Twenty years' experience with the Medtronic Hall valve

Identification of mechanical prosthetic heart valves based on distinctive cinefluoroscopic and echocardiographic markers

The past 65 years have witnessed remarkable progress in the development of safe, hemodynamically favorable mechanical heart valves. Today, there are a large number and variety of prostheses in use and many prostheses have been used for a while and then discontinued. When patients lack reliable information about their heart valve prostheses, identification of valve model becomes difficult even for specialized physicians in this area. A combination of cinefluoroscopy and echocardiography makes it possible to provide accurate and detailed information regarding identification of prosthetic valve models. Fluoroscopic examination is a useful technique to evaluate patients following mechanical heart valve replacement. However, transthoracic echocardiography and transesophageal echocardiography have almost replaced cinefluoroscopy in the evaluation of prosthetic heart valves. Especially, real-time three-dimensional transesophageal echocardiography provides distinctive images of prosthetic heart valves, particularly for those in the mitral position. A large body of literature has been published to familiarize physicians with the radiological appearance of numerous mechanical prostheses. However, there is a lack of data regarding the identification of prosthetic valve models based on echocardiographic appearance. In this review, we aimed to describe distinctive echocardiographic and cinefluoroscopic markers for identifying the type and brand of several commonly used mechanical prosthetic heart valves.

Selection of prosthetic aortic valves in the United States among elderly Medicare patients from 2006 to 2015

BACKGROUND

Both biological and mechanical prosthetic valves are treatment choices for aortic valve replacement. We aimed to characterize the selection of prosthetic aortic valves among elderly Medicare patients.

METHODS

This was a retrospective analysis of patients aged 65 years or older who underwent aortic valve replacement alone or in combination with other procedures in the 2006-2015 Medicare databases. Patients were continuously enrolled in Medicare Part A and B. We characterized the trends and regional variation of the selection of prosthetic valves. Multivariable logistic regression was used to evaluate the determinants that influenced the selection of prosthetic valves.

RESULTS

During the study period, there were 272,921 Medicare patients aged 65 years or older who underwent aortic valve replacement and met the inclusion and exclusion criteria. The selection of mechanical aortic valves decreased from 32.0% in 2006 to 24.3% in 2015 (P < .01). In comparison with 18.5% from northeastern states, 34.6% of patients from southern states selected mechanical valves (P < .01). Major determinants of the selection of prosthetic valves include age, gender, region, hospital characteristics, and physician experience. Patients being older, male, living in the northeast region, operated on in a high-volume hospital, and by more experienced physicians were more likely to receive biological valves.

CONCLUSIONS

A 24.1% decrease in the selection of mechanical aortic valves was observed among elderly Medicare patients from 2006 to 2015. A dramatic regional difference was observed in the choice of prosthetic valves across the nation.

Thirty-year experience with a bileaflet mechanical valve prosthesis

BACKGROUND

The objective was to evaluate the long-term outcomes of the St Jude Medical (Saint Paul, Minn) mechanical valve prosthesis implantation.

METHODS

Since 1979, every patient receiving this prosthesis has been followed annually.

RESULTS

From January 1979 to December 2014, 1023 patients were accrued. Patients' ages ranged from 18 to 85 years. Aortic valve replacement was performed in 584 patients, and mitral valve replacement was performed in 439 patients. Follow-up was 95% complete. Operative mortality was 3% (17/584, aortic valve replacement) and 4% (18/439, mitral valve replacement). In patients undergoing aortic valve replacement, late actuarial survival was 62% ± 2%, 32% ± 2%, and 14% ± 3% at 10, 20, and 30 years, respectively. Thirty-year freedom from reoperation, thromboembolism, valve thrombosis, bleeding, and endocarditis was 92% ± 2%, 79% ± 3%, 96% ± 1%, 56% ± 5%, and 92% ± 2%, respectively. In patients undergoing mitral valve replacement, late actuarial survival was 64% ± 3%, 28% ± 3%, and 14% ± 3% at 10, 20, and 30 years, respectively. Thirty-year freedom from reoperation, thromboembolism, valve thrombosis, bleeding, and endocarditis was 85% ± 5%, 55% ± 6%, 99% ± 1%, 57% ± 6%, and 95% ± 2%, respectively. The incidence of bleeding was 2.5% and 2.0% per patient-year for aortic valve replacement and mitral valve replacement, respectively. The incidence of thromboembolism was 1.6% and 2.9% per patient-year for aortic valve replacement and mitral valve replacement, respectively.

CONCLUSIONS

Annual follow-up of all of our patients receiving a St Jude Medical mechanical valves prosthesis has allowed better identification valve-related issues and events. After 3 decades of observation with close follow-up, the St Jude Medical mechanical valve continues to be a reliable prosthesis.

Karl Viktor Hall: From In Situ Vein Bypass to the Tilting Disc Heart Valve Prosthesis

In 1977, Karl Viktor Hall implanted a novel tilting disc heart valve prosthesis at Rikshospitalet in Oslo, Norway. The Medtronic-Hall valve was known for its excellent durability and low thrombogenicity. Hall popularized the use of the great saphenous vein in situ as an arterial shunt in the 1960s, made a metal stripper to lyse vein valves, and introduced electromagnetic flowmeters in vascular surgery. He performed the first coronary artery bypass graft in Scandinavia in 1969. Under his leadership the first heart transplantation and the first heart-lung transplantation were performed in Scandinavia by his successor Tor Frøysaker in 1983 and 1986, respectively.

