U.S.A.) nor the On-X valve (Medical Carbon Research Institute, Austin, TX, U.S.A.) exhibited movement to a fully open configuration. The overall average opening angles of the ATS and the On-X, on 3, 4, and 5 L/min flow rate for a heart rate of 70 bpm and 5, 6, and 7 L/min for 100 bpm, were 74.8 degrees and 81.6 degrees, respectively, whereas their design opening angles were 85 degrees and 90 degrees. Pressure drops across the CM and the ATS were consistently higher than those of the On-X and the SJM HP. Closing volumes for all the valves were below 8% for a heart rate of 70 bpm. This in vitro investigation yielded the following conclusions: The ATS and On-X valves are not able to open fully in the mitral position, but this does not impair their normal function; both a larger orifice diameter and a large opening angle can decrease the pressure drop; in general, the On-X valve achieves its design goals in this experiment (i.e., it produces a lower pressure drop and lower closing volume by virtue of its large orifice and high-profile design); however, the hinge flow in the non-fully open state should be investigated further.

Mitral Valve Prosthesis Regurgitation: Normal Conditions Versus Atrial Fibrillation

Valve trials are often run under simulated conditions encountered in healthy young men. However, heart valve implantation is often associated with other pathologies. The study was focused on the impact of the variation of the heart rate on prosthesis regurgitation under normal conditions and during atrial fibrillation. Trials were performed on a dual activation simulator of the left heart. Four valves (Carbomedics – CMS, Saint Jude Medical – SJM, ON'X – ONX, and Sree Chitra TTK – TTK), were tested in mitral position. Different heart rate settings were used. The trials were repeated under normal conditions and during atrial fibrillation. The results were as follows. In general, valve closing does not vary with increased heart rates. Leakage volume decreased with the increase of heart rate and the regurgitation peak decreased from normal conditions to atrial fibrillation. The SJM and ONX valves could not be differentiated. Contrary to the CMS and TTK valves, the SJM valve was not reproducible. The closing volume of the TTK valve was low in atrial fibrillation. The CMS valve appeared to be the best compromise for all flow conditions. This study underscores that regurgitation must be estimated under normal and pathological conditions and that it can be estimated with a constant rhythm in atrial fibrillation.

In Vitro Hydrodynamics of Four Bileaflet Valves in Mitral Position

Hydrodynamics of St. Jude Medical, Carbomedics, Advancing The Standard, and On-X bileaflet valves with an annular diameter of 25 mm were obtained using an in-vitro test system. Steady flow studies demonstrated different pressure drops due to differences in valve design, particularly the geometric orifice diameter and the opening angle. The On-X valve produced the least pressure drop, whereas the Carbomedics valve had the greatest pressure drop. In pulsatile flow experiments, the On-X and St. Jude Medical valves consistently produced the lowest mean positive pressure gradients, while the Carbomedics valve had the highest gradients. In spite of its parallel leaflets design, the On-X valve showed a closing volume as small as that of Carbomedics valve. The results indicate that a larger orifice diameter and greater opening angle can significantly reduce transvalvular pressure loss. This study also demonstrated that attempts to improve the hydrodynamic efficacy of the On-X valve were successful in reducing the pressure gradient as well as maintaining a low closing volume.