Bileaflet Mechanical Valve Research Articles

Could It Happen Again?

Most readers of “Twenty-Five–Year Experience With the Bjork-Shiley Convexoconcave Heart Valve: A Continuing Clinical Concern” in this issue of Circulation have not heard of the valve.1 Many elements of its story parallel those of cerivastatin2,3⇓ and rofecoxib,4 but with a twist: Recalling a heart valve may entail greater risks than leaving a possible “time bomb” in place. The Bjork-Shiley story raises many questions about balancing the benefits of drugs and devices with their risks to public safety. For example: See p 2850 My personal involvement began when a lawyer for Shiley, Inc, with a biostatistical degree read our account of the Braunwald-Cutter heart valve and wanted to understand why the University of Alabama at Birmingham and the Mayo Clinic decided to prophylactically remove every one.5 Subsequently, I served on scientific panels, spearheaded a multi-institutional effort to quantify the risks of prosthesis explant,6 and suggested ways to use this information for the tough decision making ahead.7 The Bjork-Shiley heart valve, developed by Shiley, Inc, in collaboration with Dr Viking Bjork of Sweden, was …

Impact of postoperative blood pressure control on regression of left ventricular mass following valve replacement for aortic stenosis

Considerable left ventricular (LV) hypertrophy sometimes remains after aortic valve replacement (AVR) for aortic stenosis. For this issue, most previous studies have focused solely on transprosthetic pressure gradient, although true problem is not the pressure gradient itself but an elevated LV pressure. This study investigated the impact of blood pressure on postoperative LV mass regression, which had been overlooked in previous studies. Seventy-nine adult patients with pure aortic stenosis who were treated with AVR using bileaflet mechanical valves underwent echocardiography before surgery, around 6 months later ('early'), and 2-3 years later (31.7+/-14.7 months, 'late'). Patients were divided into two groups whether postoperative systolic blood pressure was below (n=47; N group) or above 130 mmHg (n=32; H group) following recommendation of WHO-ISH and JNC 7th report. Preoperative LV mass (g/m2) did not differ significantly (232+/-80 vs. 243+/-76, P=0.91). LV mass became significantly smaller and regression was significantly more effective in N group than in H group both at 'early' (145+/-43 vs. 180+/-54, regression against preoperative value 34.6+/-19.1 vs. 19.9+/-26.6%, P=0.007) and 'late' (132+/-41 vs. 178+/-51, regression 41.1+/-16.0 vs. 21.0+/-27.0%, P<0.001) evaluations. Regression between 'early' and 'late' evaluations was significant only in N group (P=0.012). The LV mass index returned to the normal range at 'late' evaluation in 52.1% of N group and 12.5% of H group patients (P<0.001), and 25 out of 29 patients without residual LV hypertrophy were N group patients. Multivariate analyses revealed that preoperative LV mass index (P<0.001) and postoperative systolic blood pressure (P=0.007) showed significant influence on postoperative LV mass index, and postoperative systolic blood pressure alone significantly (P<0.001) influenced the regression ratio of the LV mass against the preoperative value. No prosthesis related variables (size, orifice area index, pressure gradient) had significant influence. For LV mass regression after AVR, postoperative blood pressure appeared to be more important than prosthesis selection. Controlling the systolic blood pressure below 130 mmHg was beneficial, which coincided with recommendation of WHO-ISH and JNC 7th report despite the pressure drop due to prosthesis in the aortic position.

Significant overestimation of transvalvular gradients in bileaflet mechanical heart valves by clinical-routine Doppler-echocardiography

Objectives: Doppler echocardiography measures intravalvular flow velocity to calculate transvalvular pressure loss according to the Bernoulli-equation. But due to pressure recovery valve-gradients may be overestimated significantly. We quantified overestimation of transvalvular pressure-gradients in small sized (19–23mm) aortic bileaflet mechanical valves (On-X®).

