Tilting Disc Valve Research Articles

Intravascular hemolysis in patients with normally functioning mechanical heart valves in mitral position

Traumatic intravascular hemolysis has been recognized as a potentially serious problem after heart valve replacement. Chronic subclinical hemolysis in these patients with normally functioning valvular mechanical or biologic prostheses rarely develop decompensated anemia. This prospective study evaluates the presence and severity of hemolysis in patients with normally functioning mitral prosthetic valves. In this prospective study 78 patients with normally functioning mitral prosthetic valves were evaluated for hemolysis postoperatively on 7th,30th and 180th days by clinical evaluation, transthoracic echocardiography, hemoglobin, serum lactic dehydrogenase (LDH), and reticulocyte count. Data was statistically analysed with paired t test and variance test. LDH was elevated in almost all the patients with mechanical valve replacement. None had significant anemia. All the evidence of hemolysis was not observed in any of the recipients. There was no statistically significant difference in the degree of hemolysis among the recipients of various tilting disc valves. There was no significant correlation between the severity of hemolysis and cardiac rhythm or the size of valve. The recipients of bileaflet valve had significantly more severe hemolysis than those of tilting disc valves. Almost all the recipients of mechanical mitral valves had increased LDH values at the follow up. However none had decompensated anemia during 180 days follow up. Bileaflet valves cause more hemolysis than tilting ones. Recipients of Chitra TTK valve prosthesis showed least hemolysis.

Prevalence of pannus formation after aortic valve replacement: clinical aspects and surgical management

Pannus formation after aortic valve replacement is not common, but obstruction due to chronic pannus is one of the most serious complications of valve replacement. The causes of pannus formation are still unknown and effective preventive methods have not been fully elucidated. We reviewed our clinical experience of all patients who underwent reoperation for prosthetic aortic valve obstruction due to pannus formation between 1973 and 2004. We compared the initial 18-year period of surgery, when the Björk-Shiley tilting-disk valve was used, and the subsequent 13-year period of surgery, when the St. Jude Medical valve was used. Seven of a total of 390 patients (1.8%) required reoperation for prosthetic aortic valve obstruction due to pannus formation. All seven patients were women; four patients underwent resection of the pannus and three patients needed replacement of the valve. The frequency of pannus formation in the early group was 2.4% (6/253), whereas it was 0.73% (1/137) in the late group (P < 0.05). Pannus was localized at the minor orifice of the Björk-Shiley valve in the early group and turbulent transvalvular blood flow was considered to be one of the important factors triggering its growth. We also consider that small bileaflet valves have the possibility of promoting pannus formation and that the implantation of a larger prosthesis can contribute to reducing the occurrence of pannus.

In Vitro Study of Flow Regulation for Pulmonary Insufficiency

Given the tolerance of the right heart circulation to mild regurgitation and gradient, we study the potential of using motionless devices to regulate the pulmonary circulation. In addition, we document the flow performance of two mechanical valves. A motionless diode, a nozzle, a mechanical bileaflet valve, and a tilting disk valve were tested in a pulmonary mock circulatory system over the normal human range of pulmonary vascular resistance (PVR). For the mechanical valves, regurgitant fractions (RFs) and transvalvular pressure gradients were found to be weak functions of PVR. On the low end of normal PVR, the bileaflet and tilting disk valves fluttered and would not fully close. Despite this anomaly, the regurgitant fraction of either valve did not change significantly. The values for RF and transvalvular gradient measured varied from 4 to 7% and 4 to 7 mm Hg, respectively, at 5 lpm for all tests. The diode valve was able to regulate flow with mild regurgitant fraction and trivial gradient but with values higher than either mechanical valve tested. Regurgitant fraction ranged from 2 to 17% in tests extending from PVR values of 1 to 4.5 mm Hg/lpm at 5 lpm and with concomitant increases in gradient up to 17 mm Hg. The regurgitant fraction for the nozzle increased from 2 to 23% over the range of PVR with gradients increasing to 18 mm Hg. The significant findings were: (1) the mechanical valves controlled regurgitation at normal physiological cardiac output and PVR even though they failed to close at some normal values of PVR and showed leaflet flutter; and (2) it may be possible to regulate the pulmonary circulation to tolerable levels using a motionless pulmonary valve device.