Comparison of the occurrence of thromboembolic and bleeding complications in patients with mechanical heart valve prosthesis with one and two leaflets in the mitral position

INTRODUCTION

Patients with mechanical heart valve prostheses must continuously be treated with oral anticoagulants to prevent thromboembolic events related to prosthetesis. These patients should be continually evaluated for the control of oral anticoagulation.

OBJECTIVE

To compare the occurrence of thromboembolic and hemorragic complications in patients with mechanical heart valve prosthesis with one (mono) and two (bi) leaflets in the mitral position in anticoagulant therapy.

METHODS

We studied the 10-year interval, 117 patients with prosthesis in the mitral position, 48 with prosthetic single leaflet and 69 with two leaflets. We evaluated the occurrence of thromboembolic and hemorrhagic major and minor degree under gravity. The results are presented in an actuarial study and the frequency of occurrence of linear events.

RESULTS

The actuarial survival curves showed that over time, patients with prosthetic heart valve with one leaflet were less free of thromboembolic complications than patients with two leaflet prosthetic valve, while the latter (two leaflet) were less free of hemorrhagic accidents. The linearized frequency of occurrence of thromboembolism were higher in patients with mono leaflet prosthesis. Bleeding rates were higher for patients with bi leaflet prosthetic valve.

CONCLUSION

Patients with mono leaflet prosthetic heart valve showed that they are more prone to the occurrence of serious thromboembolic events compared to those with bi leaflet prosthetic valve. Patients with bi leaflet prosthetic valve had more bleeding than patients with mono leaflet prosthetic valve, however this difference was restricted to the bleeding of minor nature.

Clinical evaluation of new heart valve prostheses: update of objective performance criteria

This article summarizes the long-term clinical results of the Food and Drug Administration-approved heart valves, provides current updates to the objective performance criteria (OPC) used to evaluate new heart valve prostheses, and documents the steps that the International Organization for Standardization Committee used to arrive at the updated OPC. Data were extracted from 19 Food and Drug Administration summaries of safety and effectiveness data reports (31 series) and 56 literature articles (85 series) published from 1999 to 2012. The OPC were calculated for five valve-related complications by valve type (mechanical and bioprosthetic) and valve position (aortic and mitral).

Thromboembolism, major bleeding and mortality in patients with mechanical heart valves- a population-based cohort study

INTRODUCTION

Low incidences of thromboembolism (TE) and bleeding in patients with mechanical heart valves (MHV) have previously been reported. This study assesses the incidence of and clinical risk factors predicting TE, major bleeding and mortality in a clinical setting.

METHODS AND RESULTS

All 546 patients undergoing anticoagulation treatment due to MHV replacement at hospitals in Malmö and Sundsvall in Sweden were monitored during 2008-2011 and the incidence of TE, major bleeding and mortality was prospectively followed. There were 398, 122 and 26 patients in the aortic group (AVR), mitral (MVR) group and the combined aortic/mitral valve group respectively. The incidence of TE was 1.8 and 2.2 per 100 patient-years in the AVR group MVR group respectively. The corresponding incidences of bleeding were 4.4 and 4.6, respectively. Independent predictor of thromboembolism was vascular disease (Odds ratio {OR}: 4.2; 95% CI: 1.0-17.4). Predictor of bleeding was previous bleeding (OR: 2.7; 95% CI: 1.4-5.3). Independent predictors of mortality was age (Hazard ratio {HR}: 1.03; 95% CI: 1.00-1.05), hypertension (HR: 2.4; 95% CI: 1.3-4.5), diabetes (HR: 2.4; 95% CI: 1.3-4.3) and alcohol overconsumption (HR: 5.2; 95% CI: 1.7-15.9). Standardized mortality/morbidity ratio for mortality and AMI was 0.99 (95% CI: 0.8-1.2) and 0.87 (95% CI: 0.5-1.2) respectively.

CONCLUSION

The incidence of TE and major bleeding in this unselected clinical population exceeds that of previously reported retrospective and randomized trials. Despite this, mortality is equal to that of the general population.

Clinical outcomes of Carbomedics Top Hat valve with a robust follow-up system

AIM

Late failure of bioprosthetic valves may limit their use in patients < 60 years. The superior hemodynamic performance offered by the Carbomedics Top Hat supraannular valve enables greater effective orifice areas to be achieved. The aim of this study was to assess the clinical outcomes of this valve, using a robust follow-up system.

METHODS

Patients who underwent aortic valve replacement with or without coronary artery bypass grafting between July 1997 and January 2010 with Carbomedics supraannular Top Hat valves were identified. Details of readmissions and late deaths were obtained from the National Hospital Episodes Statistics data and the Office of National Statistics, tracked by the Quality and Outcomes Research Unit. Late complications associated with this prosthesis were evaluated.