Small aortic annulus: The hydrodynamic performances of 5 commercially available bileaflet mechanical valves

Small aortic annulus: The hydrodynamic performances of 5 commercially available bileaflet mechanical valves

Left ventricular rupture following mitral valve replacement due to oversize prosthesis

Left ventricular rupture following mitral valve replacement is one of the most serious complications. We report our experience in successful treatment of type III left ventricular rupture following mitral valve replacement probably due to an oversize prosthesis. A 67-year-old woman, with the history of percutaneous transluminal mitral commissurotomy 11 years previously, underwent mitral valve replacement for mitral restenosis with a 27 mm CarboMedics mechanical bileaflet valve (Sulzer CarboMedics Inc., Austin, TX, U.S.A.). There were some difficulties in placing the entire prosthesis into the annulus at the posterior because of the oversize prosthesis. After the complete placement of the prosthesis, bulge of the left ventricular muscle was evident around the left lateral region. Following the cessation of cardiopulmonary bypass, type III left ventricular rupture, half a circular rip between the papillary muscles and posterior mitral annulus, occurred. The rip was suture-closed and a 23 mm CarboMedics valve was placed. Postoperative ultrasonic cardiography showed no prosthetic stenosis, periprosthetic leak, left ventricular pseudoaneurysm, nor left ventricular asynergy. Under cardioplegic arrest, we should not select the oversize prosthesis to prevent left ventricular rupture.

Influence of bileaflet prosthetic mitral valve orientation on left ventricular flow--an experimental in vivo magnetic resonance imaging study.

Orientation-related bileaflet mechanical valve flow and velocity studies in the downstream area are limited in mitral valve replacement studies. In five sheep, ventricular blood flow was visualized prior to the implantation of a mitral Edwards Mira Bileaflet Mechanical Valve Model 9600. The implant orientation was either anatomic, with a 45 degrees rotation, or anti-anatomic, with a 90 degrees rotation. Sheep were positioned within an 1.5T field strength MR scanner (Magnetom Sonata; Siemens) to assess time-dependent three-dimensional blood flow velocities displayed as color-encoded vectors. The preoperative ventricular velocity profiles presented negligible individual variances. Streamlines passed homogeneously without any spatial differences into the left ventricle. Starting from the anatomical position, the areas with inhomogeneous and accelerated local blood velocities increased in comparison to the preoperative status. Rotating the prosthesis until it was in a 45 degrees position caused a significant increase in turbulence immediately downstream; fluids stagnated longer at the apex. In the anti-anatomic orientation, mean velocities decreased. In all three positions, but less so in the anatomical position, the flow pattern of the blood helix at the apex was disturbed. The intraventricular flow patterns between prostheses in the three orientations were, however, not significant when compared to the differences between physiologic intraventricular flow and any of the postoperative measurements. To achieve optimal hemodynamics, rotation of the mitral valve has to be considered carefully, as has long been known from aortic valve replacement studies. To this end, a method for qualitative assessment of left ventricular blood flow patterns was developed.

Small aortic annulus: The hydrodynamic performances of 5 commercially available bileaflet mechanical valves

ObjectiveHemodynamic performances of mechanical valve prostheses in patients with aortic valve stenosis and a small aortic annulus are crucial. We analyzed the in vitro hydrodynamics of 5 currently available bileaflet mechanical prostheses that fitted a 21-mm-diameter valve holder of a Sheffield pulse duplicator. MethodsThree samples of 5 high-performance production-quality prostheses, including the sewing ring cuffs, were tested in the aortic chamber of a Sheffield pulse duplicator. Sizes of the prostheses fitting the 21-mm valve holder were as follows: 18-mm ATS, 19-mm SJM Regent, 19-mm Sorin Bicarbon Slimline, 19-mm On-X, and 21-mm Carbomedics Top Hat. The tests were carried out at a fixed pulse rate (70 beats/min) and at increasing cardiac outputs of 2, 4, 5, and 7 L/min. Each valve was tested 10 times for each different cardiac output. This resulted in a total of 40 tests for each valve and 120 tests for each valve model. The aortic pressure was set at 120/80 mm Hg (mean pressure, 100 mm Hg) throughout the experiment for all cardiac outputs. Forward flow pressure decrease, total regurgitant volume, closing and leakage volumes, effective orifice area, and stroke work loss were recorded while the valve operated under each cardiac output. ResultsThe SJM Regent valve and the Sorin Bicarbon Slimline prosthesis showed the lowest mean and peak gradients at increasing cardiac outputs. The closure volume was higher for the SJM Regent and Sorin Bicarbon Slimline prostheses, unlike with the ATS prosthesis at 7 L/min of cardiac output. The ATS and SJM Regent prostheses showed the largest regurgitant volume, whereas the Sorin Bicarbon Slimline prosthesis showed the lowest regurgitant volume. The calculated effective orifice area and stroke work loss were significantly better with the SJM Regent and Sorin Bicarbon Slimline prostheses. ConclusionAssuming that the 21-mm valve holder in which all the tested prostheses were accommodated is comparable with a defined aortic valve size, this hydrodynamic evaluation model allowed us to compare the efficiency of currently available valve prostheses, and among these, the SJM Regent and the Sorin Bicarbon Slimline exhibited the best performances.