Coronary embolism causing myocardial infarction in a patient with mechanical aortic valve prosthesis

Coronary embolism as a cause of myocardial infarction is an uncommon but important entity both in terms of aetiology and treatment. Previous cases of coronary emboli in association with prosthetic mechanical valves have been reported previously but the mechanism of pharmacology and lack of patient awareness of medication importance is quite unique in this case. A 65-year-old male presented to the emergency room with an anterior ST elevation myocardial infarction after 14 h of symptoms. Past medical history included aortic valve replacement with a mechanical tilting-disc valve 18 months earlier for symptomatic severe calcific aortic stenosis. Pre-operative coronary angiography revealed normal coronary arteries. On this occasion, coronary angiography revealed an occluded LAD with an embolic occlusion at the midpoint of the vessel. Successful PTCA and stenting of the lesion were performed. Amazingly, the patient had decided 1 year earlier to stop taking his warfarin medication. He had begun taking a new “herbal remedy” which was helping with his joint pains but the combination with warfarin was causing excessive bleeding each day after facial shaving. He therefore decided to abruptly stop taking his warfarin without any medical advice. Embolic myocardial infarction is underdiagnosed and it is important to diagnose the source of embolism and treat the cause. Patient education is vital in our battle to prevent this entity in high-risk patients as in our case.

Impact of Pressure Recovery in the Evaluation of the Omnicarbon™ Tilting Disc Valve

Pressure recovery is not taken into account when calculating trans-prosthetic gradients after mechanical valve replacement using Doppler echocardiography. This may lead to underestimation of valvular performance. Simultaneous measurement of Doppler and direct trans-prosthetic gradients was performed in a circulatory mock loop simulator with physiologic parameters at different heart rates and cardiac outputs for small-sized aortic Omnicarbon tilting disc valves (19 - 21 mm). In all adjustments the Doppler gradient significantly overestimated the net transvalvular gradient. The amount of pressure recovery averaged 59.3 %. Doppler echocardiography does not allow for pressure recovery, which is a significant phenomenon in the hemodynamic function of the Omnicarbon tilting disc valve. Valve performance is much better than expected from Doppler gradients.

FULLY-COUPLED FLUID-STRUCTURE SIMULATION OF TILTING-DISC VALVE IN PULSATILE FLOW

In this study, a fully-coupled two-dimensional fluid-structure interaction software system for a pulsatile flow across a moving tilting-disc valve is developed. Unsteady transvalvular blood flow coupled with induced occluder motion has been examined in details. State-of-the-art computational fluid dynamics (CFD) methods are adopted in the present flow solver development. Incompressible finite-volume method is employed to solve the Reynolds-averaged Navier-Stokes equations in conservation form. To account for nonstationary occluder motion, the grid is generated and updated in each time-marching step using hybrid structure/unstructured grid method. A single-degree-of-freedom rotational occluder model is integrated simultaneously with the CFD time-stepping. The geometrical conservation law is strictly satisfied so as to avoid spurious results generated. For code validation, cases with known solutions are compared, and good agreement between the numerical and experimental results are achieved. It is found in the present study that strong shedding vortices occur in the valve closing phase. The pivot location is found to be sensitive for the attainable maximum valve opening angle and the dynamics of valve closure. Blood damage index is also introduced to assess the turbulence-induced stresses to the blood cells. Differences resulted from various upstream flow assumptions and coupled or prescribed occluder motion adopted in the analyses are examined using the abundant simulated results.