RESULTS

Of 253 patients identified, 181 underwent isolated aortic valve replacement and 72 had aortic valve replacement with coronary artery bypass grafting. The 30-day mortality was 1.6%, and 5- and 10-year survival rates were 91.4% and 80.5%, respectively. Detailed readmission data were available after 2001 (n = 170). Two (1.2%) patients required reoperation for endocarditis and pannus formation. Of the 17 late deaths in this subset, 4 were attributable to cardiac causes. One patient was treated for heart failure, and 2 developed bleeding complications.

CONCLUSIONS

Implantation of the Carbomedics Top Hat supraannular valve in our unit resulted in satisfactory in-hospital and midterm survival with low incidences of endocarditis and late heart failure.

Clinical and hemodynamic study of tilting disc heart valve: Single-center study

BACKGROUND

The TTK Chitra heart valve has been developed and widely used in India. This study aimed to evaluate its hemodynamics, complications, and event-free survival in comparison with other commonly used prosthetic valves. The role of color Doppler echocardiography in the follow-up of patients with prosthetic valves was also studied.

PATIENTS AND METHODS

Two hundred patients underwent 249 valve replacements (122 mitral, 29 aortic, 49 both). Total follow-up was 451 patient-years.

RESULTS

There were 18 late deaths (3.98% ± 0.92% per patient-year). One mitral valve replacement patient (0.36% ± 0.36% per patient-year) developed valve thrombosis. Two aortic valve replacement patients (2.74% ± 1.91% per patient-year), 2 double-valve replacement patients (1.95% ± 1.36% per patient-year) and 3 mitral valve replacement patients (1.08% ± 0.62% per patient-year) developed embolic complications. Freedom from all valve related mortality and morbidity at 4 years was 86% ± 4% for mitral valve replacement, 56% ± 10% for double-valve replacement, and 89% ± 6% for aortic valve replacement. The average peak gradient, mean gradient, and average peak velocity for the aortic and mitral positions were found to be comparable to those of other commonly used valves.

CONCLUSION

The performance of this valve in terms of hemodynamic complications, mortality, and morbidity is comparable to other valves in common use. Hemodynamic gradients are more reproducible than effective orifice area, hence more beneficial for follow-up.

Research approaches for studying flow-induced thromboembolic complications in blood recirculating devices

The advent of implantable blood recirculating devices has provided life-saving solutions to patients with severe cardiovascular diseases. Recently it has been reported that ventricular assist devices are superior to drug therapy. The implantable total artificial heart is showing promise as a potential solution to the chronic shortage of available heart transplants. Prosthetic heart valves are routinely used for replacing diseased heart valves. However, all of these devices share a common problem--significant complications such as hemolysis and thromboembolism often arise after their implantation. Elevated flow stresses that are present in the nonphysiologic geometries of blood recirculating devices, enhance their propensity to initiate thromboembolism by chronically activating the blood platelets. This, rather than hemolysis, appears to be the salient aspect of blood trauma in devices. Limitations in characterizing and controlling relevant aspects of the flow-induced mechanical stimuli and the platelet response, hampers our ability to achieve design optimization for these devices. The main objective of this article is to describe state-of-the-art numerical, experimental, and in vivo tools, that facilitate elucidation of flow-induced mechanisms leading to thromboembolism in prosthetic devices. Such techniques are giving rise to an accountable model for flow-induced thrombogenicity, and to a methodology that has the potential to transform current device design and testing practices. It might lead to substantial time and cost savings during the research and development phase, and has the potential to reduce the risks that patients implanted with these devices face, lower the ensuing healthcare costs, and offer viable long-term solutions for these patients.

Thirty-year results after implantation of the Björk-Shiley Convexo-Concave Heart valve prosthesis

BACKGROUND

Modifications of the Björk-Shiley valve prosthesis have shown good long-term results. The convexo-concave model, however, was recalled 27 years ago because of a propensity for breakage due to outlet strut fracture. The objective of this study is to describe the 30-year outcome after implantation of the Björk-Shiley convexo-concave mechanical heart valve prosthesis (Pfizer, Rye Brook, NY).

METHODS

The study included 279 patients who were operated between 1979 and 1983 at Turku University Hospital. A total of 305 valves were implanted; 205 in the aortic position and 100 in the mitral position. Patient records were reviewed for baseline characteristics and late events, data on mortality were acquired from registries.

RESULTS

Mean actuarial survival was 19.8 years and mean follow-up was 19.2 years (maximum 34 years). Freedom from reoperation was 91.3% at 30 years. There were 3 outlet strut fractures (2 fatal) during follow-up. Statistically significant predictors of mortality were age and concomitant coronary artery bypass grafting.

CONCLUSIONS

Despite the possibility of structural valve failure the Björk-Shiley convexo-concave valve confers excellent 30-year survival.

Acute obstruction by Pannus in patients with aortic medtronic-hall valves: 30 years of experience

BACKGROUND

Acute dysfunction of mechanical aortic valve prostheses is a life-threatening adverse event. Pannus overgrowth, which is fibroelastic hyperplasia originating from the periannular area, is one cause of dysfunction. The aim of this study was to determine the annual incidence of readmittance resulting from acute obstruction caused by pannus during 30 years of observation in patients with Medtronic-Hall aortic valve prostheses and to analyze the risk factors associated with pannus development.