Antithrombotic Therapy in Valvular Heart Disease—Native and Prosthetic: The Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This chapter about antithrombotic therapy in native and prosthetic valvular heart disease is part of the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy: Evidence Based Guidelines. Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patients' values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this chapter are the following: For patients with rheumatic mitral valve disease and atrial fibrillation (AF), or a history of previous systemic embolism, we recommend long-term oral anticoagulant (OAC) therapy (target international normalized ratio [INR], 2.5; range, 2.0 to 3.0) [Grade 1C+]. For patients with rheumatic mitral valve disease with AF or a history of systemic embolism who suffer systemic embolism while receiving OACs at a therapeutic INR, we recommend adding aspirin, 75 to 100 mg/d (Grade 1C). For those patients unable to take aspirin, we recommend adding dipyridamole, 400 mg/d, or clopidogrel (Grade 1C). In people with mitral valve prolapse (MVP) without history of systemic embolism, unexplained transient ischemic attacks (TIAs), or AF, we recommended against any antithrombotic therapy (Grade 1C). In patients with MVP and documented but unexplained TIAs, we recommend long-term aspirin therapy, 50 to 162 mg/d (Grade 1A). For all patients with mechanical prosthetic heart valves, we recommend vitamin K antagonists (Grade 1C+). For patients with a St. Jude Medical (St. Paul, MN) bileaflet valve in the aortic position, we recommend a target INR of 2.5 (range, 2.0 to 3.0) [Grade 1A]. For patients with tilting disk valves and bileaflet mechanical valves in the mitral position, we recommend a target INR of 3.0 (range, 2.5 to 3.5) [Grade 1C+]. For patients with caged ball or caged disk valves, we suggest a target INR of 3.0 (range, 2.5 to 3.5) in combination with aspirin, 75 to 100 mg/d (Grade 2A). For patients with bioprosthetic valves, we recommend vitamin K antagonists with a target INR of 2.5 (range, 2.0 to 3.0) for the first 3 months after valve insertion in the mitral position (Grade 1C+) and in the aortic position (Grade 2C). For patients with bioprosthetic valves who are in sinus rhythm and do not have AF, we recommend long-term (> 3 months) therapy with aspirin, 75 to 100 mg/d (Grade 1C+).

Fluid mechanics of heart valves.

Valvular heart disease is a life-threatening disease that afflicts millions of people worldwide and leads to approximately 250,000 valve repairs and/or replacements each year. Malfunction of a native valve impairs its efficient fluid mechanic/hemodynamic performance. Artificial heart valves have been used since 1960 to replace diseased native valves and have saved millions of lives. Unfortunately, despite four decades of use, these devices are less than ideal and lead to many complications. Many of these complications/problems are directly related to the fluid mechanics associated with the various mechanical and bioprosthetic valve designs. This review focuses on the state-of-the-art experimental and computational fluid mechanics of native and prosthetic heart valves in current clinical use. The fluid dynamic performance characteristics of caged-ball, tilting-disc, bileaflet mechanical valves and porcine and pericardial stented and nonstented bioprostheic valves are reviewed. Other issues related to heart valve performance, such as biomaterials, solid mechanics, tissue mechanics, and durability, are not addressed in this review.