Comparative In Vitro Study of Bileaflet and Tilting Disk Valve Behavior in the Pulmonary Position

A study of mechanical heart valve behavior in the pulmonary position as a function of pulmonary vascular resistance is reported for the St. Jude Medical bileaflet (SJMB) valve and the MedicalCV Omnicarbon (OTD) tilting disk valve. Tests were conducted in a pulmonic mock circulatory system and impedance was varied in terms of system pulmonary vascular resistance (PVR). An impedance spectrum was found using instantaneous pulmonary artery pressure and flow rate curves. Both valves fully opened and closed at and above a nominal PVR of 3.0 mmHg/L/min. The SJMB valve was prone to leaflet bounce at closure, but otherwise completely closed, at settings above and below this nominal setting. At PVR values at and below 2.0 mmHg/L/min, the SJMB valve exhibited two types of leaflet aberrant behavior: single leaflet only closure while the other leaflet fluttered, and incomplete closure where both leaflets flutter but neither remain fully closed. The OTD valve fully opened and closed to a PVR value of 1.6 mmHg/L/min. At lower values, the valve did not close. Valves designed for the left heart can show aberrant behavior under normal conditions as pulmonary valves.

Flow in Prosthetic Heart Valves: State-of-the-Art and Future Directions

Since the first successful implantation of a prosthetic heart valve four decades ago, over 50 different designs have been developed including both mechanical and bioprosthetic valves. Today, the most widely implanted design is the mechanical bileaflet, with over 170,000 implants worldwide each year. Several different mechanical valves are currently available and many of them have good bulk forward flow hemodynamics, with lower transvalvular pressure drops, larger effective orifice areas, and fewer regions of forward flow stasis than their earlier-generation counterparts such as the ball-and-cage and tilting-disc valves. However, mechanical valve implants suffer from complications resulting from thrombus deposition and patients implanted with these valves need to be under long-term anti-coagulant therapy. In general, blood thinners are not needed with bioprosthetic implants, but tissue valves suffer from structural failure with, an average life-time of 10-12 years, before replacement is needed. Flow-induced stresses on the formed elements in blood have been implicated in thrombus initiation within the mechanical valve prostheses. Regions of stress concentration on the leaflets during the complex motion of the leaflets have been implicated with structural failure of the leaflets with bioprosthetic valves. In vivo and in vitro experimental studies have yielded valuable information on the relationship between hemodynamic stresses and the problems associated with the implants. More recently, Computational Fluid Dynamics (CFD) has emerged as a promising tool, which, alongside experimentation, can yield insights of unprecedented detail into the hemodynamics of prosthetic heart valves. For CFD to realize its full potential, however, it must rely on numerical techniques that can handle the enormous geometrical complexities of prosthetic devices with spatial and temporal resolution sufficiently high to accurately capture all hemodynamically relevant scales of motion. Such algorithms do not exist today and their development should be a major research priority. For CFD to further gain the confidence of valve designers and medical practitioners it must also undergo comprehensive validation with experimental data. Such validation requires the use of high-resolution flow measuring tools and techniques and the integration of experimental studies with CFD modeling.

Materials Characterization of Explanted Mechanical Heart Valves and Comparison to Patients’ Clinical Data

In the present study, twelve explanted mechanical heart valves (MHVs)with pyrolitic carbon tilting disc and 14 bileaflet MHVs were analyzed to investigate the effects of material properties on valve performance and patients' general health conditions. Optical and scanning electron microscopy was used to investigate material imperfections, wear patterns or damages to housing and occluder components. All analyzed tilting disc valves exhibited wear effects, particularly due to abrasion and impact to both disc and housing. Wear of pyrolitic carbon disc and housing did not influence their in vivo performance. In the bileaflet MHVs, breakaway of the pyrolitic carbon coating sometimes caused malfunctioning and required surgical retrieval of the valve. In all cases, occurrence of clinical symptoms was more likely when wear effects were located in critical areas. The study supports a correlation between the properties of the MHVs material and patients' symptoms.