METHODS

From 1982 to 2004, 1,187 patients in our department underwent aortic valve replacement with Medtronic-Hall mechanical monoleaflet valve prostheses. As of December 31, 2012, 27 of these patients (2.3%) had presented with acute valve dysfunction caused by pannus obstruction.

RESULTS

The annual incidence of pannus was 0.7 per 1,000. The median time from the primary operation to prosthetic dysfunction was 11.1 years (range, 1.2 to 26.8 years). Of the 20 patients who underwent reoperation, 2 died. Seven patients died before reoperation. Women had a higher risk for the development of obstructing pannus, and patients with pannus obstruction were younger. Valve size was not an independent risk factor.

CONCLUSIONS

Women and younger patients are at higher risk for pannus development. When acute dysfunction by pannus is suspected in a mechanical aortic valve, an immediate echocardiogram and an emergency aortic valve replacement should be carried out because of the potential of a fatal outcome.

Stentless aortic valve replacement in the young patient: long-term results

Background

Stentless aortic valve replacement (SAVR) became a common surgical procedure to treat aortic valve disease, as it offers larger orifice area and improved hemodynamics. The aim of our single-centre retrospective study was to assess long term results of first generation stentless aortic valves in young patients, where mechanical prostheses are considered first line therapy.

Methods

From 1993 to 2001, 188 (149 male and 39 female) patients (≤60 years) underwent SAVR. Indications were in 63.3% stenosis or mixed lesions and in 36.7% isolated regurgitation. Mean age of patients at surgery was 53.1 ± 7.1 years. Associated procedures were performed in 60 patients (31.9%). Follow-up data were acquired through telephone interviews. Follow-up was 90.4% complete at a mean of 8.8 ± 4.7 years. Total follow-up was 1657.6 patient-years with a maximum of 17 years.

Results

Overall hospital mortality was 3.2% (2.5% for isolated SAVR). Overall actuarial survival-rate at 10/15 years and freedom from reoperation at 10/14 years were 73.0% ± 3.5%/ 55.8% ± 5.4% and 81.0% ± 3.4%/ 58.0% ± 7.5%, respectively. For isolated SAVR, actuarial survival at 10/15 years and freedom from reoperation at 10/14 years were 70.1% ± 4.4%/ 64.1% ± 4.8% and 83.1% ± 4.0%/ 52.9% ± 9.0%, respectively. Reoperation was performed in 42 patients (22.3%) due to structural valve deterioration and endocarditis. Age (≤50 years) and associated procedures did not significantly lower survival and freedom from reoperation, however, small prosthesis sizes (≤25 mm) did.

Conclusion

In patients aged 60 and younger, SAVR provides reliable long-term results especially for larger aortic valves.

Inclusion cylinder method for aortic valve replacement utilising the Ross operation in adults with predominant aortic stenosis - 99% freedom from re-operation on the aortic valve at 15 years

BACKGROUND

To report our experience with the Ross operation in patients with predominant aortic stenosis (AS) using an inclusion cylinder (IC) method.

METHODS

Out of 324 adults undergoing a Ross operation, 204 patients of mean age of 41.3 years (limits 16-62) underwent this procedure for either AS or mixed AS and regurgitation (AS/AR) between October, 1992 and February, 2012, implanting the PA with an IC method. Clinical follow up and serial echo data for this group is 97% complete with late mortality follow up 99% complete.

RESULTS

There has been zero (0%) early mortality, and late survival at 15 years is 98% (96%, 100%). Only one re-operation on the aortic valve for progressive aortic regurgitation (AR) has been required with freedom from re-operation on the aortic valve at 15 years being 99% (96%, 100%). The freedom from all re-operations on the aortic and pulmonary valves at 15 years is 97% (94%, 100%). Echo analysis at the most recent study shows that 98% have nil, trivial or mild AR. Aortic root size has remained stable, shown by long-term (15 year) echo follow up.

CONCLUSIONS

In an experience spanning 19 years, the Ross operation used for predominant AS using the IC method described, results in 99% freedom from re-operation on the aortic valve at 15 years, better than any other tissue or mechanical valve. For adults under 65 years without significant co-morbidities who present with predominant AS, the pulmonary autograft inserted with this technique gives excellent results.

Device thrombogenicity emulation: a novel methodology for optimizing the thromboresistance of cardiovascular devices

Thrombotic complications with mechanical circulatory support (MCS) devices remain a critical limitation to their long-term use. Device-induced shear forces may enhance the thrombotic potential of MCS devices through chronic activation of platelets, with a known dose-time response of the platelets to the accumulated stress experienced while flowing through the device-mandating complex, lifelong anticoagulation therapy. To enhance the thromboresistance of these devices for facilitating their long-term use, a universal predictive methodology entitled device thrombogenicity emulation (DTE) was developed. DTE is aimed at optimizing the thromboresistance of any MCS device. It is designed to test device-mediated thrombogenicity, coupled with virtual design modifications, in an iterative approach. This disruptive technology combines in silico numerical simulations with in vitro measurements, by correlating device hemodynamics with platelet activity coagulation markers-before and after iterative design modifications aimed at achieving optimized thrombogenic performance. The design changes are first tested in the numerical domain, and the resultant device conditions are then emulated in a hemodynamic shearing device (HSD) in which platelet activity is measured under device emulated conditions. As such, DTE can be easily incorporated during the device research and development phase-achieving minimization of the device thrombogenicity before prototypes are built and tested thereby reducing the ultimate cost of preclinical and clinical trials. The robust capability of this predictive technology is demonstrated here in various MCS devices. The presented examples indicate the potential of DTE for reducing device thrombogenicity to a level that may obviate or significantly reduce the extent of anticoagulation currently mandated for patients implanted with MCS devices for safe long-term clinical use.