유체-고체 상호작용 (FSI)기법을 이용한 이엽기계식 인공심장판막을 지나는 혈액유동과 판첨거동에 관한 수치해석적 연구

Bileaflet mechanical valves have the complications such as hemolysis and thromboembolism, leaflet damage, and leaflet break. These complications are related with the fluid velocity and shear stress characteristics of mechanical heart valves. The first aim of the current study is to introduce fluid-structure interaction method for calculation of unsteady and three-dimensional blood flow through bileaflet valve and leaflet behavior interacted with its flow, and to overcome the shortness of the previous studies, where the leaflet motion has been ignored or simplified, by using FSI method. A finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and structure equations, respectively, to investigate the interaction between the blood flow and leaflet. As a result, it is observed that the leaflet is closing very slowly at the first stage of processing but it goes too fast at the last stage. And the results noted that the low pressure is formed behind leaflet to make the cavitation because of closing velocity three times faster than opening velocity. Also it is observed some fluttering phenomenon when the leaflet is completely opened. And the rebounce phenomenon due to the sudden pressure change of before and after the leaflet just before closing completely. The some of time-delay is presented between the inversion point of ventricle and aorta pressure and closing point of leaflet. The shear stress is bigger and the time of exposure is longer when the flow rate is maximum. So it is concluded that the distribution of shear stress at complete opening stage has big effect on the blood damage, and that the low-pressure region appeared behind leaflet at complete closing stage has also effect on the blood damage.

An unusual ectopic calcification in the aorta

A 49-year-old woman with end-stage renal failure who had been maintained on chronic hemodialysis since she was 40 was referred to our hospital for surgical treatment of mitral regurgitation. She had no history of infectious endocarditis. Transthoracic echocardiography (TTE) performed at the referring hospital showed severe mitral regurgitation with severely impaired left ventricular function (ejection fraction, 33%). Both anterior and posterior leaflets of the mitral valve were thickened and the annulus was dilated. No calcification was identified in a cardiac chamber by TTE. Coronary arteriography showed total occlusion of the right coronary artery. Findings on transesophageal echocardiography were extremely unusual. A hyperechoic mass was attached to the inside wall of the sinus of Valsalva (Fig 1). Although the mass was not floating, the patient was transferred urgently to the operating theater for resection of the mass. After cardiopulmonary bypass was established and the heart arrested, the aorta was incised transversely. The mass was attached to the right coronary sinus, just above the right coronary ostium, and resembled an icicle (Fig 2). This mass was dissected carefully from the intima of aorta. It was heavily calcified and friable, although its surface was smooth. The aortic valve and aortic wall were not calcified. The mitral valve was replaced with a bileaflet mechanical valve, and aorto-coronary bypass to the right coronary artery was performed using a saphenous vein graft. The postoperative course was uneventful. Histopathologic examination confirmed that the mass was fibrous tissue with dense calcifications. Address reprint requests to Dr Fukui, Department of Cardiovascular Surgery, Shin-Tokyo Hospital, 473-1 Nemoto, Matsudo City, Chiba 2710077, Japan; e-mail: tm-fukui@gem.hi-ho.ne.jp. Fig 1. Fig 2.

Reduction of bispectral index value associated with clinically significant cerebral air embolism

Reduction of bispectral index value associated with clinically significant cerebral air embolism

The Howard Gilman Foundation Lecture. Where have we come from and where are we going? Valve management past, present and future.