Non-invasive assessment of differences between bileaflet and tilting-disc aortic valve prostheses by 3D-Doppler profiles

The aim of this study was to analyse flow characteristics of two different prosthetic valves by means of a non-invasive 3D Doppler technique. As previously demonstrated, negative velocity peaks within a 3D-Doppler profile significantly correlate with the severity of aortic stenosis. Transesophageal echocardiography was performed in 42 patients with normal aortic valves and in 35 patients after aortic valve replacement (bileaflet n=23, tilting-disc n=12). Three-dimensional reconstruction of color Doppler data was performed by the EchoAnalyzer software developed at our institution. Cross-section velocity distribution in the ascending aorta was analysed 2 cm distal to the aortic valve in 3 different sectors (non-coronary (NC), left-coronary (LC) or right-coronary (RC)). The percentages of negative velocity values (PNVV) in native aortic valves (6.8+/-6.4%, range: 0-21.8%) were significantly lower (P<0.0001) than in prosthetic valves (bileaflet: 38.5+/-18.5%, range: 13.2-71%; tilting-disc: 47.2+/-17.6%, range: 21.7-78.1%). Significant differences between normal and prosthetic valves were found in all different sectors. Furthermore, Medtronic Hall showed significantly higher PNVV than St. Jude Medical within the LC sector (P=0.03). This method, which allows non-invasive analysis of 3D flow distributions in patients, revealed significant differences between prosthetic valves and native valves as well as among different prosthetic types.

A laboratory investigation of the flow in the left ventricle of a human heart with prosthetic, tilting-disk valves

The understanding of the phenomena involved in ventricular flow is becoming more and more important because of two main reasons: the continuous improvements in the field of diagnostic techniques and the increasing popularity of prosthetic devices. On one hand, more accurate investigation techniques gives the chance to better diagnose diseases before they become dangerous to the health of the patient. On the other hand, the diffusion of prosthetic devices requires very detailed assessment of the modifications that they introduce in the functioning of the heart. The present work is focussed on the experimental investigation of the flow in the left ventricle of the human heart with the presence of a tilting-disk valve in the mitral position, as this kind of valve is known to change deeply the structure of such a flow. A laboratory model has been built up, which consists of a cavity able to change its volume, representing the ventricle, on which two prosthetic valves are mounted. The facility is designed to be able to reproduce any arbitrarily assigned law of variation of the ventricular volume with time. In the present experiment, a physiologically shaped curve has been used. Velocity was measured using a feature-tracking (FT) algorithm; as a consequence, the particle trajectories are known. The flow has been studied by changing both the beat rate and the stroke volume. The flow was studied both kinematically, examining velocity and vorticity fields, and dynamically, evaluating turbulent and viscous shear stresses, and inertial forces exerted on fluid elements. The analysis of the results allows the identification of the main features of the ventricular flow, generated by a mitral, tilting-disk valve, during the whole cardiac cycle and its dependence on the frequency and the stroke volume.

Different Tilting Disc Valves Show Similar Rotation-Dependent Impairment in Hemodynamic Performance under a Tilted Implantation Position

Aortic annulus calcification can promote tilted implantation of mechanical valves. This study evaluates the hemodynamics of tilting disc valves under this condition. 23 mm and 25 mm Ultracor (UC) and Medtronic-Hall-Easy-Fit (MH) valves were investigated in a pulse-duplicator under physiological conditions. Mean pressure gradient (dP(mean)), systolic energy loss (dW(sys)), effective orifice area (EOA), closure (V(Cl)), leakage (V(L)), and total regurgitation volume (V(R)) were assessed. Valves were independently positioned at five axial rotations (0 - 180 degrees , zero defined as major orifice facing the top of the "tilt-ramp") and three tilt angles (0 degrees, 10 degrees, 20 degrees) by lifting the prosthesis in the noncoronary sinus. Diameter-enhanced MH valves exhibited a better systolic performance but a higher regurgitation than corresponding UC valves. Moderate tilting showed a rotation-independent increase in dP(mean) and dW(sys) and a decrease in V (R) and EOA with no fundamental differences between valve types. Further tilting caused small additional changes at 90 - 180 degrees rotation. At 0 degrees rotation, however, dramatic regurgitation occurred throughout. Tilting worsened systolic performance regardless of valve type. It should therefore be avoided. Due to extensive regurgitation at 0 degrees rotation, this position should be corrected whenever tilting is inevitable.