Long-term follow-up after aortic valve replacement with Edwards Prima Plus stentless bioprostheses in patients younger than 60 years of age

OBJECTIVES

The Edwards Prima Plus was one of the first stentless aortic valve bioprostheses, with larger orifice areas and improved hemodynamics compared to stented bioprostheses. The aim of the present single-center retrospective study was to assess the long-term results of the Edwards Prima Plus in patients 60 years old or younger.

METHODS

From 1993 to 2001, 120 patients (99 men and 21 women) aged 60 years or younger underwent implantation of the Edwards Prima Plus. The indications were stenosis and/or insufficiency. Associated procedures were performed in 38 patients (31.7%). Of the patients, 39% had impaired left ventricular function. Follow-up data were acquired by telephone interview. Time-to event analyses were performed using the Kaplan-Meier method. Variables affecting survival and freedom from reoperation were evaluated using Cox regression analysis. The mean patient age at surgery was 53.1 ± 8.0 years. The follow-up data were 88.8% complete at a mean of 8.5 ± 4.5 years. The total follow-up was 1022.7 patient-years.

RESULTS

At 10 and 15 years, the overall actuarial survival rate was 71.8% ± 4.4% and 48.8% ± 9.6%, respectively. Survival was significantly lower for patients with older age, aortic insufficiency as the surgical indication, and small prosthesis size (≤25 mm vs ≥27 mm). Reoperation was performed in 20 patients (16.7%), with a hospital mortality of 5%. At 10 and 14 years, the overall freedom from reoperation rate was 85.6% ± 3.7% and 65.2% ± 8.6%, respectively. Freedom from reoperation was significantly lower in patients with a small prosthesis size (≤25 mm) and insufficiency as the indication for surgery.

CONCLUSIONS

In patients aged 60 years or younger, an Edwards Prima Plus can provide reliable long-term results with acceptable freedom-from-reoperation rates.

Episodic circulatory collapse caused by intermittent prosthetic aortic valve dysfunction

An 80-year-old woman with a 20-mm Medtronic Hall (tilting-disc) aortic prosthesis presented with episodes of chest pain associated with circulatory collapse and subsequent rapid spontaneous recovery. A computed tomography angiogram demonstrated no evidence of aortic dissection, pulmonary embolus, or coronary artery disease. A transthoracic echocardiogram demonstrated a well-functioning prosthetic aortic valve. After another inpatient episode, auscultation demonstrated an intermittent absence of the prosthetic second heart sound. A transesophageal echocardiography examination revealed that the aortic valve was intermittently sticking in the open position. During the emergency replacement, the existing valve was noted to have pannus and overlying thrombus, which are rare in this type of valve but can lead to dramatic circulatory collapse when present. This case demonstrates how a diagnosis of intermittent valve dysfunction can prove elusive. It is important, as part of the assessment of mechanical valves, to perform regular, careful auscultation and echocardiographic examination, with emphasis on recording in Doppler or M-mode through the valve at slow sweep speeds for a prolonged period in order to maximize the chance of diagnosing episodic valve dysfunction.

Sources of thromboembolism in patients with correctly functioning mechanical valves: a single-center transesophageal echocardiographic study

BACKGROUND

In patients with mechanical prostheses (MP), thromboembolism is one of the most serious complications. The study aim was to assess the incidence of sources of thromboembolism in patients with correctly functioning MP with and without a history of thromboembolism.

METHODS

Two hundred ninety-seven patients with correctly functioning MP were enrolled in this single-center, transesophageal echocardiographic (TEE), retrospective, observational study. Two groups were analyzed: Group A, 183 patients with a history of thromboembolism, and Group B, 114 patients with no history of thromboembolism.

RESULTS

Definite sources of thromboembolism were revealed in 59% of patients in Group A, and sources of potential thromboembolism were revealed in 13% of patients in Group B (P < .001). Multiple sources of thromboembolism were present in 9% of patients in Group A and 1% of patients in Group B. Localization of sources of thromboembolism included MP ring (59% and 53% of patients in Groups A and B, respectively); left atrium/left atrium appendage (24%/21% and 13%/40% of patients in Groups A and B, respectively); and aorta (12% and 13% of patients in Groups A and B, respectively). Patients with multiple sources of thromboembolism were older (P < .001) and in a higher New York Heart Association (NYHA) class (P = .004). Patients with sources of thromboembolism in the aorta were older than the rest of the group (P < .01).

CONCLUSIONS

In patients with correctly functioning MP, sources of thromboembolism are observed 4 times more often in case of the positive history of thromboembolism. The most common source of thromboembolism is thrombosis of MP ring. Age and heart failure predispose multiple sources of thromboembolism. One might consider control TEE after mechanical valve implantation, but only in selected group of patients without embolic events but with a higher risk of thromboembolism.