Leonardo da Vinci's anatomical drawings of quadricuspid, tricuspid, and bicuspid aortic valves underscored the hydraulic superiority of a three leaflet valve with cuspal equality. William Harvey demonstrated that venous valves were designed for unidirectional flow and to prevent reflux from the heart, observations that served as the basis of his immortal de Mortu Cordis. Joseph Rouanet of Paris proposed that heart sounds originated from the closing movements of cardiac valves. The Cardiodynamics of Mitral Insufficiency by Wiggers and Feil was followed three decades later by Paul Wood's An Appreciation of Mitral Stenosis. The Bland/Sweet operation indirectly addressed mitral stenosis by means of a venous shunt. Sir Henry Souttar's early digital repair of mitral stenosis was later reintroduced independently by Harken and Bailey; Doyen, Sellers, and Brock employed surgical valvotomy for pulmonary stenosis, and Bailey employed surgical valvotomy for aortic stenosis. Management of abnormal cardiac valves includes repair (reconstruction), replacement with mechanical or biologic prostheses, and interventional catheterization. The first mechanical valve was inserted extracardiac by Hufnagel into the descending thoracic aorta of patients with severe aortic regurgitation. The Starr caged ball mechanical prosthesis was designed for intracardiac replacement of an abnormal cardiac valve. The peripheral flow ball valve was followed by hydraulically superior and less thrombogenic central flow monoleaflet or bileaflet mechanical valves, and by homograft and heterograft bioprosthetic valves. Improved methods of preparing exogenous bioprostheses and innovative techniques of aortic valve reconstruction are evolving. Cardiac catheterization as a therapeutic intervention is routinely applied to stenotic mitral, aortic and pulmonary valves, and transcatheter replacement of an abnormal pulmonary valve is now a reality.

Experience of the small size (25 mm) Sorin Bicarbon bileaflet prosthetic valve in patients with small mitral annuli.

Currently, there is a tendency to use large-size prosthetic valves in mitral position in order to achieve better hemodynamic performance. We aimed to evaluate hemodynamic performance of 25 mm prosthetic valves in mitral position. Between August 1998 and May 2000, a total of 40 patients, 34 women and 6 men (mean age 42 +/- 12 years), underwent mitral valve replacement with 25 mm bileaflet mechanical valve. Preoperative functional capacity was New York Heart Association classes III and IV in 31 patients. Major indication for surgery was severe mitral stenosis in all patients. Total hospital mortality was 5% (two patients). Mean follow-up period was 14.7 +/- 4.9 months (2 to 23 months). No thromboembolic event, paravalvular leak, mechanical failure, endocarditis were observed during the follow-up period. Postoperatively 92.5% of the patients were in the functional capacity of New York Heart Association class I. Postoperative echocardiographic observations have given an average pulmonary artery pressure of 29 +/- 2 mmHg, effective orifice area as 2.95 +/- 0.1 cm2, and mean prosthetic gradient as 6.5 +/- 2.7 mmHg. In short- and mid-term, small-size (25 mm) Sorin mechanical mitral valves had excellent hemodynamic performance in patients with severe mitral stenosis, moderate or serious pulmonary hypertension, and small mitral annuli, whose body surface area was smaller than 1.6 m2.

Are mechanical valves with enhanced inner diameter advantageous in the small sized aortic annulus?

Background Mechanical bileaflet valves with enhanced inner diameter may offer superior hemodynamic properties in patients with a small aortic annulus. The aim of this clinical study was to compare these valves with standard bileaflet prostheses in vivo. Methods Mechanical aortic valve replacement for combined stenosis and regurgitation was performed in 47 patients with standard CarboMedics prostheses (CM: 21 mm, 23 mm, 25 mm) and two types of diameter enhanced St. Jude Medical prostheses (SJM-AHPJ: 21 mm, 23 mm, 25 mm; SJM-Regent: 21 mm, 23 mm). Transvalvular mean gradients (TVG) were assessed intraoperatively by means of transesophageal echocardiography (TVG TEE) and simultaneous direct pressure monitoring of the left ventricle and the ascending aorta (TVG CATH), as well as early (3 months) and late (9 months) postoperatively by means of transthoracic echocardiography (TVG TTE). Left ventricular muscle mass was assessed preoperatively, early, and late postoperatively to evaluate remodeling capacity. Results In all valve types and sizes, both TVG assessments exhibited consistent findings. Small-sized conventional valves of 21 mm showed a marked initial TVG. In contrast, both valve types with enhanced inner diameter exhibited significantly lower TVG comparable with those achieved with larger valves (TVG CATH CM 21 mm, 15.6 ± 3.9 mm Hg; SJM-AHPJ 21 mm, 11.9 ± 1.6 mm Hg; SJM-Regent 21 mm, 9.9 ± 1.1 mm Hg; CM 23 mm, 7.8 ± 0.8 mm Hg; SJM-AHPJ 23 mm, 7.7 ± 1.4 mm Hg; SJM-Regent 23 mm, 9.5 ± 1.8 mm Hg). During the postoperative course TVG remained constant in all valve types and sizes. Left ventricular muscle mass, however, diminished markedly in all valves without exhibiting significant differences between size matched valve types. Conclusions In patients with a small aortic annulus, who require a 21-mm valve, diameter-enhanced prostheses provide lower transvalvular gradients than conventional valves. However, in the intermediate clinical course, appropriate left ventricular remodeling occurred in all patients independent of the size and the type of the valve.