Different tilting disc valves show similar rotation-dependent impairment in hemodynamic performance under a tilted implantation position

Different tilting disc valves show similar rotation-dependent impairment in hemodynamic performance under a tilted implantation position

Innovative developments of the heart valves designed for use in ventricular assist devices

Prosthetic heart valves are routinely used for replacing diseased natural heart valves. Even today, after five decades of prosthetic heart valve development, in the authors’ opinion the main problem associated with these valves is the risk of thromboembolic complications caused by unnatural hemodynamics. Further growing application of prosthetic heart valves is their use in the pulsatile ventricular assist devices (VADs). VADs may provide life-saving solutions to patients with severe cardiovascular diseases and are superior to drug therapy for patients with severe heart failure. However, the clinical applications of VADs still suffer from thromboembolic complications due to thrombus formations in the vicinity of the valves. Wherever the flow is stagnant or flow separation occurs, a thrombus is likely to form. The design of the heart valves with flow avoiding the formation of stagnant zones is one of the main goals in the development of new valves. This article reviews some innovative design approaches of the valves specially designed for use in VADs. Three design concepts are presented; one is based on the tilting disk valve, the second on the natural valve geometry and the third on the ball valve principle. However, these three different concepts have one common basic idea; the use of the freedom of the valve-housing design. This additional design freedom, which is available in VADs, is a key factor in the development of new valves with optimal hemodynamic performance.

NUMERICAL STUDY FOR FLOW IN PHOENIX LEFT VENTRICULAR ASSIST DEVICE AT PEAK SYSTOLE

The Phoenix left ventricular assist device is driven by pneumatic pump outside a human body to provide air flow in-and-out of a pneumatic diaphragm inside the blood chamber. The inflation and deflation of the diaphragm drives the blood flows. At peak systole, blood flows into aorta with a maximum flow rate both from natural ventricle and artificial ventricle. To assess the critical condition, blood flow pattern of the device at peak systole is studied. We apply the finite volume method with ϰ – ε turbulent model to simulate the steady flow at peak systole. Results provide a comprehension of fluid dynamic effect not only the region inside the ventricle but also that in the vicinity of the inflow channel and outflow valves of flow field. The numerical results show that maximum velocities were smaller within the ventricular chamber with bi-leaflet outflow valve than with tilting disk outflow valve. Analysis of the numerical solutions suggests that geometry similar to the bi-leaflet outflow valve results in a better flow dynamics within the ventricle chamber compared to a tilting disk valve.

Twenty-Two Year Experience with the Omniscience Prosthetic Heart Valve

This study was designed to evaluate the long-term clinical results of the Omniscience tilting disc valve. Omniscience valves were implanted in 51 patients (mean age, 50 +/- 10 years); 18 had aortic valve, 24 had mitral valve, and 9 had both aortic and mitral valve replacements. Oral warfarin potassium and dipyridamole were prescribed as our anticoagulant therapy. Preoperatively, 42 patients were in New York Heart Association class III or IV, and 23 of 25 surviving patients were in class I or II after operation. There were 2 (3.9%) early deaths and 23 late deaths (3.5 +/- 0.7% per patient-year). Cardiac related mortality including congestive heart failure, sudden death, and thromboembolism, and hemorrhagic complications were seen in 16 patients. Overall survival at 10, 15, and 20 years was 77 +/- 6%, 62 +/- 7%, and 46 +/- 7%, respectively. Thromboembolic complications were seen in 5 patients, for a rate of 0.8 +/- 0.3% per patient-year; similarly, hemorrhagic complications were also seen in 5 patients. Nonstructural prosthetic valve dysfunction was seen in 4 patients, for a rate of 0.6 +/- 0.3% per patient-year, and sudden death was seen in 2, a rate of 0.3 +/- 0.2% per patient-year. The Omniscience prosthesis demonstrated excellent postoperative clinical status with low rates of valve related complications.

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+).