A Process for Design, Verification, Validation, and Manufacture of Medical Devices Using Immersive VR Environments

This paper presents a framework and detailed vision for using immersive virtual reality (VR) environments to improve the design, verification, validation, and manufacture of medical devices. Major advances in medical device design and manufacture currently require extensive and expensive product cycles that include animal and clinical trials. The current design process limits opportunities to thoroughly understand and refine current designs and to explore new high-risk, high-payoff designs. For the past 4 years, our interdisciplinary research group has been working toward developing strategies to dramatically increase the role of simulation in medical device engineering, including linking simulations with visualization and interactive design. Although this vision aligns nicely with the stated goals of the FDA and the increasingly important role that simulation plays in engineering, manufacturing, and science today, the interdisciplinary expertise needed to realize a simulation-based visual design environment for real-world medical device design problems makes implementing (and even generating a system-level design for) such a system extremely challenging. In this paper, we present our vision for a new process of simulation-based medical device engineering and the impact it can have within the field. We also present our experiences developing the initial components of a framework to realize this vision and applying them to improve the design of replacement mechanical heart valves. Relative to commercial software packages and other systems used in engineering research, the vision and framework described are unique in the combined emphasis on 3D user interfaces, ensemble visualization, and incorporating state-of-the-art custom computational fluid dynamics codes. We believe that this holistic conception of simulation-based engineering, including abilities to not just simulate with unprecedented accuracy but also to visualize and interact with simulation results, is critical to making simulation-based engineering practical as a tool for major innovation in medical devices. Beyond the medical device arena, the framework and strategies described may well generalize to simulation-based engineering processes in other domains that also involve simulating, visualizing, and interacting with data that describe spatially complex time-varying phenomena.

Choice of prosthetic heart valve in adults an update

In the last 7 years, more data have reconfirmed that patients' comorbid conditions are very important factors determining patient outcomes. Prosthetic heart valves (PHVs) that require aortic root replacement in the absence of aortic root disease are associated with poorer outcomes. For the vast majority of patients, the choice of PHV is between a mechanical valve and a stented bioprosthesis. The choice is largely dependent upon the age of the patient at the time of PHV implantation and on which complication the patient wants to avoid: specifically, anticoagulation therapy and its complications with the mechanical valve, and structural valve deterioration with a bioprosthesis. Data on the pros and cons of the choices and exceptions to the rules are discussed, and a new algorithm is developed.

Antithrombotic management of patients with prosthetic heart valves: current evidence and future trends

Over 4 million people worldwide have received a prosthetic heart valve, and an estimated 300,000 valves are being implanted every year. Prosthetic heart valves improve quality of life and survival of patients with severe valvular heart disease, but the need for antithrombotic therapy to prevent thrombotic complications in valve recipients poses challenges for clinicians and patients. Here, we review antithrombotic therapies for patients with prosthetic heart valves and management of thromboembolic complications. Advances in antithrombotic therapy and valve technologies are likely to improve the management of patients with prosthetic heart valves in developed countries, but the most important unmet need and potential for benefit from these new therapies is in developing countries where a massive and rapidly increasing burden of valvular heart disease exists.

Observation of cavitation pits on a mechanical heart valve surface in an artificial heart used in in vivo testing

The aim of this study was to observe mechanical heart valve (MHV) cavitation pits resulting from in vivo testing of an electrohydraulic total artificial heart (EHTAH). During in vivo testing with three sets of valves (one set used in two animals), the slope of the driving pressure (left and right driving pressure) was used as a factor for investigating cavitation intensity, and the occurrence of cavitation was determined by the observation of cavitation pits on the explanted valve surfaces. Medtronic Hall valves were installed at the inlet and outlet positions of the two blood pumps. The EHTAH was tested using calves weighing 69-80 kg. The cavitation pits on the valve surface of the inlet valves of the left and right blood pumps were examined by scanning electron micrography. The driving pressure slope 5 ms before valve closure exceeded the cavitation threshold during in vitro testing. On both inlet valves, many large pits formed when the driving pressure slope was high and the pump operating time was long. When estimating cavitation intensity during in vivo testing, both a high driving pressure slope and a long operating time are important factors. The cavitation pits observed on the valve surfaces resulting from in vivo testing will eventually lead to leaflet fracture.

Effect of systolic duration on mechanical heart valve cavitation in a pneumatic ventricular assist device: using a monoleaflet valve

The cavitation intensity of a mechanical heart valve (MHV) may differ according to the geometry of the blood pump and driving mechanism. Our group is currently developing a pneumatic ventricular assist device (VAD), and the effects of different operating conditions on MHV cavitation in our pneumatic VAD were investigated. Tests were conducted under physiological pressure at heart rates ranging from 60 to 90 beats/min and at a systolic duration ranging from 38% to 43%. The valve-closing velocity was measured using a charge-coupled device (CCD) laser displacement sensor, and images of MHV cavitation were recorded using a high-speed video camera. A miniature pressure sensor was mounted 10 mm away from the inlet valve surface. The data were stored at a 1-MHz sampling rate using a digital oscilloscope. The pressure signal was band-pass filtered between 35 and 200 kHz using a digital filter. The cavitation bubbles were concentrated at the inlet valve stop, and were caused mainly by the squeeze flow. The band-pass filtered root mean squared (RMS) pressure and cavitation cycle duration increased with the closing velocity of the inlet valve. At a low heart rate and low systolic duration, the inlet valve closed before the outlet valve opened, which caused no cavitation bubbles to form around the valve stop.