Nominal size in six bileaflet mechanical aortic valves: a comparison of orifice size and biologic equivalence

Objectives Nominal size remains the standard by which valves are compared, but its relationship with orifice area and the patient tissue annulus diameter may differ according to valve design. The aims of this study were to measure the orifice size and compare biologic equivalence in six bileaflet mechanical heart valve designs. Methods The inflow aspect of each of 29 valves was photographed then digitized, and the maximum internal diameter and orifice area were calculated. Biologic equivalence was assessed with a series of machined polypropylene blocks. Results The orifice area ranged between 159 and 222 mm 2 for the six size 19 valves. The internal diameter ranged from 1.6 to 4.6 mm less than the manufacturer’s nominal size. Biologic equivalence assessed from an estimate of tissue annulus diameter with machined blocks ranged from 1.0 and 3.5 mm larger than nominal size for the intra-annular valves. This diameter ranged from 3.5 mm smaller to 1.5 mm larger than nominal size for the supra-annular valves. Conclusion There are major differences between nominal size and biologic equivalence. This may lead to confusion when attempting to make comparisons between different valve designs with the same nominal size. A clearer sizing nomenclature is required and could be based on in vitro assessment of tissue annulus diameter or an alphanumeric code.

Impact of high intensity transient signals on the choice of mechanical aortic valve substitutes.

High intensity transient signals (HITS) observed during extracorporeal circulation and following mechanical valve replacement are suspected of causing cognitive dysfunction (deterioration of episodic and working memory). This study evaluates the role played by valve design (bileaflet versus tilting disc) and other parameters in the incidence of HITS. Thirty patients were selected for the study as follows: 18 males, 58-78 years of age; ten St. Jude Medical, ten CarboMedics, ten Medtronic Hall (MH); all size 23, in optimum orientation (Ann Thorac Surg 68 (1999) 1069); all in sinus rhythm; no coronary or carotid artery disease; all in sinus rhythm, international normalized ratio greater than 2.5 and all at least 9 months postoperative. All patients had bilateral HITS measurement in both middle cerebral arteries via transcranial doppler for 30 min. If five HITS or more were observed during the initial 10 min, patients were subjected to 100% oxygen breathing followed by 10 min of normal air breathing. Simultaneously, HITS were measured in the right radial and femoral arteries. Patients with bileaflet valve substitutes revealed HITS rates varying from 32 to 108 counts/h. There was only one HITS observed in the MH valve group during the 5h observation period (0.2 HITS/h). There were no HITS detected in either the radial or the femoral arteries in any patient. After breathing 100% oxygen, HITS significantly decreased or completely disappeared (0-30 HITS/h). When normal air breathing was resumed HITS reappeared or increased. With an intravenous infusion of 100 mg of lysine acetylsalicylate (Aspisol, Bayer Leverkusen, Germany), HITS decreased by 16 to 41%. We conclude that bileaflet mechanical valve prostheses produce HITS even in their optimum orientation. HITS following bileaflet valve replacement have an unstable nature and might be composed of nitrogen and platelets. Tilting disc valves in their optimum orientation provide almost physiological conditions with HITS measured in the same range as bioprosthesis.