Late incidence and determinants of stroke after aortic and mitral valve replacement

BackgroundStroke is a devastating complication in patients with prosthetic valves, but characterization of its late occurrence from a large cohort is lacking. MethodsThree thousand one hundred eighty-nine adult patients who underwent a total of 3,576 operations for left-heart valve replacement were managed with contemporary anticoagulation guidelines and prospectively followed in a dedicated clinic. Total follow-up was 20,096 patient years. Bootstrapped survival analysis was used to determine the impact of patient and valve related factors on the incidence of stroke. ResultsMost strokes were embolic. Linearized embolic stroke rates were 1.3% ± 0.2% per year for aortic bioprostheses, 1.4% ± 0.2% per year for aortic mechanical valves, 1.3% ± 0.3% per year for mitral bioprostheses, and 2.3% ± 0.4% per year for mitral mechanical valves (p = 0.002, vs other implant types). Age more than 75 years, female gender, and smoking were independent risk factors after aortic and mitral valve replacement. Atrial fibrillation, coronary disease, and tilting-disc mechanical prostheses were independent predictors of embolic stroke after aortic valve replacement. Preoperative left ventricular (LV) dysfunction was an independent risk factor in patients with mitral prostheses. Primary operative indication, diabetes, redo status, or the presence of two prosthetic valves were not associated with an increased hazard. The addition of acetyl salicylic or dipyridamole to warfarin anticoagulation did not significantly lower embolic stroke risk in patients with mechanical prostheses. ConclusionsApproximately 20% of patients with valve prostheses have an embolic stroke by 15 years after valve replacement. Some risk factors such as the avoidance of smoking, mitral mechanical prostheses, aortic tilting-disc valves, and proceeding to mitral surgery before LV dysfunction occurs are potentially modifiable.

Mechanical heart valves: 50 years of evolution

The past 50 years have witnessed remarkable progress in the development of safe, hemodynamically favorable mechanical heart valves. Starr-Edwards aortic and mitral ball valves introduced in the mid-1960s, continue to be used successfully worldwide. More than 100,000 Omniscience and Omnicarbon tilting-disc valves have been implanted since 1978 with essentially no mechanical failure; similar results have been obtained with more than 300,000 Hall-Kaster and Medtronic-Hall tilting-disc valves over the past 25 years. Pyrolytic carbon, originally used to encapsulate nuclear fuel rods, has been adapted for the fabrication of discs, leaflets and the housings for more than 2 million mechanical valves. The St. Jude bileaflet valves, totally fabricated from pyrolytic carbon, have remained virtually unchanged in design since their introduction in 1977. More than 1.3 million of these valves have been implanted worldwide with virtually no reported failures of the carbon leaflets or housings. Similarly, pyrolytic carbon bileaflet Carbomedics valves have been implanted in more than 500,000 patients since 1986. Now, 50 years after Dr Gibbon's seminal achievement, patients with debilitating valve disease can have elective valve replacement (mechanical or tissue) with an operative mortality approaching 1% to 2% and a low lifetime complication rate.

Thrombectomy with disc rotation of medtronic valves.

Thrombotic obstruction of prosthetic valves is a serious problem. Early diagnosis and prompt treatment are life-saving in these cases. Three patients presented with subacute and chronic symptoms of prosthetic valve thrombosis of varying duration (7 days to 2 years). All 3 had a Medtronic Hall tilting disc valve implanted in a previous operation in the aortic or mitral position. Diagnosis was established by 2-dimensional echocardiography. Under cardiopulmonary or femorofemoral bypass, thrombectomy and rotation of the disc within the valve housing were performed through a median sternotomy. All the patients had an uncomplicated postoperative course. Pressure gradients fell markedly at discharge 8 to 10 days after surgery. The patients were followed up for between 3 and 11 months, during which they showed excellent prosthetic valve function and reduced gradients. The ability to rotate the valve within the housing allows adequate thrombectomy and pannus excision. Even several years after implantation (more than 10 years in 2 cases), the valve could still be rotated readily to obtain optimum flow and low pressure gradients.