Prosthetic heart valves: Types and echocardiographic evaluation

In the last five decades multiple different models of prosthetic valves have been developed. The purpose of this article is to provide a comprehensive source of information for the types and the echocardiographic evaluation of the prosthetic heart valves.

Twenty-Five–Year Experience With the Medtronic-Hall Valve Prosthesis in the Aortic Position

Background— The Medtronic-Hall valve was developed and for the first time implanted in Oslo, Norway, in 1977. A total of 1104 patients received this valve at Rikshospitalet from 1977 to 1987. In the present study, we followed up on all 816 patients undergoing aortic valve replacement over a 25-year period.

Methods and Results— This is a retrospective cohort analysis of 816 consecutive patients undergoing aortic valve replacement with the Medtronic-Hall valve at Rikshospitalet, Oslo, Norway, from 1977 to 1987. All patients were contacted by means of questionnaires or telephone. Data were checked against hospital databases and medical records. Date of death was verified by the Norwegian civil registry. Follow-up was 99.6% complete. Survival analysis included operative deaths as well as late deaths. Survival at 25 years was 24.9%. No mechanical failures were found. Valve thrombosis was seen in 4 patients, in 1 case combined with pannus formation. Small valves (20 mm to 21 mm) were associated with reduced survival; however, when controlled for the confounding effects of age and gender, valve size did not remain a significant risk factor. Patient-related factors were important: Older age, female gender, and the need for concomitant coronary artery bypass surgery significantly reduced survival, whereas surgery of the ascending aorta did not. Linearized rates of thromboembolic complications, warfarin-related bleeding, and endocarditis were 1.5%, 0.7%, and 0.16%/patient-year, respectively. At follow-up, 79% of the patients were in New York Heart Association classes I to II.

Conclusions— This study confirms the excellent long-term outcome for patients with Medtronic-Hall valves in the aortic position.

Estimation of mechanical heart valve cavitation in a pneumatic ventricular assist device

In this study, we investigated the possibility of estimating the mechanical heart valve (MHV) cavitation intensity using the slope of the driving pressure (DP) just before valve closure in a pneumatic ventricular assist device. We installed a 23-mm Medtronic Hall valve at the inlet of our pneumatic ventricular assist device (VAD). Tests were conducted under physiologic pressures at heart rates ranging from 60 to 90 beats/min and cardiac outputs ranging from 4.5 to 6.7 l/min. The valve-closing velocity was measured with a CCD laster displacement sensor, and the images of MHV cavitation were recorded using a high-speed video camera. The cavitation cycle time (equal to the observed duration of the cavitation bubbles) was used as the MHV cavitation intensity. The valve-closing velocity increased as the heart rate increased. Most of the cavitation bubbles were observed near the valve stop, and the cavitation intensity increased as the heart rate increased. The slope of the DP at 20 ms before valve closure was used as an index of the cavitation intensity. There were differences in the slope of the DP between low and high heart rates, but the slope of the DP had a tendency to linearly increase with increasing valve-closing velocity.

Hydrodynamic Characteristics of Bileaflet Mechanical Heart Valves in an Artificial Heart: Cavitation and Closing Velocity

The aim of this study was to investigate the possibility of using the bileaflet valves in an electrohydraulic total artificial heart (EHTAH). Three kinds of bileaflet valves, namely the ATS valve (ATS Medical Inc., Minneapolis, MN, USA), the St. Jude valve (St. Jude Medical Inc., St. Paul, MN, USA), and the Sorin Bicarbon valve (Sorin Biomedica, Vercelli, Italy), were mounted in the mitral position on an inclined 45 degrees plane in an EHTAH. The pressure waves near the valve surface, the valve-closing velocity, and a high-speed camera were employed to investigate the mechanism for bileaflet valve cavitation. The cavitation bubbles in the bileaflet valves were concentrated along the leaflet tip. The cavitation intensity increased with an increase in the valve-closing velocity. It was established that squeeze flow holds the key to bileaflet valve cavitation. At lower heart rates, the delay time of the asynchronous closure motion between the two leaflets of the Sorin Bicarbon valve was greater than that of the other bileaflet valves. At higher heart rates, no significant difference was observed among the bileaflet valves.

Mechanism for cavitation of monoleaflet and bileaflet valves in an artificial heart

It is possible that mechanical heart valves mounted in an artificial heart close much faster than those used for clinical valve replacement, resulting in the formation of cavitation bubbles. In this study, the mechanism for mechanical heart cavitation was investigated using the Medtronic Hall monoleaflet valve and the Sorin Bicarbon bileaflet valve mounted at the mitral position in an electrohydraulic total artificial heart. The valve-closing velocity was measured with a charge-coupled device (CCD) laser displacement sensor, and images of mechanical heart valve cavitation were recorded using a high-speed video camera. The valve-closing velocity of the Sorin Bicarbon bileaflet valve was lower than that of the Medtronic Hall monoleaflet valve. Most of the cavitation bubbles generated by the monoleaflet valve were observed near the valve stop; with the Sorin Bicarbon bileaflet valve, cavitation bubbles were concentrated along the leaflet tip. The cavitation density increased as the valve-closing velocity and the valve stop area increased. These results strongly indicate that squeeze flow holds the key to cavitation in the mechanical heart valve. From the perspective of squeeze flow, bileaflet valves with a low valve-closing velocity and a small valve stop area may cause less blood cell damage than monoleaflet valves.