Microflow fields in the hinge region of the CarboMedics bileaflet mechanical heart valve design

Objective: The design of bileaflet mechanical heart valves includes some degree of leakage flow on valve closure for the reverse flow to wash the hinge and pivot region of the valve. It is believed that this reverse flow helps to prevent areas of stasis and inhibit microthrombus formation. However, the magnitude of this retrograde flow may also give rise to unacceptable levels of blood element damage and lead to platelet activation or hemolysis as a result of the increased flow velocities through the hinge region. The purpose of this study was to evaluate the hinge flow dynamics of a 23-mm CarboMedics bileaflet mechanical valve (Sulzer CarboMedics Inc, Austin, Tex) and then to compare the results with those of the St Jude Medical 23-mm Regent (St Jude Medical Inc, Minneapolis, Minn) and Medtronic Parallel (Medtronic, Inc, Minneapolis, Minn) valves studied earlier. This comparison allows new insight into the microflow fields within the hinge region of the CarboMedics bileaflet mechanical valve, which have not been previously assessed during its clinical history. Methods: Two-dimensional laser Doppler velocimetry was used to measure the velocity and turbulent shear stress fields in the hinge regions. To conduct these measurements, exact dimensional models of the bileaflet hinge regions were cast or machined from transparent plastic materials. The experiment was conducted in a pulsatile flow loop with measurements taken at different levels within the pivot and hinge regions. Results: In the 23-mm CarboMedics valve hinge, the phase-averaged forward velocity obtained at the flat level and levels of 190 μm and 390 μm above flat and 1 mm below flat were 0.54 m/s, 0.77 m/s, 0.3 m/s, and 1.0 m/s, respectively. Corresponding values of the peak phase-averaged leakage velocities were 3.17 m/s, 2.91 m/s, 2.52 m/s, and 0.5 m/s, respectively. Corresponding turbulent shear stresses were 5510 dyne/cm2, 5640 dyne/cm2, 4380 dyne/cm2, and 4810 dyne/cm2, respectively. Conclusions: The hinge flow dynamics of the CarboMedics bileaflet design lie somewhere in between those of the St Jude Medical and the Medtronic Parallel valve designs. The fluid dynamics of the investigated valve were found to be similar to those of the St Jude Medical valves, although with slightly higher leakage velocities and turbulent shear stresses. This discrepancy may be a result of the sharper corners associated with the hinge design of the CarboMedics valve. It could also be due to the incremental enlargement of the internal orifice area of the St Jude Medical Regent design.J Thorac Cardiovasc Surg 2002;124:561-74

Lipids in patients with aortic valve replacement: impact of preoperative cholesterol levels on the embolization after bileaflet mechanical valve replacement

Lipids in patients with aortic valve replacement: impact of preoperative cholesterol levels on the embolization after bileaflet mechanical valve replacement

Prosthetic replacement of tricuspid valve: bioprosthetic or mechanical

Background. Tricuspid valve replacement is one of the most challenging operations in cardiac surgery. Selection of the suitable prosthesis is still debatable. Methods. In our institution, between January 1980 and December 2000, 129 tricuspid valve replacements were performed in 122 patients (14.7%). Bioprosthetic valves were used in 32 patients, whereas 97 patients had mechanical valve implantation. Twenty-two percent of replacements were done on men. Mean age was 35.27 ± 11.56 years. In all patients, initially an annuloplasty technique was tried. Tricuspid valve replacement was performed when annuloplasty was not sufficient. In most of the cases, tricuspid valve interventions were done under cardiopulmonary bypass and on a beating heart. Results. Early mortality was 24.5%. Patients were followed for 2 to 228 months. Seven patients underwent reoperation because of tricuspid valve dysfunction (7.6%). Nine patients died during the follow-up period. Late mortality was 9.7%. Actuarial estimates of survival in 20 years of follow-up for all tricuspid prosthetic valves, mechanical valves, and bioprosthetic valves were 65.1% ± 9.3%, 68.3% ± 10.6%, and 54.8% ± 12.1%, respectively. For the bioprosthetic valve group, freedom from structural valve degeneration was 90% ± 5.5%; for the mechanical valve group, freedom from deterioration, endocarditis, and leakage was 97.8% ± 4.2%, and freedom from thromboembolism was 92.6% ± 6.9%. Conclusions. We found that there was no statistically significant difference between the two groups in terms of early mortality, re-replacement, and midterm mortality ( p > 0.05). Nevertheless, we recommend low profile modern bileaflet mechanical valves for prosthetic replacement of the tricuspid valve, due to their favorable hemodynamic characteristics and durability.