Risk-corrected impact of mechanical versus bioprosthetic valves on long-term mortality after aortic valve replacement

OBJECTIVE

Choice of a mechanical or biologic valve in aortic valve replacement remains controversial and rotates around different complications with different time-related incidence rates. Because serious complications will always "spill over" into mortality, our aim was to perform a meta-analysis on overall mortality after aortic valve replacement from series with a maximum follow-up of at least 10 years to determine the age- and risk factor-corrected impact of currently available mechanical versus stented bioprosthetic valves.

METHODS

Following a formal study protocol, we performed a dedicated literature search of publications during 1989 to 2004 and included articles on adult aortic valve replacement with a mechanical or stented bioprosthetic valve if age, mortality statistics, and prevalences of well-known risk factors could be extracted. We used standard and robust regression analyses of the case series data with valve type as a fixed variable.

RESULTS

We could include 32 articles with 15 mechanical and 23 biologic valve series totaling 17,439 patients and 101,819 patient-years. The mechanical and biologic valve series differed in regard to mean age (58 vs 69 years), mean follow-up (6.4 vs 5.3 years), coronary artery bypass grafting (16% vs 34%), endocarditis (7% vs 2%), and overall death rate (3.99 vs 6.33 %/patient-year). Mean age of the valve series was directly related to death rate with no interaction with valve type. Death rate corrected for age, New York Heart Association classes III and IV, aortic regurgitation, and coronary artery bypass grafting left valve type with no effect. Included articles that abided by current guidelines and compared a mechanical and biologic valve found no differences in rates of thromboembolism.

CONCLUSION

There was no difference in risk factor-corrected overall death rate between mechanical or bioprosthetic aortic valves irrespective of age. Choice of prosthetic valve should therefore not be rigorously based on age alone. Risk of bioprosthetic valve degeneration in young and middle-aged patients and in the elderly and old with a long life expectancy would be an important factor because risk of stroke may primarily be related to patient factors.

Stentless bioprostheses improve postoperative coronary flow more than stented prostheses after valve replacement for aortic stenosis

OBJECTIVE

In some randomized studies, stentless aortic valves have demonstrated hemodynamic advantages in comparison with stented prostheses. The effect of more physiologic flow dynamics on coronary artery flow has not been investigated yet. This study compares coronary perfusion after aortic valve replacement with stented or stentless porcine bioprostheses in a prospective randomized study.

METHODS

A total of 24 patients (73 +/- 6 years) referred for treatment of aortic stenosis were randomized to aortic valve replacement with stented (Medtronic Mosaic; (Medtronic Inc, Minneapolis, Minn) or stentless (Medtronic Freestyle; Medtronic Inc) prostheses. Coronary flow was measured by means of magnetic resonance imaging preoperatively, 5 days after the operation, and 6 months postoperatively, then with evaluation of coronary flow reserve. Echocardiography was performed to quantify transvalvular gradients and left ventricular mass regression.

RESULTS

Coronary flow increased in both groups significantly (P < .001) after aortic valve replacement. This increase was higher in the stentless group compared with that seen in the stented group (343 +/- 137 vs 221 +/- 66 mL/min). Also, coronary flow reserve was higher for stentless valves (3.4 +/- 0.3 for stentless valves and 2.3 +/- 0.1 for stented valves). Mean pressure gradients for Freestyle valves were lower (10 +/- 4 and 8 +/- 3 mm Hg, respectively, vs 19 +/- 6 postoperatively and 15 +/- 4 mm Hg at follow-up for Mosaic valves, P < .05). Left ventricular mass regression was similar in both groups.

CONCLUSIONS

Normalization of coronary artery flow after aortic valve replacement for aortic stenosis was more pronounced for stentless valves compared with stented valves. The fact that the stentless design also demonstrated a superior hemodynamic performance with lower pressure gradients might be explained by the design being closer to physiologic anatomy and thus the presence of lower turbulence levels in the sinuses of Valsalva.

Heart valve replacement: which valve for which patient?

The ideal heart valve substitute would show no deterioration or thrombogenicity, offer no resistance to blood flow, and be easy to implant. However, such a valve does not exist and we must accept compromises in some of these qualities based on our patients' needs. In selection of cardiac valve prosthesis, valve-related factors such as durability, thrombogenicity, and fluid dynamics should be carefully matched to patient-related factors such as age, size, life expectancy, comorbidities, plans for pregnancy, and lifestyle. In addition, surgeon- or operation-related factors should be considered. Technical aspects of implantation, ease of reoperation, and operative mortalities may tip the risk and benefit balance in a particular direction. We review currently available heart valve prostheses and the clinical factors that are involved in selection of a heart valve substitute.